Micas, feldspars and columbite tantalite minerals from the...
19
eschweizerbart_xxx Micas, feldspars and columbite–tantalite minerals from the zoned granitic lepidolite-subtype pegmatite at Namivo, Alto Ligonha, Mozambique ANA M. R. NEIVA * Department of Earth Sciences and Geosciences Centre, University of Coimbra, 3000–272 Coimbra, Portugal *Corresponding author, e-mail: [email protected] Abstract: The Namivo granitic lepidolite-subtype pegmatite is concentrically zoned. Textural and chemical studies show at the crystal scale and within each zone that muscovite evolved to lithian muscovite and the latter to ‘‘mixed form’’ in the outer and inner intermediate zones and core. ‘‘Mixed form’’ also evolved to lepidolite in the inner intermediate zone and core. Each of these micas represents an evolution from the pegmatite outer intermediate zone to the inner intermediate zone and core. Some crystals are progressively zoned while others are reversely zoned, but overgrowths and replacements also occur. Albite and K-feldspar evolved from the wall zone to the core and feldspar thermometry records a decrease in temperature. Columbite-(Mn) shows a compositional trend from the outer intermediate zone to the core typical of this mineral from a lepidolite-subtype granitic pegmatite. The chemical zonation of this pegmatite is derived from crystallization of an undercooled granitic melt in which a probably local constitutional zone refining of fluxing and incompatible elements contributes to the textural and chemical changes from the wall zone to the core. The unexpected occurrence of lepidolite and Fe/Mg-containing polylithionite, the richest micas in Si, Li calc . and F, in the outer intermediate zone is attributed to disequilibrium crystallization from an undercooled melt. They are associated with tantalite, and Ta precipitation may have been caused by the local decrease of Li and F in the melt. These minerals are uncommon in this zone of granitic pegmatites. Key-words: muscovite, lithium micas, albite, K-feldspar, columbite–tantalite minerals, gahnite, electron microprobe, pegmatite evolution. 1. Introduction Micas and feldspars are good petrogenetic indicators of pegmatite evolution, and consequently their geochemistry has been used to track the consolidation history of pegma- tite bodies (e.g., Jahns, 1982; Jolliff et al., 1987; Monier et al., 1987; C ˇ erny ´ , 1994; C ˇ erny ´ et al., 1995; Kile & Foord, 1998; Alfonso et al., 2003; Roda Robles et al., 2006, 2007; Van Lichtervelde et al., 2008; Neiva & Ramos, 2010; Vieira et al., 2011). However, chemical zoning in micas from pegmatites has rarely been studied (Neiva et al., 2008, 2012; Van Lichtervelde et al., 2008). Columbite- tantalite minerals from granitic pegmatites have been stu- died widely and are tracers of pegmatite fractionation (e.g., C ˇ erny ´ et al., 1986; Beurlen et al., 2008; Neiva et al., 2008, 2012; Neiva & Ramos, 2010). The Namivo granitic pegmatite is located in the central part of the Alto Ligonha pegmatite area in northern Mozambique (Fig. 1), close to the confluence of the Namivo and Mo ´lucue ´ rivers, in the Zambe ´zia province. A geochemical evolution occurs from green and bluish green beryl in the outer intermediate zone to pink beryl in the inner intermediate zone, ‘‘core margin’’ and core (Neiva & Neiva, 2005). This paper presents the study of micas, feldspars and columbite–tantalite minerals to provide information on their geochemical evolution and paragen- esis and implications for the Namivo pegmatite evolution. 2. General geology and petrography The Namivo granitic pegmatite intruded a Precambrian migmatitic paragneiss and the contact is sharp. It is a lepidolite-subtype pegmatite (C ˇ erny ´ & Ercit, 2005), which is concentrically zoned (Fig. 2). The wall zone (WZ) consists dominantly of quartz and K-feldspar, but also contains albite and biotite altered into chlorite. The grain size (2.5–10 cm) increases inwards. The outer intermediate zone (OIZ) consists mainly of quartz and albite (,2.5–10 cm), but it also contains K- feldspar, muscovite, lithian muscovite, ‘‘mixed form’’ (with both dioctahedral and trioctahedral structures, Foster, 1960), zinnwaldite, lepidolite, polylithionite, beryl, garnet, tourmaline, a tabular variety of albite, cassi- terite, gahnite, columbite–tantalite, rutile, uranium miner- als and secondary muscovite and cookeite (an alteration 0935-1221/13/0025-2335 $ 8.55 DOI: 10.1127/0935-1221/2013/0025-2335 # 2013 E. Schweizerbart’sche Verlagsbuchhandlung, D-70176 Stuttgart Eur. J. Mineral. 2013, 25, 967–985 Published online December 2013
Transcript of Micas, feldspars and columbite tantalite minerals from the...
eschweizerbart_xxx
Micas feldspars and columbitendashtantalite minerals from the zoned granitic
lepidolite-subtype pegmatite at Namivo Alto Ligonha Mozambique
ANA M R NEIVA
Department of Earth Sciences and Geosciences Centre University of Coimbra 3000ndash272 Coimbra PortugalCorresponding author e-mail neivadctucpt
Abstract The Namivo granitic lepidolite-subtype pegmatite is concentrically zoned Textural and chemical studies show at thecrystal scale and within each zone that muscovite evolved to lithian muscovite and the latter to lsquolsquomixed formrsquorsquo in the outer and innerintermediate zones and core lsquolsquoMixed formrsquorsquo also evolved to lepidolite in the inner intermediate zone and core Each of these micasrepresents an evolution from the pegmatite outer intermediate zone to the inner intermediate zone and core Some crystals areprogressively zoned while others are reversely zoned but overgrowths and replacements also occur Albite and K-feldspar evolvedfrom the wall zone to the core and feldspar thermometry records a decrease in temperature Columbite-(Mn) shows a compositionaltrend from the outer intermediate zone to the core typical of this mineral from a lepidolite-subtype granitic pegmatite The chemicalzonation of this pegmatite is derived from crystallization of an undercooled granitic melt in which a probably local constitutional zonerefining of fluxing and incompatible elements contributes to the textural and chemical changes from the wall zone to the core Theunexpected occurrence of lepidolite and FeMg-containing polylithionite the richest micas in Si Licalc and F in the outerintermediate zone is attributed to disequilibrium crystallization from an undercooled melt They are associated with tantalite andTa precipitation may have been caused by the local decrease of Li and F in the melt These minerals are uncommon in this zone ofgranitic pegmatites
Key-words muscovite lithium micas albite K-feldspar columbitendashtantalite minerals gahnite electron microprobe pegmatiteevolution
1 Introduction
Micas and feldspars are good petrogenetic indicators ofpegmatite evolution and consequently their geochemistryhas been used to track the consolidation history of pegma-tite bodies (eg Jahns 1982 Jolliff et al 1987 Monieret al 1987 Cerny 1994 Cerny et al 1995 Kile amp Foord1998 Alfonso et al 2003 Roda Robles et al 2006 2007Van Lichtervelde et al 2008 Neiva amp Ramos 2010Vieira et al 2011) However chemical zoning in micasfrom pegmatites has rarely been studied (Neiva et al2008 2012 Van Lichtervelde et al 2008) Columbite-tantalite minerals from granitic pegmatites have been stu-died widely and are tracers of pegmatite fractionation (egCerny et al 1986 Beurlen et al 2008 Neiva et al 20082012 Neiva amp Ramos 2010)
The Namivo granitic pegmatite is located in the centralpart of the Alto Ligonha pegmatite area in northernMozambique (Fig 1) close to the confluence of theNamivo and Molucue rivers in the Zambezia province Ageochemical evolution occurs from green and bluish greenberyl in the outer intermediate zone to pink beryl in theinner intermediate zone lsquolsquocore marginrsquorsquo and core (Neiva amp
Neiva 2005) This paper presents the study of micasfeldspars and columbitendashtantalite minerals to provideinformation on their geochemical evolution and paragen-esis and implications for the Namivo pegmatite evolution
2 General geology and petrography
The Namivo granitic pegmatite intruded a Precambrianmigmatitic paragneiss and the contact is sharp It is alepidolite-subtype pegmatite (Cerny amp Ercit 2005)which is concentrically zoned (Fig 2) The wall zone(WZ) consists dominantly of quartz and K-feldspar butalso contains albite and biotite altered into chlorite Thegrain size (25ndash10 cm) increases inwards
The outer intermediate zone (OIZ) consists mainly ofquartz and albite (25ndash10 cm) but it also contains K-feldspar muscovite lithian muscovite lsquolsquomixed formrsquorsquo(with both dioctahedral and trioctahedral structuresFoster 1960) zinnwaldite lepidolite polylithioniteberyl garnet tourmaline a tabular variety of albite cassi-terite gahnite columbitendashtantalite rutile uranium miner-als and secondary muscovite and cookeite (an alteration
0935-1221130025-2335 $ 855DOI 1011270935-122120130025-2335 2013 E Schweizerbartrsquosche Verlagsbuchhandlung D-70176 Stuttgart
Eur J Mineral
2013 25 967ndash985
Published online December 2013
eschweizerbart_xxx
product of LiAl-silicates) K-feldspar content increasesinwards Albite is penetrated by quartz Micas are mainlyassociated with quartz and beryl The dark brown tourma-line is associated with micas Cassiterite is partially sur-rounded by columbitendashtantalite and rutile and they areassociated with micas and quartz Some columbitendashtanta-lite minerals are associated with lithium micas Rare andsmall uranium minerals penetrate along fractures ofcolumbitendashtantalite
The inner intermediate zone a (IIZa) consists domi-nantly of albite and perthitic K-feldspar (30 cm) andalso contains quartz muscovite lithian muscovitelsquolsquomixed formrsquorsquo lepidolite beryl columbite monazitecookeite and bismutite Micas are mainly associated withK-feldspar and albite Columbite occurs among feldsparcrystals locally penetrating them and is rarely surroundedby monazite The inner intermediate zone b (IIZb) isessentially made of lsquolsquomixed formrsquorsquo lepidolite and a tabular
variety of albite (10 to 30 cm) but also contains quartzK-feldspar muscovite lithian muscovite beryl and bismu-tite Lepidolite and lsquolsquomixed formrsquorsquo abundances increasewith depth Micas are associated with albite and quartzAlbite is the most abundant feldspar in OIZ IIZa and IIZb
The lsquolsquocore marginrsquorsquo (Cm) has mainly quartz and beryl(30 cm) but the core (Cc) consists mainly of quartz andspodumene (10 to 30 cm) and also has albite K-feldsparmuscovite lithian muscovite lsquolsquomixed formrsquorsquo lepidoliteberyl tabular variety of albite columbite and cookeiteMicas are associated with quartz K-feldspar and albiteSpodumene occurs in long crystals up to 5 cm thick cut-ting quartz but some are altered into kaolinite Albite andits tabular variety replace quartz and spodumeneColumbite is associated with albite and quartz
3 Sampling and analytical methods
Several samples from all zones of the Namivo graniticpegmatite and information was given by MB Dias whowas the exploitation manager of the company working thepegmatite in 1962 to JM Cotelo Neiva who visited thepegmatite with him All the available material was used forthis study Feldspars and micas have been selected from thezones where they occur Columbite-tantalite minerals arefrom the OIZ IIZa and Cc and tourmaline and gahnitewere only found in the OIZ
The major elements of minerals were determined using aJeol Hyperprobe JXA-8500F operated at 15 kV accelerat-ing voltage and 10 nA beam current except for columbi-tendashtantalite for which the voltage and current were 20 kVand 20 nA Detection limits (3s) above mean backgroundwere 003 wt for most oxides except for ZnO SrOBaO Rb2O Cs2O (006 wt) and F (01 wt) withcounting times of 80 s for these five oxides and F Theanalyses were carried out at LNEG S Mamede de InfestaPortugal Standards used include albite (NaKa) orthoclase(AlKa SiKa KKa) apatite (CaKa PKa) MgO (MgKa)MnTiO3 (MnKa) TiO2 (TiKa) Fe2O3 (FeKa) ZnS(ZnKa) fluorite (FKa) vanadinite (ClKa) BaSO4
(BaLa) SrTiO3 (SrLa) glasses Ge-Al-Ca containing 100wt Rb (RbLa) and Si-Al-Ca with 100 wt Cs (CsLa)cassiterite (SnKa) pure Ta (La) SrBaNb4O12 (NbLa) andscheelite (WLa)
4 Micas
41 Chemical composition of micas
As different micas are associated in the same crystals(Fig 3) it is impossible to separate them or use a laserablation inductively coupled plasma mass spectrometer(LA-ICP-MS) to determine their trace elementsTherefore ZnO BaO Rb2O and Cs2O contents weredetermined by electron microprobe In general ZnO andBaO contents are low but Rb2O and Cs2O contents are
Fig 2 Zones of the Namivo granitic pegmatite Mozambique Mainconstituents of Wall Zone (WZ ndash quartz K-feldspar) OuterIntermediate Zone (OIZ ndash quartz and albite) Inner IntermediateZone (IIZa ndash albite and perthitic K-feldspar IIZb ndash lsquolsquomixed formrsquorsquolepidolite and tabular variety of albite) and Core (Cm ndash lsquolsquocoremarginrsquorsquo quartz and beryl Cc ndash core-quartz and spodumene)
Fig 1 Location of the Namivo granitic pegmatite in the AltoLigonha pegmatite area of northern Mozambique Simplified mapafter Dias amp Wilson (2000)
968 A M R Neiva
eschweizerbart_xxx
very helpful for the interpretations Li2O contents ofzinnwaldite lepidolite polylithionite and lsquolsquomixedformrsquorsquo were calculated from the equation Li2O frac14 (0289 SiO2) 9658 and of muscovite and lithian muscovitefrom the equation Li2O frac14 03935 F1326 (Tischendorfet al 1997) Secondary micas replacing feldspars werenot analyzed
Variation in the chemical composition of micas from theNamivo granitic pegmatite is shown in Table 1 and Fig 4lsquolsquoMixed formrsquorsquo is of course not a proper mica mineral name(Rieder et al 1999) The chemical distinction between
dioctahedral and trioctahedral micas is the value of 25octahedral cations per formula unit in dioctahedral and25 octahedral cations in trioctahedral micas for a for-mula calculated on the basis of 12 O thorn F atoms (Riederet al 1999) The Li2O content of analyzed lsquolsquomixed formsrsquorsquois calculated for a trioctahedral mica and the value ofoctahedral cations per formula unit is 28 and totals ofanalyses are good (Table 1) indicating that they are trioc-tahedral micas If Li2O contents of these analyses arecalculated for a dioctahedral mica the value of octahedralcations per formula mainly ranges between 23 and 28 and
Fig 3 Backscattered-electron images of zoned micas from the Namivo granitic pegmatite Mozambique Micas a b c d d1 from the OIZ ef f1from the IIZa g h from the IIZb i j from the Cc d1 and f1 are details of d and f respectively Lep ndash lepidolite Zin ndash zinnwaldite Brl ndashberyl Mix f ndash lsquolsquomixed formrsquorsquo Q ndash quartz Pol ndash polylithionite Cst ndash cassiterite Rt ndash rutile Ct ndash columbitendashtantalite Lith mu ndash lithianmuscovite Ab ndash albite Mu ndash muscovite K-fel ndash K-feldspar
Silicate and oxide minerals from a zoned granitic pegmatite 969
eschweizerbart_xxx
Tab
le1
R
epre
sen
tati
ve
elec
tro
nm
icro
pro
be
anal
yse
sin
wt
o
fm
icas
fro
mth
eN
amiv
og
ran
itic
peg
mat
ite
Mo
zam
biq
ue
Ou
ter
Inte
rmed
iate
Zo
ne
-O
IZIn
ner
Inte
rmed
iate
Zo
ne
-II
Za
Zin
Lep
lsquolsquoM
ixed
Frsquorsquo
Lep
Lep
Po
llsquolsquo
Mix
edF
rsquorsquoL
ith
Mu
sP
ol
Lit
hM
us
lsquolsquoM
ixed
Frsquorsquo
lsquolsquoM
ixed
Frsquorsquo
Lep
Mu
sL
ith
Mu
s
Co
mp
osi
tio
nC
ore
Rim
Co
reR
imR
imC
ore
Rim
Co
reC
ore
Rim
Rim
SiO
24
37
15
42
04
52
45
63
75
23
45
87
64
67
14
63
35
91
84
58
54
85
74
81
24
94
64
55
44
61
1T
iO2
06
00
15
04
70
02
02
70
05
mdashmdash
00
2mdash
01
00
03
00
7mdash
00
4A
l 2O
32
21
81
76
52
97
81
59
01
82
11
48
13
12
63
53
31
49
43
71
92
68
82
83
32
46
43
77
03
55
0F
eO8
42
39
74
57
24
44
94
13
11
56
17
51
14
mdash2
68
11
01
50
01
21
15
Mn
O0
60
00
60
33
00
20
21
00
30
10
01
50
05
01
20
27
12
32
16
04
80
53
Mg
O5
15
17
21
06
14
01
33
10
10
87
06
80
94
00
50
09
mdash0
01
mdashmdash
Zn
O0
46
03
20
17
01
10
24
01
30
14
01
00
09
00
60
13
02
60
41
00
60
15
CaO
00
10
01
00
4mdash
00
10
02
00
30
05
00
1mdash
mdash0
02
00
10
02
mdashL
i 2O
2
97
60
13
42
66
35
47
73
23
84
03
07
45
04
34
38
42
54
64
01
60
45
Na 2
O0
08
00
60
23
01
10
23
00
70
29
03
30
06
04
40
13
02
60
13
03
80
28
K2O
10
00
98
41
00
91
02
01
05
89
77
93
39
98
95
09
91
10
28
97
79
95
99
39
81
Rb
2O
08
60
78
06
61
30
02
80
46
05
10
43
04
91
06
15
01
42
16
71
02
11
0C
s 2O
0
06
00
9
00
60
14
00
6
00
6
00
6
00
6
00
60
15
05
50
13
02
2
00
60
03
F5
10
89
92
24
10
50
10
14
10
05
24
60
81
98
41
06
53
84
89
74
10
50
11
0H
2O
18
30
23
33
9mdash
mdashmdash
33
54
12
mdash4
01
19
12
15
09
14
28
39
61
02
03
10
40
81
01
75
10
51
41
04
31
10
38
51
00
51
10
04
21
03
77
10
03
31
02
85
10
19
61
03
19
10
02
51
00
21
O
F2
14
37
80
94
44
14
26
42
21
03
03
44
13
04
52
26
20
53
11
02
10
46
To
tal
99
89
10
03
01
00
81
10
07
31
00
05
99
63
99
48
10
00
89
96
49
98
81
00
59
99
91
10
00
81
00
04
99
75
KR
b(w
t)1
11
21
47
13
41
91
62
11
88
56
26
25
48
98
1
Si
30
85
36
20
30
45
37
47
35
58
38
54
31
02
30
83
38
63
30
45
32
66
32
26
33
51
30
24
30
86
AlIV
09
15
03
80
09
55
02
53
04
42
01
46
08
98
09
17
01
37
09
55
07
34
07
74
06
49
09
76
09
14
PT
40
04
00
40
04
00
40
04
00
40
04
00
40
04
00
40
04
00
40
04
00
40
0A
lVI
09
31
10
09
14
07
09
92
10
17
09
99
15
49
18
54
10
12
19
56
13
96
14
65
13
19
19
74
18
87
Ti
00
32
00
08
00
24
00
01
00
14
00
02
mdashmdash
00
01
mdash0
00
50
00
20
00
4mdash
00
02
Fe2thorn
04
97
02
22
02
57
01
36
02
81
00
72
00
87
00
97
00
62
mdash0
15
10
06
20
08
50
00
70
06
4M
n0
03
60
00
30
01
90
00
10
01
20
00
20
00
60
00
80
00
30
00
70
01
50
07
00
12
40
02
70
03
0M
g0
54
20
17
10
10
60
13
90
13
50
09
90
08
60
06
70
09
10
00
50
00
9mdash
00
01
mdashmdash
Zn
00
24
00
16
00
08
00
05
00
12
00
06
00
07
00
05
00
04
00
03
00
06
00
13
00
21
00
03
00
07
Li
08
44
16
13
09
25
17
73
14
95
19
32
10
26
00
80
19
54
01
14
11
84
11
46
12
64
00
42
01
20
PR
29
13
04
27
53
05
29
73
11
27
62
11
31
32
09
27
72
76
28
22
05
21
1C
a0
00
10
00
10
00
3mdash
00
01
00
01
00
02
00
04
00
01
mdashmdash
00
01
00
01
00
01
mdashN
a0
01
10
00
80
03
00
01
40
03
00
00
90
03
70
04
30
00
80
05
70
01
70
03
40
01
70
04
90
03
6K
09
00
08
38
08
66
08
65
09
17
08
18
07
90
08
47
07
91
08
40
08
82
08
36
08
60
08
41
08
38
Rb
00
39
00
33
00
29
00
56
00
12
00
19
00
22
00
18
00
21
00
45
00
65
00
61
00
73
00
44
00
47
Cs
00
02
00
03
00
02
00
04
00
02
00
02
00
02
00
02
00
02
00
04
00
16
00
04
00
06
00
02
00
01
PA
09
50
88
09
30
94
09
60
85
08
50
91
08
20
95
09
80
94
09
60
94
09
2F
11
39
18
99
04
77
22
07
21
80
20
85
05
17
01
70
20
31
02
23
11
44
10
37
15
87
01
05
02
33
OH
0
86
10
10
11
52
3mdash
mdashmdash
14
83
18
30
mdash1
77
70
85
60
96
30
41
31
89
51
76
7Z
on
esL
DL
DL
DL
DD
D
LD
LD
L
F
igu
res
Fig
s3
a6
ab
Fig
3
bF
igs
3c
6c
Fig
s3
d
d1
6
dF
igs
3e
6e
fF
igs
3f
f1
6g
h
970 A M R Neiva
eschweizerbart_xxx
Tab
le1
C
on
tin
ued
Inn
erIn
term
edia
teZ
on
e-
IIZ
bC
ore
-C
c
Lit
hM
us
Lep
Mu
slsquolsquo
Mix
edF
rsquorsquoL
epL
ith
Mu
slsquolsquo
Mix
edF
rsquorsquoL
epM
us
Lit
hM
us
Co
reR
imC
ore
Rim
Rim
Co
reR
imR
im
SiO
24
69
25
21
64
62
24
90
64
99
94
71
84
90
15
09
54
63
44
65
6T
iO2
00
3mdash
00
40
03
00
30
02
00
1mdash
mdashmdash
Al 2
O3
35
72
22
89
36
17
28
04
24
87
35
10
26
26
23
49
36
31
35
53
FeO
00
10
61
00
70
05
00
70
04
21
81
55
00
10
03
Mn
O0
55
05
80
43
12
92
24
06
01
09
13
30
14
01
4M
gO
mdashmdash
mdashmdash
mdashmdash
mdashmdash
mdashmdash
Zn
O
00
60
10
00
8
00
60
19
0
06
02
50
07
0
06
0
06
CaO
00
30
04
mdashmdash
00
10
01
00
10
01
mdashmdash
Li 2
O
06
55
42
02
54
52
47
90
93
45
15
07
04
70
79
Na 2
O0
41
00
80
49
02
60
16
04
10
13
01
00
55
05
4K
2O
97
99
78
10
16
96
69
76
94
49
33
90
89
97
99
0R
b2O
12
42
30
14
31
79
21
01
34
17
52
13
14
81
69
Cs 2
O0
16
08
7
00
60
62
05
00
11
07
70
79
01
40
12
F1
46
83
40
70
49
97
63
19
25
55
73
51
15
16
9H
2O
38
30
52
41
62
14
08
23
61
18
20
95
39
63
70
10
08
61
03
69
10
02
61
02
51
10
31
61
00
77
10
26
71
02
87
10
05
81
00
75
O
F0
61
35
00
29
21
03
20
08
12
33
30
90
48
07
1T
ota
l1
00
25
10
01
99
99
71
00
41
99
96
99
96
10
03
49
97
81
00
10
10
00
4
KR
b(w
t)7
23
96
44
94
26
44
83
96
15
3
Si
31
10
34
98
30
84
32
68
33
76
31
30
33
02
34
42
30
82
31
02
AlIV
08
90
05
02
09
16
07
32
06
24
08
70
06
98
05
58
09
18
08
98
PT
40
04
00
40
04
00
40
04
00
40
04
00
40
04
00
AlV
I1
90
01
30
71
92
91
47
01
35
51
87
51
38
71
31
21
92
81
89
2T
i0
00
1mdash
00
02
00
02
00
02
00
01
00
01
mdashmdash
mdashF
e2thorn
00
01
00
34
00
04
00
03
00
04
00
02
01
23
00
88
00
01
00
02
Mn
00
31
00
33
00
24
00
73
01
28
00
34
00
62
00
76
00
08
00
08
Mg
mdashmdash
mdashmdash
mdashmdash
mdashmdash
mdashmdash
Zn
00
03
00
05
00
04
00
03
00
09
00
03
00
12
00
03
00
03
00
03
Li
01
73
14
61
00
66
12
11
13
01
02
49
12
21
13
76
01
27
02
11
PR
21
12
84
20
32
76
28
02
16
28
12
86
20
72
12
Ca
00
02
00
03
mdashmdash
00
01
00
01
00
01
00
01
mdashmdash
Na
00
53
00
10
00
63
00
34
00
21
00
53
00
17
00
13
00
71
00
70
K0
82
80
83
70
86
50
82
10
84
10
79
90
80
20
78
20
84
60
84
1R
b0
05
30
09
90
06
10
07
70
09
10
05
70
07
60
09
20
06
30
07
2C
s0
00
50
02
50
00
10
01
80
01
40
00
30
02
20
02
30
00
40
00
3P
A0
94
09
70
99
09
50
97
09
10
92
09
10
98
09
9F
03
06
17
69
01
48
10
51
16
30
04
03
11
83
15
70
02
42
03
56
OH
1
69
40
23
11
85
20
94
90
37
01
59
70
81
70
43
01
75
81
64
4Z
on
esD
LD
D
LD
LL
D
DF
igu
res
Fig
s3
g
6i
jk
Fig
s3
h
6l
Fig
s3
i6
m
nF
igs
3j
6o
p
OIZ
IIZ
aII
Zb
Cc
asin
Fig
2Z
inndash
zin
nw
ald
ite
Lep
ndashle
pid
oli
teF
ndashfo
rmP
olndash
po
lyli
thio
nit
eL
ith
Mu
sndash
lith
ian
mu
sco
vit
eM
us
ndashm
usc
ov
ite
Lndash
ligh
ter
zon
eD
ndashd
ark
erzo
ne
D
-th
ed
ark
estzo
ne
L
-th
eli
gh
test
zon
ein
BS
Eim
ages
BaO
isb
elo
wth
ed
etec
tio
nli
mit
Cal
cula
ted
nu
mb
ero
fio
ns
on
the
bas
iso
f1
2o
xy
genthorn
Fat
om
sL
i 2O
v
alu
esca
lcu
late
dfr
om
equ
atio
ns
of
Tis
chen
do
rff
eta
l
(19
97
)O
H
-ca
lcu
late
db
yd
iffe
ren
ceto
20
00
H
2O
-ca
lcu
late
db
yst
oic
hio
met
ry
Silicate and oxide minerals from a zoned granitic pegmatite 971
eschweizerbart_xxx
analytical totals are not good The analyzed lsquolsquomixedformsrsquorsquo are distinguished in backscattered-electron (BSE)images and chemically (Fig 3b d d1 e f f1 h i andFig 4) The chemical distinction between lsquolsquomixed formrsquorsquoand lepidolite from the OIZ (Fig 4) is clear in Fig 3bwhere lepidolite is darker than lsquolsquomixed formrsquorsquo because theformer has less Fe and Mn than the latter (Table 1) and inFig 3f f1 and 3h for micas from the IIZa and IIZbrespectively where lepidolite is lighter than lsquolsquomixedformrsquorsquo because the former has more Fe2thorn and Mn oronly more Mn than the latter (Table 1) The lsquolsquomixedformsrsquorsquo analyzed are distinguished in the BSE imagesfrom the lepidolite that falls in its fields in the Fig 4The fields of lepidolite composition in Foster (1960) arelarger than the field for lepidolite from the trilithionite tothe polylithionite (Rieder et al 1999) According to Fleet(2003) only a few lepidolite compositions plot on thetrilithionite-polylithionite join In general lepidolite hashigher Si Licalc Rb Cs F contents and lower AlVI andOH contents than lsquolsquomixed formrsquorsquo (Table 1 Fig4)lsquolsquoMixed formrsquorsquo is also clearly distinguished fromlithian muscovite in OIZ IIZa IIZb and Cc in BSEimages (Fig 3d d1 e f i) and chemically (Table 1 Fig4) as it generally has higher Si Licalc Rb Cs F contentsand lower AlVI and OH contents than lithian muscovite
Two distinct trends are defined in Fig 4 One trendconsists of Al-poorer micas which are zinnwaldite
lepidolite and FeMg-containing polylithionite from theOIZ A hiatus occurs between zinnwaldite and lepidolitebut the zinnwaldite series is continuous with the field oflepidolite at the high Li content (Fleet 2003) The othertrend consists of Al-richer micas (muscovite lithian mus-covite and lsquolsquomixed formrsquorsquo from the OIZ IIZa IIZb and Ccand also lepidolite from most of those zones except fromthe OIZ) There is a gap between lithian muscovite and thelsquolsquomixed formrsquorsquo which may be explained by a hiatus inmica stability (eg Jolliff et al 1987) but a solid solutionbetween dioctahedral and trioctahedral micas has beenindicated experimentally (Monier amp Robert 1986) whileother authors have shown that the octahedral site occu-pancy ranges continuously from muscovite to lepidolite(eg Roda Robles et al 2005 Van Lichterveld et al2008 Vieira et al 2011) Most lithian muscovites andlsquolsquomixed formrsquorsquo from the OIZ are richer in Fe2thornthornMg thornMn than those from the other zones due to their higherFe2thorn and Mg contents (Fig 4 Table 1)
In the Al-poorer micas from the OIZ ranging from zinn-waldite to lepidolite and FeMg-containing polylithionite(Fig 4) (AlIV thorn AlVI) Fe2thorn Mg Ti Mn and Zn contentsdecrease and Si and Licalccontents increase (Table 1) In theAl-richer micas ranging from muscovite to lithian muscoviteand lsquolsquomixed formrsquorsquo from the OIZ IIZa IIZb and Cc and alsoto lepidolite from most of those zones except from the OIZ(AlIV thorn AlVI) AlVI and OH contents and KRb ratio
Fig 4 Plots of micas from the Namivo granitic pegmatite Mozambique in the LindashR2thornndashR3thornthorn Ti diagram according to the classification ofFoster (1960) slightly modified (Rieder et al 1999) with R3thorn frac14 AlVI R2thorn frac14 (Fe2thornt thorn Mn2thornthorn Mg) showing the variety of micacompositions Two trends are defined one for Al-poorer micas (zinnwaldite lepidolite and FeMg-containing polylithionite) from theOIZ another for Al-richer micas (muscovite lithian muscovite lsquolsquomixed formrsquorsquo and lepidolite) from all zones except lepidolite from the OIZOIZ IIZa IIZb and Cc as in Fig 2
972 A M R Neiva
eschweizerbart_xxx
generally decrease and Si Licalc Rb Cs and F contentsgenerally increase (Table 1)
42 Main substitution mechanisms
The 2Si thorn Li 3Altotal mechanism operates in the diocta-hedral micas (muscovite and lithian muscovite) (Fig 5a b)whereas the 3LiVI AlVIthorn 2ampVI (amp represents a vacancy)operates in the trioctahedral micas (lsquolsquomixed formrsquorsquo lepido-lite zinnwaldite and FeMg-containing polylithionite) (Fig5c d) which agrees with findings for micas from the Tancopegmatite (Van Lichtervelde et al 2008)
43 Textures and chemical compositions of zoned micacrystals
Backscattered-electron images combined with quantita-tive spot electron-microprobe analyses made it possibleto distinguish different micas in the Namivo graniticpegmatite Similar textural aspects and geochemicalobservations were found between some Al-richer micasfrom the OIZ IIZa IIZb and Cc Some selected zonedcrystals are documented (Table 1 Fig 3 and 6) In theOIZ lepidolite penetrates zinnwaldite along cleavagesand partially surrounds it and the contacts are sharp(Fig 3a) A chemical gap occurs between zinnwalditeand lepidolite compositions (Fig 6a b) Lepidolite withhigher Si Licalc F contents similar KRb value andlower (AlIV thorn AlVI) Ti Fe2thorn Mg (Fe2thornthorn Mn thorn Mg)Zn and OH contents (Table 1) replaces zinnwaldite Athin lepidolite rim partially surrounds lsquolsquomixed formrsquorsquoand the contact is sharp (Fig 3b) The lepidolite rimhas higher Si Mg Licalc Rb F contents and lowerAlVI Ti Fe2thorn Mn Na and OH contents and KRb ratiothan the lsquolsquomixed formrsquorsquo core (Table 1) The lepidoliterim is an Al-poorer mica whereas the lsquolsquomixed formrsquorsquocore is an Al-richer mica (Fig 4) The lepidolite rimcorresponds to an overgrowth The FeMg-containingpolylithionite partially surrounds and penetrates lepido-lite along cleavages and shows well defined contacts(Fig 3c) Both contain rutile cassiterite and columbi-tendashtantalite inclusions A continuous chemical evolutiontakes place from lepidolite to FeMg-containing poly-lithionite (Figs 4 6c) The latter has higher Si LicalcRb contents and lower AlVI Ti Fe2thorn Mn Mg Zn Nacontents and KRb ratio (Table 1) and replaces lepido-lite A lithian muscovite rim with rare FeMg-containingpolylithionite surrounds the lsquolsquomixed formrsquorsquo core and thispolylithionite penetrated lithian muscovite (Fig 3d)The contact between the lithian muscovite rim andlsquolsquomixed formrsquorsquo core is irregular suggesting disequili-brium or at a cleavage (Fig 3d d1) Two linear trendsone for the lithian muscovite rim and another for thelsquolsquomixed formrsquorsquo core are defined in the (Fe2thornthornMnthornMg)vs (AlIV thornAlVI) diagram (Fig 6d) The FeMg-contain-ing polylithionite rim does not belong to any of thesetrends and plots outside this diagram because it is an Al-poorer mica whereas the others are Al-richer micas
(Fig 4) The lithian muscovite rim has higher AlVI(AlIV thorn AlVI) OH contents and KRb ratio and lowerMg (Fe2thornthorn Mn thorn Mg) Licalc Rb F contents than thelsquolsquomixed formrsquorsquo core (Table 1 Fig 6d) The crystal isreversely zoned The FeMg-containing polylithioniterim has higher Si Licalc F contents and lower AlVI(AlIV thorn AlVI) Fe2thorn Mn (Fe2thornthorn Mn thorn Mg) Na andOH contents than the lsquolsquomixed formrsquorsquo core and lithianmuscovite rim (Table 1) and replaces lithian muscovite
In the IIZa some zoned crystals have a lithian muscovitecore and a lsquolsquomixed formrsquorsquo rim and the contacts are gradual(Fig 3e) A small discontinuity occurs in the trends fromthe lithian muscovite core to lsquolsquomixed formrsquorsquo rim in the(Fe2thornthorn Mn thorn Mg) vs (AlIV thorn AlVI) and Rb2O vs KRb(Fig 6e f) The lsquolsquomixed formrsquorsquo rim has higher Si Fe2thornMn (Fe2thornthornMn thornMg) Licalc K Rb Cs F contents andlower AlVI (AlIVthornAlVI) Na OH contents and KRb ratiothan the lithian muscovite core (Table 1 Fig 6e f) indi-cating progressive zoning Similar textural relationshipsand chemical evolutions were found in other zoned crystalsfrom the OIZ IIZb and Cc In another crystal from theIIZa lithian muscovite partially surrounds lsquolsquomixed formrsquorsquointergrown with lepidolite Lithian muscovite also partiallysurrounds muscovite (Fig 3f) The contacts betweenlsquolsquomixed formrsquorsquo and lepidolite and also between muscoviteand lithian muscovite are gradual (Fig 3f f1) whereasthey are well defined for muscovite withlsquolsquomixed formrsquorsquoand lepidolite (Fig 3f f1) The crystal has a lsquolsquomixed formrsquorsquoand lepidolite core and a partial rim of muscovite andlithian muscovite The lsquolsquomixed formrsquorsquo core evolved tolepidolite core as the Si Fe2thorn Mn (Fe2thornthorn Mn thorn Mg)Licalc K Rb Cs and F contents increase and the (AlIV thornAlVI) and KRb ratio decrease (Table 1 Fig 6g h) The SiFe2thorn Mn (Fe2thornthorn Mn thorn Mg) Licalc Rb and F contentsincrease and the (AlIV thorn AlVI) and KRb ratio decreasefrom the muscovite rim to the lithian muscovite rim (Table1 Fig 6g h) suggesting that the former evolved to thelatter The muscovite rim has higher AlVI (AlIV thorn AlVI)Na OH contents and KRb ratio and lower Si Fe2thorn Mn(Fe2thornthornMn thornMg) Zn Licalc Rb and F contents than thelsquolsquomixed formrsquorsquo core and lepidolite core (Table 1 Fig 6gh) Muscovite was probably reversely formed and evolvedafterwards to lithian muscovite
In the IIZb some crystals have a lithian muscovite coreand a thinner lepidolite rim (Fig 3g) and others show asmall muscovite core and a larger rim of lsquolsquomixed formrsquorsquointergrown with lepidolite (Fig 3h) The contacts betweenthe cores and rims are well defined There are increases inthe Si Mn (Fe2thornthorn Mn thorn Mg) Licalc Rb and F contentsand decreases in the AlVI (AlIVthornAlVI) and KRb ratio fromthe lsquolsquomixed formrsquorsquo rim to the intergrown lepidolite rim(Table 1 Figs 3h 6l) suggesting that the former evolvedto the latter as also found in IIZa and Cc In both crystalsthe rim compositions have higher Si (Fe2thornthorn Mn thorn Mg)Licalc Rb Cs F contents and lower AlVI (AlIVthorn AlVI) Naand OH contents and KRb ratio than the core (Table 1 Figs3g 6i j k 3h 6l) A compositional gap occurs between coreand rim in the diagrams for both crystals (Fig 6i j k l)suggesting that both rims correspond to overgrowths and no
Silicate and oxide minerals from a zoned granitic pegmatite 973
eschweizerbart_xxx
diffuse reequilibration took place in any crystal as thecontacts between core and rim are sharp
In the Cc lithian muscovite is surrounded and pene-trated by lsquolsquomixed formrsquorsquo showing well defined contacts(Fig 3i) The lsquolsquomixed formrsquorsquo has higher Si Fe2thorn Mn(Fe2thornthorn Mn thorn Mg) Licalc Rb Cs F contents and lowerAlVI (AlIV thorn AlVI) Na OH contents and KRb ratio thanthe lithian muscovite (Table 1 Fig 6m n) and a composi-tional gap occurs between both micas suggesting thatlsquolsquomixed formrsquorsquo replaced lithian muscovite In rare crystalsa small lepidolite core is surrounded by a large muscoviterim containing K-feldspar inclusions The contact betweenthe core and rim is sharp (Fig 3j) A thin partial rim oflithian muscovite surrounds muscovite and the contact isgradual The muscovite rim has higher AlVI (AlIVthornAlVI)Na K OH contents and a greater KRb value and lower SiFe2thorn Mn Licalc Rb Cs and F contents than the lepidolitecore (Table 1 Fig 6o p) and a compositional gap occursbetween them (Fig 6o p) indicating that either muscoviteforms an overgrowth or it is reversely formed From themuscovite rim to the lithian muscovite rim the Si Licalc
Rb F contents increase whereas the AlVI (AlIV thorn AlVI)and OH contents and KRb ratio decrease (Table 1 Fig 6op) suggesting that muscovite evolved to lithian muscoviteas also found in IIZa and IIZb
44 Evolution of mica compositions within each zoneand from the outer intermediate zone to the core of theNamivo granitic pegmatite
The KRb ratio is taken as the best fractionation index inmicas (eg Cerny et al 1985 Foord et al 1995 Wise1995 Pesquera et al 1999 Roda Robles et al 2006 2007)It is hard to establish trends in the evolution of mica com-position from muscovite and lithian muscovite to lsquolsquomixedformrsquorsquo and lepidolite within each zone because the KRbratio shows some partial overlapping particularly betweenthe lithian muscovite and lsquolsquomixed formrsquorsquo and also betweenthe latter and lepidolite However an evolution from mus-covites to lepidolite (Al-richer mica Fig 4) is clearer (Fig7) In general in IIZa IIZb and Cc the Si Licalc Rb Cs and
Fig 5 The main substitutions in micas from the Namivo granitic pegmatite Mozambique a b SiIVthorn LiVI versus AlIVthornAlVI showing the 2SithornLi 3Altotal substitution mechanism operating in dioctahedral micas (Mu muscovite and Lith mu lithian muscovite) c d AlVI thornamp VI
versus LiVI (where amp represents a vacancy) and showing the 3LiVI AlVI thorn 2 amp VI substitution mechanism operating in trioctahedral micas(Mix f ndashlsquolsquomixed formrsquorsquo Lep lepidolite Zin zinnwaldite and Pol-FeMg-containing polylithionite) OIZ IIZa IIZb and Cc as in Fig 2
974 A M R Neiva
eschweizerbart_xxx
F contents tend to increase and the (AlIV thorn AlVI) AlVI
contents and KRb ratio tend to decrease from muscoviteto lepidolite (Table 1 Fig 7) This sequence is consistentbut rarely in the Cc lepidolite is rimmed by muscovite (Fig3j) But in the OIZ the evolution stops in lsquolsquomixed formrsquorsquoparticularly shown by the large range of the KRb ratiowhich mainly overlaps that of lepidolite from this zone(Fig 7) because this lepidolite is an Al-poorer mica whereasthe others are Al-richer micas (Fig 4)
In the OIZ the lepidolite has more Si Licalc and F andless (AlIV thorn AlVI) Ti Fe2thorn Mn Mg and Zn than zinn-waldite (Table 1) but it has larger ranges of Rb and KRbratio than zinnwaldite (Fig 7) The FeMg-containingpolylithionite is the richest mica in Si Licalc and thepoorest in (AlIV thorn AlVI) (Table 1) But at this zone scalethe polylithionite has Rb Cs contents and KRb ratiowithin the ranges for lepidolite and close to those of zinn-waldite (Fig 7)
Fig 6 Variation diagrams of micas from selected zoned crystals from the zones of the Namivo granitic pegmatite Mozambique to showtheir relationships lith musc lithian muscovite OIZ IIZa IIZb and Cc an in Fig 2
Silicate and oxide minerals from a zoned granitic pegmatite 975
eschweizerbart_xxx
From the OIZ to IIZa IIZb and Cc muscovite and lithianmuscovite generally show increases in the Si Licalc F and Rbcontents and decreases in the Fe2thorn and Mg contents and KRb ratio but the Mg content is very low in these micas fromthe IIZa IIZb and Cc (Table 1 Fig 7a) The lsquolsquomixed formrsquorsquoshows increases in the Si Licalc F Rb Cs contents anddecreases in the (AlIV thorn AlVI) and Mg contents and KRbratio but the Mg content is very low in this mica from theIIZb and Cc (Table 1 Fig 7b c) The lepidolite shows anincrease in the Si Licalc F Rb and Cs contents and a decreasein the KRb ratio from the IIZa to the IIZb and Cc (Table 1Fig 7d e) Furthermore the lepidolite from the OIZ has thelowest (AlIV thorn AlVI) AlVI and OH contents the highest SiFe2thorn Licalcand F contents and KRb ratio and the lowest Rband Cs contents compared to lepidolite from the other zones(Table 1 Fig 7d e)
5 Feldspars
Selected chemical analyses of albite and K-feldspar fromfive zones of the Namivo granitic pegmatite are given inTable 2 Strontium is the most abundant trace element inalbite (eg Cerny 1994) Anorthite and Sr contents and SrCa ratio of albite decrease from the WZ to the Cc (Fig 8Table 2) Rubidium is the most abundant trace element inK-feldspar followed by Cs in IIZa IIZb and Cc In gen-eral K Rb and Cs contents of K-feldspar increase and KRb and KCs values decrease from the WZ to the Cc (Table2 Fig 9)
The program SOLVCALC 20 (Wen amp Nekvasil 1994)using the Margules model Fuhrman amp Lindsley (1988) wasapplied for the purpose of thermometry The pairing ofplagioclase cores with the K-feldspars average of eachsample was used to estimate the crystallization temperaturesof primary magmatic feldspars They are 405 C (WZ)406ndash340 C (OIZ) 390ndash335 C (IIZa) 347ndash306 C (IIZb)and 333ndash289 C (Cc) at 3 kbar The metamorphic environ-ment of rare-element-Li granitic pegmatites is one of lowpressure 2ndash4 kbar (Cerny amp Ercit 2005) In general thedifference between the maximum and minimum calculatedtemperatures at 2 3 and 4 kbar for the same feldspar pairfrom the Namivo pegmatite is lower than 40 C The tem-perature decreases from the wall zone (WZ) to the core(Cc) A similar temperature behavior of feldspars wasfound in the pegmatite-aplite dike USA (Morgan ampLondon 1999)
6 Other silicates
Tourmaline of schorl composition was only found inthe OIZ (Table 2) because there was not enough Feand Mg for schorl to precipitate in the other zonesSpodumene only occurs in the Cc and its compositionis nearly pure (Table 2)
7 Columbite-tantalite
Representative chemical analyses of columbitendashtantalitefrom the Namivo granitic pegmatite are given in Table 3and plotted in the columbite quadrilateral (Fig 10a)Most crystals are unzoned but zoned crystals with dar-ker and lighter zones in BSE images are from the Cc Thelighter zone of columbite-(Mn) has higher Ta contentTa(Ta thorn Nb) and Mn(Mn thorn Fe) values and lower Nbcontent than the darker zone (Fig 10a b) The crystals ofthe columbitendashtantalite minerals are low in W Sn and Tiimpurities (Table 3)
The main trend starts from the columbite-(Mn) of theOIZ towards the more Mn-enriched and slightly Ta-enriched columbite-(Mn) from the IIZa and Cc The high-est Ta(Ta thorn Nb) values belong to the lighter zone ofcolumbite-(Mn) with Mn(Mn thorn Fe) frac14 10 from the CcThe richest columbite-(Mn) in Ta(TathornNb) and composi-tions of tantalite-(Fe) and tantalite-(Mn) were only foundin the OIZ (Fig 10a) and are associated with lepidolite andpolylithionite (Fig 3c)
8 Gahnite
Gahnite was rarely found in the OIZ and shows a darkerzone that partially surrounds a lighter zone in a BSE image(Fig 11a) The darker zone has a higher Zn content andlower Sn Ti Nb Ta Mn contents and SnZn value than thelighter zone (Table 4 Fig 11b c) These gahnite composi-tions fall within the igneous field of Batchelor amp Kinnaird(1984) The darker zone is closer in composition to thepure gahnite (Zn8Al16O32) than the lighter zone whichcontains up to 0983 apfu Sn 0195 apfu Ti 1029 apfutotal Fe2thorn 0101 apfu Mn (Table 4) and consequently hasa composition distinct from nigerite In general both thedarker and lighter zones have higher Sn Ti and Fe contentsthan gahnite from the granitic pegmatites of Nigeria(Batchelor amp Kinnaird 1984) Arga northern Portugal(Gomes et al 1995) and Cabanas northern Portugal(Neiva amp Champness 1997) Borborema province north-eastern Brazil (Soares et al 2007) The Zn=Fe2thornt values ofthe darker and lighter zones of gahnite from Namivo arelower than those reported in Neiva amp Champness (1997)and Soares et al (2007)
9 Discussion and conclusions
91 Evolution of micas in the zoned pegmatite
In general individual mica crystals show varying patternsand compositional zoning involving several elementsmainly Si AlVI (AlIV thorn AlVI) Fe2thorn Mn (Fe2thornthorn Mn thornMg) Licalc Rb Cs F and OH and the KRb ratioProgressively zoned crystals from the IIZa show grada-tional contacts between a lithian muscovite core and a
976 A M R Neiva
eschweizerbart_xxx
lsquolsquomixed formrsquorsquo rim (Figs 3e 6e f) and the zoning patternscorrespond to fractionation trends and probably reflect adrop in temperature during the crystallization of the grani-tic pegmatite melt Progressively zoned crystals also occurin OIZ IIZb and Cc Some crystals are reversely zonedwith a) a lsquolsquomixed formrsquorsquo core and a lithian muscovite rimfrom the OIZ (Figs 3d d1 6d) b) a core consisting oflsquolsquomixed formrsquorsquo and lepidolite and a rim of muscovite andlithian muscovite from the IIZa (Figs 3f f1 6g h) c) alepidolite core and a muscovite and lithian muscovite rimfrom the Cc (Figs 3j 6o p) which may be explained bythe hypothesis of oscillations in the compositions of themelt from which they grew alternating between an Li-enriched boundary layer and a bulk melt that is less frac-tionated The muscovite evolved to lithian muscovite inIIZa and Cc (Figs 3f 6g h 3j 6o p) Replacements (Figs3a 6a b 3c 6c 3i 6m n Table 1) occur in OIZ and Ccand overgrowths (Figs 3b g 6i j k 3h 6l Table 1) occurin OIZ and IIZb as found in BSE images
Muscovite evolved to lithian muscovite as observed inOIZ IIZa IIZb and Cc (Figs 3f 6g h 3j 6o p Table 1)Lithian muscovite evolved to lsquolsquomixed formrsquorsquo in OIZ IIZaIIZb and Cc (Figs 3e 6e f Table 1) and lsquolsquomixed formrsquorsquoevolved to lepidolite in IIZa IIZb and Cc (Figs 3f f1 6gh 3h 6l Table 1) All these evolutions are due to fractionalcrystallization
In the OIZ lepidolite has more Si Licalcand F butsimilar KRb to that of zinnwaldite and replaces it (Figs
3a 6a b 7d Table 1) An FeMg-containing polylithionitehas higher Si Licalcand Rb contents and a smaller KRbratio than the lepidolite that it replaces (Figs 3c 6c Table1) and a continuous chemical evolution from lepidolite topolylithionite is shown
The trends for major and trace elements of micas withineach zone are difficult to define due to some partial over-lapping but a progressive evolution from muscovite to lithianmuscovite lsquolsquomixed formrsquorsquo and lepidolite in IIZa IIZb and Ccis mainly shown by an increase in the Si Licalc F Rb and Cscontents and a decrease in the KRb ratio and this is simi-larly shown in the OIZ from muscovite to lsquolsquomixed formrsquorsquo(Table 1 Fig 7) In the OIZ Si and Licalccontents increaseprogressively from zinnwaldite to lepidolite and FeMg-containing polylithionite but a gap occurs between zinnwal-dite and lepidolite (Table 1 Fig 4) whereas a continuousevolution from lepidolite to polylithionite is observed TheKRb ratios of zinnwaldite and polylithionite are within therange of that of lepidolite (Fig 7d e)
Each Al-richer mica (muscovite lithian muscovite andlsquolsquomixed formrsquorsquo) exhibits an evolution from the OIZ to theIIZa and then to the IIZb and Cc particularly shown by anincrease in the Si Licalc F and Rb contents and adecrease in the KRb ratio but also an increase in theCs content in the lsquolsquomixed formrsquorsquo (Table 1 Fig 7) Theseelements and ratio have been used as petrogenetic indi-cators of evolution in micas from pegmatites (eg Cernyet al 2005 Roda Robles et al 2006 2007 Vieira et al
Fig 7 Plot of some variation diagrams of micas from the OIZ IIZa IIZb and Cc of the Namivo granitic pegmatite Mozambique showingthat the Rb2O and Cs2O contents increase and the KRb ratio decreases for micas from the OIZ to the Cc OIZ IIZa IIZb and Cc as in Fig 2
Silicate and oxide minerals from a zoned granitic pegmatite 977
eschweizerbart_xxx
Tab
le2
R
epre
sen
tati
ve
elec
tro
nm
icro
pro
be
anal
yse
sin
wt
o
ffe
ldsp
ars
sch
orl
and
spo
du
men
efr
om
the
Nam
ivo
gra
nit
icp
egm
atit
eM
oza
mb
iqu
e
Alb
ite
K-f
eld
spar
Sch
orl
Sp
od
um
ene
Zo
nes
WZ
OIZ
IIZ
aII
Zb
Cc
Zo
nes
WZ
OIZ
IIZ
aII
Zb
Cc
Zo
nes
OIZ
Zo
ne
Cc
SiO
26
75
76
78
86
87
06
84
76
84
1S
iO2
65
10
65
55
65
46
64
96
64
72
SiO
23
52
0S
iO2
64
65
TiO
20
02
mdash0
02
mdashmdash
TiO
2mdash
00
1mdash
mdashmdash
TiO
20
35
Al 2
O3
27
20
Al 2
O3
20
25
19
74
19
67
19
88
19
97
Al 2
O3
18
96
18
23
18
31
18
24
18
05
B2O
3
10
28
Fe 2
O3
00
6F
e 2O
3mdash
mdashmdash
mdash0
10
Fe 2
O3
mdash0
02
mdash0
03
mdashA
l 2O
33
17
2M
nO
01
3M
nO
00
6mdash
mdashmdash
mdashM
nO
mdash0
03
00
3mdash
mdashF
eO1
35
2M
gO
01
8M
gO
mdashmdash
mdashmdash
mdashM
gO
00
10
01
00
5mdash
mdashM
nO
03
3N
a 2O
01
9C
aO1
04
08
00
56
03
70
32
CaO
00
10
01
00
60
01
00
2M
gO
22
8L
i 2O
8
05
Na 2
O1
06
11
12
01
12
11
13
41
13
4N
a 2O
06
50
58
04
10
59
03
8C
aO0
23
To
tal
10
04
6K
2O
00
50
17
00
60
14
01
0K
2O
14
72
14
75
15
67
15
01
15
74
Li 2
O
02
2S
rO0
72
05
00
24
01
1mdash
Rb
2O
00
90
20
03
00
59
09
0N
a 2O
22
8S
i1
99
7P
2O
50
01
00
4mdash
mdashmdash
Cs 2
O
00
6
00
60
09
01
80
20
K2O
00
1A
lIV0
00
3T
ota
l1
00
33
10
03
31
00
46
10
03
11
00
24
P2O
5mdash
00
3mdash
mdashmdash
H2O
3
18
P2
00
To
tal
99
60
99
48
10
03
89
96
11
00
01
F0
78
AlV
I0
98
7S
rC
a(w
t)0
81
07
40
50
03
50
Cl
mdashF
e3thorn
00
01
KR
b(w
t)153
68
48
23
16
Sum
1003
8P
09
9S
i1
18
23
11
87
91
19
58
11
93
21
19
21
KC
s(w
t)4
07
20
41
63
73
69
O
F0
33
Li
10
00
P0
00
10
00
6mdash
mdashmdash
To
tal
10
00
5M
n0
00
3T
i0
00
3mdash
00
03
mdashmdash
Si
11
98
61
20
88
12
04
11
20
45
12
03
3M
g0
00
8A
l4
17
64
07
14
03
54
08
34
10
1P
mdash0
00
5mdash
mdashmdash
TS
i5
95
2N
a0
01
2F
e3thorn
mdashmdash
mdashmdash
00
13
Ti
mdash0
00
1mdash
mdashmdash
Al
00
48
P1
02
Mn
00
09
mdashmdash
mdashmdash
Al
41
14
39
62
39
70
39
86
39
55
B3
00
0M
gmdash
mdashmdash
mdashmdash
Fe3thorn
mdash0
00
3mdash
00
04
mdashZ
Al
60
00
Ca
01
95
01
50
01
04
00
69
00
60
Mn
mdash0
00
50
00
5mdash
mdashY
Al
02
74
Sr
00
73
00
51
00
24
00
11
mdashM
g0
00
30
00
30
01
4mdash
mdashT
i0
04
5N
a3
59
93
80
03
78
33
83
23
83
1C
a0
00
20
00
20
01
20
00
20
00
4M
g0
57
5K
00
11
00
38
00
13
00
31
00
22
Na
02
32
02
07
01
46
02
12
01
37
Mn
00
47
K3
45
73
47
03
67
73
55
03
73
3F
e2thorn
19
12
Z1
60
01
59
61
60
01
60
11
60
4R
b0
01
10
02
40
03
50
07
00
10
8L
i0
14
8X
38
94
04
39
33
94
39
1C
s0
00
20
00
50
00
70
01
40
01
6P
Y3
00
0m
ole
s
XC
a0
04
2A
n5
13
82
71
71
5Z
16
10
16
06
16
01
16
03
15
99
Na
07
47
Ab
94
69
53
97
09
75
97
9X
37
13
72
39
03
85
40
0K
00
02
Or
03
09
03
08
06
mo
les
amp
02
09
An
01
01
03
01
01
Ab
63
56
38
56
35
OH
35
83
Or
93
69
43
95
99
43
96
4F
04
17
Cl
mdash
WZ
ndashw
allzo
ne
OIZ
ndasho
ute
rin
term
edia
tezo
ne
IIZ
aan
dII
Zb
ndashin
ner
inte
rmed
iate
zon
esC
cndash
core
asin
Fig
2B
aOis
bel
ow
the
det
ecti
on
lim
itin
bo
thfe
ldsp
ars
Cs 2
Ofrac14
00
3w
tin
the
K-
feld
spar
fro
mth
eW
Z
mdashN
ot
det
ecte
d
Nu
mb
ero
fio
ns
on
the
bas
iso
f3
2o
xy
gen
sfo
ral
bit
ean
dK
-fel
dsp
ar
31
anio
ns
(O
OH
F
)fo
rsc
ho
rlan
d6
ox
yg
ens
for
spo
du
men
e
-A
mo
un
tin
ferr
edfr
om
con
sid
erat
ion
so
fst
oic
hio
met
ry
978 A M R Neiva
eschweizerbart_xxx
2011) Lepidolite from the OIZ is an Al-poorer mica (Fig4) and has the highest Si Licalcand F contents (Table 1)indicating that an evolution cannot be shown from thislepidolite to lepidolites from the other zones which areAl-richer micas (Fig 4) However there is a regulardecrease in the KRb ratio and a progressive increase inthe Rb and Cs contents from lepidolite of the OIZ tolepidolite of IIZa IIZb and Cc (Fig 7) which indicatesthat the KRb ratio and Rb and Cs contents must not beconsidered alone to show fractional crystallization in
lepidolites particularly if some are Al-richer micas andothers Al-poorer micas The high Licalcand F contents oflepidolite from the OIZ did not decrease its KRb ratioSuch an effect is considered to have taken place in lepi-dolite (an Al-richer mica) from the wall zone of the Tancopegmatite Manitoba Canada (Van Lichtervelde et al2008) An evolution from the lepidolite of the IIZa to thatof the Cc is generally shown by the increasing Si LicalcF Rb Cs contents and a decrease in the KRb ratio (Table1 Fig 7)
At the scale of crystals the pegmatite zones and alsothose from the OIZ to the Cc of the Namivo granitic pegma-tite Al-richer micas show fractionation because theyformed from the fractionation of an Li-rich pegmatite melt
The Al-poorer micas zinnwaldite lepidolite and FeMg-containing polylithionite only occur in the OIZ (Fig 4)Polylithionite is the mica richest in Si and Licalc and lepi-dolite from this zone is the richest in Si Licalcand F (Fig 4Table 1) The high Li contents of these micas reflect aconsiderably higher D(Li) at low temperature (Icenhoweramp London 1995) These Li-rich micas may have crystal-lized from an undercooled melt This hypothesis does notimply high Rb and Cs contents and low KRb ratios Thisagrees with the fact that these micas from the OIZ havesimilar Rb and Cs contents and KRb ratios to those of Al-richer micas (muscovite lithian muscovite and lsquolsquomixedformrsquorsquo) from the same pegmatite zone (Fig 7) Howeverthe lepidolite from the wall zone of the Tanco pegmatiteCanada of a similar origin has a low KRb ratio which isattributed to the complexly interrelated structural compo-nents of this lepidolite (Van Lichtervelde et al 2008) TheLi-rich micas from the OIZ may also represent disequili-brium These two hypotheses are considered the best forthese micas of primary magmatic origin
Another hypothesis was also considered They may havecrystallized in boundary layers which concentrate Li andF But this mechanism was suggested for the most fractio-nated tourmaline enriched in Li and F from the core of the
Fig 8 Plot of albite compositions from all zones of the Namivo granitic pegmatite Mozambique showing that the anorthite content of albitedecreases from the WZ to the Cc WZ OIZ IIZa IIZb and Cc as in Fig 2
Fig 9 The Rb vs Cs diagram of K-feldspar from all zones of theNamivo granitic pegmatite Mozambique showing that the Rb andCs contents of K-feldspar increase from the WZ to the Cc WZ OIZIIZa IIZb and Cc as in Fig 2
Silicate and oxide minerals from a zoned granitic pegmatite 979
eschweizerbart_xxx
Little Three pegmatite dike USA (Morgan amp London1999) and the micas enriched in Li and F from theNamivo pegmatite belonging to the OIZ Furthermore ina boundary layer melt that became enriched in Li and F theKRb ratio of micas decreases strongly (Van Lichterveldeet al 2008) which was not found in these micas from theOIZ (Fig 7d) Nor can they have resulted from the crystal-lization of a late melt that would have reacted with the OIZbecause these micas are among those containing the high-est KRb values (Fig 7d)
92 The importance of feldspars micas andcolumbitendashtantalite compositions to the Namivogranitic pegmatite evolution
The trace elements Rb and Cs and the KRb and KCs ratioshave been used to show the evolution of K-feldspar inpegmatites (eg Cerny 1994 Cerny et al 2005 RodaRobles et al 2005) The Rb and Cs contents increase andthe KRb and KCs ratios of K-feldspar decrease from theWZ to the Cc (Fig 9 Table 2) reflecting the growth of K-feldspar from an increasingly fractionated melt withouthaving grown from or having been chemically modifiedby an aqueous fluid as in the Swamp pegmatite section atthe Little Three Mine USA (London et al 2012) Thecrystallization of K-feldspar from an exsolved aqueousfluid from melt will reverse the magmatic fractionation ofRb Cs KRb and KCs because Rb and especially Cs areso much more compatible in vapor that both Rb and Csremain in the fluid phase (London et al 2012) The feldsparsolvus pairs in the Namivo pegmatite record magmaticcrystallization temperatures that decrease from WZ to CcAlbite shows a decrease in the Ca Sr contents and SrCaratio from the WZ to the Cc (Fig 8 Table 2) Therefore thefeldspars and also Al-richer micas as already explainedshow fractionation in this zoned pegmatite
In general lepidolite from the Namivo pegmatite hassimilar Rb2O and Cs2O contents and KRb (wt) values tothose of lepidolite from the Rozna and Dobra Voda lepi-dolite-subtype pegmatites in the Czech Republic (Cernyet al 1995) but lower Rb2O and Cs2O contents thanlepidolite from the lepidolite-subtype pegmatite at RedCross Lake Manitoba Canada (Cerny et al 2012a) K-feldspar from the Namivo pegmatite also has lower Rb2O
Table 3 Representative electron microprobe analyses in wt of columbitendashtantalite from the Namivo granitic pegmatite Mozambique
Outer Intermediate Zone - OIZ Inner Intermediate Zone - IIZa
Core - Cc
D L L
WO3 022 059 079 113 101 351 050 007Ta2O5 5487 5123 2503 3186 2888 2519 3127 4542Nb2O5 2537 3000 5483 4635 5113 5144 4911 3686SnO2 008 015 024 049 020 026 017 012TiO2 263 161 136 254 202 145 125 016FeO 860 710 665 471 236 068 mdash mdashMnO 793 952 1099 1304 1400 1725 1748 1718Total 9970 10020 9989 10012 9960 9978 9978 9981W 0004 0011 0013 0019 0016 0057 0008 0001Ta 1065 0975 0422 0552 0495 0430 0543 0847Nb 0819 0949 1538 1336 1456 1460 1418 1143Sn 0002 0004 0006 0012 0005 0007 0004 0003Ti 0141 0085 0063 0122 0096 0068 0060 0008Fe 0513 0416 0345 0251 0124 0036 mdash mdashMn 0479 0564 0578 0704 0747 0917 0945 0998P
3023 3004 2965 2996 2939 2975 2978 3000Mn(Mn thorn Fe) 048 058 063 074 086 096 100 100Ta(Ta thorn Nb) 057 051 022 029 025 023 028 043Classification tant-(Fe) tant-(Mn) col-(Mn) col-(Mn) col-(Mn) col-(Mn) col-(Mn) col-(Mn)
D ndash darker L ndash lighter zones mdash Not detected tant-tantalite col-columbite Cation formula on the basis of 6 atoms of oxygen
Fig 10 Compositions of columbitendashtantalite from the Namivogranitic pegmatite Mozambique in the columbite quadrilateralshowing that Mn(Mn thorn Fe) of columbite-(Mn) increases from theOIZ to the Cc and the richest columbite-(Mn) in Ta(Ta thorn Nb)tantalite-(Fe) and tantalite-(Mn) only occur in the OIZ OIZ IIZaand Cc as in Fig 2
980 A M R Neiva
eschweizerbart_xxx
and Cs2O contents than K-feldspar from the lepidolite-subtype pegmatite at Red Cross Lake The Rb2O andCs2O contents of primary and late K-feldspar of this peg-matite at Red Cross Lake attained unprecedented levels(Cerny et al 2012a) The lowest KRb (wt) values ofmuscovite lithian muscovite lsquolsquomixed formrsquorsquo and lepido-lite from the IIZb and Cc (Fig 7) and K-feldspar (KRb frac1414) from the Cc compare well with those found in theseminerals from the AC6frac143 lepidolite-subtype pegmatitefrom Greer Lake (Cerny et al 2005) and some of themost fractionated pegmatites worldwide which belong tothe petalite-subtype (eg Tanco Manitoba Cerny 2005Cerny et al 1998 Varutrask Sweden Cerny et al 2005)but muscovite lithian muscovite and lepidolite from theIIZb and Cc have lower Rb2O and Cs2O contents than thesemicas from the Tanco pegmatite (Cerny 2005a VanLichtervelde et al 2008) K-feldspar also has lower
contents of these oxides than the most evolved K-feldsparfrom the Tanco pegmatite (Cerny 2005a) The magmaticfractionation was strong from the WZ to IIZb and Cc of theNamivo lepidolite-subtype pegmatite
The compositional trend of columbite-(Mn) from the OIZto Cc of the Namivo granitic lepidolite-subtype pegmatite(Fig 10) is identical to that of columbite-group mineralsfrom the lepidolite-subtype complex granitic pegmatitesfrom the Dobra Voda in the Moldanubicum CzechRepublic (Novak amp Cerny 1998) and the HimalayaDistrict southern California (shown in Cerny et al 2004)Experimental data for the Fe-Mn pair (Linnen amp Cuney2005) suggest an increase in Fe with fractional crystalliza-tion which is not observed in nature Other phases seem tocontrol the bahavior of Fe and Mn in the melt eg thecrystallization of tourmaline causes a rapid increase of theMnFe in the melt (Van Lichtervelde et al 2006) When thecrystallization of tourmaline stopped the columbitendashtantaliteminerals showed a constant MnFe indicating that the Fe andMn contents in the melt remained constant Schorl onlyoccurs in the OIZ of the Namivo granitic pegmatite and itscrystallization cannot be responsible for the increase in theMnFe of the melt because Mn(Mn thorn Fe) of columbite-(Mn) increases progressively from the OIZ to the IIZa and Cc(Fig 10) Garnet zinnwaldite and gahnite containing Fe andMn also only occur in the OIZ and cannot also have causedthe increase of the MnFe in the melt The dominant Mnenrichment before Ta enrichment started in the columbitendash-tantalite composition from some granitic pegmatites isattributed to an increased alkali-fluoride activity at moderatemHF (Cerny et al 2004) and an increase in the activity offluorine (Martins et al 2011) Each Al-richer mica (musco-vite lithian muscovite and lsquolsquomixed formrsquorsquo) from the Namivogranitic pegmatite shows an increase in F content from theOIZ to the IIZa IIZb and Cc (Table 1) In general the Fcontent of lepidolite also increases from the IIZa to the IIZband Cc Therefore the extreme Fe-Mn fractionation beforeTa enrichment in columbite-(Mn) (Fig 10) may be due to anincrease in the activity of fluorine as a consequence offractional crystallization The increase in the Ta content ofcolumbite-(Mn) from the Namivo granitic pegmatite isattributed to fractional crystallization
The geochemical evolution of albite and K-feldsparfrom the WZ to the Cc Al-richer micas muscovite lithianmuscovite and lsquolsquomixed formrsquorsquo from the OIZ to the Cc andlepidolite from the IIZa to the Cc and columbite-(Mn) andalso beryl (Neiva amp Neiva 2005) from the OIZ to the Ccare caused by magma fractionation The pegmatite zonesare the product of primary crystallization from a volatile-rich silicate melt The pegmatite consolidated from the WZto the Cc The IIZb is one of the most evolved zones asalso suggested by the beryl composition (Neiva amp Neiva2005) and is the richest in lsquolsquomixed formrsquorsquo and lepidolite
The richest columbite-(Mn) in Ta(Ta thorn Nb) and com-positions of tantalite-(Fe) and tantalite-(Mn) only occur inthe OIZ (Fig 10a) associated with lepidolite and polythio-nite (Fig 3c) which may be due to the local depletion of Liand F in the melt which decreases the solubility of Ta andcauses Ta precipitation (Linnen 1998 Linnen amp Cuney
Fig 11 a Backscattered-electron image of a gahnite crystal with adarker zone partially surrounding a lighter zone from the OIZ of theNamivo granitic pegmatite b c Plot of gahnite compositions in theSn-Zn-Ti diagram (atomic proportions) showing a chemical distinc-tion between the lighter and darker zones OIZ as in Fig 2
Silicate and oxide minerals from a zoned granitic pegmatite 981
eschweizerbart_xxx
2005) At the Tanco pegmatite Ta oxides are also asso-ciated with lepidolite enriched in Li and F from the wallzone (Van Lichtervelde et al 2008)
93 Origin and evolution of the zoned graniticlepidolite-subtype pegmatite at Namivo
In general granitic pegmatites particularly those belong-ing to the rare-element class are accepted as having beenformed by the fractional crystallization of a granite melt(eg Cerny 1991a b 1992 Neiva et al 2008 2012 Roda-Robles et al 2012) But it also has been proposed thatpegmatites may be formed by partial melting of appropri-ate rock compositions (eg Nabelek et al 1992 Nabelekamp Russ-Nabelek 1992 Shearer et al 1992 Roda Robleset al 1999) The lepidolite-subtype pegmatites belong tothe LCT (lithium-cesium-tantalum) family (Cerny amp Ercit2005) They are derived by fractional crystallization of agranite magma (eg Cerny et al 2005 Neiva amp Ramos2010 Cerny et al 2012b) Experimental work by Londonet al (1989) and London (1990) using Macusani glass as astarting material equivalent to the bulk composition ofhighly fractionated rare-alkali-rich pegmatites underhighly evolved and hydrous but H2O undersaturatedmelt obtained the latest primary assemblage consisting
of an Li-rich mica thorn albite thorn quartz deposited directlyfrom the primary melt phase Other authors egZasedatelev (1974 1977) and Stewart (1978) argue thatlepidolite-bearing pegmatites are derived from direct ana-texis and Gordiyenko et al (1996) consider that they arederived from an undefined medium and the rare-elementmineralization is superimposed on preexisting barrenpegmatites
Lepidolite-subtype pegmatites may migrate a long wayfrom their parent granites because their volatile-rich highlyfluid pegmatite melts are stable at relatively low tempera-tures (eg Cerny et al 2005 Antunes et al 2013)Therefore the Namivo pegmatite is probably derived byfractional crystallization of an S-type granite magmawhich resulted from partial melting of metamorphosed juve-nile sediments containing micas that carry most of the traceelements that define the signature of the LCT pegmatites(eg Dahl et al 1993)
The two main models for the internal evolution of peg-matites that dominated for more than a century are a) thefractional crystallization of a flux-bearing granitic melt fromthe margins to the center of the pegmatite (Cameron et al1949) b) the interactions of an aqueous fluid with graniticmelt (Jahns amp Burnham 1969 Jahns 1982) The recentmodel of constitutional zone refining combines aspects ofboth models and invokes the formation of a flux-enriched
Table 4 Electron microprobe analyses in wt of zoned gahnite from the outer intermediate zone (OIZ) of the Namivo granitic pegmatiteMozambique
Darker Zone Lighter Zone
Mean s Range Mean s Range
SnO2 036 050 0ndash097 658 281 151ndash998TiO2 008 008 0ndash021 065 034 008ndash105Nb2O5 001 002 0ndash006 018 007 007ndash029Ta2O5 001 004 0ndash010 015 013 0ndash033ZnO 3998 123 3810ndash4109 3339 318 3004ndash3848FeO 367 048 331ndash442 433 065 306ndash498MnO 032 004 028ndash040 039 006 032ndash048MgO 003 004 0ndash010 ndash ndash ndashAl2O3 5507 050 5436ndash5572 5337 070 5257ndash5443SiO2 003 003 0ndash007 008 010 0ndash025Total 9956 9912n 8 8Sn 0035 0048 0ndash0095 0648 0278 0149ndash0983Ti 0015 0015 0ndash0038 0120 0064 0015ndash0195Nb ndash 0003 0ndash0006 0021 0009 0009ndash0037Ta ndash 0002 0ndash0006 0009 0009 0ndash0021Zn 7226 0182 6890ndash7382 6086 0568 5482ndash6965Fe2thornt 0752 0103 0675ndash0913 0894 0135 0628ndash1029Mn 0066 0008 0057ndash0083 0082 0013 0066ndash0101Mg 0010 0015 0ndash0037 ndash ndash ndashAl 15887 0052 15805ndash15954 15526 0170 15375ndash15853Si 0007 0008 0ndash0018 0019 0025 0ndash0062P
23998 23405Fe3thorn 0064 0230Fe2thorn 0686 0658SnZn 0005 0007 0ndash0014 0106 0052 0021ndash0179ZnFe2thornt 961 143 768ndash1093 681 190 536ndash1109
n number of analysis Cation formula based on 32 atoms of oxygen Fe2thornt total Fe2thorn estimated
982 A M R Neiva
eschweizerbart_xxx
boundary layer of silicate liquid in advance of a crystal-lization front (London 2008 London amp Morgan 2012)
Lepidolite-subtype pegmatites are generally scarce(Cerny et al 2005) particularly the zoned ones In thesymmetrically zoned lepidolite-subtype pegmatites ofRozna and Dobra Voda Czech Republic micas (Cernyet al 1995) tourmaline (Selway et al 1999) and colum-bite-group minerals (Novak amp Cerny 1998) evolve fromthe outermost zone to the innermost zone following thecrystallization sequence The same was found in tourma-line from the zoned Lastovicky Dolnı Bory and Raddovicelepidolite-subtype pegmatite dikes in the Czeck Republic(Selway et al 1999)
In general beryl (Neiva amp Neiva 2005) feldsparsmicas and columbite-(Mn) (in this paper) from theNamivo lepidolite-subtype pegmatite record the progres-sive chemical evolution of the pegmatite from the wallzone to the core These minerals were produced by crystal-lization from a silicate melt rather than an aqueous fluidphase The slow cooling of melt shown by the magmaticcrystallization temperatures of feldspars cannot explain theincrease in grain-size of minerals from the wall zone to thecore but fluxes will be necessary to promote the change oftexture particularly a flux-rich hydrosilicate liquidaccording to the experimental evidence (London 2009)The constitutional zone refining model will be the best forthis zoned pegmatite and probably for all lepidolite-sub-type pegmatites because this model also produces a higherfinal concentration of incompatible components in a smal-ler volume of rock than fractional crystallization does(Morgan amp London 1999)
The core margin at the Rozna pegmatite contains K-feld-spar and quartz and the core consists mainly of quartz but it issurrounded and penetrated by a quartz-bearing albitethorn lepi-dolite complex which contains several minerals At theDobra Voda pegmatite the center of the dike is occupiedby the lepidolite unit containing albite and other minerals(Cerny et al 1995) At the Namivo pegmatite the coremargin consists of quartz and beryl and the core containsmainly quartz and spodumene but also albite lepidolite andother minerals The last-unit assemblages of primary miner-als in most of the highly fractionated LCT pegmatites are richin albite and commonly contain lepidolite or spodumene andmost of the other rare phases These units represent the lastmost fractionated liquid that can be derived by fractionalcrystallization of a crustal melt (London 2008)
The Namivo granitic pegmatite shows a significant dis-tinction from the other zoned lepidolite-subtype pegmatitesand LCT pegmatites except the Tanco petalite-subtypepegmatite in Canada because the lepidolite richest in SiLi and F FeMg-containing polylithionite and associatedcolumbite-(Mn) with the highest Ta(Ta thorn Nb) ratio tanta-lite-(Fe) and tantalite-(Mn) only occur in the outer inter-mediate zone These minerals usually form late in theconsolidation of pegmatites The lepidolite and polylithio-nite are probably derived from the disequilibrium crystal-lization of an undercooled melt Tantalite may reflect a localdecrease in Li and F that caused Ta precipitation
This paper contributes to a better understanding of theorigin and evolution of the rare zoned lepidolite-subtypepegmatites and shows that although the pegmatite evolvedfrom the wall zone to the core it presents an unusualassociation of lepidolite polylithionite and tantalite in theouter intermediate zone
Acknowledgments Thanks are due to JM Cotelo Neivaand MB Dias for the samples and information providedand to MR Machado Leite and MF Guimaraes for theuse of the electron microprobe facilities at the LaboratorioNacional de Energia e Geologia (LNEG) PortugalFinancial support was provided by the PortugueseGovernment for the project Pest-OECTEUI00732011of the Geosciences Centre through the PortugueseFoundation for Science and Technology I would like tothank D London WB Simmons and the associated editorE Widom for their constructive reviews of this manuscriptand M Prieto for his editorial work
References
Alfonso P Melgarejo JC Yusta I Velasco F (2003)
Geochemistry of feldspars and muscovite in granitic pegmatite
from the Cap de Creus field Catalonia Spain Can Mineral 41
103ndash116
Antunes IMHR Neiva AMR Ramos JMF Silva PB
Silva MMVG Corfu F (2013) Petrogenetic links between
lepidolite-subtype aplite-pegmatite aplite veins and associated
granites at Segura (central Portugal) Chemie der Erde in press
httpdxdoiorg101016jchemer20121203
Batchelor RA amp Kinnaird JA (1984) Gahnite compositions
compared Mineral Mag 48 425ndash430
Beurlen H Da Silva MRR Thomas R Soares DR Olivier P
(2008) Nb-Ta-(Ti-Sn) oxide mineral chemistry as tracer of rare-
element granitic pegmatite fractionation in the Borborema pro-
vince Northeastern Brazil Miner Deposita 43 207ndash228
Cameron EN Jahns RH McNair AH Page LR (1949)
Internal structure of granitic pegmatites Econ Geol
Monograph 2 115 p
Cerny P (1991a) Fertile granites of Precambrian rare-element
pegmatite fields is geochemistry controlled by tectonic setting
or source lithologies Precambrian Res 51 429ndash468
mdash (1991b) Rare-element granite pegmatites I Anatomy and inter-
nal evolution of pegmatite deposits Geoscience Canada 18
49ndash67
mdash (1992) Geochemical and petrogenetic features of mineralization
in rare-element granitic pegmatites in the light of current
research Applied Geochemistry 7 393ndash416
mdash (1994) Evolution of feldspars in granitic pegmatites in
lsquolsquoFeldspars and their Reactionsrsquorsquo I Parsons ed NATO
Advanced Study Institute Series C421 501ndash539
mdash (2005) The Tanco rare-element pegmatite deposit Manitoba
regional context internal anatomy and global comparisons in
lsquolsquoRare-element Geochemistry and Mineral Depositsrsquorsquo RL
Linnen amp IM Samson eds Geochemical Association of
Canada Short Course Notes St Catherines 17 127ndash158
Silicate and oxide minerals from a zoned granitic pegmatite 983
eschweizerbart_xxx
Cerny P amp Ercit TS (2005) The classification of granitic pegma-
tites revisited Can Mineral 43 2005ndash2026
Cerny P Meintzer RE Andersen AJ (1985) Extreme fractiona-
tion in rare-element granitic pegmatites selected examples of
data and mechanisms Can Mineral 23 381ndash421
Cerny P Goad BE Hawthorne FC Chapmann R (1986)
Fractionation trends of the Nb- and Ta-bearing oxide minerals
in the Greer Lake pegmatite granite and its pegmatite aureole
southeastern Manitoba Am Mineral 71 501ndash517
Cerny P Stanek J Novak M Baadsgaard H Rieder M
Ottolini L Kavalova M Chapman R (1995) Geochemical
and structural evolution of micas in the Rozna amp Dobra Voda
pegmatites Czech Republic Mineral Petrol 55 177ndash201
Cerny P Ercit TS Vanstone PJ (1998) Mineralogy and petrol-
ogy of the Tanco rare-element pegmatite deposit southeastern
Manitoba International Mineralogical Association 17th General
Meeting Toronto Field Guidebook B6
Cerny P Chapman R Ferreira K Smeds SA (2004)
Geochemistry of oxide minerals of Nb Ta Sn and Sb in
the Varutrask granitic pegmatite Sweden The case of an
lsquolsquoanomalousrsquorsquo columbitendashtantalite trend Am Mineral 89
505ndash518
Cerny P Masau M Goad BE Ferreira K (2005) The Greer
Lake leucogranite Manitoba and the origin of lepidolite-sub-
type granitic pegmatites Lithos 80 305ndash321
Cerny P Teertstra DK Chapman R Selway JB Hawthorne
FC Ferreira K Chackowsky LE Wang X-J Meintzer
RE (2012a) Extreme fractionation and deformation of the
leucogranite-pegmatite suite at Red Cross Lake Manitoba
Canada IV Mineralogy Can Mineral 50 1839ndash1875
Cerny P Halden NM Ferreira K Meintzer RE Brisbin WC
Chackowsky LE (2012b) Extreme fractionation and deforma-
tion of the leucogranite-pegmatite suite at Red Cross Lake
Manitoba Canada II Petrology of the leucogranites and peg-
matites Can Mineral 50 1807ndash1822
Dahl PS When DC Feldmann SG (1993) The systematics of
trace-element partitioning between coexisting muscovite and
biotite in metamorphic rocks from the Black Hills South
Dakota USA Geochim Cosmochim Acta 57 2487ndash2505
Dias MB amp Wilson WE (2000) The Alto Ligonha Pegmatites
Mozambique Mineral Record 31 459ndash497
Fleet ME (2003) Rock-Forming Minerals vol 3A Sheet silicates
micas The Geological Society London second edition chap 6
Lithium micas 651ndash690
Foord EE Cerny P Jackson LL Sherman DM Eby RK
(1995) Mineralogical and geochemical evolutions of micas
from miarolitic pegmatites of the anorogenic pikes-Peak
Batholith Colorado Mineral Petrol 55 1ndash26
Foster MD (1960) Interpretation of the composition of lithium
micas US Geol Surv Prof Paper 354-E 115ndash147
Fuhrman ML amp Lindsley DK (1988) Ternary-feldspar modeling
and thermometry Am Mineral 73 201ndash215
Gomes CL Castro P Alves C (1995) Caracterizacao das espi-
nelas zincıferas e do par ganite-nigerite no campo aplito-
pegmatıtico da Serra de Arga-Minho N de Portugal IV
Congresso Nacional de Geologia Resumos Alargados
Universidade do Porto Mem 4 629ndash633
Gordiyenko VV Ilyina AN Timochina LA Badamina EB
Stanek J (1996) Geochemical model of evolution of a pegma-
tite-forming ore-magmatic system of western Moravia Proc
Russ Mineral Soc 125 38ndash48 (in Russian)
Icenhower JP amp London D (1995) An experimental study for
element partitioning between biotite muscovite and coexisting
peraluminous granitic melt at 200 MPa (H2O) Am Mineral 80
1229ndash1251
Jahns RH (1982) Internal evolution of pegmatite bodies in lsquolsquoGranitic
Pegmatites in science and industryrsquorsquo P Cerny ed Mineralogical
Association of Canada Short Course Handbook 8 293ndash327
Jahns RH amp Burnham CW (1969) Experimental studies of
pegmatite genesis I A model for the derivation and crystal-
lization of granitic pegmatites Econ Geol 64 843ndash864
Jolliff BL Papike JJ Shearer CK (1987) Fractionation trends
in mica and tourmaline as indicators of pegmatite internal evo-
lution Bob Ingersoll pegmatite Black Hills South Dakota
USA GeochimCosmochim Acta 51 519ndash534
Kile DE amp Foord EE (1998) Micas from the Pikes Peak bath-
olith and its cogenetic granitic pegmatites Colorado optical
properties composition and correlation with pegmatite evolu-
tion Can Mineral 36 463ndash482
Linnen RL (1998) The solubility of Nb-Ta-Zr-Hf-W in granitic
melts with Li and Li thorn F constraints for mineralization in rare
metal granites and pegmatites Econ Geol 93 1013ndash1025
Linnen RL amp Cuney M (2005) Granite-related rare-element
deposits and experimental constraints on Ta-Nb-W-Sn-Zr-Hf
mineralization in lsquolsquoRare-element geochemistry and mineral
depositsrsquorsquo RL Linnen amp IM Samson eds Geochemical
Association of Canada Short Course Notes 17 45ndash68
London D (1990) Internal differentiation of rare-element pegmatites
a synthesis of recent research in lsquolsquoOre Bearing Granite Systems
Petrogenesis and Mineralizing Processesrsquorsquo HJ Stein amp JL
Hannah eds Geol Soc America Special Paper 246 35ndash50
mdash (2008) Pegmatites The Canadian Mineralogist Special
Publication 10 347 p
mdash (2009) The origin of primary textures in granitic pegmatites
Can Mineral 47 697ndash724
London D amp Morgan GB VI (2012) The pegmatite puzzle
Elements 8 263ndash268
London D Morgan GB VI Hervig RL (1989) Vapor-under-
saturated experiments in the system macusanite-H2O at 200
MPa and the internal differentiation of granitic pegmatites
Contrib Mineral Petrol 102 1ndash17
London D Morgan GB VI Paul KA Guttery BM (2012)
Internal evolution of miarolitic granitic pegmatites at the Little
Three mine Ramona California USA Can Mineral 50
1025ndash1054
Martins T Lima A Simmons WB Folster AU Noronha F
(2011) Geochemical fractionation of Nb-Ta oxides in Li-bear-
ing pegmatites from the Barroso-Alvao pegmatite field northern
Portugal Can Mineral 49 777ndash791
Monier G Charoy B Cuney M Ohnenstetter D Robert JL
(1987) Evolution spatiale et temporelle de la composition des
micas du granite albitique a topaze-lepidolite de Beauvoir
Geologie De La France 2ndash3 179ndash188
Monier G amp Robert JL (1986) Evolution of the miscibility gap
between muscovite and biotite solid solutions with increasing
lithium content an experimental study in the systems
K2OndashLi2OndashMgOndashAl2O3ndashSiO2ndashH2OndashHF at 600 C 2 kbar
PH2O comparison with natural lithium micas Mineral Mag
50 641ndash651
Morgan GBVI amp London D (1999) Crystallization of the little
three layered pegmatite-aplite dike Ramona District California
Contrib Mineral Petrol 136 310ndash330
984 A M R Neiva
eschweizerbart_xxx
Nabelek PI amp Russ-Nabelek C (1992) The generation and crys-
tallization conditions of the Proterozoic Harney Peak
Leucrogranite Black Hills South Dakota USA petrologic and
geochemical constraints Contrib Mineral Petrol 110
173ndash191
Nabelek PI Russ-Nabelek C Haeussler GT (1992) Stable
isotope evidence for the petrogenesis and fluid evolution in
the Proterozoic Harney Peak leucogranite Black Hills
South Dakota Geochim Cosmochim Acta 56 403ndash417
Neiva AMR amp Champness PE (1997) Nigerite and gahnite from
the granitic pegmatite veins of Cabanas Ponte de Lima northern
Portugal N Jb Mineral Mh 9 385ndash409
Neiva AMR Gomes MEP Ramos JMF Silva PB (2008)
Geochemistry of granitic aplite-pegmatite sills and their miner-
als from Arcozelo da Serra area (Gouveia central Portugal)
Eur J Mineral 20 465ndash485
Neiva AMR amp Neiva JMC (2005) Beryl from the granitic
pegmatite at Namivo Alto Ligonha Mozambique N Jb
Mineral Abh 181 173ndash182
Neiva AMR amp Ramos JMF (2010) Geochemistry of granitic
aplite-pegmatite sills and petrogenetic links with granites
Guarda-Belmonte area central Portugal Eur J Mineral 22
837ndash854
Neiva AMR Silva PB Ramos JMF (2012) Geochemistry of
granitic aplite-pegmatite veins and sills and their minerals from the
Sabugal area central Portugal N Jb Mineral Abh 189 49ndash74
Novak M amp Cerny P (1998) Niobium-tantalum oxide minerals
from complex granitic pegmatites in the Moldanubicum Czech
Republic primary versus secondary compositional trends Can
Mineral 36 659ndash672
Pesquera Perez A Torres-Ruiz J Gil PP Velilla N (1999)
Chemistry and genetic implications of tourmaline and Li-F-Cs
micas from the Valdeflores (Caceres Spain) Am Mineral 84
55ndash69
Rieder M Cavazzini G DrsquoYakonov YuS Frank-Kamenetskii
VA Gottardi G Guggenheim S Koval PV Muller G
Neiva AMR Radoslovich EW Robert J-L Sassi FP
Takeda H Weiss Z Wones DR (1999) Nomenclature of the
micas Mineral Mag 63 267ndash279
Roda Robles E Pesquera Perez A Velasco Roldan F Fontan F
(1999) The granitic pegmatites of the Fregeneda area
(Salamanca Spain) characteristics and petrogenesis Mineral
Mag 63 535ndash558
Roda Robles E Pesquera A Gil-Crespo PP Torres-Ruiz J
Fontan F (2005) Origin and internal evolution of the Li-F-
Be-P-bearing Pinilla de Fermoselle pegmatite (Central Iberian
Zone Zamora Spain) Am Mineral 90 1887ndash1899
Roda Robles E Pesquera Perez A Gil PP Torres-Ruiz J de
Parseval P (2006) Mineralogy and geochemistry of micas from
the Pinilla de Fermoselle pegmatite (Zamora Spain) Eur J
Mineral 18 369ndash377
Roda Robles E Keller P Pesquera Perez A Fontan F (2007)
Micas of the muscovite-lepidolite series from Karibib pegma-
tites Namibia Mineral Mag 71 41ndash62
Roda Robles E Pesquera A Gil-Crespo P Torres-Ruiz J
(2012) From granite to highly evolved pegmatite a case study
of the Pinilla de Fermoselle granite-pegmatite system (Zamora
Spain) Lithos 153 192ndash207
Selway JB Novak M Cerny P Hawthorne FC (1999)
Compositional evolution of tourmaline in lepidolite-subtype
pegmatites Eur J Mineral 11 569ndash584
Shearer CK Papike JJ Jolliff B (1992) Petrogenetic links
among granites and pegmatites in the Harney Peak rare-element
granite-pegmatite system Black Hills South Dakota Can
Mineral 30 785ndash809
Soares DR Hartmut B Ferreira ACM da Silva MRR
(2007) Chemical composition of gahnite and degree of peg-
matitic fractionation in the Borborema Pegmatitic Province
northeastern Brazil Anais Da Academ Bras Cien 79
395ndash404
Stewart DB (1978) Petrogenesis of lithium-rich pegmatites Am
Mineral 63 970ndash980
Tischendorff G Gattesmann B Forster H-J Trumbull RB
(1997) On Li-bearing micas estimating Li from electron
microprobe analyses and an improved diagram for graphical
representation Mineral Mag 61 809ndash834
Van Lichtervelde M Linnen RL Salvi S Beziat D (2006)
The role of metagabbro rafts on tantalum mineralization in the
Tanco granitic pegmatite Manitoba Can Mineral 44
625ndash644
Van Lichtervelde M Gregoire M Linnen RL Beziat D Salvi
S (2008) Trace element geochemistry by laser ablation ICP-
MS of micas associated with Ta mineralization in the Tanco
pegmatite Manitoba Canada Contrib Mineral Petrol 155
791ndash806
Vieira R Roda-Robles E Pesquera A Lima A (2011)
Chemical variation and significance of micas from the
Fregeneda-Almendra pegmatitic field (Central-Iberian Zone
Spain and Portugal) Am Mineral 96 637ndash645
Wen S amp Nekvasil H (1994) SOLVCALC an interactive gra-
phics program package for calculating ternary feldspar solvus
and two-feldspar geothermometry Comput Geosci 20
1025ndash1040
Wise MA (1995) Trace element chemistry of lithium-rich micas
from rare-element granitic pegmatites Mineral Petrol 55
203ndash215
Zasedatelev AM (1974) Possible accumulation of lithium in host
rocks of lithium pegmatite veins during old sedimentation pro-
cesses Doklady Acad Sci USSR Earth Sci Ser 218 196ndash198
(in Russian)
mdash (1977) Quantitative of metamorphic generation of rare-metal
pegmatites with lithium mineralization Doklady Acad Sci
USSR Earth Sci Ser 236 219ndash221 (in Russian)
Received 26 January 2013
Modified version received 21 May 2013
Accepted 23 July 2013
Silicate and oxide minerals from a zoned granitic pegmatite 985
eschweizerbart_xxx
product of LiAl-silicates) K-feldspar content increasesinwards Albite is penetrated by quartz Micas are mainlyassociated with quartz and beryl The dark brown tourma-line is associated with micas Cassiterite is partially sur-rounded by columbitendashtantalite and rutile and they areassociated with micas and quartz Some columbitendashtanta-lite minerals are associated with lithium micas Rare andsmall uranium minerals penetrate along fractures ofcolumbitendashtantalite
The inner intermediate zone a (IIZa) consists domi-nantly of albite and perthitic K-feldspar (30 cm) andalso contains quartz muscovite lithian muscovitelsquolsquomixed formrsquorsquo lepidolite beryl columbite monazitecookeite and bismutite Micas are mainly associated withK-feldspar and albite Columbite occurs among feldsparcrystals locally penetrating them and is rarely surroundedby monazite The inner intermediate zone b (IIZb) isessentially made of lsquolsquomixed formrsquorsquo lepidolite and a tabular
variety of albite (10 to 30 cm) but also contains quartzK-feldspar muscovite lithian muscovite beryl and bismu-tite Lepidolite and lsquolsquomixed formrsquorsquo abundances increasewith depth Micas are associated with albite and quartzAlbite is the most abundant feldspar in OIZ IIZa and IIZb
The lsquolsquocore marginrsquorsquo (Cm) has mainly quartz and beryl(30 cm) but the core (Cc) consists mainly of quartz andspodumene (10 to 30 cm) and also has albite K-feldsparmuscovite lithian muscovite lsquolsquomixed formrsquorsquo lepidoliteberyl tabular variety of albite columbite and cookeiteMicas are associated with quartz K-feldspar and albiteSpodumene occurs in long crystals up to 5 cm thick cut-ting quartz but some are altered into kaolinite Albite andits tabular variety replace quartz and spodumeneColumbite is associated with albite and quartz
3 Sampling and analytical methods
Several samples from all zones of the Namivo graniticpegmatite and information was given by MB Dias whowas the exploitation manager of the company working thepegmatite in 1962 to JM Cotelo Neiva who visited thepegmatite with him All the available material was used forthis study Feldspars and micas have been selected from thezones where they occur Columbite-tantalite minerals arefrom the OIZ IIZa and Cc and tourmaline and gahnitewere only found in the OIZ
The major elements of minerals were determined using aJeol Hyperprobe JXA-8500F operated at 15 kV accelerat-ing voltage and 10 nA beam current except for columbi-tendashtantalite for which the voltage and current were 20 kVand 20 nA Detection limits (3s) above mean backgroundwere 003 wt for most oxides except for ZnO SrOBaO Rb2O Cs2O (006 wt) and F (01 wt) withcounting times of 80 s for these five oxides and F Theanalyses were carried out at LNEG S Mamede de InfestaPortugal Standards used include albite (NaKa) orthoclase(AlKa SiKa KKa) apatite (CaKa PKa) MgO (MgKa)MnTiO3 (MnKa) TiO2 (TiKa) Fe2O3 (FeKa) ZnS(ZnKa) fluorite (FKa) vanadinite (ClKa) BaSO4
(BaLa) SrTiO3 (SrLa) glasses Ge-Al-Ca containing 100wt Rb (RbLa) and Si-Al-Ca with 100 wt Cs (CsLa)cassiterite (SnKa) pure Ta (La) SrBaNb4O12 (NbLa) andscheelite (WLa)
4 Micas
41 Chemical composition of micas
As different micas are associated in the same crystals(Fig 3) it is impossible to separate them or use a laserablation inductively coupled plasma mass spectrometer(LA-ICP-MS) to determine their trace elementsTherefore ZnO BaO Rb2O and Cs2O contents weredetermined by electron microprobe In general ZnO andBaO contents are low but Rb2O and Cs2O contents are
Fig 2 Zones of the Namivo granitic pegmatite Mozambique Mainconstituents of Wall Zone (WZ ndash quartz K-feldspar) OuterIntermediate Zone (OIZ ndash quartz and albite) Inner IntermediateZone (IIZa ndash albite and perthitic K-feldspar IIZb ndash lsquolsquomixed formrsquorsquolepidolite and tabular variety of albite) and Core (Cm ndash lsquolsquocoremarginrsquorsquo quartz and beryl Cc ndash core-quartz and spodumene)
Fig 1 Location of the Namivo granitic pegmatite in the AltoLigonha pegmatite area of northern Mozambique Simplified mapafter Dias amp Wilson (2000)
968 A M R Neiva
eschweizerbart_xxx
very helpful for the interpretations Li2O contents ofzinnwaldite lepidolite polylithionite and lsquolsquomixedformrsquorsquo were calculated from the equation Li2O frac14 (0289 SiO2) 9658 and of muscovite and lithian muscovitefrom the equation Li2O frac14 03935 F1326 (Tischendorfet al 1997) Secondary micas replacing feldspars werenot analyzed
Variation in the chemical composition of micas from theNamivo granitic pegmatite is shown in Table 1 and Fig 4lsquolsquoMixed formrsquorsquo is of course not a proper mica mineral name(Rieder et al 1999) The chemical distinction between
dioctahedral and trioctahedral micas is the value of 25octahedral cations per formula unit in dioctahedral and25 octahedral cations in trioctahedral micas for a for-mula calculated on the basis of 12 O thorn F atoms (Riederet al 1999) The Li2O content of analyzed lsquolsquomixed formsrsquorsquois calculated for a trioctahedral mica and the value ofoctahedral cations per formula unit is 28 and totals ofanalyses are good (Table 1) indicating that they are trioc-tahedral micas If Li2O contents of these analyses arecalculated for a dioctahedral mica the value of octahedralcations per formula mainly ranges between 23 and 28 and
Fig 3 Backscattered-electron images of zoned micas from the Namivo granitic pegmatite Mozambique Micas a b c d d1 from the OIZ ef f1from the IIZa g h from the IIZb i j from the Cc d1 and f1 are details of d and f respectively Lep ndash lepidolite Zin ndash zinnwaldite Brl ndashberyl Mix f ndash lsquolsquomixed formrsquorsquo Q ndash quartz Pol ndash polylithionite Cst ndash cassiterite Rt ndash rutile Ct ndash columbitendashtantalite Lith mu ndash lithianmuscovite Ab ndash albite Mu ndash muscovite K-fel ndash K-feldspar
Silicate and oxide minerals from a zoned granitic pegmatite 969
eschweizerbart_xxx
Tab
le1
R
epre
sen
tati
ve
elec
tro
nm
icro
pro
be
anal
yse
sin
wt
o
fm
icas
fro
mth
eN
amiv
og
ran
itic
peg
mat
ite
Mo
zam
biq
ue
Ou
ter
Inte
rmed
iate
Zo
ne
-O
IZIn
ner
Inte
rmed
iate
Zo
ne
-II
Za
Zin
Lep
lsquolsquoM
ixed
Frsquorsquo
Lep
Lep
Po
llsquolsquo
Mix
edF
rsquorsquoL
ith
Mu
sP
ol
Lit
hM
us
lsquolsquoM
ixed
Frsquorsquo
lsquolsquoM
ixed
Frsquorsquo
Lep
Mu
sL
ith
Mu
s
Co
mp
osi
tio
nC
ore
Rim
Co
reR
imR
imC
ore
Rim
Co
reC
ore
Rim
Rim
SiO
24
37
15
42
04
52
45
63
75
23
45
87
64
67
14
63
35
91
84
58
54
85
74
81
24
94
64
55
44
61
1T
iO2
06
00
15
04
70
02
02
70
05
mdashmdash
00
2mdash
01
00
03
00
7mdash
00
4A
l 2O
32
21
81
76
52
97
81
59
01
82
11
48
13
12
63
53
31
49
43
71
92
68
82
83
32
46
43
77
03
55
0F
eO8
42
39
74
57
24
44
94
13
11
56
17
51
14
mdash2
68
11
01
50
01
21
15
Mn
O0
60
00
60
33
00
20
21
00
30
10
01
50
05
01
20
27
12
32
16
04
80
53
Mg
O5
15
17
21
06
14
01
33
10
10
87
06
80
94
00
50
09
mdash0
01
mdashmdash
Zn
O0
46
03
20
17
01
10
24
01
30
14
01
00
09
00
60
13
02
60
41
00
60
15
CaO
00
10
01
00
4mdash
00
10
02
00
30
05
00
1mdash
mdash0
02
00
10
02
mdashL
i 2O
2
97
60
13
42
66
35
47
73
23
84
03
07
45
04
34
38
42
54
64
01
60
45
Na 2
O0
08
00
60
23
01
10
23
00
70
29
03
30
06
04
40
13
02
60
13
03
80
28
K2O
10
00
98
41
00
91
02
01
05
89
77
93
39
98
95
09
91
10
28
97
79
95
99
39
81
Rb
2O
08
60
78
06
61
30
02
80
46
05
10
43
04
91
06
15
01
42
16
71
02
11
0C
s 2O
0
06
00
9
00
60
14
00
6
00
6
00
6
00
6
00
60
15
05
50
13
02
2
00
60
03
F5
10
89
92
24
10
50
10
14
10
05
24
60
81
98
41
06
53
84
89
74
10
50
11
0H
2O
18
30
23
33
9mdash
mdashmdash
33
54
12
mdash4
01
19
12
15
09
14
28
39
61
02
03
10
40
81
01
75
10
51
41
04
31
10
38
51
00
51
10
04
21
03
77
10
03
31
02
85
10
19
61
03
19
10
02
51
00
21
O
F2
14
37
80
94
44
14
26
42
21
03
03
44
13
04
52
26
20
53
11
02
10
46
To
tal
99
89
10
03
01
00
81
10
07
31
00
05
99
63
99
48
10
00
89
96
49
98
81
00
59
99
91
10
00
81
00
04
99
75
KR
b(w
t)1
11
21
47
13
41
91
62
11
88
56
26
25
48
98
1
Si
30
85
36
20
30
45
37
47
35
58
38
54
31
02
30
83
38
63
30
45
32
66
32
26
33
51
30
24
30
86
AlIV
09
15
03
80
09
55
02
53
04
42
01
46
08
98
09
17
01
37
09
55
07
34
07
74
06
49
09
76
09
14
PT
40
04
00
40
04
00
40
04
00
40
04
00
40
04
00
40
04
00
40
04
00
40
0A
lVI
09
31
10
09
14
07
09
92
10
17
09
99
15
49
18
54
10
12
19
56
13
96
14
65
13
19
19
74
18
87
Ti
00
32
00
08
00
24
00
01
00
14
00
02
mdashmdash
00
01
mdash0
00
50
00
20
00
4mdash
00
02
Fe2thorn
04
97
02
22
02
57
01
36
02
81
00
72
00
87
00
97
00
62
mdash0
15
10
06
20
08
50
00
70
06
4M
n0
03
60
00
30
01
90
00
10
01
20
00
20
00
60
00
80
00
30
00
70
01
50
07
00
12
40
02
70
03
0M
g0
54
20
17
10
10
60
13
90
13
50
09
90
08
60
06
70
09
10
00
50
00
9mdash
00
01
mdashmdash
Zn
00
24
00
16
00
08
00
05
00
12
00
06
00
07
00
05
00
04
00
03
00
06
00
13
00
21
00
03
00
07
Li
08
44
16
13
09
25
17
73
14
95
19
32
10
26
00
80
19
54
01
14
11
84
11
46
12
64
00
42
01
20
PR
29
13
04
27
53
05
29
73
11
27
62
11
31
32
09
27
72
76
28
22
05
21
1C
a0
00
10
00
10
00
3mdash
00
01
00
01
00
02
00
04
00
01
mdashmdash
00
01
00
01
00
01
mdashN
a0
01
10
00
80
03
00
01
40
03
00
00
90
03
70
04
30
00
80
05
70
01
70
03
40
01
70
04
90
03
6K
09
00
08
38
08
66
08
65
09
17
08
18
07
90
08
47
07
91
08
40
08
82
08
36
08
60
08
41
08
38
Rb
00
39
00
33
00
29
00
56
00
12
00
19
00
22
00
18
00
21
00
45
00
65
00
61
00
73
00
44
00
47
Cs
00
02
00
03
00
02
00
04
00
02
00
02
00
02
00
02
00
02
00
04
00
16
00
04
00
06
00
02
00
01
PA
09
50
88
09
30
94
09
60
85
08
50
91
08
20
95
09
80
94
09
60
94
09
2F
11
39
18
99
04
77
22
07
21
80
20
85
05
17
01
70
20
31
02
23
11
44
10
37
15
87
01
05
02
33
OH
0
86
10
10
11
52
3mdash
mdashmdash
14
83
18
30
mdash1
77
70
85
60
96
30
41
31
89
51
76
7Z
on
esL
DL
DL
DL
DD
D
LD
LD
L
F
igu
res
Fig
s3
a6
ab
Fig
3
bF
igs
3c
6c
Fig
s3
d
d1
6
dF
igs
3e
6e
fF
igs
3f
f1
6g
h
970 A M R Neiva
eschweizerbart_xxx
Tab
le1
C
on
tin
ued
Inn
erIn
term
edia
teZ
on
e-
IIZ
bC
ore
-C
c
Lit
hM
us
Lep
Mu
slsquolsquo
Mix
edF
rsquorsquoL
epL
ith
Mu
slsquolsquo
Mix
edF
rsquorsquoL
epM
us
Lit
hM
us
Co
reR
imC
ore
Rim
Rim
Co
reR
imR
im
SiO
24
69
25
21
64
62
24
90
64
99
94
71
84
90
15
09
54
63
44
65
6T
iO2
00
3mdash
00
40
03
00
30
02
00
1mdash
mdashmdash
Al 2
O3
35
72
22
89
36
17
28
04
24
87
35
10
26
26
23
49
36
31
35
53
FeO
00
10
61
00
70
05
00
70
04
21
81
55
00
10
03
Mn
O0
55
05
80
43
12
92
24
06
01
09
13
30
14
01
4M
gO
mdashmdash
mdashmdash
mdashmdash
mdashmdash
mdashmdash
Zn
O
00
60
10
00
8
00
60
19
0
06
02
50
07
0
06
0
06
CaO
00
30
04
mdashmdash
00
10
01
00
10
01
mdashmdash
Li 2
O
06
55
42
02
54
52
47
90
93
45
15
07
04
70
79
Na 2
O0
41
00
80
49
02
60
16
04
10
13
01
00
55
05
4K
2O
97
99
78
10
16
96
69
76
94
49
33
90
89
97
99
0R
b2O
12
42
30
14
31
79
21
01
34
17
52
13
14
81
69
Cs 2
O0
16
08
7
00
60
62
05
00
11
07
70
79
01
40
12
F1
46
83
40
70
49
97
63
19
25
55
73
51
15
16
9H
2O
38
30
52
41
62
14
08
23
61
18
20
95
39
63
70
10
08
61
03
69
10
02
61
02
51
10
31
61
00
77
10
26
71
02
87
10
05
81
00
75
O
F0
61
35
00
29
21
03
20
08
12
33
30
90
48
07
1T
ota
l1
00
25
10
01
99
99
71
00
41
99
96
99
96
10
03
49
97
81
00
10
10
00
4
KR
b(w
t)7
23
96
44
94
26
44
83
96
15
3
Si
31
10
34
98
30
84
32
68
33
76
31
30
33
02
34
42
30
82
31
02
AlIV
08
90
05
02
09
16
07
32
06
24
08
70
06
98
05
58
09
18
08
98
PT
40
04
00
40
04
00
40
04
00
40
04
00
40
04
00
AlV
I1
90
01
30
71
92
91
47
01
35
51
87
51
38
71
31
21
92
81
89
2T
i0
00
1mdash
00
02
00
02
00
02
00
01
00
01
mdashmdash
mdashF
e2thorn
00
01
00
34
00
04
00
03
00
04
00
02
01
23
00
88
00
01
00
02
Mn
00
31
00
33
00
24
00
73
01
28
00
34
00
62
00
76
00
08
00
08
Mg
mdashmdash
mdashmdash
mdashmdash
mdashmdash
mdashmdash
Zn
00
03
00
05
00
04
00
03
00
09
00
03
00
12
00
03
00
03
00
03
Li
01
73
14
61
00
66
12
11
13
01
02
49
12
21
13
76
01
27
02
11
PR
21
12
84
20
32
76
28
02
16
28
12
86
20
72
12
Ca
00
02
00
03
mdashmdash
00
01
00
01
00
01
00
01
mdashmdash
Na
00
53
00
10
00
63
00
34
00
21
00
53
00
17
00
13
00
71
00
70
K0
82
80
83
70
86
50
82
10
84
10
79
90
80
20
78
20
84
60
84
1R
b0
05
30
09
90
06
10
07
70
09
10
05
70
07
60
09
20
06
30
07
2C
s0
00
50
02
50
00
10
01
80
01
40
00
30
02
20
02
30
00
40
00
3P
A0
94
09
70
99
09
50
97
09
10
92
09
10
98
09
9F
03
06
17
69
01
48
10
51
16
30
04
03
11
83
15
70
02
42
03
56
OH
1
69
40
23
11
85
20
94
90
37
01
59
70
81
70
43
01
75
81
64
4Z
on
esD
LD
D
LD
LL
D
DF
igu
res
Fig
s3
g
6i
jk
Fig
s3
h
6l
Fig
s3
i6
m
nF
igs
3j
6o
p
OIZ
IIZ
aII
Zb
Cc
asin
Fig
2Z
inndash
zin
nw
ald
ite
Lep
ndashle
pid
oli
teF
ndashfo
rmP
olndash
po
lyli
thio
nit
eL
ith
Mu
sndash
lith
ian
mu
sco
vit
eM
us
ndashm
usc
ov
ite
Lndash
ligh
ter
zon
eD
ndashd
ark
erzo
ne
D
-th
ed
ark
estzo
ne
L
-th
eli
gh
test
zon
ein
BS
Eim
ages
BaO
isb
elo
wth
ed
etec
tio
nli
mit
Cal
cula
ted
nu
mb
ero
fio
ns
on
the
bas
iso
f1
2o
xy
genthorn
Fat
om
sL
i 2O
v
alu
esca
lcu
late
dfr
om
equ
atio
ns
of
Tis
chen
do
rff
eta
l
(19
97
)O
H
-ca
lcu
late
db
yd
iffe
ren
ceto
20
00
H
2O
-ca
lcu
late
db
yst
oic
hio
met
ry
Silicate and oxide minerals from a zoned granitic pegmatite 971
eschweizerbart_xxx
analytical totals are not good The analyzed lsquolsquomixedformsrsquorsquo are distinguished in backscattered-electron (BSE)images and chemically (Fig 3b d d1 e f f1 h i andFig 4) The chemical distinction between lsquolsquomixed formrsquorsquoand lepidolite from the OIZ (Fig 4) is clear in Fig 3bwhere lepidolite is darker than lsquolsquomixed formrsquorsquo because theformer has less Fe and Mn than the latter (Table 1) and inFig 3f f1 and 3h for micas from the IIZa and IIZbrespectively where lepidolite is lighter than lsquolsquomixedformrsquorsquo because the former has more Fe2thorn and Mn oronly more Mn than the latter (Table 1) The lsquolsquomixedformsrsquorsquo analyzed are distinguished in the BSE imagesfrom the lepidolite that falls in its fields in the Fig 4The fields of lepidolite composition in Foster (1960) arelarger than the field for lepidolite from the trilithionite tothe polylithionite (Rieder et al 1999) According to Fleet(2003) only a few lepidolite compositions plot on thetrilithionite-polylithionite join In general lepidolite hashigher Si Licalc Rb Cs F contents and lower AlVI andOH contents than lsquolsquomixed formrsquorsquo (Table 1 Fig4)lsquolsquoMixed formrsquorsquo is also clearly distinguished fromlithian muscovite in OIZ IIZa IIZb and Cc in BSEimages (Fig 3d d1 e f i) and chemically (Table 1 Fig4) as it generally has higher Si Licalc Rb Cs F contentsand lower AlVI and OH contents than lithian muscovite
Two distinct trends are defined in Fig 4 One trendconsists of Al-poorer micas which are zinnwaldite
lepidolite and FeMg-containing polylithionite from theOIZ A hiatus occurs between zinnwaldite and lepidolitebut the zinnwaldite series is continuous with the field oflepidolite at the high Li content (Fleet 2003) The othertrend consists of Al-richer micas (muscovite lithian mus-covite and lsquolsquomixed formrsquorsquo from the OIZ IIZa IIZb and Ccand also lepidolite from most of those zones except fromthe OIZ) There is a gap between lithian muscovite and thelsquolsquomixed formrsquorsquo which may be explained by a hiatus inmica stability (eg Jolliff et al 1987) but a solid solutionbetween dioctahedral and trioctahedral micas has beenindicated experimentally (Monier amp Robert 1986) whileother authors have shown that the octahedral site occu-pancy ranges continuously from muscovite to lepidolite(eg Roda Robles et al 2005 Van Lichterveld et al2008 Vieira et al 2011) Most lithian muscovites andlsquolsquomixed formrsquorsquo from the OIZ are richer in Fe2thornthornMg thornMn than those from the other zones due to their higherFe2thorn and Mg contents (Fig 4 Table 1)
In the Al-poorer micas from the OIZ ranging from zinn-waldite to lepidolite and FeMg-containing polylithionite(Fig 4) (AlIV thorn AlVI) Fe2thorn Mg Ti Mn and Zn contentsdecrease and Si and Licalccontents increase (Table 1) In theAl-richer micas ranging from muscovite to lithian muscoviteand lsquolsquomixed formrsquorsquo from the OIZ IIZa IIZb and Cc and alsoto lepidolite from most of those zones except from the OIZ(AlIV thorn AlVI) AlVI and OH contents and KRb ratio
Fig 4 Plots of micas from the Namivo granitic pegmatite Mozambique in the LindashR2thornndashR3thornthorn Ti diagram according to the classification ofFoster (1960) slightly modified (Rieder et al 1999) with R3thorn frac14 AlVI R2thorn frac14 (Fe2thornt thorn Mn2thornthorn Mg) showing the variety of micacompositions Two trends are defined one for Al-poorer micas (zinnwaldite lepidolite and FeMg-containing polylithionite) from theOIZ another for Al-richer micas (muscovite lithian muscovite lsquolsquomixed formrsquorsquo and lepidolite) from all zones except lepidolite from the OIZOIZ IIZa IIZb and Cc as in Fig 2
972 A M R Neiva
eschweizerbart_xxx
generally decrease and Si Licalc Rb Cs and F contentsgenerally increase (Table 1)
42 Main substitution mechanisms
The 2Si thorn Li 3Altotal mechanism operates in the diocta-hedral micas (muscovite and lithian muscovite) (Fig 5a b)whereas the 3LiVI AlVIthorn 2ampVI (amp represents a vacancy)operates in the trioctahedral micas (lsquolsquomixed formrsquorsquo lepido-lite zinnwaldite and FeMg-containing polylithionite) (Fig5c d) which agrees with findings for micas from the Tancopegmatite (Van Lichtervelde et al 2008)
43 Textures and chemical compositions of zoned micacrystals
Backscattered-electron images combined with quantita-tive spot electron-microprobe analyses made it possibleto distinguish different micas in the Namivo graniticpegmatite Similar textural aspects and geochemicalobservations were found between some Al-richer micasfrom the OIZ IIZa IIZb and Cc Some selected zonedcrystals are documented (Table 1 Fig 3 and 6) In theOIZ lepidolite penetrates zinnwaldite along cleavagesand partially surrounds it and the contacts are sharp(Fig 3a) A chemical gap occurs between zinnwalditeand lepidolite compositions (Fig 6a b) Lepidolite withhigher Si Licalc F contents similar KRb value andlower (AlIV thorn AlVI) Ti Fe2thorn Mg (Fe2thornthorn Mn thorn Mg)Zn and OH contents (Table 1) replaces zinnwaldite Athin lepidolite rim partially surrounds lsquolsquomixed formrsquorsquoand the contact is sharp (Fig 3b) The lepidolite rimhas higher Si Mg Licalc Rb F contents and lowerAlVI Ti Fe2thorn Mn Na and OH contents and KRb ratiothan the lsquolsquomixed formrsquorsquo core (Table 1) The lepidoliterim is an Al-poorer mica whereas the lsquolsquomixed formrsquorsquocore is an Al-richer mica (Fig 4) The lepidolite rimcorresponds to an overgrowth The FeMg-containingpolylithionite partially surrounds and penetrates lepido-lite along cleavages and shows well defined contacts(Fig 3c) Both contain rutile cassiterite and columbi-tendashtantalite inclusions A continuous chemical evolutiontakes place from lepidolite to FeMg-containing poly-lithionite (Figs 4 6c) The latter has higher Si LicalcRb contents and lower AlVI Ti Fe2thorn Mn Mg Zn Nacontents and KRb ratio (Table 1) and replaces lepido-lite A lithian muscovite rim with rare FeMg-containingpolylithionite surrounds the lsquolsquomixed formrsquorsquo core and thispolylithionite penetrated lithian muscovite (Fig 3d)The contact between the lithian muscovite rim andlsquolsquomixed formrsquorsquo core is irregular suggesting disequili-brium or at a cleavage (Fig 3d d1) Two linear trendsone for the lithian muscovite rim and another for thelsquolsquomixed formrsquorsquo core are defined in the (Fe2thornthornMnthornMg)vs (AlIV thornAlVI) diagram (Fig 6d) The FeMg-contain-ing polylithionite rim does not belong to any of thesetrends and plots outside this diagram because it is an Al-poorer mica whereas the others are Al-richer micas
(Fig 4) The lithian muscovite rim has higher AlVI(AlIV thorn AlVI) OH contents and KRb ratio and lowerMg (Fe2thornthorn Mn thorn Mg) Licalc Rb F contents than thelsquolsquomixed formrsquorsquo core (Table 1 Fig 6d) The crystal isreversely zoned The FeMg-containing polylithioniterim has higher Si Licalc F contents and lower AlVI(AlIV thorn AlVI) Fe2thorn Mn (Fe2thornthorn Mn thorn Mg) Na andOH contents than the lsquolsquomixed formrsquorsquo core and lithianmuscovite rim (Table 1) and replaces lithian muscovite
In the IIZa some zoned crystals have a lithian muscovitecore and a lsquolsquomixed formrsquorsquo rim and the contacts are gradual(Fig 3e) A small discontinuity occurs in the trends fromthe lithian muscovite core to lsquolsquomixed formrsquorsquo rim in the(Fe2thornthorn Mn thorn Mg) vs (AlIV thorn AlVI) and Rb2O vs KRb(Fig 6e f) The lsquolsquomixed formrsquorsquo rim has higher Si Fe2thornMn (Fe2thornthornMn thornMg) Licalc K Rb Cs F contents andlower AlVI (AlIVthornAlVI) Na OH contents and KRb ratiothan the lithian muscovite core (Table 1 Fig 6e f) indi-cating progressive zoning Similar textural relationshipsand chemical evolutions were found in other zoned crystalsfrom the OIZ IIZb and Cc In another crystal from theIIZa lithian muscovite partially surrounds lsquolsquomixed formrsquorsquointergrown with lepidolite Lithian muscovite also partiallysurrounds muscovite (Fig 3f) The contacts betweenlsquolsquomixed formrsquorsquo and lepidolite and also between muscoviteand lithian muscovite are gradual (Fig 3f f1) whereasthey are well defined for muscovite withlsquolsquomixed formrsquorsquoand lepidolite (Fig 3f f1) The crystal has a lsquolsquomixed formrsquorsquoand lepidolite core and a partial rim of muscovite andlithian muscovite The lsquolsquomixed formrsquorsquo core evolved tolepidolite core as the Si Fe2thorn Mn (Fe2thornthorn Mn thorn Mg)Licalc K Rb Cs and F contents increase and the (AlIV thornAlVI) and KRb ratio decrease (Table 1 Fig 6g h) The SiFe2thorn Mn (Fe2thornthorn Mn thorn Mg) Licalc Rb and F contentsincrease and the (AlIV thorn AlVI) and KRb ratio decreasefrom the muscovite rim to the lithian muscovite rim (Table1 Fig 6g h) suggesting that the former evolved to thelatter The muscovite rim has higher AlVI (AlIV thorn AlVI)Na OH contents and KRb ratio and lower Si Fe2thorn Mn(Fe2thornthornMn thornMg) Zn Licalc Rb and F contents than thelsquolsquomixed formrsquorsquo core and lepidolite core (Table 1 Fig 6gh) Muscovite was probably reversely formed and evolvedafterwards to lithian muscovite
In the IIZb some crystals have a lithian muscovite coreand a thinner lepidolite rim (Fig 3g) and others show asmall muscovite core and a larger rim of lsquolsquomixed formrsquorsquointergrown with lepidolite (Fig 3h) The contacts betweenthe cores and rims are well defined There are increases inthe Si Mn (Fe2thornthorn Mn thorn Mg) Licalc Rb and F contentsand decreases in the AlVI (AlIVthornAlVI) and KRb ratio fromthe lsquolsquomixed formrsquorsquo rim to the intergrown lepidolite rim(Table 1 Figs 3h 6l) suggesting that the former evolvedto the latter as also found in IIZa and Cc In both crystalsthe rim compositions have higher Si (Fe2thornthorn Mn thorn Mg)Licalc Rb Cs F contents and lower AlVI (AlIVthorn AlVI) Naand OH contents and KRb ratio than the core (Table 1 Figs3g 6i j k 3h 6l) A compositional gap occurs between coreand rim in the diagrams for both crystals (Fig 6i j k l)suggesting that both rims correspond to overgrowths and no
Silicate and oxide minerals from a zoned granitic pegmatite 973
eschweizerbart_xxx
diffuse reequilibration took place in any crystal as thecontacts between core and rim are sharp
In the Cc lithian muscovite is surrounded and pene-trated by lsquolsquomixed formrsquorsquo showing well defined contacts(Fig 3i) The lsquolsquomixed formrsquorsquo has higher Si Fe2thorn Mn(Fe2thornthorn Mn thorn Mg) Licalc Rb Cs F contents and lowerAlVI (AlIV thorn AlVI) Na OH contents and KRb ratio thanthe lithian muscovite (Table 1 Fig 6m n) and a composi-tional gap occurs between both micas suggesting thatlsquolsquomixed formrsquorsquo replaced lithian muscovite In rare crystalsa small lepidolite core is surrounded by a large muscoviterim containing K-feldspar inclusions The contact betweenthe core and rim is sharp (Fig 3j) A thin partial rim oflithian muscovite surrounds muscovite and the contact isgradual The muscovite rim has higher AlVI (AlIVthornAlVI)Na K OH contents and a greater KRb value and lower SiFe2thorn Mn Licalc Rb Cs and F contents than the lepidolitecore (Table 1 Fig 6o p) and a compositional gap occursbetween them (Fig 6o p) indicating that either muscoviteforms an overgrowth or it is reversely formed From themuscovite rim to the lithian muscovite rim the Si Licalc
Rb F contents increase whereas the AlVI (AlIV thorn AlVI)and OH contents and KRb ratio decrease (Table 1 Fig 6op) suggesting that muscovite evolved to lithian muscoviteas also found in IIZa and IIZb
44 Evolution of mica compositions within each zoneand from the outer intermediate zone to the core of theNamivo granitic pegmatite
The KRb ratio is taken as the best fractionation index inmicas (eg Cerny et al 1985 Foord et al 1995 Wise1995 Pesquera et al 1999 Roda Robles et al 2006 2007)It is hard to establish trends in the evolution of mica com-position from muscovite and lithian muscovite to lsquolsquomixedformrsquorsquo and lepidolite within each zone because the KRbratio shows some partial overlapping particularly betweenthe lithian muscovite and lsquolsquomixed formrsquorsquo and also betweenthe latter and lepidolite However an evolution from mus-covites to lepidolite (Al-richer mica Fig 4) is clearer (Fig7) In general in IIZa IIZb and Cc the Si Licalc Rb Cs and
Fig 5 The main substitutions in micas from the Namivo granitic pegmatite Mozambique a b SiIVthorn LiVI versus AlIVthornAlVI showing the 2SithornLi 3Altotal substitution mechanism operating in dioctahedral micas (Mu muscovite and Lith mu lithian muscovite) c d AlVI thornamp VI
versus LiVI (where amp represents a vacancy) and showing the 3LiVI AlVI thorn 2 amp VI substitution mechanism operating in trioctahedral micas(Mix f ndashlsquolsquomixed formrsquorsquo Lep lepidolite Zin zinnwaldite and Pol-FeMg-containing polylithionite) OIZ IIZa IIZb and Cc as in Fig 2
974 A M R Neiva
eschweizerbart_xxx
F contents tend to increase and the (AlIV thorn AlVI) AlVI
contents and KRb ratio tend to decrease from muscoviteto lepidolite (Table 1 Fig 7) This sequence is consistentbut rarely in the Cc lepidolite is rimmed by muscovite (Fig3j) But in the OIZ the evolution stops in lsquolsquomixed formrsquorsquoparticularly shown by the large range of the KRb ratiowhich mainly overlaps that of lepidolite from this zone(Fig 7) because this lepidolite is an Al-poorer mica whereasthe others are Al-richer micas (Fig 4)
In the OIZ the lepidolite has more Si Licalc and F andless (AlIV thorn AlVI) Ti Fe2thorn Mn Mg and Zn than zinn-waldite (Table 1) but it has larger ranges of Rb and KRbratio than zinnwaldite (Fig 7) The FeMg-containingpolylithionite is the richest mica in Si Licalc and thepoorest in (AlIV thorn AlVI) (Table 1) But at this zone scalethe polylithionite has Rb Cs contents and KRb ratiowithin the ranges for lepidolite and close to those of zinn-waldite (Fig 7)
Fig 6 Variation diagrams of micas from selected zoned crystals from the zones of the Namivo granitic pegmatite Mozambique to showtheir relationships lith musc lithian muscovite OIZ IIZa IIZb and Cc an in Fig 2
Silicate and oxide minerals from a zoned granitic pegmatite 975
eschweizerbart_xxx
From the OIZ to IIZa IIZb and Cc muscovite and lithianmuscovite generally show increases in the Si Licalc F and Rbcontents and decreases in the Fe2thorn and Mg contents and KRb ratio but the Mg content is very low in these micas fromthe IIZa IIZb and Cc (Table 1 Fig 7a) The lsquolsquomixed formrsquorsquoshows increases in the Si Licalc F Rb Cs contents anddecreases in the (AlIV thorn AlVI) and Mg contents and KRbratio but the Mg content is very low in this mica from theIIZb and Cc (Table 1 Fig 7b c) The lepidolite shows anincrease in the Si Licalc F Rb and Cs contents and a decreasein the KRb ratio from the IIZa to the IIZb and Cc (Table 1Fig 7d e) Furthermore the lepidolite from the OIZ has thelowest (AlIV thorn AlVI) AlVI and OH contents the highest SiFe2thorn Licalcand F contents and KRb ratio and the lowest Rband Cs contents compared to lepidolite from the other zones(Table 1 Fig 7d e)
5 Feldspars
Selected chemical analyses of albite and K-feldspar fromfive zones of the Namivo granitic pegmatite are given inTable 2 Strontium is the most abundant trace element inalbite (eg Cerny 1994) Anorthite and Sr contents and SrCa ratio of albite decrease from the WZ to the Cc (Fig 8Table 2) Rubidium is the most abundant trace element inK-feldspar followed by Cs in IIZa IIZb and Cc In gen-eral K Rb and Cs contents of K-feldspar increase and KRb and KCs values decrease from the WZ to the Cc (Table2 Fig 9)
The program SOLVCALC 20 (Wen amp Nekvasil 1994)using the Margules model Fuhrman amp Lindsley (1988) wasapplied for the purpose of thermometry The pairing ofplagioclase cores with the K-feldspars average of eachsample was used to estimate the crystallization temperaturesof primary magmatic feldspars They are 405 C (WZ)406ndash340 C (OIZ) 390ndash335 C (IIZa) 347ndash306 C (IIZb)and 333ndash289 C (Cc) at 3 kbar The metamorphic environ-ment of rare-element-Li granitic pegmatites is one of lowpressure 2ndash4 kbar (Cerny amp Ercit 2005) In general thedifference between the maximum and minimum calculatedtemperatures at 2 3 and 4 kbar for the same feldspar pairfrom the Namivo pegmatite is lower than 40 C The tem-perature decreases from the wall zone (WZ) to the core(Cc) A similar temperature behavior of feldspars wasfound in the pegmatite-aplite dike USA (Morgan ampLondon 1999)
6 Other silicates
Tourmaline of schorl composition was only found inthe OIZ (Table 2) because there was not enough Feand Mg for schorl to precipitate in the other zonesSpodumene only occurs in the Cc and its compositionis nearly pure (Table 2)
7 Columbite-tantalite
Representative chemical analyses of columbitendashtantalitefrom the Namivo granitic pegmatite are given in Table 3and plotted in the columbite quadrilateral (Fig 10a)Most crystals are unzoned but zoned crystals with dar-ker and lighter zones in BSE images are from the Cc Thelighter zone of columbite-(Mn) has higher Ta contentTa(Ta thorn Nb) and Mn(Mn thorn Fe) values and lower Nbcontent than the darker zone (Fig 10a b) The crystals ofthe columbitendashtantalite minerals are low in W Sn and Tiimpurities (Table 3)
The main trend starts from the columbite-(Mn) of theOIZ towards the more Mn-enriched and slightly Ta-enriched columbite-(Mn) from the IIZa and Cc The high-est Ta(Ta thorn Nb) values belong to the lighter zone ofcolumbite-(Mn) with Mn(Mn thorn Fe) frac14 10 from the CcThe richest columbite-(Mn) in Ta(TathornNb) and composi-tions of tantalite-(Fe) and tantalite-(Mn) were only foundin the OIZ (Fig 10a) and are associated with lepidolite andpolylithionite (Fig 3c)
8 Gahnite
Gahnite was rarely found in the OIZ and shows a darkerzone that partially surrounds a lighter zone in a BSE image(Fig 11a) The darker zone has a higher Zn content andlower Sn Ti Nb Ta Mn contents and SnZn value than thelighter zone (Table 4 Fig 11b c) These gahnite composi-tions fall within the igneous field of Batchelor amp Kinnaird(1984) The darker zone is closer in composition to thepure gahnite (Zn8Al16O32) than the lighter zone whichcontains up to 0983 apfu Sn 0195 apfu Ti 1029 apfutotal Fe2thorn 0101 apfu Mn (Table 4) and consequently hasa composition distinct from nigerite In general both thedarker and lighter zones have higher Sn Ti and Fe contentsthan gahnite from the granitic pegmatites of Nigeria(Batchelor amp Kinnaird 1984) Arga northern Portugal(Gomes et al 1995) and Cabanas northern Portugal(Neiva amp Champness 1997) Borborema province north-eastern Brazil (Soares et al 2007) The Zn=Fe2thornt values ofthe darker and lighter zones of gahnite from Namivo arelower than those reported in Neiva amp Champness (1997)and Soares et al (2007)
9 Discussion and conclusions
91 Evolution of micas in the zoned pegmatite
In general individual mica crystals show varying patternsand compositional zoning involving several elementsmainly Si AlVI (AlIV thorn AlVI) Fe2thorn Mn (Fe2thornthorn Mn thornMg) Licalc Rb Cs F and OH and the KRb ratioProgressively zoned crystals from the IIZa show grada-tional contacts between a lithian muscovite core and a
976 A M R Neiva
eschweizerbart_xxx
lsquolsquomixed formrsquorsquo rim (Figs 3e 6e f) and the zoning patternscorrespond to fractionation trends and probably reflect adrop in temperature during the crystallization of the grani-tic pegmatite melt Progressively zoned crystals also occurin OIZ IIZb and Cc Some crystals are reversely zonedwith a) a lsquolsquomixed formrsquorsquo core and a lithian muscovite rimfrom the OIZ (Figs 3d d1 6d) b) a core consisting oflsquolsquomixed formrsquorsquo and lepidolite and a rim of muscovite andlithian muscovite from the IIZa (Figs 3f f1 6g h) c) alepidolite core and a muscovite and lithian muscovite rimfrom the Cc (Figs 3j 6o p) which may be explained bythe hypothesis of oscillations in the compositions of themelt from which they grew alternating between an Li-enriched boundary layer and a bulk melt that is less frac-tionated The muscovite evolved to lithian muscovite inIIZa and Cc (Figs 3f 6g h 3j 6o p) Replacements (Figs3a 6a b 3c 6c 3i 6m n Table 1) occur in OIZ and Ccand overgrowths (Figs 3b g 6i j k 3h 6l Table 1) occurin OIZ and IIZb as found in BSE images
Muscovite evolved to lithian muscovite as observed inOIZ IIZa IIZb and Cc (Figs 3f 6g h 3j 6o p Table 1)Lithian muscovite evolved to lsquolsquomixed formrsquorsquo in OIZ IIZaIIZb and Cc (Figs 3e 6e f Table 1) and lsquolsquomixed formrsquorsquoevolved to lepidolite in IIZa IIZb and Cc (Figs 3f f1 6gh 3h 6l Table 1) All these evolutions are due to fractionalcrystallization
In the OIZ lepidolite has more Si Licalcand F butsimilar KRb to that of zinnwaldite and replaces it (Figs
3a 6a b 7d Table 1) An FeMg-containing polylithionitehas higher Si Licalcand Rb contents and a smaller KRbratio than the lepidolite that it replaces (Figs 3c 6c Table1) and a continuous chemical evolution from lepidolite topolylithionite is shown
The trends for major and trace elements of micas withineach zone are difficult to define due to some partial over-lapping but a progressive evolution from muscovite to lithianmuscovite lsquolsquomixed formrsquorsquo and lepidolite in IIZa IIZb and Ccis mainly shown by an increase in the Si Licalc F Rb and Cscontents and a decrease in the KRb ratio and this is simi-larly shown in the OIZ from muscovite to lsquolsquomixed formrsquorsquo(Table 1 Fig 7) In the OIZ Si and Licalccontents increaseprogressively from zinnwaldite to lepidolite and FeMg-containing polylithionite but a gap occurs between zinnwal-dite and lepidolite (Table 1 Fig 4) whereas a continuousevolution from lepidolite to polylithionite is observed TheKRb ratios of zinnwaldite and polylithionite are within therange of that of lepidolite (Fig 7d e)
Each Al-richer mica (muscovite lithian muscovite andlsquolsquomixed formrsquorsquo) exhibits an evolution from the OIZ to theIIZa and then to the IIZb and Cc particularly shown by anincrease in the Si Licalc F and Rb contents and adecrease in the KRb ratio but also an increase in theCs content in the lsquolsquomixed formrsquorsquo (Table 1 Fig 7) Theseelements and ratio have been used as petrogenetic indi-cators of evolution in micas from pegmatites (eg Cernyet al 2005 Roda Robles et al 2006 2007 Vieira et al
Fig 7 Plot of some variation diagrams of micas from the OIZ IIZa IIZb and Cc of the Namivo granitic pegmatite Mozambique showingthat the Rb2O and Cs2O contents increase and the KRb ratio decreases for micas from the OIZ to the Cc OIZ IIZa IIZb and Cc as in Fig 2
Silicate and oxide minerals from a zoned granitic pegmatite 977
eschweizerbart_xxx
Tab
le2
R
epre
sen
tati
ve
elec
tro
nm
icro
pro
be
anal
yse
sin
wt
o
ffe
ldsp
ars
sch
orl
and
spo
du
men
efr
om
the
Nam
ivo
gra
nit
icp
egm
atit
eM
oza
mb
iqu
e
Alb
ite
K-f
eld
spar
Sch
orl
Sp
od
um
ene
Zo
nes
WZ
OIZ
IIZ
aII
Zb
Cc
Zo
nes
WZ
OIZ
IIZ
aII
Zb
Cc
Zo
nes
OIZ
Zo
ne
Cc
SiO
26
75
76
78
86
87
06
84
76
84
1S
iO2
65
10
65
55
65
46
64
96
64
72
SiO
23
52
0S
iO2
64
65
TiO
20
02
mdash0
02
mdashmdash
TiO
2mdash
00
1mdash
mdashmdash
TiO
20
35
Al 2
O3
27
20
Al 2
O3
20
25
19
74
19
67
19
88
19
97
Al 2
O3
18
96
18
23
18
31
18
24
18
05
B2O
3
10
28
Fe 2
O3
00
6F
e 2O
3mdash
mdashmdash
mdash0
10
Fe 2
O3
mdash0
02
mdash0
03
mdashA
l 2O
33
17
2M
nO
01
3M
nO
00
6mdash
mdashmdash
mdashM
nO
mdash0
03
00
3mdash
mdashF
eO1
35
2M
gO
01
8M
gO
mdashmdash
mdashmdash
mdashM
gO
00
10
01
00
5mdash
mdashM
nO
03
3N
a 2O
01
9C
aO1
04
08
00
56
03
70
32
CaO
00
10
01
00
60
01
00
2M
gO
22
8L
i 2O
8
05
Na 2
O1
06
11
12
01
12
11
13
41
13
4N
a 2O
06
50
58
04
10
59
03
8C
aO0
23
To
tal
10
04
6K
2O
00
50
17
00
60
14
01
0K
2O
14
72
14
75
15
67
15
01
15
74
Li 2
O
02
2S
rO0
72
05
00
24
01
1mdash
Rb
2O
00
90
20
03
00
59
09
0N
a 2O
22
8S
i1
99
7P
2O
50
01
00
4mdash
mdashmdash
Cs 2
O
00
6
00
60
09
01
80
20
K2O
00
1A
lIV0
00
3T
ota
l1
00
33
10
03
31
00
46
10
03
11
00
24
P2O
5mdash
00
3mdash
mdashmdash
H2O
3
18
P2
00
To
tal
99
60
99
48
10
03
89
96
11
00
01
F0
78
AlV
I0
98
7S
rC
a(w
t)0
81
07
40
50
03
50
Cl
mdashF
e3thorn
00
01
KR
b(w
t)153
68
48
23
16
Sum
1003
8P
09
9S
i1
18
23
11
87
91
19
58
11
93
21
19
21
KC
s(w
t)4
07
20
41
63
73
69
O
F0
33
Li
10
00
P0
00
10
00
6mdash
mdashmdash
To
tal
10
00
5M
n0
00
3T
i0
00
3mdash
00
03
mdashmdash
Si
11
98
61
20
88
12
04
11
20
45
12
03
3M
g0
00
8A
l4
17
64
07
14
03
54
08
34
10
1P
mdash0
00
5mdash
mdashmdash
TS
i5
95
2N
a0
01
2F
e3thorn
mdashmdash
mdashmdash
00
13
Ti
mdash0
00
1mdash
mdashmdash
Al
00
48
P1
02
Mn
00
09
mdashmdash
mdashmdash
Al
41
14
39
62
39
70
39
86
39
55
B3
00
0M
gmdash
mdashmdash
mdashmdash
Fe3thorn
mdash0
00
3mdash
00
04
mdashZ
Al
60
00
Ca
01
95
01
50
01
04
00
69
00
60
Mn
mdash0
00
50
00
5mdash
mdashY
Al
02
74
Sr
00
73
00
51
00
24
00
11
mdashM
g0
00
30
00
30
01
4mdash
mdashT
i0
04
5N
a3
59
93
80
03
78
33
83
23
83
1C
a0
00
20
00
20
01
20
00
20
00
4M
g0
57
5K
00
11
00
38
00
13
00
31
00
22
Na
02
32
02
07
01
46
02
12
01
37
Mn
00
47
K3
45
73
47
03
67
73
55
03
73
3F
e2thorn
19
12
Z1
60
01
59
61
60
01
60
11
60
4R
b0
01
10
02
40
03
50
07
00
10
8L
i0
14
8X
38
94
04
39
33
94
39
1C
s0
00
20
00
50
00
70
01
40
01
6P
Y3
00
0m
ole
s
XC
a0
04
2A
n5
13
82
71
71
5Z
16
10
16
06
16
01
16
03
15
99
Na
07
47
Ab
94
69
53
97
09
75
97
9X
37
13
72
39
03
85
40
0K
00
02
Or
03
09
03
08
06
mo
les
amp
02
09
An
01
01
03
01
01
Ab
63
56
38
56
35
OH
35
83
Or
93
69
43
95
99
43
96
4F
04
17
Cl
mdash
WZ
ndashw
allzo
ne
OIZ
ndasho
ute
rin
term
edia
tezo
ne
IIZ
aan
dII
Zb
ndashin
ner
inte
rmed
iate
zon
esC
cndash
core
asin
Fig
2B
aOis
bel
ow
the
det
ecti
on
lim
itin
bo
thfe
ldsp
ars
Cs 2
Ofrac14
00
3w
tin
the
K-
feld
spar
fro
mth
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Z
mdashN
ot
det
ecte
d
Nu
mb
ero
fio
ns
on
the
bas
iso
f3
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ral
bit
ean
dK
-fel
dsp
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anio
ns
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)fo
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tin
ferr
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con
sid
erat
ion
so
fst
oic
hio
met
ry
978 A M R Neiva
eschweizerbart_xxx
2011) Lepidolite from the OIZ is an Al-poorer mica (Fig4) and has the highest Si Licalcand F contents (Table 1)indicating that an evolution cannot be shown from thislepidolite to lepidolites from the other zones which areAl-richer micas (Fig 4) However there is a regulardecrease in the KRb ratio and a progressive increase inthe Rb and Cs contents from lepidolite of the OIZ tolepidolite of IIZa IIZb and Cc (Fig 7) which indicatesthat the KRb ratio and Rb and Cs contents must not beconsidered alone to show fractional crystallization in
lepidolites particularly if some are Al-richer micas andothers Al-poorer micas The high Licalcand F contents oflepidolite from the OIZ did not decrease its KRb ratioSuch an effect is considered to have taken place in lepi-dolite (an Al-richer mica) from the wall zone of the Tancopegmatite Manitoba Canada (Van Lichtervelde et al2008) An evolution from the lepidolite of the IIZa to thatof the Cc is generally shown by the increasing Si LicalcF Rb Cs contents and a decrease in the KRb ratio (Table1 Fig 7)
At the scale of crystals the pegmatite zones and alsothose from the OIZ to the Cc of the Namivo granitic pegma-tite Al-richer micas show fractionation because theyformed from the fractionation of an Li-rich pegmatite melt
The Al-poorer micas zinnwaldite lepidolite and FeMg-containing polylithionite only occur in the OIZ (Fig 4)Polylithionite is the mica richest in Si and Licalc and lepi-dolite from this zone is the richest in Si Licalcand F (Fig 4Table 1) The high Li contents of these micas reflect aconsiderably higher D(Li) at low temperature (Icenhoweramp London 1995) These Li-rich micas may have crystal-lized from an undercooled melt This hypothesis does notimply high Rb and Cs contents and low KRb ratios Thisagrees with the fact that these micas from the OIZ havesimilar Rb and Cs contents and KRb ratios to those of Al-richer micas (muscovite lithian muscovite and lsquolsquomixedformrsquorsquo) from the same pegmatite zone (Fig 7) Howeverthe lepidolite from the wall zone of the Tanco pegmatiteCanada of a similar origin has a low KRb ratio which isattributed to the complexly interrelated structural compo-nents of this lepidolite (Van Lichtervelde et al 2008) TheLi-rich micas from the OIZ may also represent disequili-brium These two hypotheses are considered the best forthese micas of primary magmatic origin
Another hypothesis was also considered They may havecrystallized in boundary layers which concentrate Li andF But this mechanism was suggested for the most fractio-nated tourmaline enriched in Li and F from the core of the
Fig 8 Plot of albite compositions from all zones of the Namivo granitic pegmatite Mozambique showing that the anorthite content of albitedecreases from the WZ to the Cc WZ OIZ IIZa IIZb and Cc as in Fig 2
Fig 9 The Rb vs Cs diagram of K-feldspar from all zones of theNamivo granitic pegmatite Mozambique showing that the Rb andCs contents of K-feldspar increase from the WZ to the Cc WZ OIZIIZa IIZb and Cc as in Fig 2
Silicate and oxide minerals from a zoned granitic pegmatite 979
eschweizerbart_xxx
Little Three pegmatite dike USA (Morgan amp London1999) and the micas enriched in Li and F from theNamivo pegmatite belonging to the OIZ Furthermore ina boundary layer melt that became enriched in Li and F theKRb ratio of micas decreases strongly (Van Lichterveldeet al 2008) which was not found in these micas from theOIZ (Fig 7d) Nor can they have resulted from the crystal-lization of a late melt that would have reacted with the OIZbecause these micas are among those containing the high-est KRb values (Fig 7d)
92 The importance of feldspars micas andcolumbitendashtantalite compositions to the Namivogranitic pegmatite evolution
The trace elements Rb and Cs and the KRb and KCs ratioshave been used to show the evolution of K-feldspar inpegmatites (eg Cerny 1994 Cerny et al 2005 RodaRobles et al 2005) The Rb and Cs contents increase andthe KRb and KCs ratios of K-feldspar decrease from theWZ to the Cc (Fig 9 Table 2) reflecting the growth of K-feldspar from an increasingly fractionated melt withouthaving grown from or having been chemically modifiedby an aqueous fluid as in the Swamp pegmatite section atthe Little Three Mine USA (London et al 2012) Thecrystallization of K-feldspar from an exsolved aqueousfluid from melt will reverse the magmatic fractionation ofRb Cs KRb and KCs because Rb and especially Cs areso much more compatible in vapor that both Rb and Csremain in the fluid phase (London et al 2012) The feldsparsolvus pairs in the Namivo pegmatite record magmaticcrystallization temperatures that decrease from WZ to CcAlbite shows a decrease in the Ca Sr contents and SrCaratio from the WZ to the Cc (Fig 8 Table 2) Therefore thefeldspars and also Al-richer micas as already explainedshow fractionation in this zoned pegmatite
In general lepidolite from the Namivo pegmatite hassimilar Rb2O and Cs2O contents and KRb (wt) values tothose of lepidolite from the Rozna and Dobra Voda lepi-dolite-subtype pegmatites in the Czech Republic (Cernyet al 1995) but lower Rb2O and Cs2O contents thanlepidolite from the lepidolite-subtype pegmatite at RedCross Lake Manitoba Canada (Cerny et al 2012a) K-feldspar from the Namivo pegmatite also has lower Rb2O
Table 3 Representative electron microprobe analyses in wt of columbitendashtantalite from the Namivo granitic pegmatite Mozambique
Outer Intermediate Zone - OIZ Inner Intermediate Zone - IIZa
Core - Cc
D L L
WO3 022 059 079 113 101 351 050 007Ta2O5 5487 5123 2503 3186 2888 2519 3127 4542Nb2O5 2537 3000 5483 4635 5113 5144 4911 3686SnO2 008 015 024 049 020 026 017 012TiO2 263 161 136 254 202 145 125 016FeO 860 710 665 471 236 068 mdash mdashMnO 793 952 1099 1304 1400 1725 1748 1718Total 9970 10020 9989 10012 9960 9978 9978 9981W 0004 0011 0013 0019 0016 0057 0008 0001Ta 1065 0975 0422 0552 0495 0430 0543 0847Nb 0819 0949 1538 1336 1456 1460 1418 1143Sn 0002 0004 0006 0012 0005 0007 0004 0003Ti 0141 0085 0063 0122 0096 0068 0060 0008Fe 0513 0416 0345 0251 0124 0036 mdash mdashMn 0479 0564 0578 0704 0747 0917 0945 0998P
3023 3004 2965 2996 2939 2975 2978 3000Mn(Mn thorn Fe) 048 058 063 074 086 096 100 100Ta(Ta thorn Nb) 057 051 022 029 025 023 028 043Classification tant-(Fe) tant-(Mn) col-(Mn) col-(Mn) col-(Mn) col-(Mn) col-(Mn) col-(Mn)
D ndash darker L ndash lighter zones mdash Not detected tant-tantalite col-columbite Cation formula on the basis of 6 atoms of oxygen
Fig 10 Compositions of columbitendashtantalite from the Namivogranitic pegmatite Mozambique in the columbite quadrilateralshowing that Mn(Mn thorn Fe) of columbite-(Mn) increases from theOIZ to the Cc and the richest columbite-(Mn) in Ta(Ta thorn Nb)tantalite-(Fe) and tantalite-(Mn) only occur in the OIZ OIZ IIZaand Cc as in Fig 2
980 A M R Neiva
eschweizerbart_xxx
and Cs2O contents than K-feldspar from the lepidolite-subtype pegmatite at Red Cross Lake The Rb2O andCs2O contents of primary and late K-feldspar of this peg-matite at Red Cross Lake attained unprecedented levels(Cerny et al 2012a) The lowest KRb (wt) values ofmuscovite lithian muscovite lsquolsquomixed formrsquorsquo and lepido-lite from the IIZb and Cc (Fig 7) and K-feldspar (KRb frac1414) from the Cc compare well with those found in theseminerals from the AC6frac143 lepidolite-subtype pegmatitefrom Greer Lake (Cerny et al 2005) and some of themost fractionated pegmatites worldwide which belong tothe petalite-subtype (eg Tanco Manitoba Cerny 2005Cerny et al 1998 Varutrask Sweden Cerny et al 2005)but muscovite lithian muscovite and lepidolite from theIIZb and Cc have lower Rb2O and Cs2O contents than thesemicas from the Tanco pegmatite (Cerny 2005a VanLichtervelde et al 2008) K-feldspar also has lower
contents of these oxides than the most evolved K-feldsparfrom the Tanco pegmatite (Cerny 2005a) The magmaticfractionation was strong from the WZ to IIZb and Cc of theNamivo lepidolite-subtype pegmatite
The compositional trend of columbite-(Mn) from the OIZto Cc of the Namivo granitic lepidolite-subtype pegmatite(Fig 10) is identical to that of columbite-group mineralsfrom the lepidolite-subtype complex granitic pegmatitesfrom the Dobra Voda in the Moldanubicum CzechRepublic (Novak amp Cerny 1998) and the HimalayaDistrict southern California (shown in Cerny et al 2004)Experimental data for the Fe-Mn pair (Linnen amp Cuney2005) suggest an increase in Fe with fractional crystalliza-tion which is not observed in nature Other phases seem tocontrol the bahavior of Fe and Mn in the melt eg thecrystallization of tourmaline causes a rapid increase of theMnFe in the melt (Van Lichtervelde et al 2006) When thecrystallization of tourmaline stopped the columbitendashtantaliteminerals showed a constant MnFe indicating that the Fe andMn contents in the melt remained constant Schorl onlyoccurs in the OIZ of the Namivo granitic pegmatite and itscrystallization cannot be responsible for the increase in theMnFe of the melt because Mn(Mn thorn Fe) of columbite-(Mn) increases progressively from the OIZ to the IIZa and Cc(Fig 10) Garnet zinnwaldite and gahnite containing Fe andMn also only occur in the OIZ and cannot also have causedthe increase of the MnFe in the melt The dominant Mnenrichment before Ta enrichment started in the columbitendash-tantalite composition from some granitic pegmatites isattributed to an increased alkali-fluoride activity at moderatemHF (Cerny et al 2004) and an increase in the activity offluorine (Martins et al 2011) Each Al-richer mica (musco-vite lithian muscovite and lsquolsquomixed formrsquorsquo) from the Namivogranitic pegmatite shows an increase in F content from theOIZ to the IIZa IIZb and Cc (Table 1) In general the Fcontent of lepidolite also increases from the IIZa to the IIZband Cc Therefore the extreme Fe-Mn fractionation beforeTa enrichment in columbite-(Mn) (Fig 10) may be due to anincrease in the activity of fluorine as a consequence offractional crystallization The increase in the Ta content ofcolumbite-(Mn) from the Namivo granitic pegmatite isattributed to fractional crystallization
The geochemical evolution of albite and K-feldsparfrom the WZ to the Cc Al-richer micas muscovite lithianmuscovite and lsquolsquomixed formrsquorsquo from the OIZ to the Cc andlepidolite from the IIZa to the Cc and columbite-(Mn) andalso beryl (Neiva amp Neiva 2005) from the OIZ to the Ccare caused by magma fractionation The pegmatite zonesare the product of primary crystallization from a volatile-rich silicate melt The pegmatite consolidated from the WZto the Cc The IIZb is one of the most evolved zones asalso suggested by the beryl composition (Neiva amp Neiva2005) and is the richest in lsquolsquomixed formrsquorsquo and lepidolite
The richest columbite-(Mn) in Ta(Ta thorn Nb) and com-positions of tantalite-(Fe) and tantalite-(Mn) only occur inthe OIZ (Fig 10a) associated with lepidolite and polythio-nite (Fig 3c) which may be due to the local depletion of Liand F in the melt which decreases the solubility of Ta andcauses Ta precipitation (Linnen 1998 Linnen amp Cuney
Fig 11 a Backscattered-electron image of a gahnite crystal with adarker zone partially surrounding a lighter zone from the OIZ of theNamivo granitic pegmatite b c Plot of gahnite compositions in theSn-Zn-Ti diagram (atomic proportions) showing a chemical distinc-tion between the lighter and darker zones OIZ as in Fig 2
Silicate and oxide minerals from a zoned granitic pegmatite 981
eschweizerbart_xxx
2005) At the Tanco pegmatite Ta oxides are also asso-ciated with lepidolite enriched in Li and F from the wallzone (Van Lichtervelde et al 2008)
93 Origin and evolution of the zoned graniticlepidolite-subtype pegmatite at Namivo
In general granitic pegmatites particularly those belong-ing to the rare-element class are accepted as having beenformed by the fractional crystallization of a granite melt(eg Cerny 1991a b 1992 Neiva et al 2008 2012 Roda-Robles et al 2012) But it also has been proposed thatpegmatites may be formed by partial melting of appropri-ate rock compositions (eg Nabelek et al 1992 Nabelekamp Russ-Nabelek 1992 Shearer et al 1992 Roda Robleset al 1999) The lepidolite-subtype pegmatites belong tothe LCT (lithium-cesium-tantalum) family (Cerny amp Ercit2005) They are derived by fractional crystallization of agranite magma (eg Cerny et al 2005 Neiva amp Ramos2010 Cerny et al 2012b) Experimental work by Londonet al (1989) and London (1990) using Macusani glass as astarting material equivalent to the bulk composition ofhighly fractionated rare-alkali-rich pegmatites underhighly evolved and hydrous but H2O undersaturatedmelt obtained the latest primary assemblage consisting
of an Li-rich mica thorn albite thorn quartz deposited directlyfrom the primary melt phase Other authors egZasedatelev (1974 1977) and Stewart (1978) argue thatlepidolite-bearing pegmatites are derived from direct ana-texis and Gordiyenko et al (1996) consider that they arederived from an undefined medium and the rare-elementmineralization is superimposed on preexisting barrenpegmatites
Lepidolite-subtype pegmatites may migrate a long wayfrom their parent granites because their volatile-rich highlyfluid pegmatite melts are stable at relatively low tempera-tures (eg Cerny et al 2005 Antunes et al 2013)Therefore the Namivo pegmatite is probably derived byfractional crystallization of an S-type granite magmawhich resulted from partial melting of metamorphosed juve-nile sediments containing micas that carry most of the traceelements that define the signature of the LCT pegmatites(eg Dahl et al 1993)
The two main models for the internal evolution of peg-matites that dominated for more than a century are a) thefractional crystallization of a flux-bearing granitic melt fromthe margins to the center of the pegmatite (Cameron et al1949) b) the interactions of an aqueous fluid with graniticmelt (Jahns amp Burnham 1969 Jahns 1982) The recentmodel of constitutional zone refining combines aspects ofboth models and invokes the formation of a flux-enriched
Table 4 Electron microprobe analyses in wt of zoned gahnite from the outer intermediate zone (OIZ) of the Namivo granitic pegmatiteMozambique
Darker Zone Lighter Zone
Mean s Range Mean s Range
SnO2 036 050 0ndash097 658 281 151ndash998TiO2 008 008 0ndash021 065 034 008ndash105Nb2O5 001 002 0ndash006 018 007 007ndash029Ta2O5 001 004 0ndash010 015 013 0ndash033ZnO 3998 123 3810ndash4109 3339 318 3004ndash3848FeO 367 048 331ndash442 433 065 306ndash498MnO 032 004 028ndash040 039 006 032ndash048MgO 003 004 0ndash010 ndash ndash ndashAl2O3 5507 050 5436ndash5572 5337 070 5257ndash5443SiO2 003 003 0ndash007 008 010 0ndash025Total 9956 9912n 8 8Sn 0035 0048 0ndash0095 0648 0278 0149ndash0983Ti 0015 0015 0ndash0038 0120 0064 0015ndash0195Nb ndash 0003 0ndash0006 0021 0009 0009ndash0037Ta ndash 0002 0ndash0006 0009 0009 0ndash0021Zn 7226 0182 6890ndash7382 6086 0568 5482ndash6965Fe2thornt 0752 0103 0675ndash0913 0894 0135 0628ndash1029Mn 0066 0008 0057ndash0083 0082 0013 0066ndash0101Mg 0010 0015 0ndash0037 ndash ndash ndashAl 15887 0052 15805ndash15954 15526 0170 15375ndash15853Si 0007 0008 0ndash0018 0019 0025 0ndash0062P
23998 23405Fe3thorn 0064 0230Fe2thorn 0686 0658SnZn 0005 0007 0ndash0014 0106 0052 0021ndash0179ZnFe2thornt 961 143 768ndash1093 681 190 536ndash1109
n number of analysis Cation formula based on 32 atoms of oxygen Fe2thornt total Fe2thorn estimated
982 A M R Neiva
eschweizerbart_xxx
boundary layer of silicate liquid in advance of a crystal-lization front (London 2008 London amp Morgan 2012)
Lepidolite-subtype pegmatites are generally scarce(Cerny et al 2005) particularly the zoned ones In thesymmetrically zoned lepidolite-subtype pegmatites ofRozna and Dobra Voda Czech Republic micas (Cernyet al 1995) tourmaline (Selway et al 1999) and colum-bite-group minerals (Novak amp Cerny 1998) evolve fromthe outermost zone to the innermost zone following thecrystallization sequence The same was found in tourma-line from the zoned Lastovicky Dolnı Bory and Raddovicelepidolite-subtype pegmatite dikes in the Czeck Republic(Selway et al 1999)
In general beryl (Neiva amp Neiva 2005) feldsparsmicas and columbite-(Mn) (in this paper) from theNamivo lepidolite-subtype pegmatite record the progres-sive chemical evolution of the pegmatite from the wallzone to the core These minerals were produced by crystal-lization from a silicate melt rather than an aqueous fluidphase The slow cooling of melt shown by the magmaticcrystallization temperatures of feldspars cannot explain theincrease in grain-size of minerals from the wall zone to thecore but fluxes will be necessary to promote the change oftexture particularly a flux-rich hydrosilicate liquidaccording to the experimental evidence (London 2009)The constitutional zone refining model will be the best forthis zoned pegmatite and probably for all lepidolite-sub-type pegmatites because this model also produces a higherfinal concentration of incompatible components in a smal-ler volume of rock than fractional crystallization does(Morgan amp London 1999)
The core margin at the Rozna pegmatite contains K-feld-spar and quartz and the core consists mainly of quartz but it issurrounded and penetrated by a quartz-bearing albitethorn lepi-dolite complex which contains several minerals At theDobra Voda pegmatite the center of the dike is occupiedby the lepidolite unit containing albite and other minerals(Cerny et al 1995) At the Namivo pegmatite the coremargin consists of quartz and beryl and the core containsmainly quartz and spodumene but also albite lepidolite andother minerals The last-unit assemblages of primary miner-als in most of the highly fractionated LCT pegmatites are richin albite and commonly contain lepidolite or spodumene andmost of the other rare phases These units represent the lastmost fractionated liquid that can be derived by fractionalcrystallization of a crustal melt (London 2008)
The Namivo granitic pegmatite shows a significant dis-tinction from the other zoned lepidolite-subtype pegmatitesand LCT pegmatites except the Tanco petalite-subtypepegmatite in Canada because the lepidolite richest in SiLi and F FeMg-containing polylithionite and associatedcolumbite-(Mn) with the highest Ta(Ta thorn Nb) ratio tanta-lite-(Fe) and tantalite-(Mn) only occur in the outer inter-mediate zone These minerals usually form late in theconsolidation of pegmatites The lepidolite and polylithio-nite are probably derived from the disequilibrium crystal-lization of an undercooled melt Tantalite may reflect a localdecrease in Li and F that caused Ta precipitation
This paper contributes to a better understanding of theorigin and evolution of the rare zoned lepidolite-subtypepegmatites and shows that although the pegmatite evolvedfrom the wall zone to the core it presents an unusualassociation of lepidolite polylithionite and tantalite in theouter intermediate zone
Acknowledgments Thanks are due to JM Cotelo Neivaand MB Dias for the samples and information providedand to MR Machado Leite and MF Guimaraes for theuse of the electron microprobe facilities at the LaboratorioNacional de Energia e Geologia (LNEG) PortugalFinancial support was provided by the PortugueseGovernment for the project Pest-OECTEUI00732011of the Geosciences Centre through the PortugueseFoundation for Science and Technology I would like tothank D London WB Simmons and the associated editorE Widom for their constructive reviews of this manuscriptand M Prieto for his editorial work
References
Alfonso P Melgarejo JC Yusta I Velasco F (2003)
Geochemistry of feldspars and muscovite in granitic pegmatite
from the Cap de Creus field Catalonia Spain Can Mineral 41
103ndash116
Antunes IMHR Neiva AMR Ramos JMF Silva PB
Silva MMVG Corfu F (2013) Petrogenetic links between
lepidolite-subtype aplite-pegmatite aplite veins and associated
granites at Segura (central Portugal) Chemie der Erde in press
httpdxdoiorg101016jchemer20121203
Batchelor RA amp Kinnaird JA (1984) Gahnite compositions
compared Mineral Mag 48 425ndash430
Beurlen H Da Silva MRR Thomas R Soares DR Olivier P
(2008) Nb-Ta-(Ti-Sn) oxide mineral chemistry as tracer of rare-
element granitic pegmatite fractionation in the Borborema pro-
vince Northeastern Brazil Miner Deposita 43 207ndash228
Cameron EN Jahns RH McNair AH Page LR (1949)
Internal structure of granitic pegmatites Econ Geol
Monograph 2 115 p
Cerny P (1991a) Fertile granites of Precambrian rare-element
pegmatite fields is geochemistry controlled by tectonic setting
or source lithologies Precambrian Res 51 429ndash468
mdash (1991b) Rare-element granite pegmatites I Anatomy and inter-
nal evolution of pegmatite deposits Geoscience Canada 18
49ndash67
mdash (1992) Geochemical and petrogenetic features of mineralization
in rare-element granitic pegmatites in the light of current
research Applied Geochemistry 7 393ndash416
mdash (1994) Evolution of feldspars in granitic pegmatites in
lsquolsquoFeldspars and their Reactionsrsquorsquo I Parsons ed NATO
Advanced Study Institute Series C421 501ndash539
mdash (2005) The Tanco rare-element pegmatite deposit Manitoba
regional context internal anatomy and global comparisons in
lsquolsquoRare-element Geochemistry and Mineral Depositsrsquorsquo RL
Linnen amp IM Samson eds Geochemical Association of
Canada Short Course Notes St Catherines 17 127ndash158
Silicate and oxide minerals from a zoned granitic pegmatite 983
eschweizerbart_xxx
Cerny P amp Ercit TS (2005) The classification of granitic pegma-
tites revisited Can Mineral 43 2005ndash2026
Cerny P Meintzer RE Andersen AJ (1985) Extreme fractiona-
tion in rare-element granitic pegmatites selected examples of
data and mechanisms Can Mineral 23 381ndash421
Cerny P Goad BE Hawthorne FC Chapmann R (1986)
Fractionation trends of the Nb- and Ta-bearing oxide minerals
in the Greer Lake pegmatite granite and its pegmatite aureole
southeastern Manitoba Am Mineral 71 501ndash517
Cerny P Stanek J Novak M Baadsgaard H Rieder M
Ottolini L Kavalova M Chapman R (1995) Geochemical
and structural evolution of micas in the Rozna amp Dobra Voda
pegmatites Czech Republic Mineral Petrol 55 177ndash201
Cerny P Ercit TS Vanstone PJ (1998) Mineralogy and petrol-
ogy of the Tanco rare-element pegmatite deposit southeastern
Manitoba International Mineralogical Association 17th General
Meeting Toronto Field Guidebook B6
Cerny P Chapman R Ferreira K Smeds SA (2004)
Geochemistry of oxide minerals of Nb Ta Sn and Sb in
the Varutrask granitic pegmatite Sweden The case of an
lsquolsquoanomalousrsquorsquo columbitendashtantalite trend Am Mineral 89
505ndash518
Cerny P Masau M Goad BE Ferreira K (2005) The Greer
Lake leucogranite Manitoba and the origin of lepidolite-sub-
type granitic pegmatites Lithos 80 305ndash321
Cerny P Teertstra DK Chapman R Selway JB Hawthorne
FC Ferreira K Chackowsky LE Wang X-J Meintzer
RE (2012a) Extreme fractionation and deformation of the
leucogranite-pegmatite suite at Red Cross Lake Manitoba
Canada IV Mineralogy Can Mineral 50 1839ndash1875
Cerny P Halden NM Ferreira K Meintzer RE Brisbin WC
Chackowsky LE (2012b) Extreme fractionation and deforma-
tion of the leucogranite-pegmatite suite at Red Cross Lake
Manitoba Canada II Petrology of the leucogranites and peg-
matites Can Mineral 50 1807ndash1822
Dahl PS When DC Feldmann SG (1993) The systematics of
trace-element partitioning between coexisting muscovite and
biotite in metamorphic rocks from the Black Hills South
Dakota USA Geochim Cosmochim Acta 57 2487ndash2505
Dias MB amp Wilson WE (2000) The Alto Ligonha Pegmatites
Mozambique Mineral Record 31 459ndash497
Fleet ME (2003) Rock-Forming Minerals vol 3A Sheet silicates
micas The Geological Society London second edition chap 6
Lithium micas 651ndash690
Foord EE Cerny P Jackson LL Sherman DM Eby RK
(1995) Mineralogical and geochemical evolutions of micas
from miarolitic pegmatites of the anorogenic pikes-Peak
Batholith Colorado Mineral Petrol 55 1ndash26
Foster MD (1960) Interpretation of the composition of lithium
micas US Geol Surv Prof Paper 354-E 115ndash147
Fuhrman ML amp Lindsley DK (1988) Ternary-feldspar modeling
and thermometry Am Mineral 73 201ndash215
Gomes CL Castro P Alves C (1995) Caracterizacao das espi-
nelas zincıferas e do par ganite-nigerite no campo aplito-
pegmatıtico da Serra de Arga-Minho N de Portugal IV
Congresso Nacional de Geologia Resumos Alargados
Universidade do Porto Mem 4 629ndash633
Gordiyenko VV Ilyina AN Timochina LA Badamina EB
Stanek J (1996) Geochemical model of evolution of a pegma-
tite-forming ore-magmatic system of western Moravia Proc
Russ Mineral Soc 125 38ndash48 (in Russian)
Icenhower JP amp London D (1995) An experimental study for
element partitioning between biotite muscovite and coexisting
peraluminous granitic melt at 200 MPa (H2O) Am Mineral 80
1229ndash1251
Jahns RH (1982) Internal evolution of pegmatite bodies in lsquolsquoGranitic
Pegmatites in science and industryrsquorsquo P Cerny ed Mineralogical
Association of Canada Short Course Handbook 8 293ndash327
Jahns RH amp Burnham CW (1969) Experimental studies of
pegmatite genesis I A model for the derivation and crystal-
lization of granitic pegmatites Econ Geol 64 843ndash864
Jolliff BL Papike JJ Shearer CK (1987) Fractionation trends
in mica and tourmaline as indicators of pegmatite internal evo-
lution Bob Ingersoll pegmatite Black Hills South Dakota
USA GeochimCosmochim Acta 51 519ndash534
Kile DE amp Foord EE (1998) Micas from the Pikes Peak bath-
olith and its cogenetic granitic pegmatites Colorado optical
properties composition and correlation with pegmatite evolu-
tion Can Mineral 36 463ndash482
Linnen RL (1998) The solubility of Nb-Ta-Zr-Hf-W in granitic
melts with Li and Li thorn F constraints for mineralization in rare
metal granites and pegmatites Econ Geol 93 1013ndash1025
Linnen RL amp Cuney M (2005) Granite-related rare-element
deposits and experimental constraints on Ta-Nb-W-Sn-Zr-Hf
mineralization in lsquolsquoRare-element geochemistry and mineral
depositsrsquorsquo RL Linnen amp IM Samson eds Geochemical
Association of Canada Short Course Notes 17 45ndash68
London D (1990) Internal differentiation of rare-element pegmatites
a synthesis of recent research in lsquolsquoOre Bearing Granite Systems
Petrogenesis and Mineralizing Processesrsquorsquo HJ Stein amp JL
Hannah eds Geol Soc America Special Paper 246 35ndash50
mdash (2008) Pegmatites The Canadian Mineralogist Special
Publication 10 347 p
mdash (2009) The origin of primary textures in granitic pegmatites
Can Mineral 47 697ndash724
London D amp Morgan GB VI (2012) The pegmatite puzzle
Elements 8 263ndash268
London D Morgan GB VI Hervig RL (1989) Vapor-under-
saturated experiments in the system macusanite-H2O at 200
MPa and the internal differentiation of granitic pegmatites
Contrib Mineral Petrol 102 1ndash17
London D Morgan GB VI Paul KA Guttery BM (2012)
Internal evolution of miarolitic granitic pegmatites at the Little
Three mine Ramona California USA Can Mineral 50
1025ndash1054
Martins T Lima A Simmons WB Folster AU Noronha F
(2011) Geochemical fractionation of Nb-Ta oxides in Li-bear-
ing pegmatites from the Barroso-Alvao pegmatite field northern
Portugal Can Mineral 49 777ndash791
Monier G Charoy B Cuney M Ohnenstetter D Robert JL
(1987) Evolution spatiale et temporelle de la composition des
micas du granite albitique a topaze-lepidolite de Beauvoir
Geologie De La France 2ndash3 179ndash188
Monier G amp Robert JL (1986) Evolution of the miscibility gap
between muscovite and biotite solid solutions with increasing
lithium content an experimental study in the systems
K2OndashLi2OndashMgOndashAl2O3ndashSiO2ndashH2OndashHF at 600 C 2 kbar
PH2O comparison with natural lithium micas Mineral Mag
50 641ndash651
Morgan GBVI amp London D (1999) Crystallization of the little
three layered pegmatite-aplite dike Ramona District California
Contrib Mineral Petrol 136 310ndash330
984 A M R Neiva
eschweizerbart_xxx
Nabelek PI amp Russ-Nabelek C (1992) The generation and crys-
tallization conditions of the Proterozoic Harney Peak
Leucrogranite Black Hills South Dakota USA petrologic and
geochemical constraints Contrib Mineral Petrol 110
173ndash191
Nabelek PI Russ-Nabelek C Haeussler GT (1992) Stable
isotope evidence for the petrogenesis and fluid evolution in
the Proterozoic Harney Peak leucogranite Black Hills
South Dakota Geochim Cosmochim Acta 56 403ndash417
Neiva AMR amp Champness PE (1997) Nigerite and gahnite from
the granitic pegmatite veins of Cabanas Ponte de Lima northern
Portugal N Jb Mineral Mh 9 385ndash409
Neiva AMR Gomes MEP Ramos JMF Silva PB (2008)
Geochemistry of granitic aplite-pegmatite sills and their miner-
als from Arcozelo da Serra area (Gouveia central Portugal)
Eur J Mineral 20 465ndash485
Neiva AMR amp Neiva JMC (2005) Beryl from the granitic
pegmatite at Namivo Alto Ligonha Mozambique N Jb
Mineral Abh 181 173ndash182
Neiva AMR amp Ramos JMF (2010) Geochemistry of granitic
aplite-pegmatite sills and petrogenetic links with granites
Guarda-Belmonte area central Portugal Eur J Mineral 22
837ndash854
Neiva AMR Silva PB Ramos JMF (2012) Geochemistry of
granitic aplite-pegmatite veins and sills and their minerals from the
Sabugal area central Portugal N Jb Mineral Abh 189 49ndash74
Novak M amp Cerny P (1998) Niobium-tantalum oxide minerals
from complex granitic pegmatites in the Moldanubicum Czech
Republic primary versus secondary compositional trends Can
Mineral 36 659ndash672
Pesquera Perez A Torres-Ruiz J Gil PP Velilla N (1999)
Chemistry and genetic implications of tourmaline and Li-F-Cs
micas from the Valdeflores (Caceres Spain) Am Mineral 84
55ndash69
Rieder M Cavazzini G DrsquoYakonov YuS Frank-Kamenetskii
VA Gottardi G Guggenheim S Koval PV Muller G
Neiva AMR Radoslovich EW Robert J-L Sassi FP
Takeda H Weiss Z Wones DR (1999) Nomenclature of the
micas Mineral Mag 63 267ndash279
Roda Robles E Pesquera Perez A Velasco Roldan F Fontan F
(1999) The granitic pegmatites of the Fregeneda area
(Salamanca Spain) characteristics and petrogenesis Mineral
Mag 63 535ndash558
Roda Robles E Pesquera A Gil-Crespo PP Torres-Ruiz J
Fontan F (2005) Origin and internal evolution of the Li-F-
Be-P-bearing Pinilla de Fermoselle pegmatite (Central Iberian
Zone Zamora Spain) Am Mineral 90 1887ndash1899
Roda Robles E Pesquera Perez A Gil PP Torres-Ruiz J de
Parseval P (2006) Mineralogy and geochemistry of micas from
the Pinilla de Fermoselle pegmatite (Zamora Spain) Eur J
Mineral 18 369ndash377
Roda Robles E Keller P Pesquera Perez A Fontan F (2007)
Micas of the muscovite-lepidolite series from Karibib pegma-
tites Namibia Mineral Mag 71 41ndash62
Roda Robles E Pesquera A Gil-Crespo P Torres-Ruiz J
(2012) From granite to highly evolved pegmatite a case study
of the Pinilla de Fermoselle granite-pegmatite system (Zamora
Spain) Lithos 153 192ndash207
Selway JB Novak M Cerny P Hawthorne FC (1999)
Compositional evolution of tourmaline in lepidolite-subtype
pegmatites Eur J Mineral 11 569ndash584
Shearer CK Papike JJ Jolliff B (1992) Petrogenetic links
among granites and pegmatites in the Harney Peak rare-element
granite-pegmatite system Black Hills South Dakota Can
Mineral 30 785ndash809
Soares DR Hartmut B Ferreira ACM da Silva MRR
(2007) Chemical composition of gahnite and degree of peg-
matitic fractionation in the Borborema Pegmatitic Province
northeastern Brazil Anais Da Academ Bras Cien 79
395ndash404
Stewart DB (1978) Petrogenesis of lithium-rich pegmatites Am
Mineral 63 970ndash980
Tischendorff G Gattesmann B Forster H-J Trumbull RB
(1997) On Li-bearing micas estimating Li from electron
microprobe analyses and an improved diagram for graphical
representation Mineral Mag 61 809ndash834
Van Lichtervelde M Linnen RL Salvi S Beziat D (2006)
The role of metagabbro rafts on tantalum mineralization in the
Tanco granitic pegmatite Manitoba Can Mineral 44
625ndash644
Van Lichtervelde M Gregoire M Linnen RL Beziat D Salvi
S (2008) Trace element geochemistry by laser ablation ICP-
MS of micas associated with Ta mineralization in the Tanco
pegmatite Manitoba Canada Contrib Mineral Petrol 155
791ndash806
Vieira R Roda-Robles E Pesquera A Lima A (2011)
Chemical variation and significance of micas from the
Fregeneda-Almendra pegmatitic field (Central-Iberian Zone
Spain and Portugal) Am Mineral 96 637ndash645
Wen S amp Nekvasil H (1994) SOLVCALC an interactive gra-
phics program package for calculating ternary feldspar solvus
and two-feldspar geothermometry Comput Geosci 20
1025ndash1040
Wise MA (1995) Trace element chemistry of lithium-rich micas
from rare-element granitic pegmatites Mineral Petrol 55
203ndash215
Zasedatelev AM (1974) Possible accumulation of lithium in host
rocks of lithium pegmatite veins during old sedimentation pro-
cesses Doklady Acad Sci USSR Earth Sci Ser 218 196ndash198
(in Russian)
mdash (1977) Quantitative of metamorphic generation of rare-metal
pegmatites with lithium mineralization Doklady Acad Sci
USSR Earth Sci Ser 236 219ndash221 (in Russian)
Received 26 January 2013
Modified version received 21 May 2013
Accepted 23 July 2013
Silicate and oxide minerals from a zoned granitic pegmatite 985
eschweizerbart_xxx
very helpful for the interpretations Li2O contents ofzinnwaldite lepidolite polylithionite and lsquolsquomixedformrsquorsquo were calculated from the equation Li2O frac14 (0289 SiO2) 9658 and of muscovite and lithian muscovitefrom the equation Li2O frac14 03935 F1326 (Tischendorfet al 1997) Secondary micas replacing feldspars werenot analyzed
Variation in the chemical composition of micas from theNamivo granitic pegmatite is shown in Table 1 and Fig 4lsquolsquoMixed formrsquorsquo is of course not a proper mica mineral name(Rieder et al 1999) The chemical distinction between
dioctahedral and trioctahedral micas is the value of 25octahedral cations per formula unit in dioctahedral and25 octahedral cations in trioctahedral micas for a for-mula calculated on the basis of 12 O thorn F atoms (Riederet al 1999) The Li2O content of analyzed lsquolsquomixed formsrsquorsquois calculated for a trioctahedral mica and the value ofoctahedral cations per formula unit is 28 and totals ofanalyses are good (Table 1) indicating that they are trioc-tahedral micas If Li2O contents of these analyses arecalculated for a dioctahedral mica the value of octahedralcations per formula mainly ranges between 23 and 28 and
Fig 3 Backscattered-electron images of zoned micas from the Namivo granitic pegmatite Mozambique Micas a b c d d1 from the OIZ ef f1from the IIZa g h from the IIZb i j from the Cc d1 and f1 are details of d and f respectively Lep ndash lepidolite Zin ndash zinnwaldite Brl ndashberyl Mix f ndash lsquolsquomixed formrsquorsquo Q ndash quartz Pol ndash polylithionite Cst ndash cassiterite Rt ndash rutile Ct ndash columbitendashtantalite Lith mu ndash lithianmuscovite Ab ndash albite Mu ndash muscovite K-fel ndash K-feldspar
Silicate and oxide minerals from a zoned granitic pegmatite 969
eschweizerbart_xxx
Tab
le1
R
epre
sen
tati
ve
elec
tro
nm
icro
pro
be
anal
yse
sin
wt
o
fm
icas
fro
mth
eN
amiv
og
ran
itic
peg
mat
ite
Mo
zam
biq
ue
Ou
ter
Inte
rmed
iate
Zo
ne
-O
IZIn
ner
Inte
rmed
iate
Zo
ne
-II
Za
Zin
Lep
lsquolsquoM
ixed
Frsquorsquo
Lep
Lep
Po
llsquolsquo
Mix
edF
rsquorsquoL
ith
Mu
sP
ol
Lit
hM
us
lsquolsquoM
ixed
Frsquorsquo
lsquolsquoM
ixed
Frsquorsquo
Lep
Mu
sL
ith
Mu
s
Co
mp
osi
tio
nC
ore
Rim
Co
reR
imR
imC
ore
Rim
Co
reC
ore
Rim
Rim
SiO
24
37
15
42
04
52
45
63
75
23
45
87
64
67
14
63
35
91
84
58
54
85
74
81
24
94
64
55
44
61
1T
iO2
06
00
15
04
70
02
02
70
05
mdashmdash
00
2mdash
01
00
03
00
7mdash
00
4A
l 2O
32
21
81
76
52
97
81
59
01
82
11
48
13
12
63
53
31
49
43
71
92
68
82
83
32
46
43
77
03
55
0F
eO8
42
39
74
57
24
44
94
13
11
56
17
51
14
mdash2
68
11
01
50
01
21
15
Mn
O0
60
00
60
33
00
20
21
00
30
10
01
50
05
01
20
27
12
32
16
04
80
53
Mg
O5
15
17
21
06
14
01
33
10
10
87
06
80
94
00
50
09
mdash0
01
mdashmdash
Zn
O0
46
03
20
17
01
10
24
01
30
14
01
00
09
00
60
13
02
60
41
00
60
15
CaO
00
10
01
00
4mdash
00
10
02
00
30
05
00
1mdash
mdash0
02
00
10
02
mdashL
i 2O
2
97
60
13
42
66
35
47
73
23
84
03
07
45
04
34
38
42
54
64
01
60
45
Na 2
O0
08
00
60
23
01
10
23
00
70
29
03
30
06
04
40
13
02
60
13
03
80
28
K2O
10
00
98
41
00
91
02
01
05
89
77
93
39
98
95
09
91
10
28
97
79
95
99
39
81
Rb
2O
08
60
78
06
61
30
02
80
46
05
10
43
04
91
06
15
01
42
16
71
02
11
0C
s 2O
0
06
00
9
00
60
14
00
6
00
6
00
6
00
6
00
60
15
05
50
13
02
2
00
60
03
F5
10
89
92
24
10
50
10
14
10
05
24
60
81
98
41
06
53
84
89
74
10
50
11
0H
2O
18
30
23
33
9mdash
mdashmdash
33
54
12
mdash4
01
19
12
15
09
14
28
39
61
02
03
10
40
81
01
75
10
51
41
04
31
10
38
51
00
51
10
04
21
03
77
10
03
31
02
85
10
19
61
03
19
10
02
51
00
21
O
F2
14
37
80
94
44
14
26
42
21
03
03
44
13
04
52
26
20
53
11
02
10
46
To
tal
99
89
10
03
01
00
81
10
07
31
00
05
99
63
99
48
10
00
89
96
49
98
81
00
59
99
91
10
00
81
00
04
99
75
KR
b(w
t)1
11
21
47
13
41
91
62
11
88
56
26
25
48
98
1
Si
30
85
36
20
30
45
37
47
35
58
38
54
31
02
30
83
38
63
30
45
32
66
32
26
33
51
30
24
30
86
AlIV
09
15
03
80
09
55
02
53
04
42
01
46
08
98
09
17
01
37
09
55
07
34
07
74
06
49
09
76
09
14
PT
40
04
00
40
04
00
40
04
00
40
04
00
40
04
00
40
04
00
40
04
00
40
0A
lVI
09
31
10
09
14
07
09
92
10
17
09
99
15
49
18
54
10
12
19
56
13
96
14
65
13
19
19
74
18
87
Ti
00
32
00
08
00
24
00
01
00
14
00
02
mdashmdash
00
01
mdash0
00
50
00
20
00
4mdash
00
02
Fe2thorn
04
97
02
22
02
57
01
36
02
81
00
72
00
87
00
97
00
62
mdash0
15
10
06
20
08
50
00
70
06
4M
n0
03
60
00
30
01
90
00
10
01
20
00
20
00
60
00
80
00
30
00
70
01
50
07
00
12
40
02
70
03
0M
g0
54
20
17
10
10
60
13
90
13
50
09
90
08
60
06
70
09
10
00
50
00
9mdash
00
01
mdashmdash
Zn
00
24
00
16
00
08
00
05
00
12
00
06
00
07
00
05
00
04
00
03
00
06
00
13
00
21
00
03
00
07
Li
08
44
16
13
09
25
17
73
14
95
19
32
10
26
00
80
19
54
01
14
11
84
11
46
12
64
00
42
01
20
PR
29
13
04
27
53
05
29
73
11
27
62
11
31
32
09
27
72
76
28
22
05
21
1C
a0
00
10
00
10
00
3mdash
00
01
00
01
00
02
00
04
00
01
mdashmdash
00
01
00
01
00
01
mdashN
a0
01
10
00
80
03
00
01
40
03
00
00
90
03
70
04
30
00
80
05
70
01
70
03
40
01
70
04
90
03
6K
09
00
08
38
08
66
08
65
09
17
08
18
07
90
08
47
07
91
08
40
08
82
08
36
08
60
08
41
08
38
Rb
00
39
00
33
00
29
00
56
00
12
00
19
00
22
00
18
00
21
00
45
00
65
00
61
00
73
00
44
00
47
Cs
00
02
00
03
00
02
00
04
00
02
00
02
00
02
00
02
00
02
00
04
00
16
00
04
00
06
00
02
00
01
PA
09
50
88
09
30
94
09
60
85
08
50
91
08
20
95
09
80
94
09
60
94
09
2F
11
39
18
99
04
77
22
07
21
80
20
85
05
17
01
70
20
31
02
23
11
44
10
37
15
87
01
05
02
33
OH
0
86
10
10
11
52
3mdash
mdashmdash
14
83
18
30
mdash1
77
70
85
60
96
30
41
31
89
51
76
7Z
on
esL
DL
DL
DL
DD
D
LD
LD
L
F
igu
res
Fig
s3
a6
ab
Fig
3
bF
igs
3c
6c
Fig
s3
d
d1
6
dF
igs
3e
6e
fF
igs
3f
f1
6g
h
970 A M R Neiva
eschweizerbart_xxx
Tab
le1
C
on
tin
ued
Inn
erIn
term
edia
teZ
on
e-
IIZ
bC
ore
-C
c
Lit
hM
us
Lep
Mu
slsquolsquo
Mix
edF
rsquorsquoL
epL
ith
Mu
slsquolsquo
Mix
edF
rsquorsquoL
epM
us
Lit
hM
us
Co
reR
imC
ore
Rim
Rim
Co
reR
imR
im
SiO
24
69
25
21
64
62
24
90
64
99
94
71
84
90
15
09
54
63
44
65
6T
iO2
00
3mdash
00
40
03
00
30
02
00
1mdash
mdashmdash
Al 2
O3
35
72
22
89
36
17
28
04
24
87
35
10
26
26
23
49
36
31
35
53
FeO
00
10
61
00
70
05
00
70
04
21
81
55
00
10
03
Mn
O0
55
05
80
43
12
92
24
06
01
09
13
30
14
01
4M
gO
mdashmdash
mdashmdash
mdashmdash
mdashmdash
mdashmdash
Zn
O
00
60
10
00
8
00
60
19
0
06
02
50
07
0
06
0
06
CaO
00
30
04
mdashmdash
00
10
01
00
10
01
mdashmdash
Li 2
O
06
55
42
02
54
52
47
90
93
45
15
07
04
70
79
Na 2
O0
41
00
80
49
02
60
16
04
10
13
01
00
55
05
4K
2O
97
99
78
10
16
96
69
76
94
49
33
90
89
97
99
0R
b2O
12
42
30
14
31
79
21
01
34
17
52
13
14
81
69
Cs 2
O0
16
08
7
00
60
62
05
00
11
07
70
79
01
40
12
F1
46
83
40
70
49
97
63
19
25
55
73
51
15
16
9H
2O
38
30
52
41
62
14
08
23
61
18
20
95
39
63
70
10
08
61
03
69
10
02
61
02
51
10
31
61
00
77
10
26
71
02
87
10
05
81
00
75
O
F0
61
35
00
29
21
03
20
08
12
33
30
90
48
07
1T
ota
l1
00
25
10
01
99
99
71
00
41
99
96
99
96
10
03
49
97
81
00
10
10
00
4
KR
b(w
t)7
23
96
44
94
26
44
83
96
15
3
Si
31
10
34
98
30
84
32
68
33
76
31
30
33
02
34
42
30
82
31
02
AlIV
08
90
05
02
09
16
07
32
06
24
08
70
06
98
05
58
09
18
08
98
PT
40
04
00
40
04
00
40
04
00
40
04
00
40
04
00
AlV
I1
90
01
30
71
92
91
47
01
35
51
87
51
38
71
31
21
92
81
89
2T
i0
00
1mdash
00
02
00
02
00
02
00
01
00
01
mdashmdash
mdashF
e2thorn
00
01
00
34
00
04
00
03
00
04
00
02
01
23
00
88
00
01
00
02
Mn
00
31
00
33
00
24
00
73
01
28
00
34
00
62
00
76
00
08
00
08
Mg
mdashmdash
mdashmdash
mdashmdash
mdashmdash
mdashmdash
Zn
00
03
00
05
00
04
00
03
00
09
00
03
00
12
00
03
00
03
00
03
Li
01
73
14
61
00
66
12
11
13
01
02
49
12
21
13
76
01
27
02
11
PR
21
12
84
20
32
76
28
02
16
28
12
86
20
72
12
Ca
00
02
00
03
mdashmdash
00
01
00
01
00
01
00
01
mdashmdash
Na
00
53
00
10
00
63
00
34
00
21
00
53
00
17
00
13
00
71
00
70
K0
82
80
83
70
86
50
82
10
84
10
79
90
80
20
78
20
84
60
84
1R
b0
05
30
09
90
06
10
07
70
09
10
05
70
07
60
09
20
06
30
07
2C
s0
00
50
02
50
00
10
01
80
01
40
00
30
02
20
02
30
00
40
00
3P
A0
94
09
70
99
09
50
97
09
10
92
09
10
98
09
9F
03
06
17
69
01
48
10
51
16
30
04
03
11
83
15
70
02
42
03
56
OH
1
69
40
23
11
85
20
94
90
37
01
59
70
81
70
43
01
75
81
64
4Z
on
esD
LD
D
LD
LL
D
DF
igu
res
Fig
s3
g
6i
jk
Fig
s3
h
6l
Fig
s3
i6
m
nF
igs
3j
6o
p
OIZ
IIZ
aII
Zb
Cc
asin
Fig
2Z
inndash
zin
nw
ald
ite
Lep
ndashle
pid
oli
teF
ndashfo
rmP
olndash
po
lyli
thio
nit
eL
ith
Mu
sndash
lith
ian
mu
sco
vit
eM
us
ndashm
usc
ov
ite
Lndash
ligh
ter
zon
eD
ndashd
ark
erzo
ne
D
-th
ed
ark
estzo
ne
L
-th
eli
gh
test
zon
ein
BS
Eim
ages
BaO
isb
elo
wth
ed
etec
tio
nli
mit
Cal
cula
ted
nu
mb
ero
fio
ns
on
the
bas
iso
f1
2o
xy
genthorn
Fat
om
sL
i 2O
v
alu
esca
lcu
late
dfr
om
equ
atio
ns
of
Tis
chen
do
rff
eta
l
(19
97
)O
H
-ca
lcu
late
db
yd
iffe
ren
ceto
20
00
H
2O
-ca
lcu
late
db
yst
oic
hio
met
ry
Silicate and oxide minerals from a zoned granitic pegmatite 971
eschweizerbart_xxx
analytical totals are not good The analyzed lsquolsquomixedformsrsquorsquo are distinguished in backscattered-electron (BSE)images and chemically (Fig 3b d d1 e f f1 h i andFig 4) The chemical distinction between lsquolsquomixed formrsquorsquoand lepidolite from the OIZ (Fig 4) is clear in Fig 3bwhere lepidolite is darker than lsquolsquomixed formrsquorsquo because theformer has less Fe and Mn than the latter (Table 1) and inFig 3f f1 and 3h for micas from the IIZa and IIZbrespectively where lepidolite is lighter than lsquolsquomixedformrsquorsquo because the former has more Fe2thorn and Mn oronly more Mn than the latter (Table 1) The lsquolsquomixedformsrsquorsquo analyzed are distinguished in the BSE imagesfrom the lepidolite that falls in its fields in the Fig 4The fields of lepidolite composition in Foster (1960) arelarger than the field for lepidolite from the trilithionite tothe polylithionite (Rieder et al 1999) According to Fleet(2003) only a few lepidolite compositions plot on thetrilithionite-polylithionite join In general lepidolite hashigher Si Licalc Rb Cs F contents and lower AlVI andOH contents than lsquolsquomixed formrsquorsquo (Table 1 Fig4)lsquolsquoMixed formrsquorsquo is also clearly distinguished fromlithian muscovite in OIZ IIZa IIZb and Cc in BSEimages (Fig 3d d1 e f i) and chemically (Table 1 Fig4) as it generally has higher Si Licalc Rb Cs F contentsand lower AlVI and OH contents than lithian muscovite
Two distinct trends are defined in Fig 4 One trendconsists of Al-poorer micas which are zinnwaldite
lepidolite and FeMg-containing polylithionite from theOIZ A hiatus occurs between zinnwaldite and lepidolitebut the zinnwaldite series is continuous with the field oflepidolite at the high Li content (Fleet 2003) The othertrend consists of Al-richer micas (muscovite lithian mus-covite and lsquolsquomixed formrsquorsquo from the OIZ IIZa IIZb and Ccand also lepidolite from most of those zones except fromthe OIZ) There is a gap between lithian muscovite and thelsquolsquomixed formrsquorsquo which may be explained by a hiatus inmica stability (eg Jolliff et al 1987) but a solid solutionbetween dioctahedral and trioctahedral micas has beenindicated experimentally (Monier amp Robert 1986) whileother authors have shown that the octahedral site occu-pancy ranges continuously from muscovite to lepidolite(eg Roda Robles et al 2005 Van Lichterveld et al2008 Vieira et al 2011) Most lithian muscovites andlsquolsquomixed formrsquorsquo from the OIZ are richer in Fe2thornthornMg thornMn than those from the other zones due to their higherFe2thorn and Mg contents (Fig 4 Table 1)
In the Al-poorer micas from the OIZ ranging from zinn-waldite to lepidolite and FeMg-containing polylithionite(Fig 4) (AlIV thorn AlVI) Fe2thorn Mg Ti Mn and Zn contentsdecrease and Si and Licalccontents increase (Table 1) In theAl-richer micas ranging from muscovite to lithian muscoviteand lsquolsquomixed formrsquorsquo from the OIZ IIZa IIZb and Cc and alsoto lepidolite from most of those zones except from the OIZ(AlIV thorn AlVI) AlVI and OH contents and KRb ratio
Fig 4 Plots of micas from the Namivo granitic pegmatite Mozambique in the LindashR2thornndashR3thornthorn Ti diagram according to the classification ofFoster (1960) slightly modified (Rieder et al 1999) with R3thorn frac14 AlVI R2thorn frac14 (Fe2thornt thorn Mn2thornthorn Mg) showing the variety of micacompositions Two trends are defined one for Al-poorer micas (zinnwaldite lepidolite and FeMg-containing polylithionite) from theOIZ another for Al-richer micas (muscovite lithian muscovite lsquolsquomixed formrsquorsquo and lepidolite) from all zones except lepidolite from the OIZOIZ IIZa IIZb and Cc as in Fig 2
972 A M R Neiva
eschweizerbart_xxx
generally decrease and Si Licalc Rb Cs and F contentsgenerally increase (Table 1)
42 Main substitution mechanisms
The 2Si thorn Li 3Altotal mechanism operates in the diocta-hedral micas (muscovite and lithian muscovite) (Fig 5a b)whereas the 3LiVI AlVIthorn 2ampVI (amp represents a vacancy)operates in the trioctahedral micas (lsquolsquomixed formrsquorsquo lepido-lite zinnwaldite and FeMg-containing polylithionite) (Fig5c d) which agrees with findings for micas from the Tancopegmatite (Van Lichtervelde et al 2008)
43 Textures and chemical compositions of zoned micacrystals
Backscattered-electron images combined with quantita-tive spot electron-microprobe analyses made it possibleto distinguish different micas in the Namivo graniticpegmatite Similar textural aspects and geochemicalobservations were found between some Al-richer micasfrom the OIZ IIZa IIZb and Cc Some selected zonedcrystals are documented (Table 1 Fig 3 and 6) In theOIZ lepidolite penetrates zinnwaldite along cleavagesand partially surrounds it and the contacts are sharp(Fig 3a) A chemical gap occurs between zinnwalditeand lepidolite compositions (Fig 6a b) Lepidolite withhigher Si Licalc F contents similar KRb value andlower (AlIV thorn AlVI) Ti Fe2thorn Mg (Fe2thornthorn Mn thorn Mg)Zn and OH contents (Table 1) replaces zinnwaldite Athin lepidolite rim partially surrounds lsquolsquomixed formrsquorsquoand the contact is sharp (Fig 3b) The lepidolite rimhas higher Si Mg Licalc Rb F contents and lowerAlVI Ti Fe2thorn Mn Na and OH contents and KRb ratiothan the lsquolsquomixed formrsquorsquo core (Table 1) The lepidoliterim is an Al-poorer mica whereas the lsquolsquomixed formrsquorsquocore is an Al-richer mica (Fig 4) The lepidolite rimcorresponds to an overgrowth The FeMg-containingpolylithionite partially surrounds and penetrates lepido-lite along cleavages and shows well defined contacts(Fig 3c) Both contain rutile cassiterite and columbi-tendashtantalite inclusions A continuous chemical evolutiontakes place from lepidolite to FeMg-containing poly-lithionite (Figs 4 6c) The latter has higher Si LicalcRb contents and lower AlVI Ti Fe2thorn Mn Mg Zn Nacontents and KRb ratio (Table 1) and replaces lepido-lite A lithian muscovite rim with rare FeMg-containingpolylithionite surrounds the lsquolsquomixed formrsquorsquo core and thispolylithionite penetrated lithian muscovite (Fig 3d)The contact between the lithian muscovite rim andlsquolsquomixed formrsquorsquo core is irregular suggesting disequili-brium or at a cleavage (Fig 3d d1) Two linear trendsone for the lithian muscovite rim and another for thelsquolsquomixed formrsquorsquo core are defined in the (Fe2thornthornMnthornMg)vs (AlIV thornAlVI) diagram (Fig 6d) The FeMg-contain-ing polylithionite rim does not belong to any of thesetrends and plots outside this diagram because it is an Al-poorer mica whereas the others are Al-richer micas
(Fig 4) The lithian muscovite rim has higher AlVI(AlIV thorn AlVI) OH contents and KRb ratio and lowerMg (Fe2thornthorn Mn thorn Mg) Licalc Rb F contents than thelsquolsquomixed formrsquorsquo core (Table 1 Fig 6d) The crystal isreversely zoned The FeMg-containing polylithioniterim has higher Si Licalc F contents and lower AlVI(AlIV thorn AlVI) Fe2thorn Mn (Fe2thornthorn Mn thorn Mg) Na andOH contents than the lsquolsquomixed formrsquorsquo core and lithianmuscovite rim (Table 1) and replaces lithian muscovite
In the IIZa some zoned crystals have a lithian muscovitecore and a lsquolsquomixed formrsquorsquo rim and the contacts are gradual(Fig 3e) A small discontinuity occurs in the trends fromthe lithian muscovite core to lsquolsquomixed formrsquorsquo rim in the(Fe2thornthorn Mn thorn Mg) vs (AlIV thorn AlVI) and Rb2O vs KRb(Fig 6e f) The lsquolsquomixed formrsquorsquo rim has higher Si Fe2thornMn (Fe2thornthornMn thornMg) Licalc K Rb Cs F contents andlower AlVI (AlIVthornAlVI) Na OH contents and KRb ratiothan the lithian muscovite core (Table 1 Fig 6e f) indi-cating progressive zoning Similar textural relationshipsand chemical evolutions were found in other zoned crystalsfrom the OIZ IIZb and Cc In another crystal from theIIZa lithian muscovite partially surrounds lsquolsquomixed formrsquorsquointergrown with lepidolite Lithian muscovite also partiallysurrounds muscovite (Fig 3f) The contacts betweenlsquolsquomixed formrsquorsquo and lepidolite and also between muscoviteand lithian muscovite are gradual (Fig 3f f1) whereasthey are well defined for muscovite withlsquolsquomixed formrsquorsquoand lepidolite (Fig 3f f1) The crystal has a lsquolsquomixed formrsquorsquoand lepidolite core and a partial rim of muscovite andlithian muscovite The lsquolsquomixed formrsquorsquo core evolved tolepidolite core as the Si Fe2thorn Mn (Fe2thornthorn Mn thorn Mg)Licalc K Rb Cs and F contents increase and the (AlIV thornAlVI) and KRb ratio decrease (Table 1 Fig 6g h) The SiFe2thorn Mn (Fe2thornthorn Mn thorn Mg) Licalc Rb and F contentsincrease and the (AlIV thorn AlVI) and KRb ratio decreasefrom the muscovite rim to the lithian muscovite rim (Table1 Fig 6g h) suggesting that the former evolved to thelatter The muscovite rim has higher AlVI (AlIV thorn AlVI)Na OH contents and KRb ratio and lower Si Fe2thorn Mn(Fe2thornthornMn thornMg) Zn Licalc Rb and F contents than thelsquolsquomixed formrsquorsquo core and lepidolite core (Table 1 Fig 6gh) Muscovite was probably reversely formed and evolvedafterwards to lithian muscovite
In the IIZb some crystals have a lithian muscovite coreand a thinner lepidolite rim (Fig 3g) and others show asmall muscovite core and a larger rim of lsquolsquomixed formrsquorsquointergrown with lepidolite (Fig 3h) The contacts betweenthe cores and rims are well defined There are increases inthe Si Mn (Fe2thornthorn Mn thorn Mg) Licalc Rb and F contentsand decreases in the AlVI (AlIVthornAlVI) and KRb ratio fromthe lsquolsquomixed formrsquorsquo rim to the intergrown lepidolite rim(Table 1 Figs 3h 6l) suggesting that the former evolvedto the latter as also found in IIZa and Cc In both crystalsthe rim compositions have higher Si (Fe2thornthorn Mn thorn Mg)Licalc Rb Cs F contents and lower AlVI (AlIVthorn AlVI) Naand OH contents and KRb ratio than the core (Table 1 Figs3g 6i j k 3h 6l) A compositional gap occurs between coreand rim in the diagrams for both crystals (Fig 6i j k l)suggesting that both rims correspond to overgrowths and no
Silicate and oxide minerals from a zoned granitic pegmatite 973
eschweizerbart_xxx
diffuse reequilibration took place in any crystal as thecontacts between core and rim are sharp
In the Cc lithian muscovite is surrounded and pene-trated by lsquolsquomixed formrsquorsquo showing well defined contacts(Fig 3i) The lsquolsquomixed formrsquorsquo has higher Si Fe2thorn Mn(Fe2thornthorn Mn thorn Mg) Licalc Rb Cs F contents and lowerAlVI (AlIV thorn AlVI) Na OH contents and KRb ratio thanthe lithian muscovite (Table 1 Fig 6m n) and a composi-tional gap occurs between both micas suggesting thatlsquolsquomixed formrsquorsquo replaced lithian muscovite In rare crystalsa small lepidolite core is surrounded by a large muscoviterim containing K-feldspar inclusions The contact betweenthe core and rim is sharp (Fig 3j) A thin partial rim oflithian muscovite surrounds muscovite and the contact isgradual The muscovite rim has higher AlVI (AlIVthornAlVI)Na K OH contents and a greater KRb value and lower SiFe2thorn Mn Licalc Rb Cs and F contents than the lepidolitecore (Table 1 Fig 6o p) and a compositional gap occursbetween them (Fig 6o p) indicating that either muscoviteforms an overgrowth or it is reversely formed From themuscovite rim to the lithian muscovite rim the Si Licalc
Rb F contents increase whereas the AlVI (AlIV thorn AlVI)and OH contents and KRb ratio decrease (Table 1 Fig 6op) suggesting that muscovite evolved to lithian muscoviteas also found in IIZa and IIZb
44 Evolution of mica compositions within each zoneand from the outer intermediate zone to the core of theNamivo granitic pegmatite
The KRb ratio is taken as the best fractionation index inmicas (eg Cerny et al 1985 Foord et al 1995 Wise1995 Pesquera et al 1999 Roda Robles et al 2006 2007)It is hard to establish trends in the evolution of mica com-position from muscovite and lithian muscovite to lsquolsquomixedformrsquorsquo and lepidolite within each zone because the KRbratio shows some partial overlapping particularly betweenthe lithian muscovite and lsquolsquomixed formrsquorsquo and also betweenthe latter and lepidolite However an evolution from mus-covites to lepidolite (Al-richer mica Fig 4) is clearer (Fig7) In general in IIZa IIZb and Cc the Si Licalc Rb Cs and
Fig 5 The main substitutions in micas from the Namivo granitic pegmatite Mozambique a b SiIVthorn LiVI versus AlIVthornAlVI showing the 2SithornLi 3Altotal substitution mechanism operating in dioctahedral micas (Mu muscovite and Lith mu lithian muscovite) c d AlVI thornamp VI
versus LiVI (where amp represents a vacancy) and showing the 3LiVI AlVI thorn 2 amp VI substitution mechanism operating in trioctahedral micas(Mix f ndashlsquolsquomixed formrsquorsquo Lep lepidolite Zin zinnwaldite and Pol-FeMg-containing polylithionite) OIZ IIZa IIZb and Cc as in Fig 2
974 A M R Neiva
eschweizerbart_xxx
F contents tend to increase and the (AlIV thorn AlVI) AlVI
contents and KRb ratio tend to decrease from muscoviteto lepidolite (Table 1 Fig 7) This sequence is consistentbut rarely in the Cc lepidolite is rimmed by muscovite (Fig3j) But in the OIZ the evolution stops in lsquolsquomixed formrsquorsquoparticularly shown by the large range of the KRb ratiowhich mainly overlaps that of lepidolite from this zone(Fig 7) because this lepidolite is an Al-poorer mica whereasthe others are Al-richer micas (Fig 4)
In the OIZ the lepidolite has more Si Licalc and F andless (AlIV thorn AlVI) Ti Fe2thorn Mn Mg and Zn than zinn-waldite (Table 1) but it has larger ranges of Rb and KRbratio than zinnwaldite (Fig 7) The FeMg-containingpolylithionite is the richest mica in Si Licalc and thepoorest in (AlIV thorn AlVI) (Table 1) But at this zone scalethe polylithionite has Rb Cs contents and KRb ratiowithin the ranges for lepidolite and close to those of zinn-waldite (Fig 7)
Fig 6 Variation diagrams of micas from selected zoned crystals from the zones of the Namivo granitic pegmatite Mozambique to showtheir relationships lith musc lithian muscovite OIZ IIZa IIZb and Cc an in Fig 2
Silicate and oxide minerals from a zoned granitic pegmatite 975
eschweizerbart_xxx
From the OIZ to IIZa IIZb and Cc muscovite and lithianmuscovite generally show increases in the Si Licalc F and Rbcontents and decreases in the Fe2thorn and Mg contents and KRb ratio but the Mg content is very low in these micas fromthe IIZa IIZb and Cc (Table 1 Fig 7a) The lsquolsquomixed formrsquorsquoshows increases in the Si Licalc F Rb Cs contents anddecreases in the (AlIV thorn AlVI) and Mg contents and KRbratio but the Mg content is very low in this mica from theIIZb and Cc (Table 1 Fig 7b c) The lepidolite shows anincrease in the Si Licalc F Rb and Cs contents and a decreasein the KRb ratio from the IIZa to the IIZb and Cc (Table 1Fig 7d e) Furthermore the lepidolite from the OIZ has thelowest (AlIV thorn AlVI) AlVI and OH contents the highest SiFe2thorn Licalcand F contents and KRb ratio and the lowest Rband Cs contents compared to lepidolite from the other zones(Table 1 Fig 7d e)
5 Feldspars
Selected chemical analyses of albite and K-feldspar fromfive zones of the Namivo granitic pegmatite are given inTable 2 Strontium is the most abundant trace element inalbite (eg Cerny 1994) Anorthite and Sr contents and SrCa ratio of albite decrease from the WZ to the Cc (Fig 8Table 2) Rubidium is the most abundant trace element inK-feldspar followed by Cs in IIZa IIZb and Cc In gen-eral K Rb and Cs contents of K-feldspar increase and KRb and KCs values decrease from the WZ to the Cc (Table2 Fig 9)
The program SOLVCALC 20 (Wen amp Nekvasil 1994)using the Margules model Fuhrman amp Lindsley (1988) wasapplied for the purpose of thermometry The pairing ofplagioclase cores with the K-feldspars average of eachsample was used to estimate the crystallization temperaturesof primary magmatic feldspars They are 405 C (WZ)406ndash340 C (OIZ) 390ndash335 C (IIZa) 347ndash306 C (IIZb)and 333ndash289 C (Cc) at 3 kbar The metamorphic environ-ment of rare-element-Li granitic pegmatites is one of lowpressure 2ndash4 kbar (Cerny amp Ercit 2005) In general thedifference between the maximum and minimum calculatedtemperatures at 2 3 and 4 kbar for the same feldspar pairfrom the Namivo pegmatite is lower than 40 C The tem-perature decreases from the wall zone (WZ) to the core(Cc) A similar temperature behavior of feldspars wasfound in the pegmatite-aplite dike USA (Morgan ampLondon 1999)
6 Other silicates
Tourmaline of schorl composition was only found inthe OIZ (Table 2) because there was not enough Feand Mg for schorl to precipitate in the other zonesSpodumene only occurs in the Cc and its compositionis nearly pure (Table 2)
7 Columbite-tantalite
Representative chemical analyses of columbitendashtantalitefrom the Namivo granitic pegmatite are given in Table 3and plotted in the columbite quadrilateral (Fig 10a)Most crystals are unzoned but zoned crystals with dar-ker and lighter zones in BSE images are from the Cc Thelighter zone of columbite-(Mn) has higher Ta contentTa(Ta thorn Nb) and Mn(Mn thorn Fe) values and lower Nbcontent than the darker zone (Fig 10a b) The crystals ofthe columbitendashtantalite minerals are low in W Sn and Tiimpurities (Table 3)
The main trend starts from the columbite-(Mn) of theOIZ towards the more Mn-enriched and slightly Ta-enriched columbite-(Mn) from the IIZa and Cc The high-est Ta(Ta thorn Nb) values belong to the lighter zone ofcolumbite-(Mn) with Mn(Mn thorn Fe) frac14 10 from the CcThe richest columbite-(Mn) in Ta(TathornNb) and composi-tions of tantalite-(Fe) and tantalite-(Mn) were only foundin the OIZ (Fig 10a) and are associated with lepidolite andpolylithionite (Fig 3c)
8 Gahnite
Gahnite was rarely found in the OIZ and shows a darkerzone that partially surrounds a lighter zone in a BSE image(Fig 11a) The darker zone has a higher Zn content andlower Sn Ti Nb Ta Mn contents and SnZn value than thelighter zone (Table 4 Fig 11b c) These gahnite composi-tions fall within the igneous field of Batchelor amp Kinnaird(1984) The darker zone is closer in composition to thepure gahnite (Zn8Al16O32) than the lighter zone whichcontains up to 0983 apfu Sn 0195 apfu Ti 1029 apfutotal Fe2thorn 0101 apfu Mn (Table 4) and consequently hasa composition distinct from nigerite In general both thedarker and lighter zones have higher Sn Ti and Fe contentsthan gahnite from the granitic pegmatites of Nigeria(Batchelor amp Kinnaird 1984) Arga northern Portugal(Gomes et al 1995) and Cabanas northern Portugal(Neiva amp Champness 1997) Borborema province north-eastern Brazil (Soares et al 2007) The Zn=Fe2thornt values ofthe darker and lighter zones of gahnite from Namivo arelower than those reported in Neiva amp Champness (1997)and Soares et al (2007)
9 Discussion and conclusions
91 Evolution of micas in the zoned pegmatite
In general individual mica crystals show varying patternsand compositional zoning involving several elementsmainly Si AlVI (AlIV thorn AlVI) Fe2thorn Mn (Fe2thornthorn Mn thornMg) Licalc Rb Cs F and OH and the KRb ratioProgressively zoned crystals from the IIZa show grada-tional contacts between a lithian muscovite core and a
976 A M R Neiva
eschweizerbart_xxx
lsquolsquomixed formrsquorsquo rim (Figs 3e 6e f) and the zoning patternscorrespond to fractionation trends and probably reflect adrop in temperature during the crystallization of the grani-tic pegmatite melt Progressively zoned crystals also occurin OIZ IIZb and Cc Some crystals are reversely zonedwith a) a lsquolsquomixed formrsquorsquo core and a lithian muscovite rimfrom the OIZ (Figs 3d d1 6d) b) a core consisting oflsquolsquomixed formrsquorsquo and lepidolite and a rim of muscovite andlithian muscovite from the IIZa (Figs 3f f1 6g h) c) alepidolite core and a muscovite and lithian muscovite rimfrom the Cc (Figs 3j 6o p) which may be explained bythe hypothesis of oscillations in the compositions of themelt from which they grew alternating between an Li-enriched boundary layer and a bulk melt that is less frac-tionated The muscovite evolved to lithian muscovite inIIZa and Cc (Figs 3f 6g h 3j 6o p) Replacements (Figs3a 6a b 3c 6c 3i 6m n Table 1) occur in OIZ and Ccand overgrowths (Figs 3b g 6i j k 3h 6l Table 1) occurin OIZ and IIZb as found in BSE images
Muscovite evolved to lithian muscovite as observed inOIZ IIZa IIZb and Cc (Figs 3f 6g h 3j 6o p Table 1)Lithian muscovite evolved to lsquolsquomixed formrsquorsquo in OIZ IIZaIIZb and Cc (Figs 3e 6e f Table 1) and lsquolsquomixed formrsquorsquoevolved to lepidolite in IIZa IIZb and Cc (Figs 3f f1 6gh 3h 6l Table 1) All these evolutions are due to fractionalcrystallization
In the OIZ lepidolite has more Si Licalcand F butsimilar KRb to that of zinnwaldite and replaces it (Figs
3a 6a b 7d Table 1) An FeMg-containing polylithionitehas higher Si Licalcand Rb contents and a smaller KRbratio than the lepidolite that it replaces (Figs 3c 6c Table1) and a continuous chemical evolution from lepidolite topolylithionite is shown
The trends for major and trace elements of micas withineach zone are difficult to define due to some partial over-lapping but a progressive evolution from muscovite to lithianmuscovite lsquolsquomixed formrsquorsquo and lepidolite in IIZa IIZb and Ccis mainly shown by an increase in the Si Licalc F Rb and Cscontents and a decrease in the KRb ratio and this is simi-larly shown in the OIZ from muscovite to lsquolsquomixed formrsquorsquo(Table 1 Fig 7) In the OIZ Si and Licalccontents increaseprogressively from zinnwaldite to lepidolite and FeMg-containing polylithionite but a gap occurs between zinnwal-dite and lepidolite (Table 1 Fig 4) whereas a continuousevolution from lepidolite to polylithionite is observed TheKRb ratios of zinnwaldite and polylithionite are within therange of that of lepidolite (Fig 7d e)
Each Al-richer mica (muscovite lithian muscovite andlsquolsquomixed formrsquorsquo) exhibits an evolution from the OIZ to theIIZa and then to the IIZb and Cc particularly shown by anincrease in the Si Licalc F and Rb contents and adecrease in the KRb ratio but also an increase in theCs content in the lsquolsquomixed formrsquorsquo (Table 1 Fig 7) Theseelements and ratio have been used as petrogenetic indi-cators of evolution in micas from pegmatites (eg Cernyet al 2005 Roda Robles et al 2006 2007 Vieira et al
Fig 7 Plot of some variation diagrams of micas from the OIZ IIZa IIZb and Cc of the Namivo granitic pegmatite Mozambique showingthat the Rb2O and Cs2O contents increase and the KRb ratio decreases for micas from the OIZ to the Cc OIZ IIZa IIZb and Cc as in Fig 2
Silicate and oxide minerals from a zoned granitic pegmatite 977
eschweizerbart_xxx
Tab
le2
R
epre
sen
tati
ve
elec
tro
nm
icro
pro
be
anal
yse
sin
wt
o
ffe
ldsp
ars
sch
orl
and
spo
du
men
efr
om
the
Nam
ivo
gra
nit
icp
egm
atit
eM
oza
mb
iqu
e
Alb
ite
K-f
eld
spar
Sch
orl
Sp
od
um
ene
Zo
nes
WZ
OIZ
IIZ
aII
Zb
Cc
Zo
nes
WZ
OIZ
IIZ
aII
Zb
Cc
Zo
nes
OIZ
Zo
ne
Cc
SiO
26
75
76
78
86
87
06
84
76
84
1S
iO2
65
10
65
55
65
46
64
96
64
72
SiO
23
52
0S
iO2
64
65
TiO
20
02
mdash0
02
mdashmdash
TiO
2mdash
00
1mdash
mdashmdash
TiO
20
35
Al 2
O3
27
20
Al 2
O3
20
25
19
74
19
67
19
88
19
97
Al 2
O3
18
96
18
23
18
31
18
24
18
05
B2O
3
10
28
Fe 2
O3
00
6F
e 2O
3mdash
mdashmdash
mdash0
10
Fe 2
O3
mdash0
02
mdash0
03
mdashA
l 2O
33
17
2M
nO
01
3M
nO
00
6mdash
mdashmdash
mdashM
nO
mdash0
03
00
3mdash
mdashF
eO1
35
2M
gO
01
8M
gO
mdashmdash
mdashmdash
mdashM
gO
00
10
01
00
5mdash
mdashM
nO
03
3N
a 2O
01
9C
aO1
04
08
00
56
03
70
32
CaO
00
10
01
00
60
01
00
2M
gO
22
8L
i 2O
8
05
Na 2
O1
06
11
12
01
12
11
13
41
13
4N
a 2O
06
50
58
04
10
59
03
8C
aO0
23
To
tal
10
04
6K
2O
00
50
17
00
60
14
01
0K
2O
14
72
14
75
15
67
15
01
15
74
Li 2
O
02
2S
rO0
72
05
00
24
01
1mdash
Rb
2O
00
90
20
03
00
59
09
0N
a 2O
22
8S
i1
99
7P
2O
50
01
00
4mdash
mdashmdash
Cs 2
O
00
6
00
60
09
01
80
20
K2O
00
1A
lIV0
00
3T
ota
l1
00
33
10
03
31
00
46
10
03
11
00
24
P2O
5mdash
00
3mdash
mdashmdash
H2O
3
18
P2
00
To
tal
99
60
99
48
10
03
89
96
11
00
01
F0
78
AlV
I0
98
7S
rC
a(w
t)0
81
07
40
50
03
50
Cl
mdashF
e3thorn
00
01
KR
b(w
t)153
68
48
23
16
Sum
1003
8P
09
9S
i1
18
23
11
87
91
19
58
11
93
21
19
21
KC
s(w
t)4
07
20
41
63
73
69
O
F0
33
Li
10
00
P0
00
10
00
6mdash
mdashmdash
To
tal
10
00
5M
n0
00
3T
i0
00
3mdash
00
03
mdashmdash
Si
11
98
61
20
88
12
04
11
20
45
12
03
3M
g0
00
8A
l4
17
64
07
14
03
54
08
34
10
1P
mdash0
00
5mdash
mdashmdash
TS
i5
95
2N
a0
01
2F
e3thorn
mdashmdash
mdashmdash
00
13
Ti
mdash0
00
1mdash
mdashmdash
Al
00
48
P1
02
Mn
00
09
mdashmdash
mdashmdash
Al
41
14
39
62
39
70
39
86
39
55
B3
00
0M
gmdash
mdashmdash
mdashmdash
Fe3thorn
mdash0
00
3mdash
00
04
mdashZ
Al
60
00
Ca
01
95
01
50
01
04
00
69
00
60
Mn
mdash0
00
50
00
5mdash
mdashY
Al
02
74
Sr
00
73
00
51
00
24
00
11
mdashM
g0
00
30
00
30
01
4mdash
mdashT
i0
04
5N
a3
59
93
80
03
78
33
83
23
83
1C
a0
00
20
00
20
01
20
00
20
00
4M
g0
57
5K
00
11
00
38
00
13
00
31
00
22
Na
02
32
02
07
01
46
02
12
01
37
Mn
00
47
K3
45
73
47
03
67
73
55
03
73
3F
e2thorn
19
12
Z1
60
01
59
61
60
01
60
11
60
4R
b0
01
10
02
40
03
50
07
00
10
8L
i0
14
8X
38
94
04
39
33
94
39
1C
s0
00
20
00
50
00
70
01
40
01
6P
Y3
00
0m
ole
s
XC
a0
04
2A
n5
13
82
71
71
5Z
16
10
16
06
16
01
16
03
15
99
Na
07
47
Ab
94
69
53
97
09
75
97
9X
37
13
72
39
03
85
40
0K
00
02
Or
03
09
03
08
06
mo
les
amp
02
09
An
01
01
03
01
01
Ab
63
56
38
56
35
OH
35
83
Or
93
69
43
95
99
43
96
4F
04
17
Cl
mdash
WZ
ndashw
allzo
ne
OIZ
ndasho
ute
rin
term
edia
tezo
ne
IIZ
aan
dII
Zb
ndashin
ner
inte
rmed
iate
zon
esC
cndash
core
asin
Fig
2B
aOis
bel
ow
the
det
ecti
on
lim
itin
bo
thfe
ldsp
ars
Cs 2
Ofrac14
00
3w
tin
the
K-
feld
spar
fro
mth
eW
Z
mdashN
ot
det
ecte
d
Nu
mb
ero
fio
ns
on
the
bas
iso
f3
2o
xy
gen
sfo
ral
bit
ean
dK
-fel
dsp
ar
31
anio
ns
(O
OH
F
)fo
rsc
ho
rlan
d6
ox
yg
ens
for
spo
du
men
e
-A
mo
un
tin
ferr
edfr
om
con
sid
erat
ion
so
fst
oic
hio
met
ry
978 A M R Neiva
eschweizerbart_xxx
2011) Lepidolite from the OIZ is an Al-poorer mica (Fig4) and has the highest Si Licalcand F contents (Table 1)indicating that an evolution cannot be shown from thislepidolite to lepidolites from the other zones which areAl-richer micas (Fig 4) However there is a regulardecrease in the KRb ratio and a progressive increase inthe Rb and Cs contents from lepidolite of the OIZ tolepidolite of IIZa IIZb and Cc (Fig 7) which indicatesthat the KRb ratio and Rb and Cs contents must not beconsidered alone to show fractional crystallization in
lepidolites particularly if some are Al-richer micas andothers Al-poorer micas The high Licalcand F contents oflepidolite from the OIZ did not decrease its KRb ratioSuch an effect is considered to have taken place in lepi-dolite (an Al-richer mica) from the wall zone of the Tancopegmatite Manitoba Canada (Van Lichtervelde et al2008) An evolution from the lepidolite of the IIZa to thatof the Cc is generally shown by the increasing Si LicalcF Rb Cs contents and a decrease in the KRb ratio (Table1 Fig 7)
At the scale of crystals the pegmatite zones and alsothose from the OIZ to the Cc of the Namivo granitic pegma-tite Al-richer micas show fractionation because theyformed from the fractionation of an Li-rich pegmatite melt
The Al-poorer micas zinnwaldite lepidolite and FeMg-containing polylithionite only occur in the OIZ (Fig 4)Polylithionite is the mica richest in Si and Licalc and lepi-dolite from this zone is the richest in Si Licalcand F (Fig 4Table 1) The high Li contents of these micas reflect aconsiderably higher D(Li) at low temperature (Icenhoweramp London 1995) These Li-rich micas may have crystal-lized from an undercooled melt This hypothesis does notimply high Rb and Cs contents and low KRb ratios Thisagrees with the fact that these micas from the OIZ havesimilar Rb and Cs contents and KRb ratios to those of Al-richer micas (muscovite lithian muscovite and lsquolsquomixedformrsquorsquo) from the same pegmatite zone (Fig 7) Howeverthe lepidolite from the wall zone of the Tanco pegmatiteCanada of a similar origin has a low KRb ratio which isattributed to the complexly interrelated structural compo-nents of this lepidolite (Van Lichtervelde et al 2008) TheLi-rich micas from the OIZ may also represent disequili-brium These two hypotheses are considered the best forthese micas of primary magmatic origin
Another hypothesis was also considered They may havecrystallized in boundary layers which concentrate Li andF But this mechanism was suggested for the most fractio-nated tourmaline enriched in Li and F from the core of the
Fig 8 Plot of albite compositions from all zones of the Namivo granitic pegmatite Mozambique showing that the anorthite content of albitedecreases from the WZ to the Cc WZ OIZ IIZa IIZb and Cc as in Fig 2
Fig 9 The Rb vs Cs diagram of K-feldspar from all zones of theNamivo granitic pegmatite Mozambique showing that the Rb andCs contents of K-feldspar increase from the WZ to the Cc WZ OIZIIZa IIZb and Cc as in Fig 2
Silicate and oxide minerals from a zoned granitic pegmatite 979
eschweizerbart_xxx
Little Three pegmatite dike USA (Morgan amp London1999) and the micas enriched in Li and F from theNamivo pegmatite belonging to the OIZ Furthermore ina boundary layer melt that became enriched in Li and F theKRb ratio of micas decreases strongly (Van Lichterveldeet al 2008) which was not found in these micas from theOIZ (Fig 7d) Nor can they have resulted from the crystal-lization of a late melt that would have reacted with the OIZbecause these micas are among those containing the high-est KRb values (Fig 7d)
92 The importance of feldspars micas andcolumbitendashtantalite compositions to the Namivogranitic pegmatite evolution
The trace elements Rb and Cs and the KRb and KCs ratioshave been used to show the evolution of K-feldspar inpegmatites (eg Cerny 1994 Cerny et al 2005 RodaRobles et al 2005) The Rb and Cs contents increase andthe KRb and KCs ratios of K-feldspar decrease from theWZ to the Cc (Fig 9 Table 2) reflecting the growth of K-feldspar from an increasingly fractionated melt withouthaving grown from or having been chemically modifiedby an aqueous fluid as in the Swamp pegmatite section atthe Little Three Mine USA (London et al 2012) Thecrystallization of K-feldspar from an exsolved aqueousfluid from melt will reverse the magmatic fractionation ofRb Cs KRb and KCs because Rb and especially Cs areso much more compatible in vapor that both Rb and Csremain in the fluid phase (London et al 2012) The feldsparsolvus pairs in the Namivo pegmatite record magmaticcrystallization temperatures that decrease from WZ to CcAlbite shows a decrease in the Ca Sr contents and SrCaratio from the WZ to the Cc (Fig 8 Table 2) Therefore thefeldspars and also Al-richer micas as already explainedshow fractionation in this zoned pegmatite
In general lepidolite from the Namivo pegmatite hassimilar Rb2O and Cs2O contents and KRb (wt) values tothose of lepidolite from the Rozna and Dobra Voda lepi-dolite-subtype pegmatites in the Czech Republic (Cernyet al 1995) but lower Rb2O and Cs2O contents thanlepidolite from the lepidolite-subtype pegmatite at RedCross Lake Manitoba Canada (Cerny et al 2012a) K-feldspar from the Namivo pegmatite also has lower Rb2O
Table 3 Representative electron microprobe analyses in wt of columbitendashtantalite from the Namivo granitic pegmatite Mozambique
Outer Intermediate Zone - OIZ Inner Intermediate Zone - IIZa
Core - Cc
D L L
WO3 022 059 079 113 101 351 050 007Ta2O5 5487 5123 2503 3186 2888 2519 3127 4542Nb2O5 2537 3000 5483 4635 5113 5144 4911 3686SnO2 008 015 024 049 020 026 017 012TiO2 263 161 136 254 202 145 125 016FeO 860 710 665 471 236 068 mdash mdashMnO 793 952 1099 1304 1400 1725 1748 1718Total 9970 10020 9989 10012 9960 9978 9978 9981W 0004 0011 0013 0019 0016 0057 0008 0001Ta 1065 0975 0422 0552 0495 0430 0543 0847Nb 0819 0949 1538 1336 1456 1460 1418 1143Sn 0002 0004 0006 0012 0005 0007 0004 0003Ti 0141 0085 0063 0122 0096 0068 0060 0008Fe 0513 0416 0345 0251 0124 0036 mdash mdashMn 0479 0564 0578 0704 0747 0917 0945 0998P
3023 3004 2965 2996 2939 2975 2978 3000Mn(Mn thorn Fe) 048 058 063 074 086 096 100 100Ta(Ta thorn Nb) 057 051 022 029 025 023 028 043Classification tant-(Fe) tant-(Mn) col-(Mn) col-(Mn) col-(Mn) col-(Mn) col-(Mn) col-(Mn)
D ndash darker L ndash lighter zones mdash Not detected tant-tantalite col-columbite Cation formula on the basis of 6 atoms of oxygen
Fig 10 Compositions of columbitendashtantalite from the Namivogranitic pegmatite Mozambique in the columbite quadrilateralshowing that Mn(Mn thorn Fe) of columbite-(Mn) increases from theOIZ to the Cc and the richest columbite-(Mn) in Ta(Ta thorn Nb)tantalite-(Fe) and tantalite-(Mn) only occur in the OIZ OIZ IIZaand Cc as in Fig 2
980 A M R Neiva
eschweizerbart_xxx
and Cs2O contents than K-feldspar from the lepidolite-subtype pegmatite at Red Cross Lake The Rb2O andCs2O contents of primary and late K-feldspar of this peg-matite at Red Cross Lake attained unprecedented levels(Cerny et al 2012a) The lowest KRb (wt) values ofmuscovite lithian muscovite lsquolsquomixed formrsquorsquo and lepido-lite from the IIZb and Cc (Fig 7) and K-feldspar (KRb frac1414) from the Cc compare well with those found in theseminerals from the AC6frac143 lepidolite-subtype pegmatitefrom Greer Lake (Cerny et al 2005) and some of themost fractionated pegmatites worldwide which belong tothe petalite-subtype (eg Tanco Manitoba Cerny 2005Cerny et al 1998 Varutrask Sweden Cerny et al 2005)but muscovite lithian muscovite and lepidolite from theIIZb and Cc have lower Rb2O and Cs2O contents than thesemicas from the Tanco pegmatite (Cerny 2005a VanLichtervelde et al 2008) K-feldspar also has lower
contents of these oxides than the most evolved K-feldsparfrom the Tanco pegmatite (Cerny 2005a) The magmaticfractionation was strong from the WZ to IIZb and Cc of theNamivo lepidolite-subtype pegmatite
The compositional trend of columbite-(Mn) from the OIZto Cc of the Namivo granitic lepidolite-subtype pegmatite(Fig 10) is identical to that of columbite-group mineralsfrom the lepidolite-subtype complex granitic pegmatitesfrom the Dobra Voda in the Moldanubicum CzechRepublic (Novak amp Cerny 1998) and the HimalayaDistrict southern California (shown in Cerny et al 2004)Experimental data for the Fe-Mn pair (Linnen amp Cuney2005) suggest an increase in Fe with fractional crystalliza-tion which is not observed in nature Other phases seem tocontrol the bahavior of Fe and Mn in the melt eg thecrystallization of tourmaline causes a rapid increase of theMnFe in the melt (Van Lichtervelde et al 2006) When thecrystallization of tourmaline stopped the columbitendashtantaliteminerals showed a constant MnFe indicating that the Fe andMn contents in the melt remained constant Schorl onlyoccurs in the OIZ of the Namivo granitic pegmatite and itscrystallization cannot be responsible for the increase in theMnFe of the melt because Mn(Mn thorn Fe) of columbite-(Mn) increases progressively from the OIZ to the IIZa and Cc(Fig 10) Garnet zinnwaldite and gahnite containing Fe andMn also only occur in the OIZ and cannot also have causedthe increase of the MnFe in the melt The dominant Mnenrichment before Ta enrichment started in the columbitendash-tantalite composition from some granitic pegmatites isattributed to an increased alkali-fluoride activity at moderatemHF (Cerny et al 2004) and an increase in the activity offluorine (Martins et al 2011) Each Al-richer mica (musco-vite lithian muscovite and lsquolsquomixed formrsquorsquo) from the Namivogranitic pegmatite shows an increase in F content from theOIZ to the IIZa IIZb and Cc (Table 1) In general the Fcontent of lepidolite also increases from the IIZa to the IIZband Cc Therefore the extreme Fe-Mn fractionation beforeTa enrichment in columbite-(Mn) (Fig 10) may be due to anincrease in the activity of fluorine as a consequence offractional crystallization The increase in the Ta content ofcolumbite-(Mn) from the Namivo granitic pegmatite isattributed to fractional crystallization
The geochemical evolution of albite and K-feldsparfrom the WZ to the Cc Al-richer micas muscovite lithianmuscovite and lsquolsquomixed formrsquorsquo from the OIZ to the Cc andlepidolite from the IIZa to the Cc and columbite-(Mn) andalso beryl (Neiva amp Neiva 2005) from the OIZ to the Ccare caused by magma fractionation The pegmatite zonesare the product of primary crystallization from a volatile-rich silicate melt The pegmatite consolidated from the WZto the Cc The IIZb is one of the most evolved zones asalso suggested by the beryl composition (Neiva amp Neiva2005) and is the richest in lsquolsquomixed formrsquorsquo and lepidolite
The richest columbite-(Mn) in Ta(Ta thorn Nb) and com-positions of tantalite-(Fe) and tantalite-(Mn) only occur inthe OIZ (Fig 10a) associated with lepidolite and polythio-nite (Fig 3c) which may be due to the local depletion of Liand F in the melt which decreases the solubility of Ta andcauses Ta precipitation (Linnen 1998 Linnen amp Cuney
Fig 11 a Backscattered-electron image of a gahnite crystal with adarker zone partially surrounding a lighter zone from the OIZ of theNamivo granitic pegmatite b c Plot of gahnite compositions in theSn-Zn-Ti diagram (atomic proportions) showing a chemical distinc-tion between the lighter and darker zones OIZ as in Fig 2
Silicate and oxide minerals from a zoned granitic pegmatite 981
eschweizerbart_xxx
2005) At the Tanco pegmatite Ta oxides are also asso-ciated with lepidolite enriched in Li and F from the wallzone (Van Lichtervelde et al 2008)
93 Origin and evolution of the zoned graniticlepidolite-subtype pegmatite at Namivo
In general granitic pegmatites particularly those belong-ing to the rare-element class are accepted as having beenformed by the fractional crystallization of a granite melt(eg Cerny 1991a b 1992 Neiva et al 2008 2012 Roda-Robles et al 2012) But it also has been proposed thatpegmatites may be formed by partial melting of appropri-ate rock compositions (eg Nabelek et al 1992 Nabelekamp Russ-Nabelek 1992 Shearer et al 1992 Roda Robleset al 1999) The lepidolite-subtype pegmatites belong tothe LCT (lithium-cesium-tantalum) family (Cerny amp Ercit2005) They are derived by fractional crystallization of agranite magma (eg Cerny et al 2005 Neiva amp Ramos2010 Cerny et al 2012b) Experimental work by Londonet al (1989) and London (1990) using Macusani glass as astarting material equivalent to the bulk composition ofhighly fractionated rare-alkali-rich pegmatites underhighly evolved and hydrous but H2O undersaturatedmelt obtained the latest primary assemblage consisting
of an Li-rich mica thorn albite thorn quartz deposited directlyfrom the primary melt phase Other authors egZasedatelev (1974 1977) and Stewart (1978) argue thatlepidolite-bearing pegmatites are derived from direct ana-texis and Gordiyenko et al (1996) consider that they arederived from an undefined medium and the rare-elementmineralization is superimposed on preexisting barrenpegmatites
Lepidolite-subtype pegmatites may migrate a long wayfrom their parent granites because their volatile-rich highlyfluid pegmatite melts are stable at relatively low tempera-tures (eg Cerny et al 2005 Antunes et al 2013)Therefore the Namivo pegmatite is probably derived byfractional crystallization of an S-type granite magmawhich resulted from partial melting of metamorphosed juve-nile sediments containing micas that carry most of the traceelements that define the signature of the LCT pegmatites(eg Dahl et al 1993)
The two main models for the internal evolution of peg-matites that dominated for more than a century are a) thefractional crystallization of a flux-bearing granitic melt fromthe margins to the center of the pegmatite (Cameron et al1949) b) the interactions of an aqueous fluid with graniticmelt (Jahns amp Burnham 1969 Jahns 1982) The recentmodel of constitutional zone refining combines aspects ofboth models and invokes the formation of a flux-enriched
Table 4 Electron microprobe analyses in wt of zoned gahnite from the outer intermediate zone (OIZ) of the Namivo granitic pegmatiteMozambique
Darker Zone Lighter Zone
Mean s Range Mean s Range
SnO2 036 050 0ndash097 658 281 151ndash998TiO2 008 008 0ndash021 065 034 008ndash105Nb2O5 001 002 0ndash006 018 007 007ndash029Ta2O5 001 004 0ndash010 015 013 0ndash033ZnO 3998 123 3810ndash4109 3339 318 3004ndash3848FeO 367 048 331ndash442 433 065 306ndash498MnO 032 004 028ndash040 039 006 032ndash048MgO 003 004 0ndash010 ndash ndash ndashAl2O3 5507 050 5436ndash5572 5337 070 5257ndash5443SiO2 003 003 0ndash007 008 010 0ndash025Total 9956 9912n 8 8Sn 0035 0048 0ndash0095 0648 0278 0149ndash0983Ti 0015 0015 0ndash0038 0120 0064 0015ndash0195Nb ndash 0003 0ndash0006 0021 0009 0009ndash0037Ta ndash 0002 0ndash0006 0009 0009 0ndash0021Zn 7226 0182 6890ndash7382 6086 0568 5482ndash6965Fe2thornt 0752 0103 0675ndash0913 0894 0135 0628ndash1029Mn 0066 0008 0057ndash0083 0082 0013 0066ndash0101Mg 0010 0015 0ndash0037 ndash ndash ndashAl 15887 0052 15805ndash15954 15526 0170 15375ndash15853Si 0007 0008 0ndash0018 0019 0025 0ndash0062P
23998 23405Fe3thorn 0064 0230Fe2thorn 0686 0658SnZn 0005 0007 0ndash0014 0106 0052 0021ndash0179ZnFe2thornt 961 143 768ndash1093 681 190 536ndash1109
n number of analysis Cation formula based on 32 atoms of oxygen Fe2thornt total Fe2thorn estimated
982 A M R Neiva
eschweizerbart_xxx
boundary layer of silicate liquid in advance of a crystal-lization front (London 2008 London amp Morgan 2012)
Lepidolite-subtype pegmatites are generally scarce(Cerny et al 2005) particularly the zoned ones In thesymmetrically zoned lepidolite-subtype pegmatites ofRozna and Dobra Voda Czech Republic micas (Cernyet al 1995) tourmaline (Selway et al 1999) and colum-bite-group minerals (Novak amp Cerny 1998) evolve fromthe outermost zone to the innermost zone following thecrystallization sequence The same was found in tourma-line from the zoned Lastovicky Dolnı Bory and Raddovicelepidolite-subtype pegmatite dikes in the Czeck Republic(Selway et al 1999)
In general beryl (Neiva amp Neiva 2005) feldsparsmicas and columbite-(Mn) (in this paper) from theNamivo lepidolite-subtype pegmatite record the progres-sive chemical evolution of the pegmatite from the wallzone to the core These minerals were produced by crystal-lization from a silicate melt rather than an aqueous fluidphase The slow cooling of melt shown by the magmaticcrystallization temperatures of feldspars cannot explain theincrease in grain-size of minerals from the wall zone to thecore but fluxes will be necessary to promote the change oftexture particularly a flux-rich hydrosilicate liquidaccording to the experimental evidence (London 2009)The constitutional zone refining model will be the best forthis zoned pegmatite and probably for all lepidolite-sub-type pegmatites because this model also produces a higherfinal concentration of incompatible components in a smal-ler volume of rock than fractional crystallization does(Morgan amp London 1999)
The core margin at the Rozna pegmatite contains K-feld-spar and quartz and the core consists mainly of quartz but it issurrounded and penetrated by a quartz-bearing albitethorn lepi-dolite complex which contains several minerals At theDobra Voda pegmatite the center of the dike is occupiedby the lepidolite unit containing albite and other minerals(Cerny et al 1995) At the Namivo pegmatite the coremargin consists of quartz and beryl and the core containsmainly quartz and spodumene but also albite lepidolite andother minerals The last-unit assemblages of primary miner-als in most of the highly fractionated LCT pegmatites are richin albite and commonly contain lepidolite or spodumene andmost of the other rare phases These units represent the lastmost fractionated liquid that can be derived by fractionalcrystallization of a crustal melt (London 2008)
The Namivo granitic pegmatite shows a significant dis-tinction from the other zoned lepidolite-subtype pegmatitesand LCT pegmatites except the Tanco petalite-subtypepegmatite in Canada because the lepidolite richest in SiLi and F FeMg-containing polylithionite and associatedcolumbite-(Mn) with the highest Ta(Ta thorn Nb) ratio tanta-lite-(Fe) and tantalite-(Mn) only occur in the outer inter-mediate zone These minerals usually form late in theconsolidation of pegmatites The lepidolite and polylithio-nite are probably derived from the disequilibrium crystal-lization of an undercooled melt Tantalite may reflect a localdecrease in Li and F that caused Ta precipitation
This paper contributes to a better understanding of theorigin and evolution of the rare zoned lepidolite-subtypepegmatites and shows that although the pegmatite evolvedfrom the wall zone to the core it presents an unusualassociation of lepidolite polylithionite and tantalite in theouter intermediate zone
Acknowledgments Thanks are due to JM Cotelo Neivaand MB Dias for the samples and information providedand to MR Machado Leite and MF Guimaraes for theuse of the electron microprobe facilities at the LaboratorioNacional de Energia e Geologia (LNEG) PortugalFinancial support was provided by the PortugueseGovernment for the project Pest-OECTEUI00732011of the Geosciences Centre through the PortugueseFoundation for Science and Technology I would like tothank D London WB Simmons and the associated editorE Widom for their constructive reviews of this manuscriptand M Prieto for his editorial work
References
Alfonso P Melgarejo JC Yusta I Velasco F (2003)
Geochemistry of feldspars and muscovite in granitic pegmatite
from the Cap de Creus field Catalonia Spain Can Mineral 41
103ndash116
Antunes IMHR Neiva AMR Ramos JMF Silva PB
Silva MMVG Corfu F (2013) Petrogenetic links between
lepidolite-subtype aplite-pegmatite aplite veins and associated
granites at Segura (central Portugal) Chemie der Erde in press
httpdxdoiorg101016jchemer20121203
Batchelor RA amp Kinnaird JA (1984) Gahnite compositions
compared Mineral Mag 48 425ndash430
Beurlen H Da Silva MRR Thomas R Soares DR Olivier P
(2008) Nb-Ta-(Ti-Sn) oxide mineral chemistry as tracer of rare-
element granitic pegmatite fractionation in the Borborema pro-
vince Northeastern Brazil Miner Deposita 43 207ndash228
Cameron EN Jahns RH McNair AH Page LR (1949)
Internal structure of granitic pegmatites Econ Geol
Monograph 2 115 p
Cerny P (1991a) Fertile granites of Precambrian rare-element
pegmatite fields is geochemistry controlled by tectonic setting
or source lithologies Precambrian Res 51 429ndash468
mdash (1991b) Rare-element granite pegmatites I Anatomy and inter-
nal evolution of pegmatite deposits Geoscience Canada 18
49ndash67
mdash (1992) Geochemical and petrogenetic features of mineralization
in rare-element granitic pegmatites in the light of current
research Applied Geochemistry 7 393ndash416
mdash (1994) Evolution of feldspars in granitic pegmatites in
lsquolsquoFeldspars and their Reactionsrsquorsquo I Parsons ed NATO
Advanced Study Institute Series C421 501ndash539
mdash (2005) The Tanco rare-element pegmatite deposit Manitoba
regional context internal anatomy and global comparisons in
lsquolsquoRare-element Geochemistry and Mineral Depositsrsquorsquo RL
Linnen amp IM Samson eds Geochemical Association of
Canada Short Course Notes St Catherines 17 127ndash158
Silicate and oxide minerals from a zoned granitic pegmatite 983
eschweizerbart_xxx
Cerny P amp Ercit TS (2005) The classification of granitic pegma-
tites revisited Can Mineral 43 2005ndash2026
Cerny P Meintzer RE Andersen AJ (1985) Extreme fractiona-
tion in rare-element granitic pegmatites selected examples of
data and mechanisms Can Mineral 23 381ndash421
Cerny P Goad BE Hawthorne FC Chapmann R (1986)
Fractionation trends of the Nb- and Ta-bearing oxide minerals
in the Greer Lake pegmatite granite and its pegmatite aureole
southeastern Manitoba Am Mineral 71 501ndash517
Cerny P Stanek J Novak M Baadsgaard H Rieder M
Ottolini L Kavalova M Chapman R (1995) Geochemical
and structural evolution of micas in the Rozna amp Dobra Voda
pegmatites Czech Republic Mineral Petrol 55 177ndash201
Cerny P Ercit TS Vanstone PJ (1998) Mineralogy and petrol-
ogy of the Tanco rare-element pegmatite deposit southeastern
Manitoba International Mineralogical Association 17th General
Meeting Toronto Field Guidebook B6
Cerny P Chapman R Ferreira K Smeds SA (2004)
Geochemistry of oxide minerals of Nb Ta Sn and Sb in
the Varutrask granitic pegmatite Sweden The case of an
lsquolsquoanomalousrsquorsquo columbitendashtantalite trend Am Mineral 89
505ndash518
Cerny P Masau M Goad BE Ferreira K (2005) The Greer
Lake leucogranite Manitoba and the origin of lepidolite-sub-
type granitic pegmatites Lithos 80 305ndash321
Cerny P Teertstra DK Chapman R Selway JB Hawthorne
FC Ferreira K Chackowsky LE Wang X-J Meintzer
RE (2012a) Extreme fractionation and deformation of the
leucogranite-pegmatite suite at Red Cross Lake Manitoba
Canada IV Mineralogy Can Mineral 50 1839ndash1875
Cerny P Halden NM Ferreira K Meintzer RE Brisbin WC
Chackowsky LE (2012b) Extreme fractionation and deforma-
tion of the leucogranite-pegmatite suite at Red Cross Lake
Manitoba Canada II Petrology of the leucogranites and peg-
matites Can Mineral 50 1807ndash1822
Dahl PS When DC Feldmann SG (1993) The systematics of
trace-element partitioning between coexisting muscovite and
biotite in metamorphic rocks from the Black Hills South
Dakota USA Geochim Cosmochim Acta 57 2487ndash2505
Dias MB amp Wilson WE (2000) The Alto Ligonha Pegmatites
Mozambique Mineral Record 31 459ndash497
Fleet ME (2003) Rock-Forming Minerals vol 3A Sheet silicates
micas The Geological Society London second edition chap 6
Lithium micas 651ndash690
Foord EE Cerny P Jackson LL Sherman DM Eby RK
(1995) Mineralogical and geochemical evolutions of micas
from miarolitic pegmatites of the anorogenic pikes-Peak
Batholith Colorado Mineral Petrol 55 1ndash26
Foster MD (1960) Interpretation of the composition of lithium
micas US Geol Surv Prof Paper 354-E 115ndash147
Fuhrman ML amp Lindsley DK (1988) Ternary-feldspar modeling
and thermometry Am Mineral 73 201ndash215
Gomes CL Castro P Alves C (1995) Caracterizacao das espi-
nelas zincıferas e do par ganite-nigerite no campo aplito-
pegmatıtico da Serra de Arga-Minho N de Portugal IV
Congresso Nacional de Geologia Resumos Alargados
Universidade do Porto Mem 4 629ndash633
Gordiyenko VV Ilyina AN Timochina LA Badamina EB
Stanek J (1996) Geochemical model of evolution of a pegma-
tite-forming ore-magmatic system of western Moravia Proc
Russ Mineral Soc 125 38ndash48 (in Russian)
Icenhower JP amp London D (1995) An experimental study for
element partitioning between biotite muscovite and coexisting
peraluminous granitic melt at 200 MPa (H2O) Am Mineral 80
1229ndash1251
Jahns RH (1982) Internal evolution of pegmatite bodies in lsquolsquoGranitic
Pegmatites in science and industryrsquorsquo P Cerny ed Mineralogical
Association of Canada Short Course Handbook 8 293ndash327
Jahns RH amp Burnham CW (1969) Experimental studies of
pegmatite genesis I A model for the derivation and crystal-
lization of granitic pegmatites Econ Geol 64 843ndash864
Jolliff BL Papike JJ Shearer CK (1987) Fractionation trends
in mica and tourmaline as indicators of pegmatite internal evo-
lution Bob Ingersoll pegmatite Black Hills South Dakota
USA GeochimCosmochim Acta 51 519ndash534
Kile DE amp Foord EE (1998) Micas from the Pikes Peak bath-
olith and its cogenetic granitic pegmatites Colorado optical
properties composition and correlation with pegmatite evolu-
tion Can Mineral 36 463ndash482
Linnen RL (1998) The solubility of Nb-Ta-Zr-Hf-W in granitic
melts with Li and Li thorn F constraints for mineralization in rare
metal granites and pegmatites Econ Geol 93 1013ndash1025
Linnen RL amp Cuney M (2005) Granite-related rare-element
deposits and experimental constraints on Ta-Nb-W-Sn-Zr-Hf
mineralization in lsquolsquoRare-element geochemistry and mineral
depositsrsquorsquo RL Linnen amp IM Samson eds Geochemical
Association of Canada Short Course Notes 17 45ndash68
London D (1990) Internal differentiation of rare-element pegmatites
a synthesis of recent research in lsquolsquoOre Bearing Granite Systems
Petrogenesis and Mineralizing Processesrsquorsquo HJ Stein amp JL
Hannah eds Geol Soc America Special Paper 246 35ndash50
mdash (2008) Pegmatites The Canadian Mineralogist Special
Publication 10 347 p
mdash (2009) The origin of primary textures in granitic pegmatites
Can Mineral 47 697ndash724
London D amp Morgan GB VI (2012) The pegmatite puzzle
Elements 8 263ndash268
London D Morgan GB VI Hervig RL (1989) Vapor-under-
saturated experiments in the system macusanite-H2O at 200
MPa and the internal differentiation of granitic pegmatites
Contrib Mineral Petrol 102 1ndash17
London D Morgan GB VI Paul KA Guttery BM (2012)
Internal evolution of miarolitic granitic pegmatites at the Little
Three mine Ramona California USA Can Mineral 50
1025ndash1054
Martins T Lima A Simmons WB Folster AU Noronha F
(2011) Geochemical fractionation of Nb-Ta oxides in Li-bear-
ing pegmatites from the Barroso-Alvao pegmatite field northern
Portugal Can Mineral 49 777ndash791
Monier G Charoy B Cuney M Ohnenstetter D Robert JL
(1987) Evolution spatiale et temporelle de la composition des
micas du granite albitique a topaze-lepidolite de Beauvoir
Geologie De La France 2ndash3 179ndash188
Monier G amp Robert JL (1986) Evolution of the miscibility gap
between muscovite and biotite solid solutions with increasing
lithium content an experimental study in the systems
K2OndashLi2OndashMgOndashAl2O3ndashSiO2ndashH2OndashHF at 600 C 2 kbar
PH2O comparison with natural lithium micas Mineral Mag
50 641ndash651
Morgan GBVI amp London D (1999) Crystallization of the little
three layered pegmatite-aplite dike Ramona District California
Contrib Mineral Petrol 136 310ndash330
984 A M R Neiva
eschweizerbart_xxx
Nabelek PI amp Russ-Nabelek C (1992) The generation and crys-
tallization conditions of the Proterozoic Harney Peak
Leucrogranite Black Hills South Dakota USA petrologic and
geochemical constraints Contrib Mineral Petrol 110
173ndash191
Nabelek PI Russ-Nabelek C Haeussler GT (1992) Stable
isotope evidence for the petrogenesis and fluid evolution in
the Proterozoic Harney Peak leucogranite Black Hills
South Dakota Geochim Cosmochim Acta 56 403ndash417
Neiva AMR amp Champness PE (1997) Nigerite and gahnite from
the granitic pegmatite veins of Cabanas Ponte de Lima northern
Portugal N Jb Mineral Mh 9 385ndash409
Neiva AMR Gomes MEP Ramos JMF Silva PB (2008)
Geochemistry of granitic aplite-pegmatite sills and their miner-
als from Arcozelo da Serra area (Gouveia central Portugal)
Eur J Mineral 20 465ndash485
Neiva AMR amp Neiva JMC (2005) Beryl from the granitic
pegmatite at Namivo Alto Ligonha Mozambique N Jb
Mineral Abh 181 173ndash182
Neiva AMR amp Ramos JMF (2010) Geochemistry of granitic
aplite-pegmatite sills and petrogenetic links with granites
Guarda-Belmonte area central Portugal Eur J Mineral 22
837ndash854
Neiva AMR Silva PB Ramos JMF (2012) Geochemistry of
granitic aplite-pegmatite veins and sills and their minerals from the
Sabugal area central Portugal N Jb Mineral Abh 189 49ndash74
Novak M amp Cerny P (1998) Niobium-tantalum oxide minerals
from complex granitic pegmatites in the Moldanubicum Czech
Republic primary versus secondary compositional trends Can
Mineral 36 659ndash672
Pesquera Perez A Torres-Ruiz J Gil PP Velilla N (1999)
Chemistry and genetic implications of tourmaline and Li-F-Cs
micas from the Valdeflores (Caceres Spain) Am Mineral 84
55ndash69
Rieder M Cavazzini G DrsquoYakonov YuS Frank-Kamenetskii
VA Gottardi G Guggenheim S Koval PV Muller G
Neiva AMR Radoslovich EW Robert J-L Sassi FP
Takeda H Weiss Z Wones DR (1999) Nomenclature of the
micas Mineral Mag 63 267ndash279
Roda Robles E Pesquera Perez A Velasco Roldan F Fontan F
(1999) The granitic pegmatites of the Fregeneda area
(Salamanca Spain) characteristics and petrogenesis Mineral
Mag 63 535ndash558
Roda Robles E Pesquera A Gil-Crespo PP Torres-Ruiz J
Fontan F (2005) Origin and internal evolution of the Li-F-
Be-P-bearing Pinilla de Fermoselle pegmatite (Central Iberian
Zone Zamora Spain) Am Mineral 90 1887ndash1899
Roda Robles E Pesquera Perez A Gil PP Torres-Ruiz J de
Parseval P (2006) Mineralogy and geochemistry of micas from
the Pinilla de Fermoselle pegmatite (Zamora Spain) Eur J
Mineral 18 369ndash377
Roda Robles E Keller P Pesquera Perez A Fontan F (2007)
Micas of the muscovite-lepidolite series from Karibib pegma-
tites Namibia Mineral Mag 71 41ndash62
Roda Robles E Pesquera A Gil-Crespo P Torres-Ruiz J
(2012) From granite to highly evolved pegmatite a case study
of the Pinilla de Fermoselle granite-pegmatite system (Zamora
Spain) Lithos 153 192ndash207
Selway JB Novak M Cerny P Hawthorne FC (1999)
Compositional evolution of tourmaline in lepidolite-subtype
pegmatites Eur J Mineral 11 569ndash584
Shearer CK Papike JJ Jolliff B (1992) Petrogenetic links
among granites and pegmatites in the Harney Peak rare-element
granite-pegmatite system Black Hills South Dakota Can
Mineral 30 785ndash809
Soares DR Hartmut B Ferreira ACM da Silva MRR
(2007) Chemical composition of gahnite and degree of peg-
matitic fractionation in the Borborema Pegmatitic Province
northeastern Brazil Anais Da Academ Bras Cien 79
395ndash404
Stewart DB (1978) Petrogenesis of lithium-rich pegmatites Am
Mineral 63 970ndash980
Tischendorff G Gattesmann B Forster H-J Trumbull RB
(1997) On Li-bearing micas estimating Li from electron
microprobe analyses and an improved diagram for graphical
representation Mineral Mag 61 809ndash834
Van Lichtervelde M Linnen RL Salvi S Beziat D (2006)
The role of metagabbro rafts on tantalum mineralization in the
Tanco granitic pegmatite Manitoba Can Mineral 44
625ndash644
Van Lichtervelde M Gregoire M Linnen RL Beziat D Salvi
S (2008) Trace element geochemistry by laser ablation ICP-
MS of micas associated with Ta mineralization in the Tanco
pegmatite Manitoba Canada Contrib Mineral Petrol 155
791ndash806
Vieira R Roda-Robles E Pesquera A Lima A (2011)
Chemical variation and significance of micas from the
Fregeneda-Almendra pegmatitic field (Central-Iberian Zone
Spain and Portugal) Am Mineral 96 637ndash645
Wen S amp Nekvasil H (1994) SOLVCALC an interactive gra-
phics program package for calculating ternary feldspar solvus
and two-feldspar geothermometry Comput Geosci 20
1025ndash1040
Wise MA (1995) Trace element chemistry of lithium-rich micas
from rare-element granitic pegmatites Mineral Petrol 55
203ndash215
Zasedatelev AM (1974) Possible accumulation of lithium in host
rocks of lithium pegmatite veins during old sedimentation pro-
cesses Doklady Acad Sci USSR Earth Sci Ser 218 196ndash198
(in Russian)
mdash (1977) Quantitative of metamorphic generation of rare-metal
pegmatites with lithium mineralization Doklady Acad Sci
USSR Earth Sci Ser 236 219ndash221 (in Russian)
Received 26 January 2013
Modified version received 21 May 2013
Accepted 23 July 2013
Silicate and oxide minerals from a zoned granitic pegmatite 985
eschweizerbart_xxx
Tab
le1
R
epre
sen
tati
ve
elec
tro
nm
icro
pro
be
anal
yse
sin
wt
o
fm
icas
fro
mth
eN
amiv
og
ran
itic
peg
mat
ite
Mo
zam
biq
ue
Ou
ter
Inte
rmed
iate
Zo
ne
-O
IZIn
ner
Inte
rmed
iate
Zo
ne
-II
Za
Zin
Lep
lsquolsquoM
ixed
Frsquorsquo
Lep
Lep
Po
llsquolsquo
Mix
edF
rsquorsquoL
ith
Mu
sP
ol
Lit
hM
us
lsquolsquoM
ixed
Frsquorsquo
lsquolsquoM
ixed
Frsquorsquo
Lep
Mu
sL
ith
Mu
s
Co
mp
osi
tio
nC
ore
Rim
Co
reR
imR
imC
ore
Rim
Co
reC
ore
Rim
Rim
SiO
24
37
15
42
04
52
45
63
75
23
45
87
64
67
14
63
35
91
84
58
54
85
74
81
24
94
64
55
44
61
1T
iO2
06
00
15
04
70
02
02
70
05
mdashmdash
00
2mdash
01
00
03
00
7mdash
00
4A
l 2O
32
21
81
76
52
97
81
59
01
82
11
48
13
12
63
53
31
49
43
71
92
68
82
83
32
46
43
77
03
55
0F
eO8
42
39
74
57
24
44
94
13
11
56
17
51
14
mdash2
68
11
01
50
01
21
15
Mn
O0
60
00
60
33
00
20
21
00
30
10
01
50
05
01
20
27
12
32
16
04
80
53
Mg
O5
15
17
21
06
14
01
33
10
10
87
06
80
94
00
50
09
mdash0
01
mdashmdash
Zn
O0
46
03
20
17
01
10
24
01
30
14
01
00
09
00
60
13
02
60
41
00
60
15
CaO
00
10
01
00
4mdash
00
10
02
00
30
05
00
1mdash
mdash0
02
00
10
02
mdashL
i 2O
2
97
60
13
42
66
35
47
73
23
84
03
07
45
04
34
38
42
54
64
01
60
45
Na 2
O0
08
00
60
23
01
10
23
00
70
29
03
30
06
04
40
13
02
60
13
03
80
28
K2O
10
00
98
41
00
91
02
01
05
89
77
93
39
98
95
09
91
10
28
97
79
95
99
39
81
Rb
2O
08
60
78
06
61
30
02
80
46
05
10
43
04
91
06
15
01
42
16
71
02
11
0C
s 2O
0
06
00
9
00
60
14
00
6
00
6
00
6
00
6
00
60
15
05
50
13
02
2
00
60
03
F5
10
89
92
24
10
50
10
14
10
05
24
60
81
98
41
06
53
84
89
74
10
50
11
0H
2O
18
30
23
33
9mdash
mdashmdash
33
54
12
mdash4
01
19
12
15
09
14
28
39
61
02
03
10
40
81
01
75
10
51
41
04
31
10
38
51
00
51
10
04
21
03
77
10
03
31
02
85
10
19
61
03
19
10
02
51
00
21
O
F2
14
37
80
94
44
14
26
42
21
03
03
44
13
04
52
26
20
53
11
02
10
46
To
tal
99
89
10
03
01
00
81
10
07
31
00
05
99
63
99
48
10
00
89
96
49
98
81
00
59
99
91
10
00
81
00
04
99
75
KR
b(w
t)1
11
21
47
13
41
91
62
11
88
56
26
25
48
98
1
Si
30
85
36
20
30
45
37
47
35
58
38
54
31
02
30
83
38
63
30
45
32
66
32
26
33
51
30
24
30
86
AlIV
09
15
03
80
09
55
02
53
04
42
01
46
08
98
09
17
01
37
09
55
07
34
07
74
06
49
09
76
09
14
PT
40
04
00
40
04
00
40
04
00
40
04
00
40
04
00
40
04
00
40
04
00
40
0A
lVI
09
31
10
09
14
07
09
92
10
17
09
99
15
49
18
54
10
12
19
56
13
96
14
65
13
19
19
74
18
87
Ti
00
32
00
08
00
24
00
01
00
14
00
02
mdashmdash
00
01
mdash0
00
50
00
20
00
4mdash
00
02
Fe2thorn
04
97
02
22
02
57
01
36
02
81
00
72
00
87
00
97
00
62
mdash0
15
10
06
20
08
50
00
70
06
4M
n0
03
60
00
30
01
90
00
10
01
20
00
20
00
60
00
80
00
30
00
70
01
50
07
00
12
40
02
70
03
0M
g0
54
20
17
10
10
60
13
90
13
50
09
90
08
60
06
70
09
10
00
50
00
9mdash
00
01
mdashmdash
Zn
00
24
00
16
00
08
00
05
00
12
00
06
00
07
00
05
00
04
00
03
00
06
00
13
00
21
00
03
00
07
Li
08
44
16
13
09
25
17
73
14
95
19
32
10
26
00
80
19
54
01
14
11
84
11
46
12
64
00
42
01
20
PR
29
13
04
27
53
05
29
73
11
27
62
11
31
32
09
27
72
76
28
22
05
21
1C
a0
00
10
00
10
00
3mdash
00
01
00
01
00
02
00
04
00
01
mdashmdash
00
01
00
01
00
01
mdashN
a0
01
10
00
80
03
00
01
40
03
00
00
90
03
70
04
30
00
80
05
70
01
70
03
40
01
70
04
90
03
6K
09
00
08
38
08
66
08
65
09
17
08
18
07
90
08
47
07
91
08
40
08
82
08
36
08
60
08
41
08
38
Rb
00
39
00
33
00
29
00
56
00
12
00
19
00
22
00
18
00
21
00
45
00
65
00
61
00
73
00
44
00
47
Cs
00
02
00
03
00
02
00
04
00
02
00
02
00
02
00
02
00
02
00
04
00
16
00
04
00
06
00
02
00
01
PA
09
50
88
09
30
94
09
60
85
08
50
91
08
20
95
09
80
94
09
60
94
09
2F
11
39
18
99
04
77
22
07
21
80
20
85
05
17
01
70
20
31
02
23
11
44
10
37
15
87
01
05
02
33
OH
0
86
10
10
11
52
3mdash
mdashmdash
14
83
18
30
mdash1
77
70
85
60
96
30
41
31
89
51
76
7Z
on
esL
DL
DL
DL
DD
D
LD
LD
L
F
igu
res
Fig
s3
a6
ab
Fig
3
bF
igs
3c
6c
Fig
s3
d
d1
6
dF
igs
3e
6e
fF
igs
3f
f1
6g
h
970 A M R Neiva
eschweizerbart_xxx
Tab
le1
C
on
tin
ued
Inn
erIn
term
edia
teZ
on
e-
IIZ
bC
ore
-C
c
Lit
hM
us
Lep
Mu
slsquolsquo
Mix
edF
rsquorsquoL
epL
ith
Mu
slsquolsquo
Mix
edF
rsquorsquoL
epM
us
Lit
hM
us
Co
reR
imC
ore
Rim
Rim
Co
reR
imR
im
SiO
24
69
25
21
64
62
24
90
64
99
94
71
84
90
15
09
54
63
44
65
6T
iO2
00
3mdash
00
40
03
00
30
02
00
1mdash
mdashmdash
Al 2
O3
35
72
22
89
36
17
28
04
24
87
35
10
26
26
23
49
36
31
35
53
FeO
00
10
61
00
70
05
00
70
04
21
81
55
00
10
03
Mn
O0
55
05
80
43
12
92
24
06
01
09
13
30
14
01
4M
gO
mdashmdash
mdashmdash
mdashmdash
mdashmdash
mdashmdash
Zn
O
00
60
10
00
8
00
60
19
0
06
02
50
07
0
06
0
06
CaO
00
30
04
mdashmdash
00
10
01
00
10
01
mdashmdash
Li 2
O
06
55
42
02
54
52
47
90
93
45
15
07
04
70
79
Na 2
O0
41
00
80
49
02
60
16
04
10
13
01
00
55
05
4K
2O
97
99
78
10
16
96
69
76
94
49
33
90
89
97
99
0R
b2O
12
42
30
14
31
79
21
01
34
17
52
13
14
81
69
Cs 2
O0
16
08
7
00
60
62
05
00
11
07
70
79
01
40
12
F1
46
83
40
70
49
97
63
19
25
55
73
51
15
16
9H
2O
38
30
52
41
62
14
08
23
61
18
20
95
39
63
70
10
08
61
03
69
10
02
61
02
51
10
31
61
00
77
10
26
71
02
87
10
05
81
00
75
O
F0
61
35
00
29
21
03
20
08
12
33
30
90
48
07
1T
ota
l1
00
25
10
01
99
99
71
00
41
99
96
99
96
10
03
49
97
81
00
10
10
00
4
KR
b(w
t)7
23
96
44
94
26
44
83
96
15
3
Si
31
10
34
98
30
84
32
68
33
76
31
30
33
02
34
42
30
82
31
02
AlIV
08
90
05
02
09
16
07
32
06
24
08
70
06
98
05
58
09
18
08
98
PT
40
04
00
40
04
00
40
04
00
40
04
00
40
04
00
AlV
I1
90
01
30
71
92
91
47
01
35
51
87
51
38
71
31
21
92
81
89
2T
i0
00
1mdash
00
02
00
02
00
02
00
01
00
01
mdashmdash
mdashF
e2thorn
00
01
00
34
00
04
00
03
00
04
00
02
01
23
00
88
00
01
00
02
Mn
00
31
00
33
00
24
00
73
01
28
00
34
00
62
00
76
00
08
00
08
Mg
mdashmdash
mdashmdash
mdashmdash
mdashmdash
mdashmdash
Zn
00
03
00
05
00
04
00
03
00
09
00
03
00
12
00
03
00
03
00
03
Li
01
73
14
61
00
66
12
11
13
01
02
49
12
21
13
76
01
27
02
11
PR
21
12
84
20
32
76
28
02
16
28
12
86
20
72
12
Ca
00
02
00
03
mdashmdash
00
01
00
01
00
01
00
01
mdashmdash
Na
00
53
00
10
00
63
00
34
00
21
00
53
00
17
00
13
00
71
00
70
K0
82
80
83
70
86
50
82
10
84
10
79
90
80
20
78
20
84
60
84
1R
b0
05
30
09
90
06
10
07
70
09
10
05
70
07
60
09
20
06
30
07
2C
s0
00
50
02
50
00
10
01
80
01
40
00
30
02
20
02
30
00
40
00
3P
A0
94
09
70
99
09
50
97
09
10
92
09
10
98
09
9F
03
06
17
69
01
48
10
51
16
30
04
03
11
83
15
70
02
42
03
56
OH
1
69
40
23
11
85
20
94
90
37
01
59
70
81
70
43
01
75
81
64
4Z
on
esD
LD
D
LD
LL
D
DF
igu
res
Fig
s3
g
6i
jk
Fig
s3
h
6l
Fig
s3
i6
m
nF
igs
3j
6o
p
OIZ
IIZ
aII
Zb
Cc
asin
Fig
2Z
inndash
zin
nw
ald
ite
Lep
ndashle
pid
oli
teF
ndashfo
rmP
olndash
po
lyli
thio
nit
eL
ith
Mu
sndash
lith
ian
mu
sco
vit
eM
us
ndashm
usc
ov
ite
Lndash
ligh
ter
zon
eD
ndashd
ark
erzo
ne
D
-th
ed
ark
estzo
ne
L
-th
eli
gh
test
zon
ein
BS
Eim
ages
BaO
isb
elo
wth
ed
etec
tio
nli
mit
Cal
cula
ted
nu
mb
ero
fio
ns
on
the
bas
iso
f1
2o
xy
genthorn
Fat
om
sL
i 2O
v
alu
esca
lcu
late
dfr
om
equ
atio
ns
of
Tis
chen
do
rff
eta
l
(19
97
)O
H
-ca
lcu
late
db
yd
iffe
ren
ceto
20
00
H
2O
-ca
lcu
late
db
yst
oic
hio
met
ry
Silicate and oxide minerals from a zoned granitic pegmatite 971
eschweizerbart_xxx
analytical totals are not good The analyzed lsquolsquomixedformsrsquorsquo are distinguished in backscattered-electron (BSE)images and chemically (Fig 3b d d1 e f f1 h i andFig 4) The chemical distinction between lsquolsquomixed formrsquorsquoand lepidolite from the OIZ (Fig 4) is clear in Fig 3bwhere lepidolite is darker than lsquolsquomixed formrsquorsquo because theformer has less Fe and Mn than the latter (Table 1) and inFig 3f f1 and 3h for micas from the IIZa and IIZbrespectively where lepidolite is lighter than lsquolsquomixedformrsquorsquo because the former has more Fe2thorn and Mn oronly more Mn than the latter (Table 1) The lsquolsquomixedformsrsquorsquo analyzed are distinguished in the BSE imagesfrom the lepidolite that falls in its fields in the Fig 4The fields of lepidolite composition in Foster (1960) arelarger than the field for lepidolite from the trilithionite tothe polylithionite (Rieder et al 1999) According to Fleet(2003) only a few lepidolite compositions plot on thetrilithionite-polylithionite join In general lepidolite hashigher Si Licalc Rb Cs F contents and lower AlVI andOH contents than lsquolsquomixed formrsquorsquo (Table 1 Fig4)lsquolsquoMixed formrsquorsquo is also clearly distinguished fromlithian muscovite in OIZ IIZa IIZb and Cc in BSEimages (Fig 3d d1 e f i) and chemically (Table 1 Fig4) as it generally has higher Si Licalc Rb Cs F contentsand lower AlVI and OH contents than lithian muscovite
Two distinct trends are defined in Fig 4 One trendconsists of Al-poorer micas which are zinnwaldite
lepidolite and FeMg-containing polylithionite from theOIZ A hiatus occurs between zinnwaldite and lepidolitebut the zinnwaldite series is continuous with the field oflepidolite at the high Li content (Fleet 2003) The othertrend consists of Al-richer micas (muscovite lithian mus-covite and lsquolsquomixed formrsquorsquo from the OIZ IIZa IIZb and Ccand also lepidolite from most of those zones except fromthe OIZ) There is a gap between lithian muscovite and thelsquolsquomixed formrsquorsquo which may be explained by a hiatus inmica stability (eg Jolliff et al 1987) but a solid solutionbetween dioctahedral and trioctahedral micas has beenindicated experimentally (Monier amp Robert 1986) whileother authors have shown that the octahedral site occu-pancy ranges continuously from muscovite to lepidolite(eg Roda Robles et al 2005 Van Lichterveld et al2008 Vieira et al 2011) Most lithian muscovites andlsquolsquomixed formrsquorsquo from the OIZ are richer in Fe2thornthornMg thornMn than those from the other zones due to their higherFe2thorn and Mg contents (Fig 4 Table 1)
In the Al-poorer micas from the OIZ ranging from zinn-waldite to lepidolite and FeMg-containing polylithionite(Fig 4) (AlIV thorn AlVI) Fe2thorn Mg Ti Mn and Zn contentsdecrease and Si and Licalccontents increase (Table 1) In theAl-richer micas ranging from muscovite to lithian muscoviteand lsquolsquomixed formrsquorsquo from the OIZ IIZa IIZb and Cc and alsoto lepidolite from most of those zones except from the OIZ(AlIV thorn AlVI) AlVI and OH contents and KRb ratio
Fig 4 Plots of micas from the Namivo granitic pegmatite Mozambique in the LindashR2thornndashR3thornthorn Ti diagram according to the classification ofFoster (1960) slightly modified (Rieder et al 1999) with R3thorn frac14 AlVI R2thorn frac14 (Fe2thornt thorn Mn2thornthorn Mg) showing the variety of micacompositions Two trends are defined one for Al-poorer micas (zinnwaldite lepidolite and FeMg-containing polylithionite) from theOIZ another for Al-richer micas (muscovite lithian muscovite lsquolsquomixed formrsquorsquo and lepidolite) from all zones except lepidolite from the OIZOIZ IIZa IIZb and Cc as in Fig 2
972 A M R Neiva
eschweizerbart_xxx
generally decrease and Si Licalc Rb Cs and F contentsgenerally increase (Table 1)
42 Main substitution mechanisms
The 2Si thorn Li 3Altotal mechanism operates in the diocta-hedral micas (muscovite and lithian muscovite) (Fig 5a b)whereas the 3LiVI AlVIthorn 2ampVI (amp represents a vacancy)operates in the trioctahedral micas (lsquolsquomixed formrsquorsquo lepido-lite zinnwaldite and FeMg-containing polylithionite) (Fig5c d) which agrees with findings for micas from the Tancopegmatite (Van Lichtervelde et al 2008)
43 Textures and chemical compositions of zoned micacrystals
Backscattered-electron images combined with quantita-tive spot electron-microprobe analyses made it possibleto distinguish different micas in the Namivo graniticpegmatite Similar textural aspects and geochemicalobservations were found between some Al-richer micasfrom the OIZ IIZa IIZb and Cc Some selected zonedcrystals are documented (Table 1 Fig 3 and 6) In theOIZ lepidolite penetrates zinnwaldite along cleavagesand partially surrounds it and the contacts are sharp(Fig 3a) A chemical gap occurs between zinnwalditeand lepidolite compositions (Fig 6a b) Lepidolite withhigher Si Licalc F contents similar KRb value andlower (AlIV thorn AlVI) Ti Fe2thorn Mg (Fe2thornthorn Mn thorn Mg)Zn and OH contents (Table 1) replaces zinnwaldite Athin lepidolite rim partially surrounds lsquolsquomixed formrsquorsquoand the contact is sharp (Fig 3b) The lepidolite rimhas higher Si Mg Licalc Rb F contents and lowerAlVI Ti Fe2thorn Mn Na and OH contents and KRb ratiothan the lsquolsquomixed formrsquorsquo core (Table 1) The lepidoliterim is an Al-poorer mica whereas the lsquolsquomixed formrsquorsquocore is an Al-richer mica (Fig 4) The lepidolite rimcorresponds to an overgrowth The FeMg-containingpolylithionite partially surrounds and penetrates lepido-lite along cleavages and shows well defined contacts(Fig 3c) Both contain rutile cassiterite and columbi-tendashtantalite inclusions A continuous chemical evolutiontakes place from lepidolite to FeMg-containing poly-lithionite (Figs 4 6c) The latter has higher Si LicalcRb contents and lower AlVI Ti Fe2thorn Mn Mg Zn Nacontents and KRb ratio (Table 1) and replaces lepido-lite A lithian muscovite rim with rare FeMg-containingpolylithionite surrounds the lsquolsquomixed formrsquorsquo core and thispolylithionite penetrated lithian muscovite (Fig 3d)The contact between the lithian muscovite rim andlsquolsquomixed formrsquorsquo core is irregular suggesting disequili-brium or at a cleavage (Fig 3d d1) Two linear trendsone for the lithian muscovite rim and another for thelsquolsquomixed formrsquorsquo core are defined in the (Fe2thornthornMnthornMg)vs (AlIV thornAlVI) diagram (Fig 6d) The FeMg-contain-ing polylithionite rim does not belong to any of thesetrends and plots outside this diagram because it is an Al-poorer mica whereas the others are Al-richer micas
(Fig 4) The lithian muscovite rim has higher AlVI(AlIV thorn AlVI) OH contents and KRb ratio and lowerMg (Fe2thornthorn Mn thorn Mg) Licalc Rb F contents than thelsquolsquomixed formrsquorsquo core (Table 1 Fig 6d) The crystal isreversely zoned The FeMg-containing polylithioniterim has higher Si Licalc F contents and lower AlVI(AlIV thorn AlVI) Fe2thorn Mn (Fe2thornthorn Mn thorn Mg) Na andOH contents than the lsquolsquomixed formrsquorsquo core and lithianmuscovite rim (Table 1) and replaces lithian muscovite
In the IIZa some zoned crystals have a lithian muscovitecore and a lsquolsquomixed formrsquorsquo rim and the contacts are gradual(Fig 3e) A small discontinuity occurs in the trends fromthe lithian muscovite core to lsquolsquomixed formrsquorsquo rim in the(Fe2thornthorn Mn thorn Mg) vs (AlIV thorn AlVI) and Rb2O vs KRb(Fig 6e f) The lsquolsquomixed formrsquorsquo rim has higher Si Fe2thornMn (Fe2thornthornMn thornMg) Licalc K Rb Cs F contents andlower AlVI (AlIVthornAlVI) Na OH contents and KRb ratiothan the lithian muscovite core (Table 1 Fig 6e f) indi-cating progressive zoning Similar textural relationshipsand chemical evolutions were found in other zoned crystalsfrom the OIZ IIZb and Cc In another crystal from theIIZa lithian muscovite partially surrounds lsquolsquomixed formrsquorsquointergrown with lepidolite Lithian muscovite also partiallysurrounds muscovite (Fig 3f) The contacts betweenlsquolsquomixed formrsquorsquo and lepidolite and also between muscoviteand lithian muscovite are gradual (Fig 3f f1) whereasthey are well defined for muscovite withlsquolsquomixed formrsquorsquoand lepidolite (Fig 3f f1) The crystal has a lsquolsquomixed formrsquorsquoand lepidolite core and a partial rim of muscovite andlithian muscovite The lsquolsquomixed formrsquorsquo core evolved tolepidolite core as the Si Fe2thorn Mn (Fe2thornthorn Mn thorn Mg)Licalc K Rb Cs and F contents increase and the (AlIV thornAlVI) and KRb ratio decrease (Table 1 Fig 6g h) The SiFe2thorn Mn (Fe2thornthorn Mn thorn Mg) Licalc Rb and F contentsincrease and the (AlIV thorn AlVI) and KRb ratio decreasefrom the muscovite rim to the lithian muscovite rim (Table1 Fig 6g h) suggesting that the former evolved to thelatter The muscovite rim has higher AlVI (AlIV thorn AlVI)Na OH contents and KRb ratio and lower Si Fe2thorn Mn(Fe2thornthornMn thornMg) Zn Licalc Rb and F contents than thelsquolsquomixed formrsquorsquo core and lepidolite core (Table 1 Fig 6gh) Muscovite was probably reversely formed and evolvedafterwards to lithian muscovite
In the IIZb some crystals have a lithian muscovite coreand a thinner lepidolite rim (Fig 3g) and others show asmall muscovite core and a larger rim of lsquolsquomixed formrsquorsquointergrown with lepidolite (Fig 3h) The contacts betweenthe cores and rims are well defined There are increases inthe Si Mn (Fe2thornthorn Mn thorn Mg) Licalc Rb and F contentsand decreases in the AlVI (AlIVthornAlVI) and KRb ratio fromthe lsquolsquomixed formrsquorsquo rim to the intergrown lepidolite rim(Table 1 Figs 3h 6l) suggesting that the former evolvedto the latter as also found in IIZa and Cc In both crystalsthe rim compositions have higher Si (Fe2thornthorn Mn thorn Mg)Licalc Rb Cs F contents and lower AlVI (AlIVthorn AlVI) Naand OH contents and KRb ratio than the core (Table 1 Figs3g 6i j k 3h 6l) A compositional gap occurs between coreand rim in the diagrams for both crystals (Fig 6i j k l)suggesting that both rims correspond to overgrowths and no
Silicate and oxide minerals from a zoned granitic pegmatite 973
eschweizerbart_xxx
diffuse reequilibration took place in any crystal as thecontacts between core and rim are sharp
In the Cc lithian muscovite is surrounded and pene-trated by lsquolsquomixed formrsquorsquo showing well defined contacts(Fig 3i) The lsquolsquomixed formrsquorsquo has higher Si Fe2thorn Mn(Fe2thornthorn Mn thorn Mg) Licalc Rb Cs F contents and lowerAlVI (AlIV thorn AlVI) Na OH contents and KRb ratio thanthe lithian muscovite (Table 1 Fig 6m n) and a composi-tional gap occurs between both micas suggesting thatlsquolsquomixed formrsquorsquo replaced lithian muscovite In rare crystalsa small lepidolite core is surrounded by a large muscoviterim containing K-feldspar inclusions The contact betweenthe core and rim is sharp (Fig 3j) A thin partial rim oflithian muscovite surrounds muscovite and the contact isgradual The muscovite rim has higher AlVI (AlIVthornAlVI)Na K OH contents and a greater KRb value and lower SiFe2thorn Mn Licalc Rb Cs and F contents than the lepidolitecore (Table 1 Fig 6o p) and a compositional gap occursbetween them (Fig 6o p) indicating that either muscoviteforms an overgrowth or it is reversely formed From themuscovite rim to the lithian muscovite rim the Si Licalc
Rb F contents increase whereas the AlVI (AlIV thorn AlVI)and OH contents and KRb ratio decrease (Table 1 Fig 6op) suggesting that muscovite evolved to lithian muscoviteas also found in IIZa and IIZb
44 Evolution of mica compositions within each zoneand from the outer intermediate zone to the core of theNamivo granitic pegmatite
The KRb ratio is taken as the best fractionation index inmicas (eg Cerny et al 1985 Foord et al 1995 Wise1995 Pesquera et al 1999 Roda Robles et al 2006 2007)It is hard to establish trends in the evolution of mica com-position from muscovite and lithian muscovite to lsquolsquomixedformrsquorsquo and lepidolite within each zone because the KRbratio shows some partial overlapping particularly betweenthe lithian muscovite and lsquolsquomixed formrsquorsquo and also betweenthe latter and lepidolite However an evolution from mus-covites to lepidolite (Al-richer mica Fig 4) is clearer (Fig7) In general in IIZa IIZb and Cc the Si Licalc Rb Cs and
Fig 5 The main substitutions in micas from the Namivo granitic pegmatite Mozambique a b SiIVthorn LiVI versus AlIVthornAlVI showing the 2SithornLi 3Altotal substitution mechanism operating in dioctahedral micas (Mu muscovite and Lith mu lithian muscovite) c d AlVI thornamp VI
versus LiVI (where amp represents a vacancy) and showing the 3LiVI AlVI thorn 2 amp VI substitution mechanism operating in trioctahedral micas(Mix f ndashlsquolsquomixed formrsquorsquo Lep lepidolite Zin zinnwaldite and Pol-FeMg-containing polylithionite) OIZ IIZa IIZb and Cc as in Fig 2
974 A M R Neiva
eschweizerbart_xxx
F contents tend to increase and the (AlIV thorn AlVI) AlVI
contents and KRb ratio tend to decrease from muscoviteto lepidolite (Table 1 Fig 7) This sequence is consistentbut rarely in the Cc lepidolite is rimmed by muscovite (Fig3j) But in the OIZ the evolution stops in lsquolsquomixed formrsquorsquoparticularly shown by the large range of the KRb ratiowhich mainly overlaps that of lepidolite from this zone(Fig 7) because this lepidolite is an Al-poorer mica whereasthe others are Al-richer micas (Fig 4)
In the OIZ the lepidolite has more Si Licalc and F andless (AlIV thorn AlVI) Ti Fe2thorn Mn Mg and Zn than zinn-waldite (Table 1) but it has larger ranges of Rb and KRbratio than zinnwaldite (Fig 7) The FeMg-containingpolylithionite is the richest mica in Si Licalc and thepoorest in (AlIV thorn AlVI) (Table 1) But at this zone scalethe polylithionite has Rb Cs contents and KRb ratiowithin the ranges for lepidolite and close to those of zinn-waldite (Fig 7)
Fig 6 Variation diagrams of micas from selected zoned crystals from the zones of the Namivo granitic pegmatite Mozambique to showtheir relationships lith musc lithian muscovite OIZ IIZa IIZb and Cc an in Fig 2
Silicate and oxide minerals from a zoned granitic pegmatite 975
eschweizerbart_xxx
From the OIZ to IIZa IIZb and Cc muscovite and lithianmuscovite generally show increases in the Si Licalc F and Rbcontents and decreases in the Fe2thorn and Mg contents and KRb ratio but the Mg content is very low in these micas fromthe IIZa IIZb and Cc (Table 1 Fig 7a) The lsquolsquomixed formrsquorsquoshows increases in the Si Licalc F Rb Cs contents anddecreases in the (AlIV thorn AlVI) and Mg contents and KRbratio but the Mg content is very low in this mica from theIIZb and Cc (Table 1 Fig 7b c) The lepidolite shows anincrease in the Si Licalc F Rb and Cs contents and a decreasein the KRb ratio from the IIZa to the IIZb and Cc (Table 1Fig 7d e) Furthermore the lepidolite from the OIZ has thelowest (AlIV thorn AlVI) AlVI and OH contents the highest SiFe2thorn Licalcand F contents and KRb ratio and the lowest Rband Cs contents compared to lepidolite from the other zones(Table 1 Fig 7d e)
5 Feldspars
Selected chemical analyses of albite and K-feldspar fromfive zones of the Namivo granitic pegmatite are given inTable 2 Strontium is the most abundant trace element inalbite (eg Cerny 1994) Anorthite and Sr contents and SrCa ratio of albite decrease from the WZ to the Cc (Fig 8Table 2) Rubidium is the most abundant trace element inK-feldspar followed by Cs in IIZa IIZb and Cc In gen-eral K Rb and Cs contents of K-feldspar increase and KRb and KCs values decrease from the WZ to the Cc (Table2 Fig 9)
The program SOLVCALC 20 (Wen amp Nekvasil 1994)using the Margules model Fuhrman amp Lindsley (1988) wasapplied for the purpose of thermometry The pairing ofplagioclase cores with the K-feldspars average of eachsample was used to estimate the crystallization temperaturesof primary magmatic feldspars They are 405 C (WZ)406ndash340 C (OIZ) 390ndash335 C (IIZa) 347ndash306 C (IIZb)and 333ndash289 C (Cc) at 3 kbar The metamorphic environ-ment of rare-element-Li granitic pegmatites is one of lowpressure 2ndash4 kbar (Cerny amp Ercit 2005) In general thedifference between the maximum and minimum calculatedtemperatures at 2 3 and 4 kbar for the same feldspar pairfrom the Namivo pegmatite is lower than 40 C The tem-perature decreases from the wall zone (WZ) to the core(Cc) A similar temperature behavior of feldspars wasfound in the pegmatite-aplite dike USA (Morgan ampLondon 1999)
6 Other silicates
Tourmaline of schorl composition was only found inthe OIZ (Table 2) because there was not enough Feand Mg for schorl to precipitate in the other zonesSpodumene only occurs in the Cc and its compositionis nearly pure (Table 2)
7 Columbite-tantalite
Representative chemical analyses of columbitendashtantalitefrom the Namivo granitic pegmatite are given in Table 3and plotted in the columbite quadrilateral (Fig 10a)Most crystals are unzoned but zoned crystals with dar-ker and lighter zones in BSE images are from the Cc Thelighter zone of columbite-(Mn) has higher Ta contentTa(Ta thorn Nb) and Mn(Mn thorn Fe) values and lower Nbcontent than the darker zone (Fig 10a b) The crystals ofthe columbitendashtantalite minerals are low in W Sn and Tiimpurities (Table 3)
The main trend starts from the columbite-(Mn) of theOIZ towards the more Mn-enriched and slightly Ta-enriched columbite-(Mn) from the IIZa and Cc The high-est Ta(Ta thorn Nb) values belong to the lighter zone ofcolumbite-(Mn) with Mn(Mn thorn Fe) frac14 10 from the CcThe richest columbite-(Mn) in Ta(TathornNb) and composi-tions of tantalite-(Fe) and tantalite-(Mn) were only foundin the OIZ (Fig 10a) and are associated with lepidolite andpolylithionite (Fig 3c)
8 Gahnite
Gahnite was rarely found in the OIZ and shows a darkerzone that partially surrounds a lighter zone in a BSE image(Fig 11a) The darker zone has a higher Zn content andlower Sn Ti Nb Ta Mn contents and SnZn value than thelighter zone (Table 4 Fig 11b c) These gahnite composi-tions fall within the igneous field of Batchelor amp Kinnaird(1984) The darker zone is closer in composition to thepure gahnite (Zn8Al16O32) than the lighter zone whichcontains up to 0983 apfu Sn 0195 apfu Ti 1029 apfutotal Fe2thorn 0101 apfu Mn (Table 4) and consequently hasa composition distinct from nigerite In general both thedarker and lighter zones have higher Sn Ti and Fe contentsthan gahnite from the granitic pegmatites of Nigeria(Batchelor amp Kinnaird 1984) Arga northern Portugal(Gomes et al 1995) and Cabanas northern Portugal(Neiva amp Champness 1997) Borborema province north-eastern Brazil (Soares et al 2007) The Zn=Fe2thornt values ofthe darker and lighter zones of gahnite from Namivo arelower than those reported in Neiva amp Champness (1997)and Soares et al (2007)
9 Discussion and conclusions
91 Evolution of micas in the zoned pegmatite
In general individual mica crystals show varying patternsand compositional zoning involving several elementsmainly Si AlVI (AlIV thorn AlVI) Fe2thorn Mn (Fe2thornthorn Mn thornMg) Licalc Rb Cs F and OH and the KRb ratioProgressively zoned crystals from the IIZa show grada-tional contacts between a lithian muscovite core and a
976 A M R Neiva
eschweizerbart_xxx
lsquolsquomixed formrsquorsquo rim (Figs 3e 6e f) and the zoning patternscorrespond to fractionation trends and probably reflect adrop in temperature during the crystallization of the grani-tic pegmatite melt Progressively zoned crystals also occurin OIZ IIZb and Cc Some crystals are reversely zonedwith a) a lsquolsquomixed formrsquorsquo core and a lithian muscovite rimfrom the OIZ (Figs 3d d1 6d) b) a core consisting oflsquolsquomixed formrsquorsquo and lepidolite and a rim of muscovite andlithian muscovite from the IIZa (Figs 3f f1 6g h) c) alepidolite core and a muscovite and lithian muscovite rimfrom the Cc (Figs 3j 6o p) which may be explained bythe hypothesis of oscillations in the compositions of themelt from which they grew alternating between an Li-enriched boundary layer and a bulk melt that is less frac-tionated The muscovite evolved to lithian muscovite inIIZa and Cc (Figs 3f 6g h 3j 6o p) Replacements (Figs3a 6a b 3c 6c 3i 6m n Table 1) occur in OIZ and Ccand overgrowths (Figs 3b g 6i j k 3h 6l Table 1) occurin OIZ and IIZb as found in BSE images
Muscovite evolved to lithian muscovite as observed inOIZ IIZa IIZb and Cc (Figs 3f 6g h 3j 6o p Table 1)Lithian muscovite evolved to lsquolsquomixed formrsquorsquo in OIZ IIZaIIZb and Cc (Figs 3e 6e f Table 1) and lsquolsquomixed formrsquorsquoevolved to lepidolite in IIZa IIZb and Cc (Figs 3f f1 6gh 3h 6l Table 1) All these evolutions are due to fractionalcrystallization
In the OIZ lepidolite has more Si Licalcand F butsimilar KRb to that of zinnwaldite and replaces it (Figs
3a 6a b 7d Table 1) An FeMg-containing polylithionitehas higher Si Licalcand Rb contents and a smaller KRbratio than the lepidolite that it replaces (Figs 3c 6c Table1) and a continuous chemical evolution from lepidolite topolylithionite is shown
The trends for major and trace elements of micas withineach zone are difficult to define due to some partial over-lapping but a progressive evolution from muscovite to lithianmuscovite lsquolsquomixed formrsquorsquo and lepidolite in IIZa IIZb and Ccis mainly shown by an increase in the Si Licalc F Rb and Cscontents and a decrease in the KRb ratio and this is simi-larly shown in the OIZ from muscovite to lsquolsquomixed formrsquorsquo(Table 1 Fig 7) In the OIZ Si and Licalccontents increaseprogressively from zinnwaldite to lepidolite and FeMg-containing polylithionite but a gap occurs between zinnwal-dite and lepidolite (Table 1 Fig 4) whereas a continuousevolution from lepidolite to polylithionite is observed TheKRb ratios of zinnwaldite and polylithionite are within therange of that of lepidolite (Fig 7d e)
Each Al-richer mica (muscovite lithian muscovite andlsquolsquomixed formrsquorsquo) exhibits an evolution from the OIZ to theIIZa and then to the IIZb and Cc particularly shown by anincrease in the Si Licalc F and Rb contents and adecrease in the KRb ratio but also an increase in theCs content in the lsquolsquomixed formrsquorsquo (Table 1 Fig 7) Theseelements and ratio have been used as petrogenetic indi-cators of evolution in micas from pegmatites (eg Cernyet al 2005 Roda Robles et al 2006 2007 Vieira et al
Fig 7 Plot of some variation diagrams of micas from the OIZ IIZa IIZb and Cc of the Namivo granitic pegmatite Mozambique showingthat the Rb2O and Cs2O contents increase and the KRb ratio decreases for micas from the OIZ to the Cc OIZ IIZa IIZb and Cc as in Fig 2
Silicate and oxide minerals from a zoned granitic pegmatite 977
eschweizerbart_xxx
Tab
le2
R
epre
sen
tati
ve
elec
tro
nm
icro
pro
be
anal
yse
sin
wt
o
ffe
ldsp
ars
sch
orl
and
spo
du
men
efr
om
the
Nam
ivo
gra
nit
icp
egm
atit
eM
oza
mb
iqu
e
Alb
ite
K-f
eld
spar
Sch
orl
Sp
od
um
ene
Zo
nes
WZ
OIZ
IIZ
aII
Zb
Cc
Zo
nes
WZ
OIZ
IIZ
aII
Zb
Cc
Zo
nes
OIZ
Zo
ne
Cc
SiO
26
75
76
78
86
87
06
84
76
84
1S
iO2
65
10
65
55
65
46
64
96
64
72
SiO
23
52
0S
iO2
64
65
TiO
20
02
mdash0
02
mdashmdash
TiO
2mdash
00
1mdash
mdashmdash
TiO
20
35
Al 2
O3
27
20
Al 2
O3
20
25
19
74
19
67
19
88
19
97
Al 2
O3
18
96
18
23
18
31
18
24
18
05
B2O
3
10
28
Fe 2
O3
00
6F
e 2O
3mdash
mdashmdash
mdash0
10
Fe 2
O3
mdash0
02
mdash0
03
mdashA
l 2O
33
17
2M
nO
01
3M
nO
00
6mdash
mdashmdash
mdashM
nO
mdash0
03
00
3mdash
mdashF
eO1
35
2M
gO
01
8M
gO
mdashmdash
mdashmdash
mdashM
gO
00
10
01
00
5mdash
mdashM
nO
03
3N
a 2O
01
9C
aO1
04
08
00
56
03
70
32
CaO
00
10
01
00
60
01
00
2M
gO
22
8L
i 2O
8
05
Na 2
O1
06
11
12
01
12
11
13
41
13
4N
a 2O
06
50
58
04
10
59
03
8C
aO0
23
To
tal
10
04
6K
2O
00
50
17
00
60
14
01
0K
2O
14
72
14
75
15
67
15
01
15
74
Li 2
O
02
2S
rO0
72
05
00
24
01
1mdash
Rb
2O
00
90
20
03
00
59
09
0N
a 2O
22
8S
i1
99
7P
2O
50
01
00
4mdash
mdashmdash
Cs 2
O
00
6
00
60
09
01
80
20
K2O
00
1A
lIV0
00
3T
ota
l1
00
33
10
03
31
00
46
10
03
11
00
24
P2O
5mdash
00
3mdash
mdashmdash
H2O
3
18
P2
00
To
tal
99
60
99
48
10
03
89
96
11
00
01
F0
78
AlV
I0
98
7S
rC
a(w
t)0
81
07
40
50
03
50
Cl
mdashF
e3thorn
00
01
KR
b(w
t)153
68
48
23
16
Sum
1003
8P
09
9S
i1
18
23
11
87
91
19
58
11
93
21
19
21
KC
s(w
t)4
07
20
41
63
73
69
O
F0
33
Li
10
00
P0
00
10
00
6mdash
mdashmdash
To
tal
10
00
5M
n0
00
3T
i0
00
3mdash
00
03
mdashmdash
Si
11
98
61
20
88
12
04
11
20
45
12
03
3M
g0
00
8A
l4
17
64
07
14
03
54
08
34
10
1P
mdash0
00
5mdash
mdashmdash
TS
i5
95
2N
a0
01
2F
e3thorn
mdashmdash
mdashmdash
00
13
Ti
mdash0
00
1mdash
mdashmdash
Al
00
48
P1
02
Mn
00
09
mdashmdash
mdashmdash
Al
41
14
39
62
39
70
39
86
39
55
B3
00
0M
gmdash
mdashmdash
mdashmdash
Fe3thorn
mdash0
00
3mdash
00
04
mdashZ
Al
60
00
Ca
01
95
01
50
01
04
00
69
00
60
Mn
mdash0
00
50
00
5mdash
mdashY
Al
02
74
Sr
00
73
00
51
00
24
00
11
mdashM
g0
00
30
00
30
01
4mdash
mdashT
i0
04
5N
a3
59
93
80
03
78
33
83
23
83
1C
a0
00
20
00
20
01
20
00
20
00
4M
g0
57
5K
00
11
00
38
00
13
00
31
00
22
Na
02
32
02
07
01
46
02
12
01
37
Mn
00
47
K3
45
73
47
03
67
73
55
03
73
3F
e2thorn
19
12
Z1
60
01
59
61
60
01
60
11
60
4R
b0
01
10
02
40
03
50
07
00
10
8L
i0
14
8X
38
94
04
39
33
94
39
1C
s0
00
20
00
50
00
70
01
40
01
6P
Y3
00
0m
ole
s
XC
a0
04
2A
n5
13
82
71
71
5Z
16
10
16
06
16
01
16
03
15
99
Na
07
47
Ab
94
69
53
97
09
75
97
9X
37
13
72
39
03
85
40
0K
00
02
Or
03
09
03
08
06
mo
les
amp
02
09
An
01
01
03
01
01
Ab
63
56
38
56
35
OH
35
83
Or
93
69
43
95
99
43
96
4F
04
17
Cl
mdash
WZ
ndashw
allzo
ne
OIZ
ndasho
ute
rin
term
edia
tezo
ne
IIZ
aan
dII
Zb
ndashin
ner
inte
rmed
iate
zon
esC
cndash
core
asin
Fig
2B
aOis
bel
ow
the
det
ecti
on
lim
itin
bo
thfe
ldsp
ars
Cs 2
Ofrac14
00
3w
tin
the
K-
feld
spar
fro
mth
eW
Z
mdashN
ot
det
ecte
d
Nu
mb
ero
fio
ns
on
the
bas
iso
f3
2o
xy
gen
sfo
ral
bit
ean
dK
-fel
dsp
ar
31
anio
ns
(O
OH
F
)fo
rsc
ho
rlan
d6
ox
yg
ens
for
spo
du
men
e
-A
mo
un
tin
ferr
edfr
om
con
sid
erat
ion
so
fst
oic
hio
met
ry
978 A M R Neiva
eschweizerbart_xxx
2011) Lepidolite from the OIZ is an Al-poorer mica (Fig4) and has the highest Si Licalcand F contents (Table 1)indicating that an evolution cannot be shown from thislepidolite to lepidolites from the other zones which areAl-richer micas (Fig 4) However there is a regulardecrease in the KRb ratio and a progressive increase inthe Rb and Cs contents from lepidolite of the OIZ tolepidolite of IIZa IIZb and Cc (Fig 7) which indicatesthat the KRb ratio and Rb and Cs contents must not beconsidered alone to show fractional crystallization in
lepidolites particularly if some are Al-richer micas andothers Al-poorer micas The high Licalcand F contents oflepidolite from the OIZ did not decrease its KRb ratioSuch an effect is considered to have taken place in lepi-dolite (an Al-richer mica) from the wall zone of the Tancopegmatite Manitoba Canada (Van Lichtervelde et al2008) An evolution from the lepidolite of the IIZa to thatof the Cc is generally shown by the increasing Si LicalcF Rb Cs contents and a decrease in the KRb ratio (Table1 Fig 7)
At the scale of crystals the pegmatite zones and alsothose from the OIZ to the Cc of the Namivo granitic pegma-tite Al-richer micas show fractionation because theyformed from the fractionation of an Li-rich pegmatite melt
The Al-poorer micas zinnwaldite lepidolite and FeMg-containing polylithionite only occur in the OIZ (Fig 4)Polylithionite is the mica richest in Si and Licalc and lepi-dolite from this zone is the richest in Si Licalcand F (Fig 4Table 1) The high Li contents of these micas reflect aconsiderably higher D(Li) at low temperature (Icenhoweramp London 1995) These Li-rich micas may have crystal-lized from an undercooled melt This hypothesis does notimply high Rb and Cs contents and low KRb ratios Thisagrees with the fact that these micas from the OIZ havesimilar Rb and Cs contents and KRb ratios to those of Al-richer micas (muscovite lithian muscovite and lsquolsquomixedformrsquorsquo) from the same pegmatite zone (Fig 7) Howeverthe lepidolite from the wall zone of the Tanco pegmatiteCanada of a similar origin has a low KRb ratio which isattributed to the complexly interrelated structural compo-nents of this lepidolite (Van Lichtervelde et al 2008) TheLi-rich micas from the OIZ may also represent disequili-brium These two hypotheses are considered the best forthese micas of primary magmatic origin
Another hypothesis was also considered They may havecrystallized in boundary layers which concentrate Li andF But this mechanism was suggested for the most fractio-nated tourmaline enriched in Li and F from the core of the
Fig 8 Plot of albite compositions from all zones of the Namivo granitic pegmatite Mozambique showing that the anorthite content of albitedecreases from the WZ to the Cc WZ OIZ IIZa IIZb and Cc as in Fig 2
Fig 9 The Rb vs Cs diagram of K-feldspar from all zones of theNamivo granitic pegmatite Mozambique showing that the Rb andCs contents of K-feldspar increase from the WZ to the Cc WZ OIZIIZa IIZb and Cc as in Fig 2
Silicate and oxide minerals from a zoned granitic pegmatite 979
eschweizerbart_xxx
Little Three pegmatite dike USA (Morgan amp London1999) and the micas enriched in Li and F from theNamivo pegmatite belonging to the OIZ Furthermore ina boundary layer melt that became enriched in Li and F theKRb ratio of micas decreases strongly (Van Lichterveldeet al 2008) which was not found in these micas from theOIZ (Fig 7d) Nor can they have resulted from the crystal-lization of a late melt that would have reacted with the OIZbecause these micas are among those containing the high-est KRb values (Fig 7d)
92 The importance of feldspars micas andcolumbitendashtantalite compositions to the Namivogranitic pegmatite evolution
The trace elements Rb and Cs and the KRb and KCs ratioshave been used to show the evolution of K-feldspar inpegmatites (eg Cerny 1994 Cerny et al 2005 RodaRobles et al 2005) The Rb and Cs contents increase andthe KRb and KCs ratios of K-feldspar decrease from theWZ to the Cc (Fig 9 Table 2) reflecting the growth of K-feldspar from an increasingly fractionated melt withouthaving grown from or having been chemically modifiedby an aqueous fluid as in the Swamp pegmatite section atthe Little Three Mine USA (London et al 2012) Thecrystallization of K-feldspar from an exsolved aqueousfluid from melt will reverse the magmatic fractionation ofRb Cs KRb and KCs because Rb and especially Cs areso much more compatible in vapor that both Rb and Csremain in the fluid phase (London et al 2012) The feldsparsolvus pairs in the Namivo pegmatite record magmaticcrystallization temperatures that decrease from WZ to CcAlbite shows a decrease in the Ca Sr contents and SrCaratio from the WZ to the Cc (Fig 8 Table 2) Therefore thefeldspars and also Al-richer micas as already explainedshow fractionation in this zoned pegmatite
In general lepidolite from the Namivo pegmatite hassimilar Rb2O and Cs2O contents and KRb (wt) values tothose of lepidolite from the Rozna and Dobra Voda lepi-dolite-subtype pegmatites in the Czech Republic (Cernyet al 1995) but lower Rb2O and Cs2O contents thanlepidolite from the lepidolite-subtype pegmatite at RedCross Lake Manitoba Canada (Cerny et al 2012a) K-feldspar from the Namivo pegmatite also has lower Rb2O
Table 3 Representative electron microprobe analyses in wt of columbitendashtantalite from the Namivo granitic pegmatite Mozambique
Outer Intermediate Zone - OIZ Inner Intermediate Zone - IIZa
Core - Cc
D L L
WO3 022 059 079 113 101 351 050 007Ta2O5 5487 5123 2503 3186 2888 2519 3127 4542Nb2O5 2537 3000 5483 4635 5113 5144 4911 3686SnO2 008 015 024 049 020 026 017 012TiO2 263 161 136 254 202 145 125 016FeO 860 710 665 471 236 068 mdash mdashMnO 793 952 1099 1304 1400 1725 1748 1718Total 9970 10020 9989 10012 9960 9978 9978 9981W 0004 0011 0013 0019 0016 0057 0008 0001Ta 1065 0975 0422 0552 0495 0430 0543 0847Nb 0819 0949 1538 1336 1456 1460 1418 1143Sn 0002 0004 0006 0012 0005 0007 0004 0003Ti 0141 0085 0063 0122 0096 0068 0060 0008Fe 0513 0416 0345 0251 0124 0036 mdash mdashMn 0479 0564 0578 0704 0747 0917 0945 0998P
3023 3004 2965 2996 2939 2975 2978 3000Mn(Mn thorn Fe) 048 058 063 074 086 096 100 100Ta(Ta thorn Nb) 057 051 022 029 025 023 028 043Classification tant-(Fe) tant-(Mn) col-(Mn) col-(Mn) col-(Mn) col-(Mn) col-(Mn) col-(Mn)
D ndash darker L ndash lighter zones mdash Not detected tant-tantalite col-columbite Cation formula on the basis of 6 atoms of oxygen
Fig 10 Compositions of columbitendashtantalite from the Namivogranitic pegmatite Mozambique in the columbite quadrilateralshowing that Mn(Mn thorn Fe) of columbite-(Mn) increases from theOIZ to the Cc and the richest columbite-(Mn) in Ta(Ta thorn Nb)tantalite-(Fe) and tantalite-(Mn) only occur in the OIZ OIZ IIZaand Cc as in Fig 2
980 A M R Neiva
eschweizerbart_xxx
and Cs2O contents than K-feldspar from the lepidolite-subtype pegmatite at Red Cross Lake The Rb2O andCs2O contents of primary and late K-feldspar of this peg-matite at Red Cross Lake attained unprecedented levels(Cerny et al 2012a) The lowest KRb (wt) values ofmuscovite lithian muscovite lsquolsquomixed formrsquorsquo and lepido-lite from the IIZb and Cc (Fig 7) and K-feldspar (KRb frac1414) from the Cc compare well with those found in theseminerals from the AC6frac143 lepidolite-subtype pegmatitefrom Greer Lake (Cerny et al 2005) and some of themost fractionated pegmatites worldwide which belong tothe petalite-subtype (eg Tanco Manitoba Cerny 2005Cerny et al 1998 Varutrask Sweden Cerny et al 2005)but muscovite lithian muscovite and lepidolite from theIIZb and Cc have lower Rb2O and Cs2O contents than thesemicas from the Tanco pegmatite (Cerny 2005a VanLichtervelde et al 2008) K-feldspar also has lower
contents of these oxides than the most evolved K-feldsparfrom the Tanco pegmatite (Cerny 2005a) The magmaticfractionation was strong from the WZ to IIZb and Cc of theNamivo lepidolite-subtype pegmatite
The compositional trend of columbite-(Mn) from the OIZto Cc of the Namivo granitic lepidolite-subtype pegmatite(Fig 10) is identical to that of columbite-group mineralsfrom the lepidolite-subtype complex granitic pegmatitesfrom the Dobra Voda in the Moldanubicum CzechRepublic (Novak amp Cerny 1998) and the HimalayaDistrict southern California (shown in Cerny et al 2004)Experimental data for the Fe-Mn pair (Linnen amp Cuney2005) suggest an increase in Fe with fractional crystalliza-tion which is not observed in nature Other phases seem tocontrol the bahavior of Fe and Mn in the melt eg thecrystallization of tourmaline causes a rapid increase of theMnFe in the melt (Van Lichtervelde et al 2006) When thecrystallization of tourmaline stopped the columbitendashtantaliteminerals showed a constant MnFe indicating that the Fe andMn contents in the melt remained constant Schorl onlyoccurs in the OIZ of the Namivo granitic pegmatite and itscrystallization cannot be responsible for the increase in theMnFe of the melt because Mn(Mn thorn Fe) of columbite-(Mn) increases progressively from the OIZ to the IIZa and Cc(Fig 10) Garnet zinnwaldite and gahnite containing Fe andMn also only occur in the OIZ and cannot also have causedthe increase of the MnFe in the melt The dominant Mnenrichment before Ta enrichment started in the columbitendash-tantalite composition from some granitic pegmatites isattributed to an increased alkali-fluoride activity at moderatemHF (Cerny et al 2004) and an increase in the activity offluorine (Martins et al 2011) Each Al-richer mica (musco-vite lithian muscovite and lsquolsquomixed formrsquorsquo) from the Namivogranitic pegmatite shows an increase in F content from theOIZ to the IIZa IIZb and Cc (Table 1) In general the Fcontent of lepidolite also increases from the IIZa to the IIZband Cc Therefore the extreme Fe-Mn fractionation beforeTa enrichment in columbite-(Mn) (Fig 10) may be due to anincrease in the activity of fluorine as a consequence offractional crystallization The increase in the Ta content ofcolumbite-(Mn) from the Namivo granitic pegmatite isattributed to fractional crystallization
The geochemical evolution of albite and K-feldsparfrom the WZ to the Cc Al-richer micas muscovite lithianmuscovite and lsquolsquomixed formrsquorsquo from the OIZ to the Cc andlepidolite from the IIZa to the Cc and columbite-(Mn) andalso beryl (Neiva amp Neiva 2005) from the OIZ to the Ccare caused by magma fractionation The pegmatite zonesare the product of primary crystallization from a volatile-rich silicate melt The pegmatite consolidated from the WZto the Cc The IIZb is one of the most evolved zones asalso suggested by the beryl composition (Neiva amp Neiva2005) and is the richest in lsquolsquomixed formrsquorsquo and lepidolite
The richest columbite-(Mn) in Ta(Ta thorn Nb) and com-positions of tantalite-(Fe) and tantalite-(Mn) only occur inthe OIZ (Fig 10a) associated with lepidolite and polythio-nite (Fig 3c) which may be due to the local depletion of Liand F in the melt which decreases the solubility of Ta andcauses Ta precipitation (Linnen 1998 Linnen amp Cuney
Fig 11 a Backscattered-electron image of a gahnite crystal with adarker zone partially surrounding a lighter zone from the OIZ of theNamivo granitic pegmatite b c Plot of gahnite compositions in theSn-Zn-Ti diagram (atomic proportions) showing a chemical distinc-tion between the lighter and darker zones OIZ as in Fig 2
Silicate and oxide minerals from a zoned granitic pegmatite 981
eschweizerbart_xxx
2005) At the Tanco pegmatite Ta oxides are also asso-ciated with lepidolite enriched in Li and F from the wallzone (Van Lichtervelde et al 2008)
93 Origin and evolution of the zoned graniticlepidolite-subtype pegmatite at Namivo
In general granitic pegmatites particularly those belong-ing to the rare-element class are accepted as having beenformed by the fractional crystallization of a granite melt(eg Cerny 1991a b 1992 Neiva et al 2008 2012 Roda-Robles et al 2012) But it also has been proposed thatpegmatites may be formed by partial melting of appropri-ate rock compositions (eg Nabelek et al 1992 Nabelekamp Russ-Nabelek 1992 Shearer et al 1992 Roda Robleset al 1999) The lepidolite-subtype pegmatites belong tothe LCT (lithium-cesium-tantalum) family (Cerny amp Ercit2005) They are derived by fractional crystallization of agranite magma (eg Cerny et al 2005 Neiva amp Ramos2010 Cerny et al 2012b) Experimental work by Londonet al (1989) and London (1990) using Macusani glass as astarting material equivalent to the bulk composition ofhighly fractionated rare-alkali-rich pegmatites underhighly evolved and hydrous but H2O undersaturatedmelt obtained the latest primary assemblage consisting
of an Li-rich mica thorn albite thorn quartz deposited directlyfrom the primary melt phase Other authors egZasedatelev (1974 1977) and Stewart (1978) argue thatlepidolite-bearing pegmatites are derived from direct ana-texis and Gordiyenko et al (1996) consider that they arederived from an undefined medium and the rare-elementmineralization is superimposed on preexisting barrenpegmatites
Lepidolite-subtype pegmatites may migrate a long wayfrom their parent granites because their volatile-rich highlyfluid pegmatite melts are stable at relatively low tempera-tures (eg Cerny et al 2005 Antunes et al 2013)Therefore the Namivo pegmatite is probably derived byfractional crystallization of an S-type granite magmawhich resulted from partial melting of metamorphosed juve-nile sediments containing micas that carry most of the traceelements that define the signature of the LCT pegmatites(eg Dahl et al 1993)
The two main models for the internal evolution of peg-matites that dominated for more than a century are a) thefractional crystallization of a flux-bearing granitic melt fromthe margins to the center of the pegmatite (Cameron et al1949) b) the interactions of an aqueous fluid with graniticmelt (Jahns amp Burnham 1969 Jahns 1982) The recentmodel of constitutional zone refining combines aspects ofboth models and invokes the formation of a flux-enriched
Table 4 Electron microprobe analyses in wt of zoned gahnite from the outer intermediate zone (OIZ) of the Namivo granitic pegmatiteMozambique
Darker Zone Lighter Zone
Mean s Range Mean s Range
SnO2 036 050 0ndash097 658 281 151ndash998TiO2 008 008 0ndash021 065 034 008ndash105Nb2O5 001 002 0ndash006 018 007 007ndash029Ta2O5 001 004 0ndash010 015 013 0ndash033ZnO 3998 123 3810ndash4109 3339 318 3004ndash3848FeO 367 048 331ndash442 433 065 306ndash498MnO 032 004 028ndash040 039 006 032ndash048MgO 003 004 0ndash010 ndash ndash ndashAl2O3 5507 050 5436ndash5572 5337 070 5257ndash5443SiO2 003 003 0ndash007 008 010 0ndash025Total 9956 9912n 8 8Sn 0035 0048 0ndash0095 0648 0278 0149ndash0983Ti 0015 0015 0ndash0038 0120 0064 0015ndash0195Nb ndash 0003 0ndash0006 0021 0009 0009ndash0037Ta ndash 0002 0ndash0006 0009 0009 0ndash0021Zn 7226 0182 6890ndash7382 6086 0568 5482ndash6965Fe2thornt 0752 0103 0675ndash0913 0894 0135 0628ndash1029Mn 0066 0008 0057ndash0083 0082 0013 0066ndash0101Mg 0010 0015 0ndash0037 ndash ndash ndashAl 15887 0052 15805ndash15954 15526 0170 15375ndash15853Si 0007 0008 0ndash0018 0019 0025 0ndash0062P
23998 23405Fe3thorn 0064 0230Fe2thorn 0686 0658SnZn 0005 0007 0ndash0014 0106 0052 0021ndash0179ZnFe2thornt 961 143 768ndash1093 681 190 536ndash1109
n number of analysis Cation formula based on 32 atoms of oxygen Fe2thornt total Fe2thorn estimated
982 A M R Neiva
eschweizerbart_xxx
boundary layer of silicate liquid in advance of a crystal-lization front (London 2008 London amp Morgan 2012)
Lepidolite-subtype pegmatites are generally scarce(Cerny et al 2005) particularly the zoned ones In thesymmetrically zoned lepidolite-subtype pegmatites ofRozna and Dobra Voda Czech Republic micas (Cernyet al 1995) tourmaline (Selway et al 1999) and colum-bite-group minerals (Novak amp Cerny 1998) evolve fromthe outermost zone to the innermost zone following thecrystallization sequence The same was found in tourma-line from the zoned Lastovicky Dolnı Bory and Raddovicelepidolite-subtype pegmatite dikes in the Czeck Republic(Selway et al 1999)
In general beryl (Neiva amp Neiva 2005) feldsparsmicas and columbite-(Mn) (in this paper) from theNamivo lepidolite-subtype pegmatite record the progres-sive chemical evolution of the pegmatite from the wallzone to the core These minerals were produced by crystal-lization from a silicate melt rather than an aqueous fluidphase The slow cooling of melt shown by the magmaticcrystallization temperatures of feldspars cannot explain theincrease in grain-size of minerals from the wall zone to thecore but fluxes will be necessary to promote the change oftexture particularly a flux-rich hydrosilicate liquidaccording to the experimental evidence (London 2009)The constitutional zone refining model will be the best forthis zoned pegmatite and probably for all lepidolite-sub-type pegmatites because this model also produces a higherfinal concentration of incompatible components in a smal-ler volume of rock than fractional crystallization does(Morgan amp London 1999)
The core margin at the Rozna pegmatite contains K-feld-spar and quartz and the core consists mainly of quartz but it issurrounded and penetrated by a quartz-bearing albitethorn lepi-dolite complex which contains several minerals At theDobra Voda pegmatite the center of the dike is occupiedby the lepidolite unit containing albite and other minerals(Cerny et al 1995) At the Namivo pegmatite the coremargin consists of quartz and beryl and the core containsmainly quartz and spodumene but also albite lepidolite andother minerals The last-unit assemblages of primary miner-als in most of the highly fractionated LCT pegmatites are richin albite and commonly contain lepidolite or spodumene andmost of the other rare phases These units represent the lastmost fractionated liquid that can be derived by fractionalcrystallization of a crustal melt (London 2008)
The Namivo granitic pegmatite shows a significant dis-tinction from the other zoned lepidolite-subtype pegmatitesand LCT pegmatites except the Tanco petalite-subtypepegmatite in Canada because the lepidolite richest in SiLi and F FeMg-containing polylithionite and associatedcolumbite-(Mn) with the highest Ta(Ta thorn Nb) ratio tanta-lite-(Fe) and tantalite-(Mn) only occur in the outer inter-mediate zone These minerals usually form late in theconsolidation of pegmatites The lepidolite and polylithio-nite are probably derived from the disequilibrium crystal-lization of an undercooled melt Tantalite may reflect a localdecrease in Li and F that caused Ta precipitation
This paper contributes to a better understanding of theorigin and evolution of the rare zoned lepidolite-subtypepegmatites and shows that although the pegmatite evolvedfrom the wall zone to the core it presents an unusualassociation of lepidolite polylithionite and tantalite in theouter intermediate zone
Acknowledgments Thanks are due to JM Cotelo Neivaand MB Dias for the samples and information providedand to MR Machado Leite and MF Guimaraes for theuse of the electron microprobe facilities at the LaboratorioNacional de Energia e Geologia (LNEG) PortugalFinancial support was provided by the PortugueseGovernment for the project Pest-OECTEUI00732011of the Geosciences Centre through the PortugueseFoundation for Science and Technology I would like tothank D London WB Simmons and the associated editorE Widom for their constructive reviews of this manuscriptand M Prieto for his editorial work
References
Alfonso P Melgarejo JC Yusta I Velasco F (2003)
Geochemistry of feldspars and muscovite in granitic pegmatite
from the Cap de Creus field Catalonia Spain Can Mineral 41
103ndash116
Antunes IMHR Neiva AMR Ramos JMF Silva PB
Silva MMVG Corfu F (2013) Petrogenetic links between
lepidolite-subtype aplite-pegmatite aplite veins and associated
granites at Segura (central Portugal) Chemie der Erde in press
httpdxdoiorg101016jchemer20121203
Batchelor RA amp Kinnaird JA (1984) Gahnite compositions
compared Mineral Mag 48 425ndash430
Beurlen H Da Silva MRR Thomas R Soares DR Olivier P
(2008) Nb-Ta-(Ti-Sn) oxide mineral chemistry as tracer of rare-
element granitic pegmatite fractionation in the Borborema pro-
vince Northeastern Brazil Miner Deposita 43 207ndash228
Cameron EN Jahns RH McNair AH Page LR (1949)
Internal structure of granitic pegmatites Econ Geol
Monograph 2 115 p
Cerny P (1991a) Fertile granites of Precambrian rare-element
pegmatite fields is geochemistry controlled by tectonic setting
or source lithologies Precambrian Res 51 429ndash468
mdash (1991b) Rare-element granite pegmatites I Anatomy and inter-
nal evolution of pegmatite deposits Geoscience Canada 18
49ndash67
mdash (1992) Geochemical and petrogenetic features of mineralization
in rare-element granitic pegmatites in the light of current
research Applied Geochemistry 7 393ndash416
mdash (1994) Evolution of feldspars in granitic pegmatites in
lsquolsquoFeldspars and their Reactionsrsquorsquo I Parsons ed NATO
Advanced Study Institute Series C421 501ndash539
mdash (2005) The Tanco rare-element pegmatite deposit Manitoba
regional context internal anatomy and global comparisons in
lsquolsquoRare-element Geochemistry and Mineral Depositsrsquorsquo RL
Linnen amp IM Samson eds Geochemical Association of
Canada Short Course Notes St Catherines 17 127ndash158
Silicate and oxide minerals from a zoned granitic pegmatite 983
eschweizerbart_xxx
Cerny P amp Ercit TS (2005) The classification of granitic pegma-
tites revisited Can Mineral 43 2005ndash2026
Cerny P Meintzer RE Andersen AJ (1985) Extreme fractiona-
tion in rare-element granitic pegmatites selected examples of
data and mechanisms Can Mineral 23 381ndash421
Cerny P Goad BE Hawthorne FC Chapmann R (1986)
Fractionation trends of the Nb- and Ta-bearing oxide minerals
in the Greer Lake pegmatite granite and its pegmatite aureole
southeastern Manitoba Am Mineral 71 501ndash517
Cerny P Stanek J Novak M Baadsgaard H Rieder M
Ottolini L Kavalova M Chapman R (1995) Geochemical
and structural evolution of micas in the Rozna amp Dobra Voda
pegmatites Czech Republic Mineral Petrol 55 177ndash201
Cerny P Ercit TS Vanstone PJ (1998) Mineralogy and petrol-
ogy of the Tanco rare-element pegmatite deposit southeastern
Manitoba International Mineralogical Association 17th General
Meeting Toronto Field Guidebook B6
Cerny P Chapman R Ferreira K Smeds SA (2004)
Geochemistry of oxide minerals of Nb Ta Sn and Sb in
the Varutrask granitic pegmatite Sweden The case of an
lsquolsquoanomalousrsquorsquo columbitendashtantalite trend Am Mineral 89
505ndash518
Cerny P Masau M Goad BE Ferreira K (2005) The Greer
Lake leucogranite Manitoba and the origin of lepidolite-sub-
type granitic pegmatites Lithos 80 305ndash321
Cerny P Teertstra DK Chapman R Selway JB Hawthorne
FC Ferreira K Chackowsky LE Wang X-J Meintzer
RE (2012a) Extreme fractionation and deformation of the
leucogranite-pegmatite suite at Red Cross Lake Manitoba
Canada IV Mineralogy Can Mineral 50 1839ndash1875
Cerny P Halden NM Ferreira K Meintzer RE Brisbin WC
Chackowsky LE (2012b) Extreme fractionation and deforma-
tion of the leucogranite-pegmatite suite at Red Cross Lake
Manitoba Canada II Petrology of the leucogranites and peg-
matites Can Mineral 50 1807ndash1822
Dahl PS When DC Feldmann SG (1993) The systematics of
trace-element partitioning between coexisting muscovite and
biotite in metamorphic rocks from the Black Hills South
Dakota USA Geochim Cosmochim Acta 57 2487ndash2505
Dias MB amp Wilson WE (2000) The Alto Ligonha Pegmatites
Mozambique Mineral Record 31 459ndash497
Fleet ME (2003) Rock-Forming Minerals vol 3A Sheet silicates
micas The Geological Society London second edition chap 6
Lithium micas 651ndash690
Foord EE Cerny P Jackson LL Sherman DM Eby RK
(1995) Mineralogical and geochemical evolutions of micas
from miarolitic pegmatites of the anorogenic pikes-Peak
Batholith Colorado Mineral Petrol 55 1ndash26
Foster MD (1960) Interpretation of the composition of lithium
micas US Geol Surv Prof Paper 354-E 115ndash147
Fuhrman ML amp Lindsley DK (1988) Ternary-feldspar modeling
and thermometry Am Mineral 73 201ndash215
Gomes CL Castro P Alves C (1995) Caracterizacao das espi-
nelas zincıferas e do par ganite-nigerite no campo aplito-
pegmatıtico da Serra de Arga-Minho N de Portugal IV
Congresso Nacional de Geologia Resumos Alargados
Universidade do Porto Mem 4 629ndash633
Gordiyenko VV Ilyina AN Timochina LA Badamina EB
Stanek J (1996) Geochemical model of evolution of a pegma-
tite-forming ore-magmatic system of western Moravia Proc
Russ Mineral Soc 125 38ndash48 (in Russian)
Icenhower JP amp London D (1995) An experimental study for
element partitioning between biotite muscovite and coexisting
peraluminous granitic melt at 200 MPa (H2O) Am Mineral 80
1229ndash1251
Jahns RH (1982) Internal evolution of pegmatite bodies in lsquolsquoGranitic
Pegmatites in science and industryrsquorsquo P Cerny ed Mineralogical
Association of Canada Short Course Handbook 8 293ndash327
Jahns RH amp Burnham CW (1969) Experimental studies of
pegmatite genesis I A model for the derivation and crystal-
lization of granitic pegmatites Econ Geol 64 843ndash864
Jolliff BL Papike JJ Shearer CK (1987) Fractionation trends
in mica and tourmaline as indicators of pegmatite internal evo-
lution Bob Ingersoll pegmatite Black Hills South Dakota
USA GeochimCosmochim Acta 51 519ndash534
Kile DE amp Foord EE (1998) Micas from the Pikes Peak bath-
olith and its cogenetic granitic pegmatites Colorado optical
properties composition and correlation with pegmatite evolu-
tion Can Mineral 36 463ndash482
Linnen RL (1998) The solubility of Nb-Ta-Zr-Hf-W in granitic
melts with Li and Li thorn F constraints for mineralization in rare
metal granites and pegmatites Econ Geol 93 1013ndash1025
Linnen RL amp Cuney M (2005) Granite-related rare-element
deposits and experimental constraints on Ta-Nb-W-Sn-Zr-Hf
mineralization in lsquolsquoRare-element geochemistry and mineral
depositsrsquorsquo RL Linnen amp IM Samson eds Geochemical
Association of Canada Short Course Notes 17 45ndash68
London D (1990) Internal differentiation of rare-element pegmatites
a synthesis of recent research in lsquolsquoOre Bearing Granite Systems
Petrogenesis and Mineralizing Processesrsquorsquo HJ Stein amp JL
Hannah eds Geol Soc America Special Paper 246 35ndash50
mdash (2008) Pegmatites The Canadian Mineralogist Special
Publication 10 347 p
mdash (2009) The origin of primary textures in granitic pegmatites
Can Mineral 47 697ndash724
London D amp Morgan GB VI (2012) The pegmatite puzzle
Elements 8 263ndash268
London D Morgan GB VI Hervig RL (1989) Vapor-under-
saturated experiments in the system macusanite-H2O at 200
MPa and the internal differentiation of granitic pegmatites
Contrib Mineral Petrol 102 1ndash17
London D Morgan GB VI Paul KA Guttery BM (2012)
Internal evolution of miarolitic granitic pegmatites at the Little
Three mine Ramona California USA Can Mineral 50
1025ndash1054
Martins T Lima A Simmons WB Folster AU Noronha F
(2011) Geochemical fractionation of Nb-Ta oxides in Li-bear-
ing pegmatites from the Barroso-Alvao pegmatite field northern
Portugal Can Mineral 49 777ndash791
Monier G Charoy B Cuney M Ohnenstetter D Robert JL
(1987) Evolution spatiale et temporelle de la composition des
micas du granite albitique a topaze-lepidolite de Beauvoir
Geologie De La France 2ndash3 179ndash188
Monier G amp Robert JL (1986) Evolution of the miscibility gap
between muscovite and biotite solid solutions with increasing
lithium content an experimental study in the systems
K2OndashLi2OndashMgOndashAl2O3ndashSiO2ndashH2OndashHF at 600 C 2 kbar
PH2O comparison with natural lithium micas Mineral Mag
50 641ndash651
Morgan GBVI amp London D (1999) Crystallization of the little
three layered pegmatite-aplite dike Ramona District California
Contrib Mineral Petrol 136 310ndash330
984 A M R Neiva
eschweizerbart_xxx
Nabelek PI amp Russ-Nabelek C (1992) The generation and crys-
tallization conditions of the Proterozoic Harney Peak
Leucrogranite Black Hills South Dakota USA petrologic and
geochemical constraints Contrib Mineral Petrol 110
173ndash191
Nabelek PI Russ-Nabelek C Haeussler GT (1992) Stable
isotope evidence for the petrogenesis and fluid evolution in
the Proterozoic Harney Peak leucogranite Black Hills
South Dakota Geochim Cosmochim Acta 56 403ndash417
Neiva AMR amp Champness PE (1997) Nigerite and gahnite from
the granitic pegmatite veins of Cabanas Ponte de Lima northern
Portugal N Jb Mineral Mh 9 385ndash409
Neiva AMR Gomes MEP Ramos JMF Silva PB (2008)
Geochemistry of granitic aplite-pegmatite sills and their miner-
als from Arcozelo da Serra area (Gouveia central Portugal)
Eur J Mineral 20 465ndash485
Neiva AMR amp Neiva JMC (2005) Beryl from the granitic
pegmatite at Namivo Alto Ligonha Mozambique N Jb
Mineral Abh 181 173ndash182
Neiva AMR amp Ramos JMF (2010) Geochemistry of granitic
aplite-pegmatite sills and petrogenetic links with granites
Guarda-Belmonte area central Portugal Eur J Mineral 22
837ndash854
Neiva AMR Silva PB Ramos JMF (2012) Geochemistry of
granitic aplite-pegmatite veins and sills and their minerals from the
Sabugal area central Portugal N Jb Mineral Abh 189 49ndash74
Novak M amp Cerny P (1998) Niobium-tantalum oxide minerals
from complex granitic pegmatites in the Moldanubicum Czech
Republic primary versus secondary compositional trends Can
Mineral 36 659ndash672
Pesquera Perez A Torres-Ruiz J Gil PP Velilla N (1999)
Chemistry and genetic implications of tourmaline and Li-F-Cs
micas from the Valdeflores (Caceres Spain) Am Mineral 84
55ndash69
Rieder M Cavazzini G DrsquoYakonov YuS Frank-Kamenetskii
VA Gottardi G Guggenheim S Koval PV Muller G
Neiva AMR Radoslovich EW Robert J-L Sassi FP
Takeda H Weiss Z Wones DR (1999) Nomenclature of the
micas Mineral Mag 63 267ndash279
Roda Robles E Pesquera Perez A Velasco Roldan F Fontan F
(1999) The granitic pegmatites of the Fregeneda area
(Salamanca Spain) characteristics and petrogenesis Mineral
Mag 63 535ndash558
Roda Robles E Pesquera A Gil-Crespo PP Torres-Ruiz J
Fontan F (2005) Origin and internal evolution of the Li-F-
Be-P-bearing Pinilla de Fermoselle pegmatite (Central Iberian
Zone Zamora Spain) Am Mineral 90 1887ndash1899
Roda Robles E Pesquera Perez A Gil PP Torres-Ruiz J de
Parseval P (2006) Mineralogy and geochemistry of micas from
the Pinilla de Fermoselle pegmatite (Zamora Spain) Eur J
Mineral 18 369ndash377
Roda Robles E Keller P Pesquera Perez A Fontan F (2007)
Micas of the muscovite-lepidolite series from Karibib pegma-
tites Namibia Mineral Mag 71 41ndash62
Roda Robles E Pesquera A Gil-Crespo P Torres-Ruiz J
(2012) From granite to highly evolved pegmatite a case study
of the Pinilla de Fermoselle granite-pegmatite system (Zamora
Spain) Lithos 153 192ndash207
Selway JB Novak M Cerny P Hawthorne FC (1999)
Compositional evolution of tourmaline in lepidolite-subtype
pegmatites Eur J Mineral 11 569ndash584
Shearer CK Papike JJ Jolliff B (1992) Petrogenetic links
among granites and pegmatites in the Harney Peak rare-element
granite-pegmatite system Black Hills South Dakota Can
Mineral 30 785ndash809
Soares DR Hartmut B Ferreira ACM da Silva MRR
(2007) Chemical composition of gahnite and degree of peg-
matitic fractionation in the Borborema Pegmatitic Province
northeastern Brazil Anais Da Academ Bras Cien 79
395ndash404
Stewart DB (1978) Petrogenesis of lithium-rich pegmatites Am
Mineral 63 970ndash980
Tischendorff G Gattesmann B Forster H-J Trumbull RB
(1997) On Li-bearing micas estimating Li from electron
microprobe analyses and an improved diagram for graphical
representation Mineral Mag 61 809ndash834
Van Lichtervelde M Linnen RL Salvi S Beziat D (2006)
The role of metagabbro rafts on tantalum mineralization in the
Tanco granitic pegmatite Manitoba Can Mineral 44
625ndash644
Van Lichtervelde M Gregoire M Linnen RL Beziat D Salvi
S (2008) Trace element geochemistry by laser ablation ICP-
MS of micas associated with Ta mineralization in the Tanco
pegmatite Manitoba Canada Contrib Mineral Petrol 155
791ndash806
Vieira R Roda-Robles E Pesquera A Lima A (2011)
Chemical variation and significance of micas from the
Fregeneda-Almendra pegmatitic field (Central-Iberian Zone
Spain and Portugal) Am Mineral 96 637ndash645
Wen S amp Nekvasil H (1994) SOLVCALC an interactive gra-
phics program package for calculating ternary feldspar solvus
and two-feldspar geothermometry Comput Geosci 20
1025ndash1040
Wise MA (1995) Trace element chemistry of lithium-rich micas
from rare-element granitic pegmatites Mineral Petrol 55
203ndash215
Zasedatelev AM (1974) Possible accumulation of lithium in host
rocks of lithium pegmatite veins during old sedimentation pro-
cesses Doklady Acad Sci USSR Earth Sci Ser 218 196ndash198
(in Russian)
mdash (1977) Quantitative of metamorphic generation of rare-metal
pegmatites with lithium mineralization Doklady Acad Sci
USSR Earth Sci Ser 236 219ndash221 (in Russian)
Received 26 January 2013
Modified version received 21 May 2013
Accepted 23 July 2013
Silicate and oxide minerals from a zoned granitic pegmatite 985
eschweizerbart_xxx
Tab
le1
C
on
tin
ued
Inn
erIn
term
edia
teZ
on
e-
IIZ
bC
ore
-C
c
Lit
hM
us
Lep
Mu
slsquolsquo
Mix
edF
rsquorsquoL
epL
ith
Mu
slsquolsquo
Mix
edF
rsquorsquoL
epM
us
Lit
hM
us
Co
reR
imC
ore
Rim
Rim
Co
reR
imR
im
SiO
24
69
25
21
64
62
24
90
64
99
94
71
84
90
15
09
54
63
44
65
6T
iO2
00
3mdash
00
40
03
00
30
02
00
1mdash
mdashmdash
Al 2
O3
35
72
22
89
36
17
28
04
24
87
35
10
26
26
23
49
36
31
35
53
FeO
00
10
61
00
70
05
00
70
04
21
81
55
00
10
03
Mn
O0
55
05
80
43
12
92
24
06
01
09
13
30
14
01
4M
gO
mdashmdash
mdashmdash
mdashmdash
mdashmdash
mdashmdash
Zn
O
00
60
10
00
8
00
60
19
0
06
02
50
07
0
06
0
06
CaO
00
30
04
mdashmdash
00
10
01
00
10
01
mdashmdash
Li 2
O
06
55
42
02
54
52
47
90
93
45
15
07
04
70
79
Na 2
O0
41
00
80
49
02
60
16
04
10
13
01
00
55
05
4K
2O
97
99
78
10
16
96
69
76
94
49
33
90
89
97
99
0R
b2O
12
42
30
14
31
79
21
01
34
17
52
13
14
81
69
Cs 2
O0
16
08
7
00
60
62
05
00
11
07
70
79
01
40
12
F1
46
83
40
70
49
97
63
19
25
55
73
51
15
16
9H
2O
38
30
52
41
62
14
08
23
61
18
20
95
39
63
70
10
08
61
03
69
10
02
61
02
51
10
31
61
00
77
10
26
71
02
87
10
05
81
00
75
O
F0
61
35
00
29
21
03
20
08
12
33
30
90
48
07
1T
ota
l1
00
25
10
01
99
99
71
00
41
99
96
99
96
10
03
49
97
81
00
10
10
00
4
KR
b(w
t)7
23
96
44
94
26
44
83
96
15
3
Si
31
10
34
98
30
84
32
68
33
76
31
30
33
02
34
42
30
82
31
02
AlIV
08
90
05
02
09
16
07
32
06
24
08
70
06
98
05
58
09
18
08
98
PT
40
04
00
40
04
00
40
04
00
40
04
00
40
04
00
AlV
I1
90
01
30
71
92
91
47
01
35
51
87
51
38
71
31
21
92
81
89
2T
i0
00
1mdash
00
02
00
02
00
02
00
01
00
01
mdashmdash
mdashF
e2thorn
00
01
00
34
00
04
00
03
00
04
00
02
01
23
00
88
00
01
00
02
Mn
00
31
00
33
00
24
00
73
01
28
00
34
00
62
00
76
00
08
00
08
Mg
mdashmdash
mdashmdash
mdashmdash
mdashmdash
mdashmdash
Zn
00
03
00
05
00
04
00
03
00
09
00
03
00
12
00
03
00
03
00
03
Li
01
73
14
61
00
66
12
11
13
01
02
49
12
21
13
76
01
27
02
11
PR
21
12
84
20
32
76
28
02
16
28
12
86
20
72
12
Ca
00
02
00
03
mdashmdash
00
01
00
01
00
01
00
01
mdashmdash
Na
00
53
00
10
00
63
00
34
00
21
00
53
00
17
00
13
00
71
00
70
K0
82
80
83
70
86
50
82
10
84
10
79
90
80
20
78
20
84
60
84
1R
b0
05
30
09
90
06
10
07
70
09
10
05
70
07
60
09
20
06
30
07
2C
s0
00
50
02
50
00
10
01
80
01
40
00
30
02
20
02
30
00
40
00
3P
A0
94
09
70
99
09
50
97
09
10
92
09
10
98
09
9F
03
06
17
69
01
48
10
51
16
30
04
03
11
83
15
70
02
42
03
56
OH
1
69
40
23
11
85
20
94
90
37
01
59
70
81
70
43
01
75
81
64
4Z
on
esD
LD
D
LD
LL
D
DF
igu
res
Fig
s3
g
6i
jk
Fig
s3
h
6l
Fig
s3
i6
m
nF
igs
3j
6o
p
OIZ
IIZ
aII
Zb
Cc
asin
Fig
2Z
inndash
zin
nw
ald
ite
Lep
ndashle
pid
oli
teF
ndashfo
rmP
olndash
po
lyli
thio
nit
eL
ith
Mu
sndash
lith
ian
mu
sco
vit
eM
us
ndashm
usc
ov
ite
Lndash
ligh
ter
zon
eD
ndashd
ark
erzo
ne
D
-th
ed
ark
estzo
ne
L
-th
eli
gh
test
zon
ein
BS
Eim
ages
BaO
isb
elo
wth
ed
etec
tio
nli
mit
Cal
cula
ted
nu
mb
ero
fio
ns
on
the
bas
iso
f1
2o
xy
genthorn
Fat
om
sL
i 2O
v
alu
esca
lcu
late
dfr
om
equ
atio
ns
of
Tis
chen
do
rff
eta
l
(19
97
)O
H
-ca
lcu
late
db
yd
iffe
ren
ceto
20
00
H
2O
-ca
lcu
late
db
yst
oic
hio
met
ry
Silicate and oxide minerals from a zoned granitic pegmatite 971
eschweizerbart_xxx
analytical totals are not good The analyzed lsquolsquomixedformsrsquorsquo are distinguished in backscattered-electron (BSE)images and chemically (Fig 3b d d1 e f f1 h i andFig 4) The chemical distinction between lsquolsquomixed formrsquorsquoand lepidolite from the OIZ (Fig 4) is clear in Fig 3bwhere lepidolite is darker than lsquolsquomixed formrsquorsquo because theformer has less Fe and Mn than the latter (Table 1) and inFig 3f f1 and 3h for micas from the IIZa and IIZbrespectively where lepidolite is lighter than lsquolsquomixedformrsquorsquo because the former has more Fe2thorn and Mn oronly more Mn than the latter (Table 1) The lsquolsquomixedformsrsquorsquo analyzed are distinguished in the BSE imagesfrom the lepidolite that falls in its fields in the Fig 4The fields of lepidolite composition in Foster (1960) arelarger than the field for lepidolite from the trilithionite tothe polylithionite (Rieder et al 1999) According to Fleet(2003) only a few lepidolite compositions plot on thetrilithionite-polylithionite join In general lepidolite hashigher Si Licalc Rb Cs F contents and lower AlVI andOH contents than lsquolsquomixed formrsquorsquo (Table 1 Fig4)lsquolsquoMixed formrsquorsquo is also clearly distinguished fromlithian muscovite in OIZ IIZa IIZb and Cc in BSEimages (Fig 3d d1 e f i) and chemically (Table 1 Fig4) as it generally has higher Si Licalc Rb Cs F contentsand lower AlVI and OH contents than lithian muscovite
Two distinct trends are defined in Fig 4 One trendconsists of Al-poorer micas which are zinnwaldite
lepidolite and FeMg-containing polylithionite from theOIZ A hiatus occurs between zinnwaldite and lepidolitebut the zinnwaldite series is continuous with the field oflepidolite at the high Li content (Fleet 2003) The othertrend consists of Al-richer micas (muscovite lithian mus-covite and lsquolsquomixed formrsquorsquo from the OIZ IIZa IIZb and Ccand also lepidolite from most of those zones except fromthe OIZ) There is a gap between lithian muscovite and thelsquolsquomixed formrsquorsquo which may be explained by a hiatus inmica stability (eg Jolliff et al 1987) but a solid solutionbetween dioctahedral and trioctahedral micas has beenindicated experimentally (Monier amp Robert 1986) whileother authors have shown that the octahedral site occu-pancy ranges continuously from muscovite to lepidolite(eg Roda Robles et al 2005 Van Lichterveld et al2008 Vieira et al 2011) Most lithian muscovites andlsquolsquomixed formrsquorsquo from the OIZ are richer in Fe2thornthornMg thornMn than those from the other zones due to their higherFe2thorn and Mg contents (Fig 4 Table 1)
In the Al-poorer micas from the OIZ ranging from zinn-waldite to lepidolite and FeMg-containing polylithionite(Fig 4) (AlIV thorn AlVI) Fe2thorn Mg Ti Mn and Zn contentsdecrease and Si and Licalccontents increase (Table 1) In theAl-richer micas ranging from muscovite to lithian muscoviteand lsquolsquomixed formrsquorsquo from the OIZ IIZa IIZb and Cc and alsoto lepidolite from most of those zones except from the OIZ(AlIV thorn AlVI) AlVI and OH contents and KRb ratio
Fig 4 Plots of micas from the Namivo granitic pegmatite Mozambique in the LindashR2thornndashR3thornthorn Ti diagram according to the classification ofFoster (1960) slightly modified (Rieder et al 1999) with R3thorn frac14 AlVI R2thorn frac14 (Fe2thornt thorn Mn2thornthorn Mg) showing the variety of micacompositions Two trends are defined one for Al-poorer micas (zinnwaldite lepidolite and FeMg-containing polylithionite) from theOIZ another for Al-richer micas (muscovite lithian muscovite lsquolsquomixed formrsquorsquo and lepidolite) from all zones except lepidolite from the OIZOIZ IIZa IIZb and Cc as in Fig 2
972 A M R Neiva
eschweizerbart_xxx
generally decrease and Si Licalc Rb Cs and F contentsgenerally increase (Table 1)
42 Main substitution mechanisms
The 2Si thorn Li 3Altotal mechanism operates in the diocta-hedral micas (muscovite and lithian muscovite) (Fig 5a b)whereas the 3LiVI AlVIthorn 2ampVI (amp represents a vacancy)operates in the trioctahedral micas (lsquolsquomixed formrsquorsquo lepido-lite zinnwaldite and FeMg-containing polylithionite) (Fig5c d) which agrees with findings for micas from the Tancopegmatite (Van Lichtervelde et al 2008)
43 Textures and chemical compositions of zoned micacrystals
Backscattered-electron images combined with quantita-tive spot electron-microprobe analyses made it possibleto distinguish different micas in the Namivo graniticpegmatite Similar textural aspects and geochemicalobservations were found between some Al-richer micasfrom the OIZ IIZa IIZb and Cc Some selected zonedcrystals are documented (Table 1 Fig 3 and 6) In theOIZ lepidolite penetrates zinnwaldite along cleavagesand partially surrounds it and the contacts are sharp(Fig 3a) A chemical gap occurs between zinnwalditeand lepidolite compositions (Fig 6a b) Lepidolite withhigher Si Licalc F contents similar KRb value andlower (AlIV thorn AlVI) Ti Fe2thorn Mg (Fe2thornthorn Mn thorn Mg)Zn and OH contents (Table 1) replaces zinnwaldite Athin lepidolite rim partially surrounds lsquolsquomixed formrsquorsquoand the contact is sharp (Fig 3b) The lepidolite rimhas higher Si Mg Licalc Rb F contents and lowerAlVI Ti Fe2thorn Mn Na and OH contents and KRb ratiothan the lsquolsquomixed formrsquorsquo core (Table 1) The lepidoliterim is an Al-poorer mica whereas the lsquolsquomixed formrsquorsquocore is an Al-richer mica (Fig 4) The lepidolite rimcorresponds to an overgrowth The FeMg-containingpolylithionite partially surrounds and penetrates lepido-lite along cleavages and shows well defined contacts(Fig 3c) Both contain rutile cassiterite and columbi-tendashtantalite inclusions A continuous chemical evolutiontakes place from lepidolite to FeMg-containing poly-lithionite (Figs 4 6c) The latter has higher Si LicalcRb contents and lower AlVI Ti Fe2thorn Mn Mg Zn Nacontents and KRb ratio (Table 1) and replaces lepido-lite A lithian muscovite rim with rare FeMg-containingpolylithionite surrounds the lsquolsquomixed formrsquorsquo core and thispolylithionite penetrated lithian muscovite (Fig 3d)The contact between the lithian muscovite rim andlsquolsquomixed formrsquorsquo core is irregular suggesting disequili-brium or at a cleavage (Fig 3d d1) Two linear trendsone for the lithian muscovite rim and another for thelsquolsquomixed formrsquorsquo core are defined in the (Fe2thornthornMnthornMg)vs (AlIV thornAlVI) diagram (Fig 6d) The FeMg-contain-ing polylithionite rim does not belong to any of thesetrends and plots outside this diagram because it is an Al-poorer mica whereas the others are Al-richer micas
(Fig 4) The lithian muscovite rim has higher AlVI(AlIV thorn AlVI) OH contents and KRb ratio and lowerMg (Fe2thornthorn Mn thorn Mg) Licalc Rb F contents than thelsquolsquomixed formrsquorsquo core (Table 1 Fig 6d) The crystal isreversely zoned The FeMg-containing polylithioniterim has higher Si Licalc F contents and lower AlVI(AlIV thorn AlVI) Fe2thorn Mn (Fe2thornthorn Mn thorn Mg) Na andOH contents than the lsquolsquomixed formrsquorsquo core and lithianmuscovite rim (Table 1) and replaces lithian muscovite
In the IIZa some zoned crystals have a lithian muscovitecore and a lsquolsquomixed formrsquorsquo rim and the contacts are gradual(Fig 3e) A small discontinuity occurs in the trends fromthe lithian muscovite core to lsquolsquomixed formrsquorsquo rim in the(Fe2thornthorn Mn thorn Mg) vs (AlIV thorn AlVI) and Rb2O vs KRb(Fig 6e f) The lsquolsquomixed formrsquorsquo rim has higher Si Fe2thornMn (Fe2thornthornMn thornMg) Licalc K Rb Cs F contents andlower AlVI (AlIVthornAlVI) Na OH contents and KRb ratiothan the lithian muscovite core (Table 1 Fig 6e f) indi-cating progressive zoning Similar textural relationshipsand chemical evolutions were found in other zoned crystalsfrom the OIZ IIZb and Cc In another crystal from theIIZa lithian muscovite partially surrounds lsquolsquomixed formrsquorsquointergrown with lepidolite Lithian muscovite also partiallysurrounds muscovite (Fig 3f) The contacts betweenlsquolsquomixed formrsquorsquo and lepidolite and also between muscoviteand lithian muscovite are gradual (Fig 3f f1) whereasthey are well defined for muscovite withlsquolsquomixed formrsquorsquoand lepidolite (Fig 3f f1) The crystal has a lsquolsquomixed formrsquorsquoand lepidolite core and a partial rim of muscovite andlithian muscovite The lsquolsquomixed formrsquorsquo core evolved tolepidolite core as the Si Fe2thorn Mn (Fe2thornthorn Mn thorn Mg)Licalc K Rb Cs and F contents increase and the (AlIV thornAlVI) and KRb ratio decrease (Table 1 Fig 6g h) The SiFe2thorn Mn (Fe2thornthorn Mn thorn Mg) Licalc Rb and F contentsincrease and the (AlIV thorn AlVI) and KRb ratio decreasefrom the muscovite rim to the lithian muscovite rim (Table1 Fig 6g h) suggesting that the former evolved to thelatter The muscovite rim has higher AlVI (AlIV thorn AlVI)Na OH contents and KRb ratio and lower Si Fe2thorn Mn(Fe2thornthornMn thornMg) Zn Licalc Rb and F contents than thelsquolsquomixed formrsquorsquo core and lepidolite core (Table 1 Fig 6gh) Muscovite was probably reversely formed and evolvedafterwards to lithian muscovite
In the IIZb some crystals have a lithian muscovite coreand a thinner lepidolite rim (Fig 3g) and others show asmall muscovite core and a larger rim of lsquolsquomixed formrsquorsquointergrown with lepidolite (Fig 3h) The contacts betweenthe cores and rims are well defined There are increases inthe Si Mn (Fe2thornthorn Mn thorn Mg) Licalc Rb and F contentsand decreases in the AlVI (AlIVthornAlVI) and KRb ratio fromthe lsquolsquomixed formrsquorsquo rim to the intergrown lepidolite rim(Table 1 Figs 3h 6l) suggesting that the former evolvedto the latter as also found in IIZa and Cc In both crystalsthe rim compositions have higher Si (Fe2thornthorn Mn thorn Mg)Licalc Rb Cs F contents and lower AlVI (AlIVthorn AlVI) Naand OH contents and KRb ratio than the core (Table 1 Figs3g 6i j k 3h 6l) A compositional gap occurs between coreand rim in the diagrams for both crystals (Fig 6i j k l)suggesting that both rims correspond to overgrowths and no
Silicate and oxide minerals from a zoned granitic pegmatite 973
eschweizerbart_xxx
diffuse reequilibration took place in any crystal as thecontacts between core and rim are sharp
In the Cc lithian muscovite is surrounded and pene-trated by lsquolsquomixed formrsquorsquo showing well defined contacts(Fig 3i) The lsquolsquomixed formrsquorsquo has higher Si Fe2thorn Mn(Fe2thornthorn Mn thorn Mg) Licalc Rb Cs F contents and lowerAlVI (AlIV thorn AlVI) Na OH contents and KRb ratio thanthe lithian muscovite (Table 1 Fig 6m n) and a composi-tional gap occurs between both micas suggesting thatlsquolsquomixed formrsquorsquo replaced lithian muscovite In rare crystalsa small lepidolite core is surrounded by a large muscoviterim containing K-feldspar inclusions The contact betweenthe core and rim is sharp (Fig 3j) A thin partial rim oflithian muscovite surrounds muscovite and the contact isgradual The muscovite rim has higher AlVI (AlIVthornAlVI)Na K OH contents and a greater KRb value and lower SiFe2thorn Mn Licalc Rb Cs and F contents than the lepidolitecore (Table 1 Fig 6o p) and a compositional gap occursbetween them (Fig 6o p) indicating that either muscoviteforms an overgrowth or it is reversely formed From themuscovite rim to the lithian muscovite rim the Si Licalc
Rb F contents increase whereas the AlVI (AlIV thorn AlVI)and OH contents and KRb ratio decrease (Table 1 Fig 6op) suggesting that muscovite evolved to lithian muscoviteas also found in IIZa and IIZb
44 Evolution of mica compositions within each zoneand from the outer intermediate zone to the core of theNamivo granitic pegmatite
The KRb ratio is taken as the best fractionation index inmicas (eg Cerny et al 1985 Foord et al 1995 Wise1995 Pesquera et al 1999 Roda Robles et al 2006 2007)It is hard to establish trends in the evolution of mica com-position from muscovite and lithian muscovite to lsquolsquomixedformrsquorsquo and lepidolite within each zone because the KRbratio shows some partial overlapping particularly betweenthe lithian muscovite and lsquolsquomixed formrsquorsquo and also betweenthe latter and lepidolite However an evolution from mus-covites to lepidolite (Al-richer mica Fig 4) is clearer (Fig7) In general in IIZa IIZb and Cc the Si Licalc Rb Cs and
Fig 5 The main substitutions in micas from the Namivo granitic pegmatite Mozambique a b SiIVthorn LiVI versus AlIVthornAlVI showing the 2SithornLi 3Altotal substitution mechanism operating in dioctahedral micas (Mu muscovite and Lith mu lithian muscovite) c d AlVI thornamp VI
versus LiVI (where amp represents a vacancy) and showing the 3LiVI AlVI thorn 2 amp VI substitution mechanism operating in trioctahedral micas(Mix f ndashlsquolsquomixed formrsquorsquo Lep lepidolite Zin zinnwaldite and Pol-FeMg-containing polylithionite) OIZ IIZa IIZb and Cc as in Fig 2
974 A M R Neiva
eschweizerbart_xxx
F contents tend to increase and the (AlIV thorn AlVI) AlVI
contents and KRb ratio tend to decrease from muscoviteto lepidolite (Table 1 Fig 7) This sequence is consistentbut rarely in the Cc lepidolite is rimmed by muscovite (Fig3j) But in the OIZ the evolution stops in lsquolsquomixed formrsquorsquoparticularly shown by the large range of the KRb ratiowhich mainly overlaps that of lepidolite from this zone(Fig 7) because this lepidolite is an Al-poorer mica whereasthe others are Al-richer micas (Fig 4)
In the OIZ the lepidolite has more Si Licalc and F andless (AlIV thorn AlVI) Ti Fe2thorn Mn Mg and Zn than zinn-waldite (Table 1) but it has larger ranges of Rb and KRbratio than zinnwaldite (Fig 7) The FeMg-containingpolylithionite is the richest mica in Si Licalc and thepoorest in (AlIV thorn AlVI) (Table 1) But at this zone scalethe polylithionite has Rb Cs contents and KRb ratiowithin the ranges for lepidolite and close to those of zinn-waldite (Fig 7)
Fig 6 Variation diagrams of micas from selected zoned crystals from the zones of the Namivo granitic pegmatite Mozambique to showtheir relationships lith musc lithian muscovite OIZ IIZa IIZb and Cc an in Fig 2
Silicate and oxide minerals from a zoned granitic pegmatite 975
eschweizerbart_xxx
From the OIZ to IIZa IIZb and Cc muscovite and lithianmuscovite generally show increases in the Si Licalc F and Rbcontents and decreases in the Fe2thorn and Mg contents and KRb ratio but the Mg content is very low in these micas fromthe IIZa IIZb and Cc (Table 1 Fig 7a) The lsquolsquomixed formrsquorsquoshows increases in the Si Licalc F Rb Cs contents anddecreases in the (AlIV thorn AlVI) and Mg contents and KRbratio but the Mg content is very low in this mica from theIIZb and Cc (Table 1 Fig 7b c) The lepidolite shows anincrease in the Si Licalc F Rb and Cs contents and a decreasein the KRb ratio from the IIZa to the IIZb and Cc (Table 1Fig 7d e) Furthermore the lepidolite from the OIZ has thelowest (AlIV thorn AlVI) AlVI and OH contents the highest SiFe2thorn Licalcand F contents and KRb ratio and the lowest Rband Cs contents compared to lepidolite from the other zones(Table 1 Fig 7d e)
5 Feldspars
Selected chemical analyses of albite and K-feldspar fromfive zones of the Namivo granitic pegmatite are given inTable 2 Strontium is the most abundant trace element inalbite (eg Cerny 1994) Anorthite and Sr contents and SrCa ratio of albite decrease from the WZ to the Cc (Fig 8Table 2) Rubidium is the most abundant trace element inK-feldspar followed by Cs in IIZa IIZb and Cc In gen-eral K Rb and Cs contents of K-feldspar increase and KRb and KCs values decrease from the WZ to the Cc (Table2 Fig 9)
The program SOLVCALC 20 (Wen amp Nekvasil 1994)using the Margules model Fuhrman amp Lindsley (1988) wasapplied for the purpose of thermometry The pairing ofplagioclase cores with the K-feldspars average of eachsample was used to estimate the crystallization temperaturesof primary magmatic feldspars They are 405 C (WZ)406ndash340 C (OIZ) 390ndash335 C (IIZa) 347ndash306 C (IIZb)and 333ndash289 C (Cc) at 3 kbar The metamorphic environ-ment of rare-element-Li granitic pegmatites is one of lowpressure 2ndash4 kbar (Cerny amp Ercit 2005) In general thedifference between the maximum and minimum calculatedtemperatures at 2 3 and 4 kbar for the same feldspar pairfrom the Namivo pegmatite is lower than 40 C The tem-perature decreases from the wall zone (WZ) to the core(Cc) A similar temperature behavior of feldspars wasfound in the pegmatite-aplite dike USA (Morgan ampLondon 1999)
6 Other silicates
Tourmaline of schorl composition was only found inthe OIZ (Table 2) because there was not enough Feand Mg for schorl to precipitate in the other zonesSpodumene only occurs in the Cc and its compositionis nearly pure (Table 2)
7 Columbite-tantalite
Representative chemical analyses of columbitendashtantalitefrom the Namivo granitic pegmatite are given in Table 3and plotted in the columbite quadrilateral (Fig 10a)Most crystals are unzoned but zoned crystals with dar-ker and lighter zones in BSE images are from the Cc Thelighter zone of columbite-(Mn) has higher Ta contentTa(Ta thorn Nb) and Mn(Mn thorn Fe) values and lower Nbcontent than the darker zone (Fig 10a b) The crystals ofthe columbitendashtantalite minerals are low in W Sn and Tiimpurities (Table 3)
The main trend starts from the columbite-(Mn) of theOIZ towards the more Mn-enriched and slightly Ta-enriched columbite-(Mn) from the IIZa and Cc The high-est Ta(Ta thorn Nb) values belong to the lighter zone ofcolumbite-(Mn) with Mn(Mn thorn Fe) frac14 10 from the CcThe richest columbite-(Mn) in Ta(TathornNb) and composi-tions of tantalite-(Fe) and tantalite-(Mn) were only foundin the OIZ (Fig 10a) and are associated with lepidolite andpolylithionite (Fig 3c)
8 Gahnite
Gahnite was rarely found in the OIZ and shows a darkerzone that partially surrounds a lighter zone in a BSE image(Fig 11a) The darker zone has a higher Zn content andlower Sn Ti Nb Ta Mn contents and SnZn value than thelighter zone (Table 4 Fig 11b c) These gahnite composi-tions fall within the igneous field of Batchelor amp Kinnaird(1984) The darker zone is closer in composition to thepure gahnite (Zn8Al16O32) than the lighter zone whichcontains up to 0983 apfu Sn 0195 apfu Ti 1029 apfutotal Fe2thorn 0101 apfu Mn (Table 4) and consequently hasa composition distinct from nigerite In general both thedarker and lighter zones have higher Sn Ti and Fe contentsthan gahnite from the granitic pegmatites of Nigeria(Batchelor amp Kinnaird 1984) Arga northern Portugal(Gomes et al 1995) and Cabanas northern Portugal(Neiva amp Champness 1997) Borborema province north-eastern Brazil (Soares et al 2007) The Zn=Fe2thornt values ofthe darker and lighter zones of gahnite from Namivo arelower than those reported in Neiva amp Champness (1997)and Soares et al (2007)
9 Discussion and conclusions
91 Evolution of micas in the zoned pegmatite
In general individual mica crystals show varying patternsand compositional zoning involving several elementsmainly Si AlVI (AlIV thorn AlVI) Fe2thorn Mn (Fe2thornthorn Mn thornMg) Licalc Rb Cs F and OH and the KRb ratioProgressively zoned crystals from the IIZa show grada-tional contacts between a lithian muscovite core and a
976 A M R Neiva
eschweizerbart_xxx
lsquolsquomixed formrsquorsquo rim (Figs 3e 6e f) and the zoning patternscorrespond to fractionation trends and probably reflect adrop in temperature during the crystallization of the grani-tic pegmatite melt Progressively zoned crystals also occurin OIZ IIZb and Cc Some crystals are reversely zonedwith a) a lsquolsquomixed formrsquorsquo core and a lithian muscovite rimfrom the OIZ (Figs 3d d1 6d) b) a core consisting oflsquolsquomixed formrsquorsquo and lepidolite and a rim of muscovite andlithian muscovite from the IIZa (Figs 3f f1 6g h) c) alepidolite core and a muscovite and lithian muscovite rimfrom the Cc (Figs 3j 6o p) which may be explained bythe hypothesis of oscillations in the compositions of themelt from which they grew alternating between an Li-enriched boundary layer and a bulk melt that is less frac-tionated The muscovite evolved to lithian muscovite inIIZa and Cc (Figs 3f 6g h 3j 6o p) Replacements (Figs3a 6a b 3c 6c 3i 6m n Table 1) occur in OIZ and Ccand overgrowths (Figs 3b g 6i j k 3h 6l Table 1) occurin OIZ and IIZb as found in BSE images
Muscovite evolved to lithian muscovite as observed inOIZ IIZa IIZb and Cc (Figs 3f 6g h 3j 6o p Table 1)Lithian muscovite evolved to lsquolsquomixed formrsquorsquo in OIZ IIZaIIZb and Cc (Figs 3e 6e f Table 1) and lsquolsquomixed formrsquorsquoevolved to lepidolite in IIZa IIZb and Cc (Figs 3f f1 6gh 3h 6l Table 1) All these evolutions are due to fractionalcrystallization
In the OIZ lepidolite has more Si Licalcand F butsimilar KRb to that of zinnwaldite and replaces it (Figs
3a 6a b 7d Table 1) An FeMg-containing polylithionitehas higher Si Licalcand Rb contents and a smaller KRbratio than the lepidolite that it replaces (Figs 3c 6c Table1) and a continuous chemical evolution from lepidolite topolylithionite is shown
The trends for major and trace elements of micas withineach zone are difficult to define due to some partial over-lapping but a progressive evolution from muscovite to lithianmuscovite lsquolsquomixed formrsquorsquo and lepidolite in IIZa IIZb and Ccis mainly shown by an increase in the Si Licalc F Rb and Cscontents and a decrease in the KRb ratio and this is simi-larly shown in the OIZ from muscovite to lsquolsquomixed formrsquorsquo(Table 1 Fig 7) In the OIZ Si and Licalccontents increaseprogressively from zinnwaldite to lepidolite and FeMg-containing polylithionite but a gap occurs between zinnwal-dite and lepidolite (Table 1 Fig 4) whereas a continuousevolution from lepidolite to polylithionite is observed TheKRb ratios of zinnwaldite and polylithionite are within therange of that of lepidolite (Fig 7d e)
Each Al-richer mica (muscovite lithian muscovite andlsquolsquomixed formrsquorsquo) exhibits an evolution from the OIZ to theIIZa and then to the IIZb and Cc particularly shown by anincrease in the Si Licalc F and Rb contents and adecrease in the KRb ratio but also an increase in theCs content in the lsquolsquomixed formrsquorsquo (Table 1 Fig 7) Theseelements and ratio have been used as petrogenetic indi-cators of evolution in micas from pegmatites (eg Cernyet al 2005 Roda Robles et al 2006 2007 Vieira et al
Fig 7 Plot of some variation diagrams of micas from the OIZ IIZa IIZb and Cc of the Namivo granitic pegmatite Mozambique showingthat the Rb2O and Cs2O contents increase and the KRb ratio decreases for micas from the OIZ to the Cc OIZ IIZa IIZb and Cc as in Fig 2
Silicate and oxide minerals from a zoned granitic pegmatite 977
eschweizerbart_xxx
Tab
le2
R
epre
sen
tati
ve
elec
tro
nm
icro
pro
be
anal
yse
sin
wt
o
ffe
ldsp
ars
sch
orl
and
spo
du
men
efr
om
the
Nam
ivo
gra
nit
icp
egm
atit
eM
oza
mb
iqu
e
Alb
ite
K-f
eld
spar
Sch
orl
Sp
od
um
ene
Zo
nes
WZ
OIZ
IIZ
aII
Zb
Cc
Zo
nes
WZ
OIZ
IIZ
aII
Zb
Cc
Zo
nes
OIZ
Zo
ne
Cc
SiO
26
75
76
78
86
87
06
84
76
84
1S
iO2
65
10
65
55
65
46
64
96
64
72
SiO
23
52
0S
iO2
64
65
TiO
20
02
mdash0
02
mdashmdash
TiO
2mdash
00
1mdash
mdashmdash
TiO
20
35
Al 2
O3
27
20
Al 2
O3
20
25
19
74
19
67
19
88
19
97
Al 2
O3
18
96
18
23
18
31
18
24
18
05
B2O
3
10
28
Fe 2
O3
00
6F
e 2O
3mdash
mdashmdash
mdash0
10
Fe 2
O3
mdash0
02
mdash0
03
mdashA
l 2O
33
17
2M
nO
01
3M
nO
00
6mdash
mdashmdash
mdashM
nO
mdash0
03
00
3mdash
mdashF
eO1
35
2M
gO
01
8M
gO
mdashmdash
mdashmdash
mdashM
gO
00
10
01
00
5mdash
mdashM
nO
03
3N
a 2O
01
9C
aO1
04
08
00
56
03
70
32
CaO
00
10
01
00
60
01
00
2M
gO
22
8L
i 2O
8
05
Na 2
O1
06
11
12
01
12
11
13
41
13
4N
a 2O
06
50
58
04
10
59
03
8C
aO0
23
To
tal
10
04
6K
2O
00
50
17
00
60
14
01
0K
2O
14
72
14
75
15
67
15
01
15
74
Li 2
O
02
2S
rO0
72
05
00
24
01
1mdash
Rb
2O
00
90
20
03
00
59
09
0N
a 2O
22
8S
i1
99
7P
2O
50
01
00
4mdash
mdashmdash
Cs 2
O
00
6
00
60
09
01
80
20
K2O
00
1A
lIV0
00
3T
ota
l1
00
33
10
03
31
00
46
10
03
11
00
24
P2O
5mdash
00
3mdash
mdashmdash
H2O
3
18
P2
00
To
tal
99
60
99
48
10
03
89
96
11
00
01
F0
78
AlV
I0
98
7S
rC
a(w
t)0
81
07
40
50
03
50
Cl
mdashF
e3thorn
00
01
KR
b(w
t)153
68
48
23
16
Sum
1003
8P
09
9S
i1
18
23
11
87
91
19
58
11
93
21
19
21
KC
s(w
t)4
07
20
41
63
73
69
O
F0
33
Li
10
00
P0
00
10
00
6mdash
mdashmdash
To
tal
10
00
5M
n0
00
3T
i0
00
3mdash
00
03
mdashmdash
Si
11
98
61
20
88
12
04
11
20
45
12
03
3M
g0
00
8A
l4
17
64
07
14
03
54
08
34
10
1P
mdash0
00
5mdash
mdashmdash
TS
i5
95
2N
a0
01
2F
e3thorn
mdashmdash
mdashmdash
00
13
Ti
mdash0
00
1mdash
mdashmdash
Al
00
48
P1
02
Mn
00
09
mdashmdash
mdashmdash
Al
41
14
39
62
39
70
39
86
39
55
B3
00
0M
gmdash
mdashmdash
mdashmdash
Fe3thorn
mdash0
00
3mdash
00
04
mdashZ
Al
60
00
Ca
01
95
01
50
01
04
00
69
00
60
Mn
mdash0
00
50
00
5mdash
mdashY
Al
02
74
Sr
00
73
00
51
00
24
00
11
mdashM
g0
00
30
00
30
01
4mdash
mdashT
i0
04
5N
a3
59
93
80
03
78
33
83
23
83
1C
a0
00
20
00
20
01
20
00
20
00
4M
g0
57
5K
00
11
00
38
00
13
00
31
00
22
Na
02
32
02
07
01
46
02
12
01
37
Mn
00
47
K3
45
73
47
03
67
73
55
03
73
3F
e2thorn
19
12
Z1
60
01
59
61
60
01
60
11
60
4R
b0
01
10
02
40
03
50
07
00
10
8L
i0
14
8X
38
94
04
39
33
94
39
1C
s0
00
20
00
50
00
70
01
40
01
6P
Y3
00
0m
ole
s
XC
a0
04
2A
n5
13
82
71
71
5Z
16
10
16
06
16
01
16
03
15
99
Na
07
47
Ab
94
69
53
97
09
75
97
9X
37
13
72
39
03
85
40
0K
00
02
Or
03
09
03
08
06
mo
les
amp
02
09
An
01
01
03
01
01
Ab
63
56
38
56
35
OH
35
83
Or
93
69
43
95
99
43
96
4F
04
17
Cl
mdash
WZ
ndashw
allzo
ne
OIZ
ndasho
ute
rin
term
edia
tezo
ne
IIZ
aan
dII
Zb
ndashin
ner
inte
rmed
iate
zon
esC
cndash
core
asin
Fig
2B
aOis
bel
ow
the
det
ecti
on
lim
itin
bo
thfe
ldsp
ars
Cs 2
Ofrac14
00
3w
tin
the
K-
feld
spar
fro
mth
eW
Z
mdashN
ot
det
ecte
d
Nu
mb
ero
fio
ns
on
the
bas
iso
f3
2o
xy
gen
sfo
ral
bit
ean
dK
-fel
dsp
ar
31
anio
ns
(O
OH
F
)fo
rsc
ho
rlan
d6
ox
yg
ens
for
spo
du
men
e
-A
mo
un
tin
ferr
edfr
om
con
sid
erat
ion
so
fst
oic
hio
met
ry
978 A M R Neiva
eschweizerbart_xxx
2011) Lepidolite from the OIZ is an Al-poorer mica (Fig4) and has the highest Si Licalcand F contents (Table 1)indicating that an evolution cannot be shown from thislepidolite to lepidolites from the other zones which areAl-richer micas (Fig 4) However there is a regulardecrease in the KRb ratio and a progressive increase inthe Rb and Cs contents from lepidolite of the OIZ tolepidolite of IIZa IIZb and Cc (Fig 7) which indicatesthat the KRb ratio and Rb and Cs contents must not beconsidered alone to show fractional crystallization in
lepidolites particularly if some are Al-richer micas andothers Al-poorer micas The high Licalcand F contents oflepidolite from the OIZ did not decrease its KRb ratioSuch an effect is considered to have taken place in lepi-dolite (an Al-richer mica) from the wall zone of the Tancopegmatite Manitoba Canada (Van Lichtervelde et al2008) An evolution from the lepidolite of the IIZa to thatof the Cc is generally shown by the increasing Si LicalcF Rb Cs contents and a decrease in the KRb ratio (Table1 Fig 7)
At the scale of crystals the pegmatite zones and alsothose from the OIZ to the Cc of the Namivo granitic pegma-tite Al-richer micas show fractionation because theyformed from the fractionation of an Li-rich pegmatite melt
The Al-poorer micas zinnwaldite lepidolite and FeMg-containing polylithionite only occur in the OIZ (Fig 4)Polylithionite is the mica richest in Si and Licalc and lepi-dolite from this zone is the richest in Si Licalcand F (Fig 4Table 1) The high Li contents of these micas reflect aconsiderably higher D(Li) at low temperature (Icenhoweramp London 1995) These Li-rich micas may have crystal-lized from an undercooled melt This hypothesis does notimply high Rb and Cs contents and low KRb ratios Thisagrees with the fact that these micas from the OIZ havesimilar Rb and Cs contents and KRb ratios to those of Al-richer micas (muscovite lithian muscovite and lsquolsquomixedformrsquorsquo) from the same pegmatite zone (Fig 7) Howeverthe lepidolite from the wall zone of the Tanco pegmatiteCanada of a similar origin has a low KRb ratio which isattributed to the complexly interrelated structural compo-nents of this lepidolite (Van Lichtervelde et al 2008) TheLi-rich micas from the OIZ may also represent disequili-brium These two hypotheses are considered the best forthese micas of primary magmatic origin
Another hypothesis was also considered They may havecrystallized in boundary layers which concentrate Li andF But this mechanism was suggested for the most fractio-nated tourmaline enriched in Li and F from the core of the
Fig 8 Plot of albite compositions from all zones of the Namivo granitic pegmatite Mozambique showing that the anorthite content of albitedecreases from the WZ to the Cc WZ OIZ IIZa IIZb and Cc as in Fig 2
Fig 9 The Rb vs Cs diagram of K-feldspar from all zones of theNamivo granitic pegmatite Mozambique showing that the Rb andCs contents of K-feldspar increase from the WZ to the Cc WZ OIZIIZa IIZb and Cc as in Fig 2
Silicate and oxide minerals from a zoned granitic pegmatite 979
eschweizerbart_xxx
Little Three pegmatite dike USA (Morgan amp London1999) and the micas enriched in Li and F from theNamivo pegmatite belonging to the OIZ Furthermore ina boundary layer melt that became enriched in Li and F theKRb ratio of micas decreases strongly (Van Lichterveldeet al 2008) which was not found in these micas from theOIZ (Fig 7d) Nor can they have resulted from the crystal-lization of a late melt that would have reacted with the OIZbecause these micas are among those containing the high-est KRb values (Fig 7d)
92 The importance of feldspars micas andcolumbitendashtantalite compositions to the Namivogranitic pegmatite evolution
The trace elements Rb and Cs and the KRb and KCs ratioshave been used to show the evolution of K-feldspar inpegmatites (eg Cerny 1994 Cerny et al 2005 RodaRobles et al 2005) The Rb and Cs contents increase andthe KRb and KCs ratios of K-feldspar decrease from theWZ to the Cc (Fig 9 Table 2) reflecting the growth of K-feldspar from an increasingly fractionated melt withouthaving grown from or having been chemically modifiedby an aqueous fluid as in the Swamp pegmatite section atthe Little Three Mine USA (London et al 2012) Thecrystallization of K-feldspar from an exsolved aqueousfluid from melt will reverse the magmatic fractionation ofRb Cs KRb and KCs because Rb and especially Cs areso much more compatible in vapor that both Rb and Csremain in the fluid phase (London et al 2012) The feldsparsolvus pairs in the Namivo pegmatite record magmaticcrystallization temperatures that decrease from WZ to CcAlbite shows a decrease in the Ca Sr contents and SrCaratio from the WZ to the Cc (Fig 8 Table 2) Therefore thefeldspars and also Al-richer micas as already explainedshow fractionation in this zoned pegmatite
In general lepidolite from the Namivo pegmatite hassimilar Rb2O and Cs2O contents and KRb (wt) values tothose of lepidolite from the Rozna and Dobra Voda lepi-dolite-subtype pegmatites in the Czech Republic (Cernyet al 1995) but lower Rb2O and Cs2O contents thanlepidolite from the lepidolite-subtype pegmatite at RedCross Lake Manitoba Canada (Cerny et al 2012a) K-feldspar from the Namivo pegmatite also has lower Rb2O
Table 3 Representative electron microprobe analyses in wt of columbitendashtantalite from the Namivo granitic pegmatite Mozambique
Outer Intermediate Zone - OIZ Inner Intermediate Zone - IIZa
Core - Cc
D L L
WO3 022 059 079 113 101 351 050 007Ta2O5 5487 5123 2503 3186 2888 2519 3127 4542Nb2O5 2537 3000 5483 4635 5113 5144 4911 3686SnO2 008 015 024 049 020 026 017 012TiO2 263 161 136 254 202 145 125 016FeO 860 710 665 471 236 068 mdash mdashMnO 793 952 1099 1304 1400 1725 1748 1718Total 9970 10020 9989 10012 9960 9978 9978 9981W 0004 0011 0013 0019 0016 0057 0008 0001Ta 1065 0975 0422 0552 0495 0430 0543 0847Nb 0819 0949 1538 1336 1456 1460 1418 1143Sn 0002 0004 0006 0012 0005 0007 0004 0003Ti 0141 0085 0063 0122 0096 0068 0060 0008Fe 0513 0416 0345 0251 0124 0036 mdash mdashMn 0479 0564 0578 0704 0747 0917 0945 0998P
3023 3004 2965 2996 2939 2975 2978 3000Mn(Mn thorn Fe) 048 058 063 074 086 096 100 100Ta(Ta thorn Nb) 057 051 022 029 025 023 028 043Classification tant-(Fe) tant-(Mn) col-(Mn) col-(Mn) col-(Mn) col-(Mn) col-(Mn) col-(Mn)
D ndash darker L ndash lighter zones mdash Not detected tant-tantalite col-columbite Cation formula on the basis of 6 atoms of oxygen
Fig 10 Compositions of columbitendashtantalite from the Namivogranitic pegmatite Mozambique in the columbite quadrilateralshowing that Mn(Mn thorn Fe) of columbite-(Mn) increases from theOIZ to the Cc and the richest columbite-(Mn) in Ta(Ta thorn Nb)tantalite-(Fe) and tantalite-(Mn) only occur in the OIZ OIZ IIZaand Cc as in Fig 2
980 A M R Neiva
eschweizerbart_xxx
and Cs2O contents than K-feldspar from the lepidolite-subtype pegmatite at Red Cross Lake The Rb2O andCs2O contents of primary and late K-feldspar of this peg-matite at Red Cross Lake attained unprecedented levels(Cerny et al 2012a) The lowest KRb (wt) values ofmuscovite lithian muscovite lsquolsquomixed formrsquorsquo and lepido-lite from the IIZb and Cc (Fig 7) and K-feldspar (KRb frac1414) from the Cc compare well with those found in theseminerals from the AC6frac143 lepidolite-subtype pegmatitefrom Greer Lake (Cerny et al 2005) and some of themost fractionated pegmatites worldwide which belong tothe petalite-subtype (eg Tanco Manitoba Cerny 2005Cerny et al 1998 Varutrask Sweden Cerny et al 2005)but muscovite lithian muscovite and lepidolite from theIIZb and Cc have lower Rb2O and Cs2O contents than thesemicas from the Tanco pegmatite (Cerny 2005a VanLichtervelde et al 2008) K-feldspar also has lower
contents of these oxides than the most evolved K-feldsparfrom the Tanco pegmatite (Cerny 2005a) The magmaticfractionation was strong from the WZ to IIZb and Cc of theNamivo lepidolite-subtype pegmatite
The compositional trend of columbite-(Mn) from the OIZto Cc of the Namivo granitic lepidolite-subtype pegmatite(Fig 10) is identical to that of columbite-group mineralsfrom the lepidolite-subtype complex granitic pegmatitesfrom the Dobra Voda in the Moldanubicum CzechRepublic (Novak amp Cerny 1998) and the HimalayaDistrict southern California (shown in Cerny et al 2004)Experimental data for the Fe-Mn pair (Linnen amp Cuney2005) suggest an increase in Fe with fractional crystalliza-tion which is not observed in nature Other phases seem tocontrol the bahavior of Fe and Mn in the melt eg thecrystallization of tourmaline causes a rapid increase of theMnFe in the melt (Van Lichtervelde et al 2006) When thecrystallization of tourmaline stopped the columbitendashtantaliteminerals showed a constant MnFe indicating that the Fe andMn contents in the melt remained constant Schorl onlyoccurs in the OIZ of the Namivo granitic pegmatite and itscrystallization cannot be responsible for the increase in theMnFe of the melt because Mn(Mn thorn Fe) of columbite-(Mn) increases progressively from the OIZ to the IIZa and Cc(Fig 10) Garnet zinnwaldite and gahnite containing Fe andMn also only occur in the OIZ and cannot also have causedthe increase of the MnFe in the melt The dominant Mnenrichment before Ta enrichment started in the columbitendash-tantalite composition from some granitic pegmatites isattributed to an increased alkali-fluoride activity at moderatemHF (Cerny et al 2004) and an increase in the activity offluorine (Martins et al 2011) Each Al-richer mica (musco-vite lithian muscovite and lsquolsquomixed formrsquorsquo) from the Namivogranitic pegmatite shows an increase in F content from theOIZ to the IIZa IIZb and Cc (Table 1) In general the Fcontent of lepidolite also increases from the IIZa to the IIZband Cc Therefore the extreme Fe-Mn fractionation beforeTa enrichment in columbite-(Mn) (Fig 10) may be due to anincrease in the activity of fluorine as a consequence offractional crystallization The increase in the Ta content ofcolumbite-(Mn) from the Namivo granitic pegmatite isattributed to fractional crystallization
The geochemical evolution of albite and K-feldsparfrom the WZ to the Cc Al-richer micas muscovite lithianmuscovite and lsquolsquomixed formrsquorsquo from the OIZ to the Cc andlepidolite from the IIZa to the Cc and columbite-(Mn) andalso beryl (Neiva amp Neiva 2005) from the OIZ to the Ccare caused by magma fractionation The pegmatite zonesare the product of primary crystallization from a volatile-rich silicate melt The pegmatite consolidated from the WZto the Cc The IIZb is one of the most evolved zones asalso suggested by the beryl composition (Neiva amp Neiva2005) and is the richest in lsquolsquomixed formrsquorsquo and lepidolite
The richest columbite-(Mn) in Ta(Ta thorn Nb) and com-positions of tantalite-(Fe) and tantalite-(Mn) only occur inthe OIZ (Fig 10a) associated with lepidolite and polythio-nite (Fig 3c) which may be due to the local depletion of Liand F in the melt which decreases the solubility of Ta andcauses Ta precipitation (Linnen 1998 Linnen amp Cuney
Fig 11 a Backscattered-electron image of a gahnite crystal with adarker zone partially surrounding a lighter zone from the OIZ of theNamivo granitic pegmatite b c Plot of gahnite compositions in theSn-Zn-Ti diagram (atomic proportions) showing a chemical distinc-tion between the lighter and darker zones OIZ as in Fig 2
Silicate and oxide minerals from a zoned granitic pegmatite 981
eschweizerbart_xxx
2005) At the Tanco pegmatite Ta oxides are also asso-ciated with lepidolite enriched in Li and F from the wallzone (Van Lichtervelde et al 2008)
93 Origin and evolution of the zoned graniticlepidolite-subtype pegmatite at Namivo
In general granitic pegmatites particularly those belong-ing to the rare-element class are accepted as having beenformed by the fractional crystallization of a granite melt(eg Cerny 1991a b 1992 Neiva et al 2008 2012 Roda-Robles et al 2012) But it also has been proposed thatpegmatites may be formed by partial melting of appropri-ate rock compositions (eg Nabelek et al 1992 Nabelekamp Russ-Nabelek 1992 Shearer et al 1992 Roda Robleset al 1999) The lepidolite-subtype pegmatites belong tothe LCT (lithium-cesium-tantalum) family (Cerny amp Ercit2005) They are derived by fractional crystallization of agranite magma (eg Cerny et al 2005 Neiva amp Ramos2010 Cerny et al 2012b) Experimental work by Londonet al (1989) and London (1990) using Macusani glass as astarting material equivalent to the bulk composition ofhighly fractionated rare-alkali-rich pegmatites underhighly evolved and hydrous but H2O undersaturatedmelt obtained the latest primary assemblage consisting
of an Li-rich mica thorn albite thorn quartz deposited directlyfrom the primary melt phase Other authors egZasedatelev (1974 1977) and Stewart (1978) argue thatlepidolite-bearing pegmatites are derived from direct ana-texis and Gordiyenko et al (1996) consider that they arederived from an undefined medium and the rare-elementmineralization is superimposed on preexisting barrenpegmatites
Lepidolite-subtype pegmatites may migrate a long wayfrom their parent granites because their volatile-rich highlyfluid pegmatite melts are stable at relatively low tempera-tures (eg Cerny et al 2005 Antunes et al 2013)Therefore the Namivo pegmatite is probably derived byfractional crystallization of an S-type granite magmawhich resulted from partial melting of metamorphosed juve-nile sediments containing micas that carry most of the traceelements that define the signature of the LCT pegmatites(eg Dahl et al 1993)
The two main models for the internal evolution of peg-matites that dominated for more than a century are a) thefractional crystallization of a flux-bearing granitic melt fromthe margins to the center of the pegmatite (Cameron et al1949) b) the interactions of an aqueous fluid with graniticmelt (Jahns amp Burnham 1969 Jahns 1982) The recentmodel of constitutional zone refining combines aspects ofboth models and invokes the formation of a flux-enriched
Table 4 Electron microprobe analyses in wt of zoned gahnite from the outer intermediate zone (OIZ) of the Namivo granitic pegmatiteMozambique
Darker Zone Lighter Zone
Mean s Range Mean s Range
SnO2 036 050 0ndash097 658 281 151ndash998TiO2 008 008 0ndash021 065 034 008ndash105Nb2O5 001 002 0ndash006 018 007 007ndash029Ta2O5 001 004 0ndash010 015 013 0ndash033ZnO 3998 123 3810ndash4109 3339 318 3004ndash3848FeO 367 048 331ndash442 433 065 306ndash498MnO 032 004 028ndash040 039 006 032ndash048MgO 003 004 0ndash010 ndash ndash ndashAl2O3 5507 050 5436ndash5572 5337 070 5257ndash5443SiO2 003 003 0ndash007 008 010 0ndash025Total 9956 9912n 8 8Sn 0035 0048 0ndash0095 0648 0278 0149ndash0983Ti 0015 0015 0ndash0038 0120 0064 0015ndash0195Nb ndash 0003 0ndash0006 0021 0009 0009ndash0037Ta ndash 0002 0ndash0006 0009 0009 0ndash0021Zn 7226 0182 6890ndash7382 6086 0568 5482ndash6965Fe2thornt 0752 0103 0675ndash0913 0894 0135 0628ndash1029Mn 0066 0008 0057ndash0083 0082 0013 0066ndash0101Mg 0010 0015 0ndash0037 ndash ndash ndashAl 15887 0052 15805ndash15954 15526 0170 15375ndash15853Si 0007 0008 0ndash0018 0019 0025 0ndash0062P
23998 23405Fe3thorn 0064 0230Fe2thorn 0686 0658SnZn 0005 0007 0ndash0014 0106 0052 0021ndash0179ZnFe2thornt 961 143 768ndash1093 681 190 536ndash1109
n number of analysis Cation formula based on 32 atoms of oxygen Fe2thornt total Fe2thorn estimated
982 A M R Neiva
eschweizerbart_xxx
boundary layer of silicate liquid in advance of a crystal-lization front (London 2008 London amp Morgan 2012)
Lepidolite-subtype pegmatites are generally scarce(Cerny et al 2005) particularly the zoned ones In thesymmetrically zoned lepidolite-subtype pegmatites ofRozna and Dobra Voda Czech Republic micas (Cernyet al 1995) tourmaline (Selway et al 1999) and colum-bite-group minerals (Novak amp Cerny 1998) evolve fromthe outermost zone to the innermost zone following thecrystallization sequence The same was found in tourma-line from the zoned Lastovicky Dolnı Bory and Raddovicelepidolite-subtype pegmatite dikes in the Czeck Republic(Selway et al 1999)
In general beryl (Neiva amp Neiva 2005) feldsparsmicas and columbite-(Mn) (in this paper) from theNamivo lepidolite-subtype pegmatite record the progres-sive chemical evolution of the pegmatite from the wallzone to the core These minerals were produced by crystal-lization from a silicate melt rather than an aqueous fluidphase The slow cooling of melt shown by the magmaticcrystallization temperatures of feldspars cannot explain theincrease in grain-size of minerals from the wall zone to thecore but fluxes will be necessary to promote the change oftexture particularly a flux-rich hydrosilicate liquidaccording to the experimental evidence (London 2009)The constitutional zone refining model will be the best forthis zoned pegmatite and probably for all lepidolite-sub-type pegmatites because this model also produces a higherfinal concentration of incompatible components in a smal-ler volume of rock than fractional crystallization does(Morgan amp London 1999)
The core margin at the Rozna pegmatite contains K-feld-spar and quartz and the core consists mainly of quartz but it issurrounded and penetrated by a quartz-bearing albitethorn lepi-dolite complex which contains several minerals At theDobra Voda pegmatite the center of the dike is occupiedby the lepidolite unit containing albite and other minerals(Cerny et al 1995) At the Namivo pegmatite the coremargin consists of quartz and beryl and the core containsmainly quartz and spodumene but also albite lepidolite andother minerals The last-unit assemblages of primary miner-als in most of the highly fractionated LCT pegmatites are richin albite and commonly contain lepidolite or spodumene andmost of the other rare phases These units represent the lastmost fractionated liquid that can be derived by fractionalcrystallization of a crustal melt (London 2008)
The Namivo granitic pegmatite shows a significant dis-tinction from the other zoned lepidolite-subtype pegmatitesand LCT pegmatites except the Tanco petalite-subtypepegmatite in Canada because the lepidolite richest in SiLi and F FeMg-containing polylithionite and associatedcolumbite-(Mn) with the highest Ta(Ta thorn Nb) ratio tanta-lite-(Fe) and tantalite-(Mn) only occur in the outer inter-mediate zone These minerals usually form late in theconsolidation of pegmatites The lepidolite and polylithio-nite are probably derived from the disequilibrium crystal-lization of an undercooled melt Tantalite may reflect a localdecrease in Li and F that caused Ta precipitation
This paper contributes to a better understanding of theorigin and evolution of the rare zoned lepidolite-subtypepegmatites and shows that although the pegmatite evolvedfrom the wall zone to the core it presents an unusualassociation of lepidolite polylithionite and tantalite in theouter intermediate zone
Acknowledgments Thanks are due to JM Cotelo Neivaand MB Dias for the samples and information providedand to MR Machado Leite and MF Guimaraes for theuse of the electron microprobe facilities at the LaboratorioNacional de Energia e Geologia (LNEG) PortugalFinancial support was provided by the PortugueseGovernment for the project Pest-OECTEUI00732011of the Geosciences Centre through the PortugueseFoundation for Science and Technology I would like tothank D London WB Simmons and the associated editorE Widom for their constructive reviews of this manuscriptand M Prieto for his editorial work
References
Alfonso P Melgarejo JC Yusta I Velasco F (2003)
Geochemistry of feldspars and muscovite in granitic pegmatite
from the Cap de Creus field Catalonia Spain Can Mineral 41
103ndash116
Antunes IMHR Neiva AMR Ramos JMF Silva PB
Silva MMVG Corfu F (2013) Petrogenetic links between
lepidolite-subtype aplite-pegmatite aplite veins and associated
granites at Segura (central Portugal) Chemie der Erde in press
httpdxdoiorg101016jchemer20121203
Batchelor RA amp Kinnaird JA (1984) Gahnite compositions
compared Mineral Mag 48 425ndash430
Beurlen H Da Silva MRR Thomas R Soares DR Olivier P
(2008) Nb-Ta-(Ti-Sn) oxide mineral chemistry as tracer of rare-
element granitic pegmatite fractionation in the Borborema pro-
vince Northeastern Brazil Miner Deposita 43 207ndash228
Cameron EN Jahns RH McNair AH Page LR (1949)
Internal structure of granitic pegmatites Econ Geol
Monograph 2 115 p
Cerny P (1991a) Fertile granites of Precambrian rare-element
pegmatite fields is geochemistry controlled by tectonic setting
or source lithologies Precambrian Res 51 429ndash468
mdash (1991b) Rare-element granite pegmatites I Anatomy and inter-
nal evolution of pegmatite deposits Geoscience Canada 18
49ndash67
mdash (1992) Geochemical and petrogenetic features of mineralization
in rare-element granitic pegmatites in the light of current
research Applied Geochemistry 7 393ndash416
mdash (1994) Evolution of feldspars in granitic pegmatites in
lsquolsquoFeldspars and their Reactionsrsquorsquo I Parsons ed NATO
Advanced Study Institute Series C421 501ndash539
mdash (2005) The Tanco rare-element pegmatite deposit Manitoba
regional context internal anatomy and global comparisons in
lsquolsquoRare-element Geochemistry and Mineral Depositsrsquorsquo RL
Linnen amp IM Samson eds Geochemical Association of
Canada Short Course Notes St Catherines 17 127ndash158
Silicate and oxide minerals from a zoned granitic pegmatite 983
eschweizerbart_xxx
Cerny P amp Ercit TS (2005) The classification of granitic pegma-
tites revisited Can Mineral 43 2005ndash2026
Cerny P Meintzer RE Andersen AJ (1985) Extreme fractiona-
tion in rare-element granitic pegmatites selected examples of
data and mechanisms Can Mineral 23 381ndash421
Cerny P Goad BE Hawthorne FC Chapmann R (1986)
Fractionation trends of the Nb- and Ta-bearing oxide minerals
in the Greer Lake pegmatite granite and its pegmatite aureole
southeastern Manitoba Am Mineral 71 501ndash517
Cerny P Stanek J Novak M Baadsgaard H Rieder M
Ottolini L Kavalova M Chapman R (1995) Geochemical
and structural evolution of micas in the Rozna amp Dobra Voda
pegmatites Czech Republic Mineral Petrol 55 177ndash201
Cerny P Ercit TS Vanstone PJ (1998) Mineralogy and petrol-
ogy of the Tanco rare-element pegmatite deposit southeastern
Manitoba International Mineralogical Association 17th General
Meeting Toronto Field Guidebook B6
Cerny P Chapman R Ferreira K Smeds SA (2004)
Geochemistry of oxide minerals of Nb Ta Sn and Sb in
the Varutrask granitic pegmatite Sweden The case of an
lsquolsquoanomalousrsquorsquo columbitendashtantalite trend Am Mineral 89
505ndash518
Cerny P Masau M Goad BE Ferreira K (2005) The Greer
Lake leucogranite Manitoba and the origin of lepidolite-sub-
type granitic pegmatites Lithos 80 305ndash321
Cerny P Teertstra DK Chapman R Selway JB Hawthorne
FC Ferreira K Chackowsky LE Wang X-J Meintzer
RE (2012a) Extreme fractionation and deformation of the
leucogranite-pegmatite suite at Red Cross Lake Manitoba
Canada IV Mineralogy Can Mineral 50 1839ndash1875
Cerny P Halden NM Ferreira K Meintzer RE Brisbin WC
Chackowsky LE (2012b) Extreme fractionation and deforma-
tion of the leucogranite-pegmatite suite at Red Cross Lake
Manitoba Canada II Petrology of the leucogranites and peg-
matites Can Mineral 50 1807ndash1822
Dahl PS When DC Feldmann SG (1993) The systematics of
trace-element partitioning between coexisting muscovite and
biotite in metamorphic rocks from the Black Hills South
Dakota USA Geochim Cosmochim Acta 57 2487ndash2505
Dias MB amp Wilson WE (2000) The Alto Ligonha Pegmatites
Mozambique Mineral Record 31 459ndash497
Fleet ME (2003) Rock-Forming Minerals vol 3A Sheet silicates
micas The Geological Society London second edition chap 6
Lithium micas 651ndash690
Foord EE Cerny P Jackson LL Sherman DM Eby RK
(1995) Mineralogical and geochemical evolutions of micas
from miarolitic pegmatites of the anorogenic pikes-Peak
Batholith Colorado Mineral Petrol 55 1ndash26
Foster MD (1960) Interpretation of the composition of lithium
micas US Geol Surv Prof Paper 354-E 115ndash147
Fuhrman ML amp Lindsley DK (1988) Ternary-feldspar modeling
and thermometry Am Mineral 73 201ndash215
Gomes CL Castro P Alves C (1995) Caracterizacao das espi-
nelas zincıferas e do par ganite-nigerite no campo aplito-
pegmatıtico da Serra de Arga-Minho N de Portugal IV
Congresso Nacional de Geologia Resumos Alargados
Universidade do Porto Mem 4 629ndash633
Gordiyenko VV Ilyina AN Timochina LA Badamina EB
Stanek J (1996) Geochemical model of evolution of a pegma-
tite-forming ore-magmatic system of western Moravia Proc
Russ Mineral Soc 125 38ndash48 (in Russian)
Icenhower JP amp London D (1995) An experimental study for
element partitioning between biotite muscovite and coexisting
peraluminous granitic melt at 200 MPa (H2O) Am Mineral 80
1229ndash1251
Jahns RH (1982) Internal evolution of pegmatite bodies in lsquolsquoGranitic
Pegmatites in science and industryrsquorsquo P Cerny ed Mineralogical
Association of Canada Short Course Handbook 8 293ndash327
Jahns RH amp Burnham CW (1969) Experimental studies of
pegmatite genesis I A model for the derivation and crystal-
lization of granitic pegmatites Econ Geol 64 843ndash864
Jolliff BL Papike JJ Shearer CK (1987) Fractionation trends
in mica and tourmaline as indicators of pegmatite internal evo-
lution Bob Ingersoll pegmatite Black Hills South Dakota
USA GeochimCosmochim Acta 51 519ndash534
Kile DE amp Foord EE (1998) Micas from the Pikes Peak bath-
olith and its cogenetic granitic pegmatites Colorado optical
properties composition and correlation with pegmatite evolu-
tion Can Mineral 36 463ndash482
Linnen RL (1998) The solubility of Nb-Ta-Zr-Hf-W in granitic
melts with Li and Li thorn F constraints for mineralization in rare
metal granites and pegmatites Econ Geol 93 1013ndash1025
Linnen RL amp Cuney M (2005) Granite-related rare-element
deposits and experimental constraints on Ta-Nb-W-Sn-Zr-Hf
mineralization in lsquolsquoRare-element geochemistry and mineral
depositsrsquorsquo RL Linnen amp IM Samson eds Geochemical
Association of Canada Short Course Notes 17 45ndash68
London D (1990) Internal differentiation of rare-element pegmatites
a synthesis of recent research in lsquolsquoOre Bearing Granite Systems
Petrogenesis and Mineralizing Processesrsquorsquo HJ Stein amp JL
Hannah eds Geol Soc America Special Paper 246 35ndash50
mdash (2008) Pegmatites The Canadian Mineralogist Special
Publication 10 347 p
mdash (2009) The origin of primary textures in granitic pegmatites
Can Mineral 47 697ndash724
London D amp Morgan GB VI (2012) The pegmatite puzzle
Elements 8 263ndash268
London D Morgan GB VI Hervig RL (1989) Vapor-under-
saturated experiments in the system macusanite-H2O at 200
MPa and the internal differentiation of granitic pegmatites
Contrib Mineral Petrol 102 1ndash17
London D Morgan GB VI Paul KA Guttery BM (2012)
Internal evolution of miarolitic granitic pegmatites at the Little
Three mine Ramona California USA Can Mineral 50
1025ndash1054
Martins T Lima A Simmons WB Folster AU Noronha F
(2011) Geochemical fractionation of Nb-Ta oxides in Li-bear-
ing pegmatites from the Barroso-Alvao pegmatite field northern
Portugal Can Mineral 49 777ndash791
Monier G Charoy B Cuney M Ohnenstetter D Robert JL
(1987) Evolution spatiale et temporelle de la composition des
micas du granite albitique a topaze-lepidolite de Beauvoir
Geologie De La France 2ndash3 179ndash188
Monier G amp Robert JL (1986) Evolution of the miscibility gap
between muscovite and biotite solid solutions with increasing
lithium content an experimental study in the systems
K2OndashLi2OndashMgOndashAl2O3ndashSiO2ndashH2OndashHF at 600 C 2 kbar
PH2O comparison with natural lithium micas Mineral Mag
50 641ndash651
Morgan GBVI amp London D (1999) Crystallization of the little
three layered pegmatite-aplite dike Ramona District California
Contrib Mineral Petrol 136 310ndash330
984 A M R Neiva
eschweizerbart_xxx
Nabelek PI amp Russ-Nabelek C (1992) The generation and crys-
tallization conditions of the Proterozoic Harney Peak
Leucrogranite Black Hills South Dakota USA petrologic and
geochemical constraints Contrib Mineral Petrol 110
173ndash191
Nabelek PI Russ-Nabelek C Haeussler GT (1992) Stable
isotope evidence for the petrogenesis and fluid evolution in
the Proterozoic Harney Peak leucogranite Black Hills
South Dakota Geochim Cosmochim Acta 56 403ndash417
Neiva AMR amp Champness PE (1997) Nigerite and gahnite from
the granitic pegmatite veins of Cabanas Ponte de Lima northern
Portugal N Jb Mineral Mh 9 385ndash409
Neiva AMR Gomes MEP Ramos JMF Silva PB (2008)
Geochemistry of granitic aplite-pegmatite sills and their miner-
als from Arcozelo da Serra area (Gouveia central Portugal)
Eur J Mineral 20 465ndash485
Neiva AMR amp Neiva JMC (2005) Beryl from the granitic
pegmatite at Namivo Alto Ligonha Mozambique N Jb
Mineral Abh 181 173ndash182
Neiva AMR amp Ramos JMF (2010) Geochemistry of granitic
aplite-pegmatite sills and petrogenetic links with granites
Guarda-Belmonte area central Portugal Eur J Mineral 22
837ndash854
Neiva AMR Silva PB Ramos JMF (2012) Geochemistry of
granitic aplite-pegmatite veins and sills and their minerals from the
Sabugal area central Portugal N Jb Mineral Abh 189 49ndash74
Novak M amp Cerny P (1998) Niobium-tantalum oxide minerals
from complex granitic pegmatites in the Moldanubicum Czech
Republic primary versus secondary compositional trends Can
Mineral 36 659ndash672
Pesquera Perez A Torres-Ruiz J Gil PP Velilla N (1999)
Chemistry and genetic implications of tourmaline and Li-F-Cs
micas from the Valdeflores (Caceres Spain) Am Mineral 84
55ndash69
Rieder M Cavazzini G DrsquoYakonov YuS Frank-Kamenetskii
VA Gottardi G Guggenheim S Koval PV Muller G
Neiva AMR Radoslovich EW Robert J-L Sassi FP
Takeda H Weiss Z Wones DR (1999) Nomenclature of the
micas Mineral Mag 63 267ndash279
Roda Robles E Pesquera Perez A Velasco Roldan F Fontan F
(1999) The granitic pegmatites of the Fregeneda area
(Salamanca Spain) characteristics and petrogenesis Mineral
Mag 63 535ndash558
Roda Robles E Pesquera A Gil-Crespo PP Torres-Ruiz J
Fontan F (2005) Origin and internal evolution of the Li-F-
Be-P-bearing Pinilla de Fermoselle pegmatite (Central Iberian
Zone Zamora Spain) Am Mineral 90 1887ndash1899
Roda Robles E Pesquera Perez A Gil PP Torres-Ruiz J de
Parseval P (2006) Mineralogy and geochemistry of micas from
the Pinilla de Fermoselle pegmatite (Zamora Spain) Eur J
Mineral 18 369ndash377
Roda Robles E Keller P Pesquera Perez A Fontan F (2007)
Micas of the muscovite-lepidolite series from Karibib pegma-
tites Namibia Mineral Mag 71 41ndash62
Roda Robles E Pesquera A Gil-Crespo P Torres-Ruiz J
(2012) From granite to highly evolved pegmatite a case study
of the Pinilla de Fermoselle granite-pegmatite system (Zamora
Spain) Lithos 153 192ndash207
Selway JB Novak M Cerny P Hawthorne FC (1999)
Compositional evolution of tourmaline in lepidolite-subtype
pegmatites Eur J Mineral 11 569ndash584
Shearer CK Papike JJ Jolliff B (1992) Petrogenetic links
among granites and pegmatites in the Harney Peak rare-element
granite-pegmatite system Black Hills South Dakota Can
Mineral 30 785ndash809
Soares DR Hartmut B Ferreira ACM da Silva MRR
(2007) Chemical composition of gahnite and degree of peg-
matitic fractionation in the Borborema Pegmatitic Province
northeastern Brazil Anais Da Academ Bras Cien 79
395ndash404
Stewart DB (1978) Petrogenesis of lithium-rich pegmatites Am
Mineral 63 970ndash980
Tischendorff G Gattesmann B Forster H-J Trumbull RB
(1997) On Li-bearing micas estimating Li from electron
microprobe analyses and an improved diagram for graphical
representation Mineral Mag 61 809ndash834
Van Lichtervelde M Linnen RL Salvi S Beziat D (2006)
The role of metagabbro rafts on tantalum mineralization in the
Tanco granitic pegmatite Manitoba Can Mineral 44
625ndash644
Van Lichtervelde M Gregoire M Linnen RL Beziat D Salvi
S (2008) Trace element geochemistry by laser ablation ICP-
MS of micas associated with Ta mineralization in the Tanco
pegmatite Manitoba Canada Contrib Mineral Petrol 155
791ndash806
Vieira R Roda-Robles E Pesquera A Lima A (2011)
Chemical variation and significance of micas from the
Fregeneda-Almendra pegmatitic field (Central-Iberian Zone
Spain and Portugal) Am Mineral 96 637ndash645
Wen S amp Nekvasil H (1994) SOLVCALC an interactive gra-
phics program package for calculating ternary feldspar solvus
and two-feldspar geothermometry Comput Geosci 20
1025ndash1040
Wise MA (1995) Trace element chemistry of lithium-rich micas
from rare-element granitic pegmatites Mineral Petrol 55
203ndash215
Zasedatelev AM (1974) Possible accumulation of lithium in host
rocks of lithium pegmatite veins during old sedimentation pro-
cesses Doklady Acad Sci USSR Earth Sci Ser 218 196ndash198
(in Russian)
mdash (1977) Quantitative of metamorphic generation of rare-metal
pegmatites with lithium mineralization Doklady Acad Sci
USSR Earth Sci Ser 236 219ndash221 (in Russian)
Received 26 January 2013
Modified version received 21 May 2013
Accepted 23 July 2013
Silicate and oxide minerals from a zoned granitic pegmatite 985
eschweizerbart_xxx
analytical totals are not good The analyzed lsquolsquomixedformsrsquorsquo are distinguished in backscattered-electron (BSE)images and chemically (Fig 3b d d1 e f f1 h i andFig 4) The chemical distinction between lsquolsquomixed formrsquorsquoand lepidolite from the OIZ (Fig 4) is clear in Fig 3bwhere lepidolite is darker than lsquolsquomixed formrsquorsquo because theformer has less Fe and Mn than the latter (Table 1) and inFig 3f f1 and 3h for micas from the IIZa and IIZbrespectively where lepidolite is lighter than lsquolsquomixedformrsquorsquo because the former has more Fe2thorn and Mn oronly more Mn than the latter (Table 1) The lsquolsquomixedformsrsquorsquo analyzed are distinguished in the BSE imagesfrom the lepidolite that falls in its fields in the Fig 4The fields of lepidolite composition in Foster (1960) arelarger than the field for lepidolite from the trilithionite tothe polylithionite (Rieder et al 1999) According to Fleet(2003) only a few lepidolite compositions plot on thetrilithionite-polylithionite join In general lepidolite hashigher Si Licalc Rb Cs F contents and lower AlVI andOH contents than lsquolsquomixed formrsquorsquo (Table 1 Fig4)lsquolsquoMixed formrsquorsquo is also clearly distinguished fromlithian muscovite in OIZ IIZa IIZb and Cc in BSEimages (Fig 3d d1 e f i) and chemically (Table 1 Fig4) as it generally has higher Si Licalc Rb Cs F contentsand lower AlVI and OH contents than lithian muscovite
Two distinct trends are defined in Fig 4 One trendconsists of Al-poorer micas which are zinnwaldite
lepidolite and FeMg-containing polylithionite from theOIZ A hiatus occurs between zinnwaldite and lepidolitebut the zinnwaldite series is continuous with the field oflepidolite at the high Li content (Fleet 2003) The othertrend consists of Al-richer micas (muscovite lithian mus-covite and lsquolsquomixed formrsquorsquo from the OIZ IIZa IIZb and Ccand also lepidolite from most of those zones except fromthe OIZ) There is a gap between lithian muscovite and thelsquolsquomixed formrsquorsquo which may be explained by a hiatus inmica stability (eg Jolliff et al 1987) but a solid solutionbetween dioctahedral and trioctahedral micas has beenindicated experimentally (Monier amp Robert 1986) whileother authors have shown that the octahedral site occu-pancy ranges continuously from muscovite to lepidolite(eg Roda Robles et al 2005 Van Lichterveld et al2008 Vieira et al 2011) Most lithian muscovites andlsquolsquomixed formrsquorsquo from the OIZ are richer in Fe2thornthornMg thornMn than those from the other zones due to their higherFe2thorn and Mg contents (Fig 4 Table 1)
In the Al-poorer micas from the OIZ ranging from zinn-waldite to lepidolite and FeMg-containing polylithionite(Fig 4) (AlIV thorn AlVI) Fe2thorn Mg Ti Mn and Zn contentsdecrease and Si and Licalccontents increase (Table 1) In theAl-richer micas ranging from muscovite to lithian muscoviteand lsquolsquomixed formrsquorsquo from the OIZ IIZa IIZb and Cc and alsoto lepidolite from most of those zones except from the OIZ(AlIV thorn AlVI) AlVI and OH contents and KRb ratio
Fig 4 Plots of micas from the Namivo granitic pegmatite Mozambique in the LindashR2thornndashR3thornthorn Ti diagram according to the classification ofFoster (1960) slightly modified (Rieder et al 1999) with R3thorn frac14 AlVI R2thorn frac14 (Fe2thornt thorn Mn2thornthorn Mg) showing the variety of micacompositions Two trends are defined one for Al-poorer micas (zinnwaldite lepidolite and FeMg-containing polylithionite) from theOIZ another for Al-richer micas (muscovite lithian muscovite lsquolsquomixed formrsquorsquo and lepidolite) from all zones except lepidolite from the OIZOIZ IIZa IIZb and Cc as in Fig 2
972 A M R Neiva
eschweizerbart_xxx
generally decrease and Si Licalc Rb Cs and F contentsgenerally increase (Table 1)
42 Main substitution mechanisms
The 2Si thorn Li 3Altotal mechanism operates in the diocta-hedral micas (muscovite and lithian muscovite) (Fig 5a b)whereas the 3LiVI AlVIthorn 2ampVI (amp represents a vacancy)operates in the trioctahedral micas (lsquolsquomixed formrsquorsquo lepido-lite zinnwaldite and FeMg-containing polylithionite) (Fig5c d) which agrees with findings for micas from the Tancopegmatite (Van Lichtervelde et al 2008)
43 Textures and chemical compositions of zoned micacrystals
Backscattered-electron images combined with quantita-tive spot electron-microprobe analyses made it possibleto distinguish different micas in the Namivo graniticpegmatite Similar textural aspects and geochemicalobservations were found between some Al-richer micasfrom the OIZ IIZa IIZb and Cc Some selected zonedcrystals are documented (Table 1 Fig 3 and 6) In theOIZ lepidolite penetrates zinnwaldite along cleavagesand partially surrounds it and the contacts are sharp(Fig 3a) A chemical gap occurs between zinnwalditeand lepidolite compositions (Fig 6a b) Lepidolite withhigher Si Licalc F contents similar KRb value andlower (AlIV thorn AlVI) Ti Fe2thorn Mg (Fe2thornthorn Mn thorn Mg)Zn and OH contents (Table 1) replaces zinnwaldite Athin lepidolite rim partially surrounds lsquolsquomixed formrsquorsquoand the contact is sharp (Fig 3b) The lepidolite rimhas higher Si Mg Licalc Rb F contents and lowerAlVI Ti Fe2thorn Mn Na and OH contents and KRb ratiothan the lsquolsquomixed formrsquorsquo core (Table 1) The lepidoliterim is an Al-poorer mica whereas the lsquolsquomixed formrsquorsquocore is an Al-richer mica (Fig 4) The lepidolite rimcorresponds to an overgrowth The FeMg-containingpolylithionite partially surrounds and penetrates lepido-lite along cleavages and shows well defined contacts(Fig 3c) Both contain rutile cassiterite and columbi-tendashtantalite inclusions A continuous chemical evolutiontakes place from lepidolite to FeMg-containing poly-lithionite (Figs 4 6c) The latter has higher Si LicalcRb contents and lower AlVI Ti Fe2thorn Mn Mg Zn Nacontents and KRb ratio (Table 1) and replaces lepido-lite A lithian muscovite rim with rare FeMg-containingpolylithionite surrounds the lsquolsquomixed formrsquorsquo core and thispolylithionite penetrated lithian muscovite (Fig 3d)The contact between the lithian muscovite rim andlsquolsquomixed formrsquorsquo core is irregular suggesting disequili-brium or at a cleavage (Fig 3d d1) Two linear trendsone for the lithian muscovite rim and another for thelsquolsquomixed formrsquorsquo core are defined in the (Fe2thornthornMnthornMg)vs (AlIV thornAlVI) diagram (Fig 6d) The FeMg-contain-ing polylithionite rim does not belong to any of thesetrends and plots outside this diagram because it is an Al-poorer mica whereas the others are Al-richer micas
(Fig 4) The lithian muscovite rim has higher AlVI(AlIV thorn AlVI) OH contents and KRb ratio and lowerMg (Fe2thornthorn Mn thorn Mg) Licalc Rb F contents than thelsquolsquomixed formrsquorsquo core (Table 1 Fig 6d) The crystal isreversely zoned The FeMg-containing polylithioniterim has higher Si Licalc F contents and lower AlVI(AlIV thorn AlVI) Fe2thorn Mn (Fe2thornthorn Mn thorn Mg) Na andOH contents than the lsquolsquomixed formrsquorsquo core and lithianmuscovite rim (Table 1) and replaces lithian muscovite
In the IIZa some zoned crystals have a lithian muscovitecore and a lsquolsquomixed formrsquorsquo rim and the contacts are gradual(Fig 3e) A small discontinuity occurs in the trends fromthe lithian muscovite core to lsquolsquomixed formrsquorsquo rim in the(Fe2thornthorn Mn thorn Mg) vs (AlIV thorn AlVI) and Rb2O vs KRb(Fig 6e f) The lsquolsquomixed formrsquorsquo rim has higher Si Fe2thornMn (Fe2thornthornMn thornMg) Licalc K Rb Cs F contents andlower AlVI (AlIVthornAlVI) Na OH contents and KRb ratiothan the lithian muscovite core (Table 1 Fig 6e f) indi-cating progressive zoning Similar textural relationshipsand chemical evolutions were found in other zoned crystalsfrom the OIZ IIZb and Cc In another crystal from theIIZa lithian muscovite partially surrounds lsquolsquomixed formrsquorsquointergrown with lepidolite Lithian muscovite also partiallysurrounds muscovite (Fig 3f) The contacts betweenlsquolsquomixed formrsquorsquo and lepidolite and also between muscoviteand lithian muscovite are gradual (Fig 3f f1) whereasthey are well defined for muscovite withlsquolsquomixed formrsquorsquoand lepidolite (Fig 3f f1) The crystal has a lsquolsquomixed formrsquorsquoand lepidolite core and a partial rim of muscovite andlithian muscovite The lsquolsquomixed formrsquorsquo core evolved tolepidolite core as the Si Fe2thorn Mn (Fe2thornthorn Mn thorn Mg)Licalc K Rb Cs and F contents increase and the (AlIV thornAlVI) and KRb ratio decrease (Table 1 Fig 6g h) The SiFe2thorn Mn (Fe2thornthorn Mn thorn Mg) Licalc Rb and F contentsincrease and the (AlIV thorn AlVI) and KRb ratio decreasefrom the muscovite rim to the lithian muscovite rim (Table1 Fig 6g h) suggesting that the former evolved to thelatter The muscovite rim has higher AlVI (AlIV thorn AlVI)Na OH contents and KRb ratio and lower Si Fe2thorn Mn(Fe2thornthornMn thornMg) Zn Licalc Rb and F contents than thelsquolsquomixed formrsquorsquo core and lepidolite core (Table 1 Fig 6gh) Muscovite was probably reversely formed and evolvedafterwards to lithian muscovite
In the IIZb some crystals have a lithian muscovite coreand a thinner lepidolite rim (Fig 3g) and others show asmall muscovite core and a larger rim of lsquolsquomixed formrsquorsquointergrown with lepidolite (Fig 3h) The contacts betweenthe cores and rims are well defined There are increases inthe Si Mn (Fe2thornthorn Mn thorn Mg) Licalc Rb and F contentsand decreases in the AlVI (AlIVthornAlVI) and KRb ratio fromthe lsquolsquomixed formrsquorsquo rim to the intergrown lepidolite rim(Table 1 Figs 3h 6l) suggesting that the former evolvedto the latter as also found in IIZa and Cc In both crystalsthe rim compositions have higher Si (Fe2thornthorn Mn thorn Mg)Licalc Rb Cs F contents and lower AlVI (AlIVthorn AlVI) Naand OH contents and KRb ratio than the core (Table 1 Figs3g 6i j k 3h 6l) A compositional gap occurs between coreand rim in the diagrams for both crystals (Fig 6i j k l)suggesting that both rims correspond to overgrowths and no
Silicate and oxide minerals from a zoned granitic pegmatite 973
eschweizerbart_xxx
diffuse reequilibration took place in any crystal as thecontacts between core and rim are sharp
In the Cc lithian muscovite is surrounded and pene-trated by lsquolsquomixed formrsquorsquo showing well defined contacts(Fig 3i) The lsquolsquomixed formrsquorsquo has higher Si Fe2thorn Mn(Fe2thornthorn Mn thorn Mg) Licalc Rb Cs F contents and lowerAlVI (AlIV thorn AlVI) Na OH contents and KRb ratio thanthe lithian muscovite (Table 1 Fig 6m n) and a composi-tional gap occurs between both micas suggesting thatlsquolsquomixed formrsquorsquo replaced lithian muscovite In rare crystalsa small lepidolite core is surrounded by a large muscoviterim containing K-feldspar inclusions The contact betweenthe core and rim is sharp (Fig 3j) A thin partial rim oflithian muscovite surrounds muscovite and the contact isgradual The muscovite rim has higher AlVI (AlIVthornAlVI)Na K OH contents and a greater KRb value and lower SiFe2thorn Mn Licalc Rb Cs and F contents than the lepidolitecore (Table 1 Fig 6o p) and a compositional gap occursbetween them (Fig 6o p) indicating that either muscoviteforms an overgrowth or it is reversely formed From themuscovite rim to the lithian muscovite rim the Si Licalc
Rb F contents increase whereas the AlVI (AlIV thorn AlVI)and OH contents and KRb ratio decrease (Table 1 Fig 6op) suggesting that muscovite evolved to lithian muscoviteas also found in IIZa and IIZb
44 Evolution of mica compositions within each zoneand from the outer intermediate zone to the core of theNamivo granitic pegmatite
The KRb ratio is taken as the best fractionation index inmicas (eg Cerny et al 1985 Foord et al 1995 Wise1995 Pesquera et al 1999 Roda Robles et al 2006 2007)It is hard to establish trends in the evolution of mica com-position from muscovite and lithian muscovite to lsquolsquomixedformrsquorsquo and lepidolite within each zone because the KRbratio shows some partial overlapping particularly betweenthe lithian muscovite and lsquolsquomixed formrsquorsquo and also betweenthe latter and lepidolite However an evolution from mus-covites to lepidolite (Al-richer mica Fig 4) is clearer (Fig7) In general in IIZa IIZb and Cc the Si Licalc Rb Cs and
Fig 5 The main substitutions in micas from the Namivo granitic pegmatite Mozambique a b SiIVthorn LiVI versus AlIVthornAlVI showing the 2SithornLi 3Altotal substitution mechanism operating in dioctahedral micas (Mu muscovite and Lith mu lithian muscovite) c d AlVI thornamp VI
versus LiVI (where amp represents a vacancy) and showing the 3LiVI AlVI thorn 2 amp VI substitution mechanism operating in trioctahedral micas(Mix f ndashlsquolsquomixed formrsquorsquo Lep lepidolite Zin zinnwaldite and Pol-FeMg-containing polylithionite) OIZ IIZa IIZb and Cc as in Fig 2
974 A M R Neiva
eschweizerbart_xxx
F contents tend to increase and the (AlIV thorn AlVI) AlVI
contents and KRb ratio tend to decrease from muscoviteto lepidolite (Table 1 Fig 7) This sequence is consistentbut rarely in the Cc lepidolite is rimmed by muscovite (Fig3j) But in the OIZ the evolution stops in lsquolsquomixed formrsquorsquoparticularly shown by the large range of the KRb ratiowhich mainly overlaps that of lepidolite from this zone(Fig 7) because this lepidolite is an Al-poorer mica whereasthe others are Al-richer micas (Fig 4)
In the OIZ the lepidolite has more Si Licalc and F andless (AlIV thorn AlVI) Ti Fe2thorn Mn Mg and Zn than zinn-waldite (Table 1) but it has larger ranges of Rb and KRbratio than zinnwaldite (Fig 7) The FeMg-containingpolylithionite is the richest mica in Si Licalc and thepoorest in (AlIV thorn AlVI) (Table 1) But at this zone scalethe polylithionite has Rb Cs contents and KRb ratiowithin the ranges for lepidolite and close to those of zinn-waldite (Fig 7)
Fig 6 Variation diagrams of micas from selected zoned crystals from the zones of the Namivo granitic pegmatite Mozambique to showtheir relationships lith musc lithian muscovite OIZ IIZa IIZb and Cc an in Fig 2
Silicate and oxide minerals from a zoned granitic pegmatite 975
eschweizerbart_xxx
From the OIZ to IIZa IIZb and Cc muscovite and lithianmuscovite generally show increases in the Si Licalc F and Rbcontents and decreases in the Fe2thorn and Mg contents and KRb ratio but the Mg content is very low in these micas fromthe IIZa IIZb and Cc (Table 1 Fig 7a) The lsquolsquomixed formrsquorsquoshows increases in the Si Licalc F Rb Cs contents anddecreases in the (AlIV thorn AlVI) and Mg contents and KRbratio but the Mg content is very low in this mica from theIIZb and Cc (Table 1 Fig 7b c) The lepidolite shows anincrease in the Si Licalc F Rb and Cs contents and a decreasein the KRb ratio from the IIZa to the IIZb and Cc (Table 1Fig 7d e) Furthermore the lepidolite from the OIZ has thelowest (AlIV thorn AlVI) AlVI and OH contents the highest SiFe2thorn Licalcand F contents and KRb ratio and the lowest Rband Cs contents compared to lepidolite from the other zones(Table 1 Fig 7d e)
5 Feldspars
Selected chemical analyses of albite and K-feldspar fromfive zones of the Namivo granitic pegmatite are given inTable 2 Strontium is the most abundant trace element inalbite (eg Cerny 1994) Anorthite and Sr contents and SrCa ratio of albite decrease from the WZ to the Cc (Fig 8Table 2) Rubidium is the most abundant trace element inK-feldspar followed by Cs in IIZa IIZb and Cc In gen-eral K Rb and Cs contents of K-feldspar increase and KRb and KCs values decrease from the WZ to the Cc (Table2 Fig 9)
The program SOLVCALC 20 (Wen amp Nekvasil 1994)using the Margules model Fuhrman amp Lindsley (1988) wasapplied for the purpose of thermometry The pairing ofplagioclase cores with the K-feldspars average of eachsample was used to estimate the crystallization temperaturesof primary magmatic feldspars They are 405 C (WZ)406ndash340 C (OIZ) 390ndash335 C (IIZa) 347ndash306 C (IIZb)and 333ndash289 C (Cc) at 3 kbar The metamorphic environ-ment of rare-element-Li granitic pegmatites is one of lowpressure 2ndash4 kbar (Cerny amp Ercit 2005) In general thedifference between the maximum and minimum calculatedtemperatures at 2 3 and 4 kbar for the same feldspar pairfrom the Namivo pegmatite is lower than 40 C The tem-perature decreases from the wall zone (WZ) to the core(Cc) A similar temperature behavior of feldspars wasfound in the pegmatite-aplite dike USA (Morgan ampLondon 1999)
6 Other silicates
Tourmaline of schorl composition was only found inthe OIZ (Table 2) because there was not enough Feand Mg for schorl to precipitate in the other zonesSpodumene only occurs in the Cc and its compositionis nearly pure (Table 2)
7 Columbite-tantalite
Representative chemical analyses of columbitendashtantalitefrom the Namivo granitic pegmatite are given in Table 3and plotted in the columbite quadrilateral (Fig 10a)Most crystals are unzoned but zoned crystals with dar-ker and lighter zones in BSE images are from the Cc Thelighter zone of columbite-(Mn) has higher Ta contentTa(Ta thorn Nb) and Mn(Mn thorn Fe) values and lower Nbcontent than the darker zone (Fig 10a b) The crystals ofthe columbitendashtantalite minerals are low in W Sn and Tiimpurities (Table 3)
The main trend starts from the columbite-(Mn) of theOIZ towards the more Mn-enriched and slightly Ta-enriched columbite-(Mn) from the IIZa and Cc The high-est Ta(Ta thorn Nb) values belong to the lighter zone ofcolumbite-(Mn) with Mn(Mn thorn Fe) frac14 10 from the CcThe richest columbite-(Mn) in Ta(TathornNb) and composi-tions of tantalite-(Fe) and tantalite-(Mn) were only foundin the OIZ (Fig 10a) and are associated with lepidolite andpolylithionite (Fig 3c)
8 Gahnite
Gahnite was rarely found in the OIZ and shows a darkerzone that partially surrounds a lighter zone in a BSE image(Fig 11a) The darker zone has a higher Zn content andlower Sn Ti Nb Ta Mn contents and SnZn value than thelighter zone (Table 4 Fig 11b c) These gahnite composi-tions fall within the igneous field of Batchelor amp Kinnaird(1984) The darker zone is closer in composition to thepure gahnite (Zn8Al16O32) than the lighter zone whichcontains up to 0983 apfu Sn 0195 apfu Ti 1029 apfutotal Fe2thorn 0101 apfu Mn (Table 4) and consequently hasa composition distinct from nigerite In general both thedarker and lighter zones have higher Sn Ti and Fe contentsthan gahnite from the granitic pegmatites of Nigeria(Batchelor amp Kinnaird 1984) Arga northern Portugal(Gomes et al 1995) and Cabanas northern Portugal(Neiva amp Champness 1997) Borborema province north-eastern Brazil (Soares et al 2007) The Zn=Fe2thornt values ofthe darker and lighter zones of gahnite from Namivo arelower than those reported in Neiva amp Champness (1997)and Soares et al (2007)
9 Discussion and conclusions
91 Evolution of micas in the zoned pegmatite
In general individual mica crystals show varying patternsand compositional zoning involving several elementsmainly Si AlVI (AlIV thorn AlVI) Fe2thorn Mn (Fe2thornthorn Mn thornMg) Licalc Rb Cs F and OH and the KRb ratioProgressively zoned crystals from the IIZa show grada-tional contacts between a lithian muscovite core and a
976 A M R Neiva
eschweizerbart_xxx
lsquolsquomixed formrsquorsquo rim (Figs 3e 6e f) and the zoning patternscorrespond to fractionation trends and probably reflect adrop in temperature during the crystallization of the grani-tic pegmatite melt Progressively zoned crystals also occurin OIZ IIZb and Cc Some crystals are reversely zonedwith a) a lsquolsquomixed formrsquorsquo core and a lithian muscovite rimfrom the OIZ (Figs 3d d1 6d) b) a core consisting oflsquolsquomixed formrsquorsquo and lepidolite and a rim of muscovite andlithian muscovite from the IIZa (Figs 3f f1 6g h) c) alepidolite core and a muscovite and lithian muscovite rimfrom the Cc (Figs 3j 6o p) which may be explained bythe hypothesis of oscillations in the compositions of themelt from which they grew alternating between an Li-enriched boundary layer and a bulk melt that is less frac-tionated The muscovite evolved to lithian muscovite inIIZa and Cc (Figs 3f 6g h 3j 6o p) Replacements (Figs3a 6a b 3c 6c 3i 6m n Table 1) occur in OIZ and Ccand overgrowths (Figs 3b g 6i j k 3h 6l Table 1) occurin OIZ and IIZb as found in BSE images
Muscovite evolved to lithian muscovite as observed inOIZ IIZa IIZb and Cc (Figs 3f 6g h 3j 6o p Table 1)Lithian muscovite evolved to lsquolsquomixed formrsquorsquo in OIZ IIZaIIZb and Cc (Figs 3e 6e f Table 1) and lsquolsquomixed formrsquorsquoevolved to lepidolite in IIZa IIZb and Cc (Figs 3f f1 6gh 3h 6l Table 1) All these evolutions are due to fractionalcrystallization
In the OIZ lepidolite has more Si Licalcand F butsimilar KRb to that of zinnwaldite and replaces it (Figs
3a 6a b 7d Table 1) An FeMg-containing polylithionitehas higher Si Licalcand Rb contents and a smaller KRbratio than the lepidolite that it replaces (Figs 3c 6c Table1) and a continuous chemical evolution from lepidolite topolylithionite is shown
The trends for major and trace elements of micas withineach zone are difficult to define due to some partial over-lapping but a progressive evolution from muscovite to lithianmuscovite lsquolsquomixed formrsquorsquo and lepidolite in IIZa IIZb and Ccis mainly shown by an increase in the Si Licalc F Rb and Cscontents and a decrease in the KRb ratio and this is simi-larly shown in the OIZ from muscovite to lsquolsquomixed formrsquorsquo(Table 1 Fig 7) In the OIZ Si and Licalccontents increaseprogressively from zinnwaldite to lepidolite and FeMg-containing polylithionite but a gap occurs between zinnwal-dite and lepidolite (Table 1 Fig 4) whereas a continuousevolution from lepidolite to polylithionite is observed TheKRb ratios of zinnwaldite and polylithionite are within therange of that of lepidolite (Fig 7d e)
Each Al-richer mica (muscovite lithian muscovite andlsquolsquomixed formrsquorsquo) exhibits an evolution from the OIZ to theIIZa and then to the IIZb and Cc particularly shown by anincrease in the Si Licalc F and Rb contents and adecrease in the KRb ratio but also an increase in theCs content in the lsquolsquomixed formrsquorsquo (Table 1 Fig 7) Theseelements and ratio have been used as petrogenetic indi-cators of evolution in micas from pegmatites (eg Cernyet al 2005 Roda Robles et al 2006 2007 Vieira et al
Fig 7 Plot of some variation diagrams of micas from the OIZ IIZa IIZb and Cc of the Namivo granitic pegmatite Mozambique showingthat the Rb2O and Cs2O contents increase and the KRb ratio decreases for micas from the OIZ to the Cc OIZ IIZa IIZb and Cc as in Fig 2
Silicate and oxide minerals from a zoned granitic pegmatite 977
eschweizerbart_xxx
Tab
le2
R
epre
sen
tati
ve
elec
tro
nm
icro
pro
be
anal
yse
sin
wt
o
ffe
ldsp
ars
sch
orl
and
spo
du
men
efr
om
the
Nam
ivo
gra
nit
icp
egm
atit
eM
oza
mb
iqu
e
Alb
ite
K-f
eld
spar
Sch
orl
Sp
od
um
ene
Zo
nes
WZ
OIZ
IIZ
aII
Zb
Cc
Zo
nes
WZ
OIZ
IIZ
aII
Zb
Cc
Zo
nes
OIZ
Zo
ne
Cc
SiO
26
75
76
78
86
87
06
84
76
84
1S
iO2
65
10
65
55
65
46
64
96
64
72
SiO
23
52
0S
iO2
64
65
TiO
20
02
mdash0
02
mdashmdash
TiO
2mdash
00
1mdash
mdashmdash
TiO
20
35
Al 2
O3
27
20
Al 2
O3
20
25
19
74
19
67
19
88
19
97
Al 2
O3
18
96
18
23
18
31
18
24
18
05
B2O
3
10
28
Fe 2
O3
00
6F
e 2O
3mdash
mdashmdash
mdash0
10
Fe 2
O3
mdash0
02
mdash0
03
mdashA
l 2O
33
17
2M
nO
01
3M
nO
00
6mdash
mdashmdash
mdashM
nO
mdash0
03
00
3mdash
mdashF
eO1
35
2M
gO
01
8M
gO
mdashmdash
mdashmdash
mdashM
gO
00
10
01
00
5mdash
mdashM
nO
03
3N
a 2O
01
9C
aO1
04
08
00
56
03
70
32
CaO
00
10
01
00
60
01
00
2M
gO
22
8L
i 2O
8
05
Na 2
O1
06
11
12
01
12
11
13
41
13
4N
a 2O
06
50
58
04
10
59
03
8C
aO0
23
To
tal
10
04
6K
2O
00
50
17
00
60
14
01
0K
2O
14
72
14
75
15
67
15
01
15
74
Li 2
O
02
2S
rO0
72
05
00
24
01
1mdash
Rb
2O
00
90
20
03
00
59
09
0N
a 2O
22
8S
i1
99
7P
2O
50
01
00
4mdash
mdashmdash
Cs 2
O
00
6
00
60
09
01
80
20
K2O
00
1A
lIV0
00
3T
ota
l1
00
33
10
03
31
00
46
10
03
11
00
24
P2O
5mdash
00
3mdash
mdashmdash
H2O
3
18
P2
00
To
tal
99
60
99
48
10
03
89
96
11
00
01
F0
78
AlV
I0
98
7S
rC
a(w
t)0
81
07
40
50
03
50
Cl
mdashF
e3thorn
00
01
KR
b(w
t)153
68
48
23
16
Sum
1003
8P
09
9S
i1
18
23
11
87
91
19
58
11
93
21
19
21
KC
s(w
t)4
07
20
41
63
73
69
O
F0
33
Li
10
00
P0
00
10
00
6mdash
mdashmdash
To
tal
10
00
5M
n0
00
3T
i0
00
3mdash
00
03
mdashmdash
Si
11
98
61
20
88
12
04
11
20
45
12
03
3M
g0
00
8A
l4
17
64
07
14
03
54
08
34
10
1P
mdash0
00
5mdash
mdashmdash
TS
i5
95
2N
a0
01
2F
e3thorn
mdashmdash
mdashmdash
00
13
Ti
mdash0
00
1mdash
mdashmdash
Al
00
48
P1
02
Mn
00
09
mdashmdash
mdashmdash
Al
41
14
39
62
39
70
39
86
39
55
B3
00
0M
gmdash
mdashmdash
mdashmdash
Fe3thorn
mdash0
00
3mdash
00
04
mdashZ
Al
60
00
Ca
01
95
01
50
01
04
00
69
00
60
Mn
mdash0
00
50
00
5mdash
mdashY
Al
02
74
Sr
00
73
00
51
00
24
00
11
mdashM
g0
00
30
00
30
01
4mdash
mdashT
i0
04
5N
a3
59
93
80
03
78
33
83
23
83
1C
a0
00
20
00
20
01
20
00
20
00
4M
g0
57
5K
00
11
00
38
00
13
00
31
00
22
Na
02
32
02
07
01
46
02
12
01
37
Mn
00
47
K3
45
73
47
03
67
73
55
03
73
3F
e2thorn
19
12
Z1
60
01
59
61
60
01
60
11
60
4R
b0
01
10
02
40
03
50
07
00
10
8L
i0
14
8X
38
94
04
39
33
94
39
1C
s0
00
20
00
50
00
70
01
40
01
6P
Y3
00
0m
ole
s
XC
a0
04
2A
n5
13
82
71
71
5Z
16
10
16
06
16
01
16
03
15
99
Na
07
47
Ab
94
69
53
97
09
75
97
9X
37
13
72
39
03
85
40
0K
00
02
Or
03
09
03
08
06
mo
les
amp
02
09
An
01
01
03
01
01
Ab
63
56
38
56
35
OH
35
83
Or
93
69
43
95
99
43
96
4F
04
17
Cl
mdash
WZ
ndashw
allzo
ne
OIZ
ndasho
ute
rin
term
edia
tezo
ne
IIZ
aan
dII
Zb
ndashin
ner
inte
rmed
iate
zon
esC
cndash
core
asin
Fig
2B
aOis
bel
ow
the
det
ecti
on
lim
itin
bo
thfe
ldsp
ars
Cs 2
Ofrac14
00
3w
tin
the
K-
feld
spar
fro
mth
eW
Z
mdashN
ot
det
ecte
d
Nu
mb
ero
fio
ns
on
the
bas
iso
f3
2o
xy
gen
sfo
ral
bit
ean
dK
-fel
dsp
ar
31
anio
ns
(O
OH
F
)fo
rsc
ho
rlan
d6
ox
yg
ens
for
spo
du
men
e
-A
mo
un
tin
ferr
edfr
om
con
sid
erat
ion
so
fst
oic
hio
met
ry
978 A M R Neiva
eschweizerbart_xxx
2011) Lepidolite from the OIZ is an Al-poorer mica (Fig4) and has the highest Si Licalcand F contents (Table 1)indicating that an evolution cannot be shown from thislepidolite to lepidolites from the other zones which areAl-richer micas (Fig 4) However there is a regulardecrease in the KRb ratio and a progressive increase inthe Rb and Cs contents from lepidolite of the OIZ tolepidolite of IIZa IIZb and Cc (Fig 7) which indicatesthat the KRb ratio and Rb and Cs contents must not beconsidered alone to show fractional crystallization in
lepidolites particularly if some are Al-richer micas andothers Al-poorer micas The high Licalcand F contents oflepidolite from the OIZ did not decrease its KRb ratioSuch an effect is considered to have taken place in lepi-dolite (an Al-richer mica) from the wall zone of the Tancopegmatite Manitoba Canada (Van Lichtervelde et al2008) An evolution from the lepidolite of the IIZa to thatof the Cc is generally shown by the increasing Si LicalcF Rb Cs contents and a decrease in the KRb ratio (Table1 Fig 7)
At the scale of crystals the pegmatite zones and alsothose from the OIZ to the Cc of the Namivo granitic pegma-tite Al-richer micas show fractionation because theyformed from the fractionation of an Li-rich pegmatite melt
The Al-poorer micas zinnwaldite lepidolite and FeMg-containing polylithionite only occur in the OIZ (Fig 4)Polylithionite is the mica richest in Si and Licalc and lepi-dolite from this zone is the richest in Si Licalcand F (Fig 4Table 1) The high Li contents of these micas reflect aconsiderably higher D(Li) at low temperature (Icenhoweramp London 1995) These Li-rich micas may have crystal-lized from an undercooled melt This hypothesis does notimply high Rb and Cs contents and low KRb ratios Thisagrees with the fact that these micas from the OIZ havesimilar Rb and Cs contents and KRb ratios to those of Al-richer micas (muscovite lithian muscovite and lsquolsquomixedformrsquorsquo) from the same pegmatite zone (Fig 7) Howeverthe lepidolite from the wall zone of the Tanco pegmatiteCanada of a similar origin has a low KRb ratio which isattributed to the complexly interrelated structural compo-nents of this lepidolite (Van Lichtervelde et al 2008) TheLi-rich micas from the OIZ may also represent disequili-brium These two hypotheses are considered the best forthese micas of primary magmatic origin
Another hypothesis was also considered They may havecrystallized in boundary layers which concentrate Li andF But this mechanism was suggested for the most fractio-nated tourmaline enriched in Li and F from the core of the
Fig 8 Plot of albite compositions from all zones of the Namivo granitic pegmatite Mozambique showing that the anorthite content of albitedecreases from the WZ to the Cc WZ OIZ IIZa IIZb and Cc as in Fig 2
Fig 9 The Rb vs Cs diagram of K-feldspar from all zones of theNamivo granitic pegmatite Mozambique showing that the Rb andCs contents of K-feldspar increase from the WZ to the Cc WZ OIZIIZa IIZb and Cc as in Fig 2
Silicate and oxide minerals from a zoned granitic pegmatite 979
eschweizerbart_xxx
Little Three pegmatite dike USA (Morgan amp London1999) and the micas enriched in Li and F from theNamivo pegmatite belonging to the OIZ Furthermore ina boundary layer melt that became enriched in Li and F theKRb ratio of micas decreases strongly (Van Lichterveldeet al 2008) which was not found in these micas from theOIZ (Fig 7d) Nor can they have resulted from the crystal-lization of a late melt that would have reacted with the OIZbecause these micas are among those containing the high-est KRb values (Fig 7d)
92 The importance of feldspars micas andcolumbitendashtantalite compositions to the Namivogranitic pegmatite evolution
The trace elements Rb and Cs and the KRb and KCs ratioshave been used to show the evolution of K-feldspar inpegmatites (eg Cerny 1994 Cerny et al 2005 RodaRobles et al 2005) The Rb and Cs contents increase andthe KRb and KCs ratios of K-feldspar decrease from theWZ to the Cc (Fig 9 Table 2) reflecting the growth of K-feldspar from an increasingly fractionated melt withouthaving grown from or having been chemically modifiedby an aqueous fluid as in the Swamp pegmatite section atthe Little Three Mine USA (London et al 2012) Thecrystallization of K-feldspar from an exsolved aqueousfluid from melt will reverse the magmatic fractionation ofRb Cs KRb and KCs because Rb and especially Cs areso much more compatible in vapor that both Rb and Csremain in the fluid phase (London et al 2012) The feldsparsolvus pairs in the Namivo pegmatite record magmaticcrystallization temperatures that decrease from WZ to CcAlbite shows a decrease in the Ca Sr contents and SrCaratio from the WZ to the Cc (Fig 8 Table 2) Therefore thefeldspars and also Al-richer micas as already explainedshow fractionation in this zoned pegmatite
In general lepidolite from the Namivo pegmatite hassimilar Rb2O and Cs2O contents and KRb (wt) values tothose of lepidolite from the Rozna and Dobra Voda lepi-dolite-subtype pegmatites in the Czech Republic (Cernyet al 1995) but lower Rb2O and Cs2O contents thanlepidolite from the lepidolite-subtype pegmatite at RedCross Lake Manitoba Canada (Cerny et al 2012a) K-feldspar from the Namivo pegmatite also has lower Rb2O
Table 3 Representative electron microprobe analyses in wt of columbitendashtantalite from the Namivo granitic pegmatite Mozambique
Outer Intermediate Zone - OIZ Inner Intermediate Zone - IIZa
Core - Cc
D L L
WO3 022 059 079 113 101 351 050 007Ta2O5 5487 5123 2503 3186 2888 2519 3127 4542Nb2O5 2537 3000 5483 4635 5113 5144 4911 3686SnO2 008 015 024 049 020 026 017 012TiO2 263 161 136 254 202 145 125 016FeO 860 710 665 471 236 068 mdash mdashMnO 793 952 1099 1304 1400 1725 1748 1718Total 9970 10020 9989 10012 9960 9978 9978 9981W 0004 0011 0013 0019 0016 0057 0008 0001Ta 1065 0975 0422 0552 0495 0430 0543 0847Nb 0819 0949 1538 1336 1456 1460 1418 1143Sn 0002 0004 0006 0012 0005 0007 0004 0003Ti 0141 0085 0063 0122 0096 0068 0060 0008Fe 0513 0416 0345 0251 0124 0036 mdash mdashMn 0479 0564 0578 0704 0747 0917 0945 0998P
3023 3004 2965 2996 2939 2975 2978 3000Mn(Mn thorn Fe) 048 058 063 074 086 096 100 100Ta(Ta thorn Nb) 057 051 022 029 025 023 028 043Classification tant-(Fe) tant-(Mn) col-(Mn) col-(Mn) col-(Mn) col-(Mn) col-(Mn) col-(Mn)
D ndash darker L ndash lighter zones mdash Not detected tant-tantalite col-columbite Cation formula on the basis of 6 atoms of oxygen
Fig 10 Compositions of columbitendashtantalite from the Namivogranitic pegmatite Mozambique in the columbite quadrilateralshowing that Mn(Mn thorn Fe) of columbite-(Mn) increases from theOIZ to the Cc and the richest columbite-(Mn) in Ta(Ta thorn Nb)tantalite-(Fe) and tantalite-(Mn) only occur in the OIZ OIZ IIZaand Cc as in Fig 2
980 A M R Neiva
eschweizerbart_xxx
and Cs2O contents than K-feldspar from the lepidolite-subtype pegmatite at Red Cross Lake The Rb2O andCs2O contents of primary and late K-feldspar of this peg-matite at Red Cross Lake attained unprecedented levels(Cerny et al 2012a) The lowest KRb (wt) values ofmuscovite lithian muscovite lsquolsquomixed formrsquorsquo and lepido-lite from the IIZb and Cc (Fig 7) and K-feldspar (KRb frac1414) from the Cc compare well with those found in theseminerals from the AC6frac143 lepidolite-subtype pegmatitefrom Greer Lake (Cerny et al 2005) and some of themost fractionated pegmatites worldwide which belong tothe petalite-subtype (eg Tanco Manitoba Cerny 2005Cerny et al 1998 Varutrask Sweden Cerny et al 2005)but muscovite lithian muscovite and lepidolite from theIIZb and Cc have lower Rb2O and Cs2O contents than thesemicas from the Tanco pegmatite (Cerny 2005a VanLichtervelde et al 2008) K-feldspar also has lower
contents of these oxides than the most evolved K-feldsparfrom the Tanco pegmatite (Cerny 2005a) The magmaticfractionation was strong from the WZ to IIZb and Cc of theNamivo lepidolite-subtype pegmatite
The compositional trend of columbite-(Mn) from the OIZto Cc of the Namivo granitic lepidolite-subtype pegmatite(Fig 10) is identical to that of columbite-group mineralsfrom the lepidolite-subtype complex granitic pegmatitesfrom the Dobra Voda in the Moldanubicum CzechRepublic (Novak amp Cerny 1998) and the HimalayaDistrict southern California (shown in Cerny et al 2004)Experimental data for the Fe-Mn pair (Linnen amp Cuney2005) suggest an increase in Fe with fractional crystalliza-tion which is not observed in nature Other phases seem tocontrol the bahavior of Fe and Mn in the melt eg thecrystallization of tourmaline causes a rapid increase of theMnFe in the melt (Van Lichtervelde et al 2006) When thecrystallization of tourmaline stopped the columbitendashtantaliteminerals showed a constant MnFe indicating that the Fe andMn contents in the melt remained constant Schorl onlyoccurs in the OIZ of the Namivo granitic pegmatite and itscrystallization cannot be responsible for the increase in theMnFe of the melt because Mn(Mn thorn Fe) of columbite-(Mn) increases progressively from the OIZ to the IIZa and Cc(Fig 10) Garnet zinnwaldite and gahnite containing Fe andMn also only occur in the OIZ and cannot also have causedthe increase of the MnFe in the melt The dominant Mnenrichment before Ta enrichment started in the columbitendash-tantalite composition from some granitic pegmatites isattributed to an increased alkali-fluoride activity at moderatemHF (Cerny et al 2004) and an increase in the activity offluorine (Martins et al 2011) Each Al-richer mica (musco-vite lithian muscovite and lsquolsquomixed formrsquorsquo) from the Namivogranitic pegmatite shows an increase in F content from theOIZ to the IIZa IIZb and Cc (Table 1) In general the Fcontent of lepidolite also increases from the IIZa to the IIZband Cc Therefore the extreme Fe-Mn fractionation beforeTa enrichment in columbite-(Mn) (Fig 10) may be due to anincrease in the activity of fluorine as a consequence offractional crystallization The increase in the Ta content ofcolumbite-(Mn) from the Namivo granitic pegmatite isattributed to fractional crystallization
The geochemical evolution of albite and K-feldsparfrom the WZ to the Cc Al-richer micas muscovite lithianmuscovite and lsquolsquomixed formrsquorsquo from the OIZ to the Cc andlepidolite from the IIZa to the Cc and columbite-(Mn) andalso beryl (Neiva amp Neiva 2005) from the OIZ to the Ccare caused by magma fractionation The pegmatite zonesare the product of primary crystallization from a volatile-rich silicate melt The pegmatite consolidated from the WZto the Cc The IIZb is one of the most evolved zones asalso suggested by the beryl composition (Neiva amp Neiva2005) and is the richest in lsquolsquomixed formrsquorsquo and lepidolite
The richest columbite-(Mn) in Ta(Ta thorn Nb) and com-positions of tantalite-(Fe) and tantalite-(Mn) only occur inthe OIZ (Fig 10a) associated with lepidolite and polythio-nite (Fig 3c) which may be due to the local depletion of Liand F in the melt which decreases the solubility of Ta andcauses Ta precipitation (Linnen 1998 Linnen amp Cuney
Fig 11 a Backscattered-electron image of a gahnite crystal with adarker zone partially surrounding a lighter zone from the OIZ of theNamivo granitic pegmatite b c Plot of gahnite compositions in theSn-Zn-Ti diagram (atomic proportions) showing a chemical distinc-tion between the lighter and darker zones OIZ as in Fig 2
Silicate and oxide minerals from a zoned granitic pegmatite 981
eschweizerbart_xxx
2005) At the Tanco pegmatite Ta oxides are also asso-ciated with lepidolite enriched in Li and F from the wallzone (Van Lichtervelde et al 2008)
93 Origin and evolution of the zoned graniticlepidolite-subtype pegmatite at Namivo
In general granitic pegmatites particularly those belong-ing to the rare-element class are accepted as having beenformed by the fractional crystallization of a granite melt(eg Cerny 1991a b 1992 Neiva et al 2008 2012 Roda-Robles et al 2012) But it also has been proposed thatpegmatites may be formed by partial melting of appropri-ate rock compositions (eg Nabelek et al 1992 Nabelekamp Russ-Nabelek 1992 Shearer et al 1992 Roda Robleset al 1999) The lepidolite-subtype pegmatites belong tothe LCT (lithium-cesium-tantalum) family (Cerny amp Ercit2005) They are derived by fractional crystallization of agranite magma (eg Cerny et al 2005 Neiva amp Ramos2010 Cerny et al 2012b) Experimental work by Londonet al (1989) and London (1990) using Macusani glass as astarting material equivalent to the bulk composition ofhighly fractionated rare-alkali-rich pegmatites underhighly evolved and hydrous but H2O undersaturatedmelt obtained the latest primary assemblage consisting
of an Li-rich mica thorn albite thorn quartz deposited directlyfrom the primary melt phase Other authors egZasedatelev (1974 1977) and Stewart (1978) argue thatlepidolite-bearing pegmatites are derived from direct ana-texis and Gordiyenko et al (1996) consider that they arederived from an undefined medium and the rare-elementmineralization is superimposed on preexisting barrenpegmatites
Lepidolite-subtype pegmatites may migrate a long wayfrom their parent granites because their volatile-rich highlyfluid pegmatite melts are stable at relatively low tempera-tures (eg Cerny et al 2005 Antunes et al 2013)Therefore the Namivo pegmatite is probably derived byfractional crystallization of an S-type granite magmawhich resulted from partial melting of metamorphosed juve-nile sediments containing micas that carry most of the traceelements that define the signature of the LCT pegmatites(eg Dahl et al 1993)
The two main models for the internal evolution of peg-matites that dominated for more than a century are a) thefractional crystallization of a flux-bearing granitic melt fromthe margins to the center of the pegmatite (Cameron et al1949) b) the interactions of an aqueous fluid with graniticmelt (Jahns amp Burnham 1969 Jahns 1982) The recentmodel of constitutional zone refining combines aspects ofboth models and invokes the formation of a flux-enriched
Table 4 Electron microprobe analyses in wt of zoned gahnite from the outer intermediate zone (OIZ) of the Namivo granitic pegmatiteMozambique
Darker Zone Lighter Zone
Mean s Range Mean s Range
SnO2 036 050 0ndash097 658 281 151ndash998TiO2 008 008 0ndash021 065 034 008ndash105Nb2O5 001 002 0ndash006 018 007 007ndash029Ta2O5 001 004 0ndash010 015 013 0ndash033ZnO 3998 123 3810ndash4109 3339 318 3004ndash3848FeO 367 048 331ndash442 433 065 306ndash498MnO 032 004 028ndash040 039 006 032ndash048MgO 003 004 0ndash010 ndash ndash ndashAl2O3 5507 050 5436ndash5572 5337 070 5257ndash5443SiO2 003 003 0ndash007 008 010 0ndash025Total 9956 9912n 8 8Sn 0035 0048 0ndash0095 0648 0278 0149ndash0983Ti 0015 0015 0ndash0038 0120 0064 0015ndash0195Nb ndash 0003 0ndash0006 0021 0009 0009ndash0037Ta ndash 0002 0ndash0006 0009 0009 0ndash0021Zn 7226 0182 6890ndash7382 6086 0568 5482ndash6965Fe2thornt 0752 0103 0675ndash0913 0894 0135 0628ndash1029Mn 0066 0008 0057ndash0083 0082 0013 0066ndash0101Mg 0010 0015 0ndash0037 ndash ndash ndashAl 15887 0052 15805ndash15954 15526 0170 15375ndash15853Si 0007 0008 0ndash0018 0019 0025 0ndash0062P
23998 23405Fe3thorn 0064 0230Fe2thorn 0686 0658SnZn 0005 0007 0ndash0014 0106 0052 0021ndash0179ZnFe2thornt 961 143 768ndash1093 681 190 536ndash1109
n number of analysis Cation formula based on 32 atoms of oxygen Fe2thornt total Fe2thorn estimated
982 A M R Neiva
eschweizerbart_xxx
boundary layer of silicate liquid in advance of a crystal-lization front (London 2008 London amp Morgan 2012)
Lepidolite-subtype pegmatites are generally scarce(Cerny et al 2005) particularly the zoned ones In thesymmetrically zoned lepidolite-subtype pegmatites ofRozna and Dobra Voda Czech Republic micas (Cernyet al 1995) tourmaline (Selway et al 1999) and colum-bite-group minerals (Novak amp Cerny 1998) evolve fromthe outermost zone to the innermost zone following thecrystallization sequence The same was found in tourma-line from the zoned Lastovicky Dolnı Bory and Raddovicelepidolite-subtype pegmatite dikes in the Czeck Republic(Selway et al 1999)
In general beryl (Neiva amp Neiva 2005) feldsparsmicas and columbite-(Mn) (in this paper) from theNamivo lepidolite-subtype pegmatite record the progres-sive chemical evolution of the pegmatite from the wallzone to the core These minerals were produced by crystal-lization from a silicate melt rather than an aqueous fluidphase The slow cooling of melt shown by the magmaticcrystallization temperatures of feldspars cannot explain theincrease in grain-size of minerals from the wall zone to thecore but fluxes will be necessary to promote the change oftexture particularly a flux-rich hydrosilicate liquidaccording to the experimental evidence (London 2009)The constitutional zone refining model will be the best forthis zoned pegmatite and probably for all lepidolite-sub-type pegmatites because this model also produces a higherfinal concentration of incompatible components in a smal-ler volume of rock than fractional crystallization does(Morgan amp London 1999)
The core margin at the Rozna pegmatite contains K-feld-spar and quartz and the core consists mainly of quartz but it issurrounded and penetrated by a quartz-bearing albitethorn lepi-dolite complex which contains several minerals At theDobra Voda pegmatite the center of the dike is occupiedby the lepidolite unit containing albite and other minerals(Cerny et al 1995) At the Namivo pegmatite the coremargin consists of quartz and beryl and the core containsmainly quartz and spodumene but also albite lepidolite andother minerals The last-unit assemblages of primary miner-als in most of the highly fractionated LCT pegmatites are richin albite and commonly contain lepidolite or spodumene andmost of the other rare phases These units represent the lastmost fractionated liquid that can be derived by fractionalcrystallization of a crustal melt (London 2008)
The Namivo granitic pegmatite shows a significant dis-tinction from the other zoned lepidolite-subtype pegmatitesand LCT pegmatites except the Tanco petalite-subtypepegmatite in Canada because the lepidolite richest in SiLi and F FeMg-containing polylithionite and associatedcolumbite-(Mn) with the highest Ta(Ta thorn Nb) ratio tanta-lite-(Fe) and tantalite-(Mn) only occur in the outer inter-mediate zone These minerals usually form late in theconsolidation of pegmatites The lepidolite and polylithio-nite are probably derived from the disequilibrium crystal-lization of an undercooled melt Tantalite may reflect a localdecrease in Li and F that caused Ta precipitation
This paper contributes to a better understanding of theorigin and evolution of the rare zoned lepidolite-subtypepegmatites and shows that although the pegmatite evolvedfrom the wall zone to the core it presents an unusualassociation of lepidolite polylithionite and tantalite in theouter intermediate zone
Acknowledgments Thanks are due to JM Cotelo Neivaand MB Dias for the samples and information providedand to MR Machado Leite and MF Guimaraes for theuse of the electron microprobe facilities at the LaboratorioNacional de Energia e Geologia (LNEG) PortugalFinancial support was provided by the PortugueseGovernment for the project Pest-OECTEUI00732011of the Geosciences Centre through the PortugueseFoundation for Science and Technology I would like tothank D London WB Simmons and the associated editorE Widom for their constructive reviews of this manuscriptand M Prieto for his editorial work
References
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Geochemistry of feldspars and muscovite in granitic pegmatite
from the Cap de Creus field Catalonia Spain Can Mineral 41
103ndash116
Antunes IMHR Neiva AMR Ramos JMF Silva PB
Silva MMVG Corfu F (2013) Petrogenetic links between
lepidolite-subtype aplite-pegmatite aplite veins and associated
granites at Segura (central Portugal) Chemie der Erde in press
httpdxdoiorg101016jchemer20121203
Batchelor RA amp Kinnaird JA (1984) Gahnite compositions
compared Mineral Mag 48 425ndash430
Beurlen H Da Silva MRR Thomas R Soares DR Olivier P
(2008) Nb-Ta-(Ti-Sn) oxide mineral chemistry as tracer of rare-
element granitic pegmatite fractionation in the Borborema pro-
vince Northeastern Brazil Miner Deposita 43 207ndash228
Cameron EN Jahns RH McNair AH Page LR (1949)
Internal structure of granitic pegmatites Econ Geol
Monograph 2 115 p
Cerny P (1991a) Fertile granites of Precambrian rare-element
pegmatite fields is geochemistry controlled by tectonic setting
or source lithologies Precambrian Res 51 429ndash468
mdash (1991b) Rare-element granite pegmatites I Anatomy and inter-
nal evolution of pegmatite deposits Geoscience Canada 18
49ndash67
mdash (1992) Geochemical and petrogenetic features of mineralization
in rare-element granitic pegmatites in the light of current
research Applied Geochemistry 7 393ndash416
mdash (1994) Evolution of feldspars in granitic pegmatites in
lsquolsquoFeldspars and their Reactionsrsquorsquo I Parsons ed NATO
Advanced Study Institute Series C421 501ndash539
mdash (2005) The Tanco rare-element pegmatite deposit Manitoba
regional context internal anatomy and global comparisons in
lsquolsquoRare-element Geochemistry and Mineral Depositsrsquorsquo RL
Linnen amp IM Samson eds Geochemical Association of
Canada Short Course Notes St Catherines 17 127ndash158
Silicate and oxide minerals from a zoned granitic pegmatite 983
eschweizerbart_xxx
Cerny P amp Ercit TS (2005) The classification of granitic pegma-
tites revisited Can Mineral 43 2005ndash2026
Cerny P Meintzer RE Andersen AJ (1985) Extreme fractiona-
tion in rare-element granitic pegmatites selected examples of
data and mechanisms Can Mineral 23 381ndash421
Cerny P Goad BE Hawthorne FC Chapmann R (1986)
Fractionation trends of the Nb- and Ta-bearing oxide minerals
in the Greer Lake pegmatite granite and its pegmatite aureole
southeastern Manitoba Am Mineral 71 501ndash517
Cerny P Stanek J Novak M Baadsgaard H Rieder M
Ottolini L Kavalova M Chapman R (1995) Geochemical
and structural evolution of micas in the Rozna amp Dobra Voda
pegmatites Czech Republic Mineral Petrol 55 177ndash201
Cerny P Ercit TS Vanstone PJ (1998) Mineralogy and petrol-
ogy of the Tanco rare-element pegmatite deposit southeastern
Manitoba International Mineralogical Association 17th General
Meeting Toronto Field Guidebook B6
Cerny P Chapman R Ferreira K Smeds SA (2004)
Geochemistry of oxide minerals of Nb Ta Sn and Sb in
the Varutrask granitic pegmatite Sweden The case of an
lsquolsquoanomalousrsquorsquo columbitendashtantalite trend Am Mineral 89
505ndash518
Cerny P Masau M Goad BE Ferreira K (2005) The Greer
Lake leucogranite Manitoba and the origin of lepidolite-sub-
type granitic pegmatites Lithos 80 305ndash321
Cerny P Teertstra DK Chapman R Selway JB Hawthorne
FC Ferreira K Chackowsky LE Wang X-J Meintzer
RE (2012a) Extreme fractionation and deformation of the
leucogranite-pegmatite suite at Red Cross Lake Manitoba
Canada IV Mineralogy Can Mineral 50 1839ndash1875
Cerny P Halden NM Ferreira K Meintzer RE Brisbin WC
Chackowsky LE (2012b) Extreme fractionation and deforma-
tion of the leucogranite-pegmatite suite at Red Cross Lake
Manitoba Canada II Petrology of the leucogranites and peg-
matites Can Mineral 50 1807ndash1822
Dahl PS When DC Feldmann SG (1993) The systematics of
trace-element partitioning between coexisting muscovite and
biotite in metamorphic rocks from the Black Hills South
Dakota USA Geochim Cosmochim Acta 57 2487ndash2505
Dias MB amp Wilson WE (2000) The Alto Ligonha Pegmatites
Mozambique Mineral Record 31 459ndash497
Fleet ME (2003) Rock-Forming Minerals vol 3A Sheet silicates
micas The Geological Society London second edition chap 6
Lithium micas 651ndash690
Foord EE Cerny P Jackson LL Sherman DM Eby RK
(1995) Mineralogical and geochemical evolutions of micas
from miarolitic pegmatites of the anorogenic pikes-Peak
Batholith Colorado Mineral Petrol 55 1ndash26
Foster MD (1960) Interpretation of the composition of lithium
micas US Geol Surv Prof Paper 354-E 115ndash147
Fuhrman ML amp Lindsley DK (1988) Ternary-feldspar modeling
and thermometry Am Mineral 73 201ndash215
Gomes CL Castro P Alves C (1995) Caracterizacao das espi-
nelas zincıferas e do par ganite-nigerite no campo aplito-
pegmatıtico da Serra de Arga-Minho N de Portugal IV
Congresso Nacional de Geologia Resumos Alargados
Universidade do Porto Mem 4 629ndash633
Gordiyenko VV Ilyina AN Timochina LA Badamina EB
Stanek J (1996) Geochemical model of evolution of a pegma-
tite-forming ore-magmatic system of western Moravia Proc
Russ Mineral Soc 125 38ndash48 (in Russian)
Icenhower JP amp London D (1995) An experimental study for
element partitioning between biotite muscovite and coexisting
peraluminous granitic melt at 200 MPa (H2O) Am Mineral 80
1229ndash1251
Jahns RH (1982) Internal evolution of pegmatite bodies in lsquolsquoGranitic
Pegmatites in science and industryrsquorsquo P Cerny ed Mineralogical
Association of Canada Short Course Handbook 8 293ndash327
Jahns RH amp Burnham CW (1969) Experimental studies of
pegmatite genesis I A model for the derivation and crystal-
lization of granitic pegmatites Econ Geol 64 843ndash864
Jolliff BL Papike JJ Shearer CK (1987) Fractionation trends
in mica and tourmaline as indicators of pegmatite internal evo-
lution Bob Ingersoll pegmatite Black Hills South Dakota
USA GeochimCosmochim Acta 51 519ndash534
Kile DE amp Foord EE (1998) Micas from the Pikes Peak bath-
olith and its cogenetic granitic pegmatites Colorado optical
properties composition and correlation with pegmatite evolu-
tion Can Mineral 36 463ndash482
Linnen RL (1998) The solubility of Nb-Ta-Zr-Hf-W in granitic
melts with Li and Li thorn F constraints for mineralization in rare
metal granites and pegmatites Econ Geol 93 1013ndash1025
Linnen RL amp Cuney M (2005) Granite-related rare-element
deposits and experimental constraints on Ta-Nb-W-Sn-Zr-Hf
mineralization in lsquolsquoRare-element geochemistry and mineral
depositsrsquorsquo RL Linnen amp IM Samson eds Geochemical
Association of Canada Short Course Notes 17 45ndash68
London D (1990) Internal differentiation of rare-element pegmatites
a synthesis of recent research in lsquolsquoOre Bearing Granite Systems
Petrogenesis and Mineralizing Processesrsquorsquo HJ Stein amp JL
Hannah eds Geol Soc America Special Paper 246 35ndash50
mdash (2008) Pegmatites The Canadian Mineralogist Special
Publication 10 347 p
mdash (2009) The origin of primary textures in granitic pegmatites
Can Mineral 47 697ndash724
London D amp Morgan GB VI (2012) The pegmatite puzzle
Elements 8 263ndash268
London D Morgan GB VI Hervig RL (1989) Vapor-under-
saturated experiments in the system macusanite-H2O at 200
MPa and the internal differentiation of granitic pegmatites
Contrib Mineral Petrol 102 1ndash17
London D Morgan GB VI Paul KA Guttery BM (2012)
Internal evolution of miarolitic granitic pegmatites at the Little
Three mine Ramona California USA Can Mineral 50
1025ndash1054
Martins T Lima A Simmons WB Folster AU Noronha F
(2011) Geochemical fractionation of Nb-Ta oxides in Li-bear-
ing pegmatites from the Barroso-Alvao pegmatite field northern
Portugal Can Mineral 49 777ndash791
Monier G Charoy B Cuney M Ohnenstetter D Robert JL
(1987) Evolution spatiale et temporelle de la composition des
micas du granite albitique a topaze-lepidolite de Beauvoir
Geologie De La France 2ndash3 179ndash188
Monier G amp Robert JL (1986) Evolution of the miscibility gap
between muscovite and biotite solid solutions with increasing
lithium content an experimental study in the systems
K2OndashLi2OndashMgOndashAl2O3ndashSiO2ndashH2OndashHF at 600 C 2 kbar
PH2O comparison with natural lithium micas Mineral Mag
50 641ndash651
Morgan GBVI amp London D (1999) Crystallization of the little
three layered pegmatite-aplite dike Ramona District California
Contrib Mineral Petrol 136 310ndash330
984 A M R Neiva
eschweizerbart_xxx
Nabelek PI amp Russ-Nabelek C (1992) The generation and crys-
tallization conditions of the Proterozoic Harney Peak
Leucrogranite Black Hills South Dakota USA petrologic and
geochemical constraints Contrib Mineral Petrol 110
173ndash191
Nabelek PI Russ-Nabelek C Haeussler GT (1992) Stable
isotope evidence for the petrogenesis and fluid evolution in
the Proterozoic Harney Peak leucogranite Black Hills
South Dakota Geochim Cosmochim Acta 56 403ndash417
Neiva AMR amp Champness PE (1997) Nigerite and gahnite from
the granitic pegmatite veins of Cabanas Ponte de Lima northern
Portugal N Jb Mineral Mh 9 385ndash409
Neiva AMR Gomes MEP Ramos JMF Silva PB (2008)
Geochemistry of granitic aplite-pegmatite sills and their miner-
als from Arcozelo da Serra area (Gouveia central Portugal)
Eur J Mineral 20 465ndash485
Neiva AMR amp Neiva JMC (2005) Beryl from the granitic
pegmatite at Namivo Alto Ligonha Mozambique N Jb
Mineral Abh 181 173ndash182
Neiva AMR amp Ramos JMF (2010) Geochemistry of granitic
aplite-pegmatite sills and petrogenetic links with granites
Guarda-Belmonte area central Portugal Eur J Mineral 22
837ndash854
Neiva AMR Silva PB Ramos JMF (2012) Geochemistry of
granitic aplite-pegmatite veins and sills and their minerals from the
Sabugal area central Portugal N Jb Mineral Abh 189 49ndash74
Novak M amp Cerny P (1998) Niobium-tantalum oxide minerals
from complex granitic pegmatites in the Moldanubicum Czech
Republic primary versus secondary compositional trends Can
Mineral 36 659ndash672
Pesquera Perez A Torres-Ruiz J Gil PP Velilla N (1999)
Chemistry and genetic implications of tourmaline and Li-F-Cs
micas from the Valdeflores (Caceres Spain) Am Mineral 84
55ndash69
Rieder M Cavazzini G DrsquoYakonov YuS Frank-Kamenetskii
VA Gottardi G Guggenheim S Koval PV Muller G
Neiva AMR Radoslovich EW Robert J-L Sassi FP
Takeda H Weiss Z Wones DR (1999) Nomenclature of the
micas Mineral Mag 63 267ndash279
Roda Robles E Pesquera Perez A Velasco Roldan F Fontan F
(1999) The granitic pegmatites of the Fregeneda area
(Salamanca Spain) characteristics and petrogenesis Mineral
Mag 63 535ndash558
Roda Robles E Pesquera A Gil-Crespo PP Torres-Ruiz J
Fontan F (2005) Origin and internal evolution of the Li-F-
Be-P-bearing Pinilla de Fermoselle pegmatite (Central Iberian
Zone Zamora Spain) Am Mineral 90 1887ndash1899
Roda Robles E Pesquera Perez A Gil PP Torres-Ruiz J de
Parseval P (2006) Mineralogy and geochemistry of micas from
the Pinilla de Fermoselle pegmatite (Zamora Spain) Eur J
Mineral 18 369ndash377
Roda Robles E Keller P Pesquera Perez A Fontan F (2007)
Micas of the muscovite-lepidolite series from Karibib pegma-
tites Namibia Mineral Mag 71 41ndash62
Roda Robles E Pesquera A Gil-Crespo P Torres-Ruiz J
(2012) From granite to highly evolved pegmatite a case study
of the Pinilla de Fermoselle granite-pegmatite system (Zamora
Spain) Lithos 153 192ndash207
Selway JB Novak M Cerny P Hawthorne FC (1999)
Compositional evolution of tourmaline in lepidolite-subtype
pegmatites Eur J Mineral 11 569ndash584
Shearer CK Papike JJ Jolliff B (1992) Petrogenetic links
among granites and pegmatites in the Harney Peak rare-element
granite-pegmatite system Black Hills South Dakota Can
Mineral 30 785ndash809
Soares DR Hartmut B Ferreira ACM da Silva MRR
(2007) Chemical composition of gahnite and degree of peg-
matitic fractionation in the Borborema Pegmatitic Province
northeastern Brazil Anais Da Academ Bras Cien 79
395ndash404
Stewart DB (1978) Petrogenesis of lithium-rich pegmatites Am
Mineral 63 970ndash980
Tischendorff G Gattesmann B Forster H-J Trumbull RB
(1997) On Li-bearing micas estimating Li from electron
microprobe analyses and an improved diagram for graphical
representation Mineral Mag 61 809ndash834
Van Lichtervelde M Linnen RL Salvi S Beziat D (2006)
The role of metagabbro rafts on tantalum mineralization in the
Tanco granitic pegmatite Manitoba Can Mineral 44
625ndash644
Van Lichtervelde M Gregoire M Linnen RL Beziat D Salvi
S (2008) Trace element geochemistry by laser ablation ICP-
MS of micas associated with Ta mineralization in the Tanco
pegmatite Manitoba Canada Contrib Mineral Petrol 155
791ndash806
Vieira R Roda-Robles E Pesquera A Lima A (2011)
Chemical variation and significance of micas from the
Fregeneda-Almendra pegmatitic field (Central-Iberian Zone
Spain and Portugal) Am Mineral 96 637ndash645
Wen S amp Nekvasil H (1994) SOLVCALC an interactive gra-
phics program package for calculating ternary feldspar solvus
and two-feldspar geothermometry Comput Geosci 20
1025ndash1040
Wise MA (1995) Trace element chemistry of lithium-rich micas
from rare-element granitic pegmatites Mineral Petrol 55
203ndash215
Zasedatelev AM (1974) Possible accumulation of lithium in host
rocks of lithium pegmatite veins during old sedimentation pro-
cesses Doklady Acad Sci USSR Earth Sci Ser 218 196ndash198
(in Russian)
mdash (1977) Quantitative of metamorphic generation of rare-metal
pegmatites with lithium mineralization Doklady Acad Sci
USSR Earth Sci Ser 236 219ndash221 (in Russian)
Received 26 January 2013
Modified version received 21 May 2013
Accepted 23 July 2013
Silicate and oxide minerals from a zoned granitic pegmatite 985
eschweizerbart_xxx
generally decrease and Si Licalc Rb Cs and F contentsgenerally increase (Table 1)
42 Main substitution mechanisms
The 2Si thorn Li 3Altotal mechanism operates in the diocta-hedral micas (muscovite and lithian muscovite) (Fig 5a b)whereas the 3LiVI AlVIthorn 2ampVI (amp represents a vacancy)operates in the trioctahedral micas (lsquolsquomixed formrsquorsquo lepido-lite zinnwaldite and FeMg-containing polylithionite) (Fig5c d) which agrees with findings for micas from the Tancopegmatite (Van Lichtervelde et al 2008)
43 Textures and chemical compositions of zoned micacrystals
Backscattered-electron images combined with quantita-tive spot electron-microprobe analyses made it possibleto distinguish different micas in the Namivo graniticpegmatite Similar textural aspects and geochemicalobservations were found between some Al-richer micasfrom the OIZ IIZa IIZb and Cc Some selected zonedcrystals are documented (Table 1 Fig 3 and 6) In theOIZ lepidolite penetrates zinnwaldite along cleavagesand partially surrounds it and the contacts are sharp(Fig 3a) A chemical gap occurs between zinnwalditeand lepidolite compositions (Fig 6a b) Lepidolite withhigher Si Licalc F contents similar KRb value andlower (AlIV thorn AlVI) Ti Fe2thorn Mg (Fe2thornthorn Mn thorn Mg)Zn and OH contents (Table 1) replaces zinnwaldite Athin lepidolite rim partially surrounds lsquolsquomixed formrsquorsquoand the contact is sharp (Fig 3b) The lepidolite rimhas higher Si Mg Licalc Rb F contents and lowerAlVI Ti Fe2thorn Mn Na and OH contents and KRb ratiothan the lsquolsquomixed formrsquorsquo core (Table 1) The lepidoliterim is an Al-poorer mica whereas the lsquolsquomixed formrsquorsquocore is an Al-richer mica (Fig 4) The lepidolite rimcorresponds to an overgrowth The FeMg-containingpolylithionite partially surrounds and penetrates lepido-lite along cleavages and shows well defined contacts(Fig 3c) Both contain rutile cassiterite and columbi-tendashtantalite inclusions A continuous chemical evolutiontakes place from lepidolite to FeMg-containing poly-lithionite (Figs 4 6c) The latter has higher Si LicalcRb contents and lower AlVI Ti Fe2thorn Mn Mg Zn Nacontents and KRb ratio (Table 1) and replaces lepido-lite A lithian muscovite rim with rare FeMg-containingpolylithionite surrounds the lsquolsquomixed formrsquorsquo core and thispolylithionite penetrated lithian muscovite (Fig 3d)The contact between the lithian muscovite rim andlsquolsquomixed formrsquorsquo core is irregular suggesting disequili-brium or at a cleavage (Fig 3d d1) Two linear trendsone for the lithian muscovite rim and another for thelsquolsquomixed formrsquorsquo core are defined in the (Fe2thornthornMnthornMg)vs (AlIV thornAlVI) diagram (Fig 6d) The FeMg-contain-ing polylithionite rim does not belong to any of thesetrends and plots outside this diagram because it is an Al-poorer mica whereas the others are Al-richer micas
(Fig 4) The lithian muscovite rim has higher AlVI(AlIV thorn AlVI) OH contents and KRb ratio and lowerMg (Fe2thornthorn Mn thorn Mg) Licalc Rb F contents than thelsquolsquomixed formrsquorsquo core (Table 1 Fig 6d) The crystal isreversely zoned The FeMg-containing polylithioniterim has higher Si Licalc F contents and lower AlVI(AlIV thorn AlVI) Fe2thorn Mn (Fe2thornthorn Mn thorn Mg) Na andOH contents than the lsquolsquomixed formrsquorsquo core and lithianmuscovite rim (Table 1) and replaces lithian muscovite
In the IIZa some zoned crystals have a lithian muscovitecore and a lsquolsquomixed formrsquorsquo rim and the contacts are gradual(Fig 3e) A small discontinuity occurs in the trends fromthe lithian muscovite core to lsquolsquomixed formrsquorsquo rim in the(Fe2thornthorn Mn thorn Mg) vs (AlIV thorn AlVI) and Rb2O vs KRb(Fig 6e f) The lsquolsquomixed formrsquorsquo rim has higher Si Fe2thornMn (Fe2thornthornMn thornMg) Licalc K Rb Cs F contents andlower AlVI (AlIVthornAlVI) Na OH contents and KRb ratiothan the lithian muscovite core (Table 1 Fig 6e f) indi-cating progressive zoning Similar textural relationshipsand chemical evolutions were found in other zoned crystalsfrom the OIZ IIZb and Cc In another crystal from theIIZa lithian muscovite partially surrounds lsquolsquomixed formrsquorsquointergrown with lepidolite Lithian muscovite also partiallysurrounds muscovite (Fig 3f) The contacts betweenlsquolsquomixed formrsquorsquo and lepidolite and also between muscoviteand lithian muscovite are gradual (Fig 3f f1) whereasthey are well defined for muscovite withlsquolsquomixed formrsquorsquoand lepidolite (Fig 3f f1) The crystal has a lsquolsquomixed formrsquorsquoand lepidolite core and a partial rim of muscovite andlithian muscovite The lsquolsquomixed formrsquorsquo core evolved tolepidolite core as the Si Fe2thorn Mn (Fe2thornthorn Mn thorn Mg)Licalc K Rb Cs and F contents increase and the (AlIV thornAlVI) and KRb ratio decrease (Table 1 Fig 6g h) The SiFe2thorn Mn (Fe2thornthorn Mn thorn Mg) Licalc Rb and F contentsincrease and the (AlIV thorn AlVI) and KRb ratio decreasefrom the muscovite rim to the lithian muscovite rim (Table1 Fig 6g h) suggesting that the former evolved to thelatter The muscovite rim has higher AlVI (AlIV thorn AlVI)Na OH contents and KRb ratio and lower Si Fe2thorn Mn(Fe2thornthornMn thornMg) Zn Licalc Rb and F contents than thelsquolsquomixed formrsquorsquo core and lepidolite core (Table 1 Fig 6gh) Muscovite was probably reversely formed and evolvedafterwards to lithian muscovite
In the IIZb some crystals have a lithian muscovite coreand a thinner lepidolite rim (Fig 3g) and others show asmall muscovite core and a larger rim of lsquolsquomixed formrsquorsquointergrown with lepidolite (Fig 3h) The contacts betweenthe cores and rims are well defined There are increases inthe Si Mn (Fe2thornthorn Mn thorn Mg) Licalc Rb and F contentsand decreases in the AlVI (AlIVthornAlVI) and KRb ratio fromthe lsquolsquomixed formrsquorsquo rim to the intergrown lepidolite rim(Table 1 Figs 3h 6l) suggesting that the former evolvedto the latter as also found in IIZa and Cc In both crystalsthe rim compositions have higher Si (Fe2thornthorn Mn thorn Mg)Licalc Rb Cs F contents and lower AlVI (AlIVthorn AlVI) Naand OH contents and KRb ratio than the core (Table 1 Figs3g 6i j k 3h 6l) A compositional gap occurs between coreand rim in the diagrams for both crystals (Fig 6i j k l)suggesting that both rims correspond to overgrowths and no
Silicate and oxide minerals from a zoned granitic pegmatite 973
eschweizerbart_xxx
diffuse reequilibration took place in any crystal as thecontacts between core and rim are sharp
In the Cc lithian muscovite is surrounded and pene-trated by lsquolsquomixed formrsquorsquo showing well defined contacts(Fig 3i) The lsquolsquomixed formrsquorsquo has higher Si Fe2thorn Mn(Fe2thornthorn Mn thorn Mg) Licalc Rb Cs F contents and lowerAlVI (AlIV thorn AlVI) Na OH contents and KRb ratio thanthe lithian muscovite (Table 1 Fig 6m n) and a composi-tional gap occurs between both micas suggesting thatlsquolsquomixed formrsquorsquo replaced lithian muscovite In rare crystalsa small lepidolite core is surrounded by a large muscoviterim containing K-feldspar inclusions The contact betweenthe core and rim is sharp (Fig 3j) A thin partial rim oflithian muscovite surrounds muscovite and the contact isgradual The muscovite rim has higher AlVI (AlIVthornAlVI)Na K OH contents and a greater KRb value and lower SiFe2thorn Mn Licalc Rb Cs and F contents than the lepidolitecore (Table 1 Fig 6o p) and a compositional gap occursbetween them (Fig 6o p) indicating that either muscoviteforms an overgrowth or it is reversely formed From themuscovite rim to the lithian muscovite rim the Si Licalc
Rb F contents increase whereas the AlVI (AlIV thorn AlVI)and OH contents and KRb ratio decrease (Table 1 Fig 6op) suggesting that muscovite evolved to lithian muscoviteas also found in IIZa and IIZb
44 Evolution of mica compositions within each zoneand from the outer intermediate zone to the core of theNamivo granitic pegmatite
The KRb ratio is taken as the best fractionation index inmicas (eg Cerny et al 1985 Foord et al 1995 Wise1995 Pesquera et al 1999 Roda Robles et al 2006 2007)It is hard to establish trends in the evolution of mica com-position from muscovite and lithian muscovite to lsquolsquomixedformrsquorsquo and lepidolite within each zone because the KRbratio shows some partial overlapping particularly betweenthe lithian muscovite and lsquolsquomixed formrsquorsquo and also betweenthe latter and lepidolite However an evolution from mus-covites to lepidolite (Al-richer mica Fig 4) is clearer (Fig7) In general in IIZa IIZb and Cc the Si Licalc Rb Cs and
Fig 5 The main substitutions in micas from the Namivo granitic pegmatite Mozambique a b SiIVthorn LiVI versus AlIVthornAlVI showing the 2SithornLi 3Altotal substitution mechanism operating in dioctahedral micas (Mu muscovite and Lith mu lithian muscovite) c d AlVI thornamp VI
versus LiVI (where amp represents a vacancy) and showing the 3LiVI AlVI thorn 2 amp VI substitution mechanism operating in trioctahedral micas(Mix f ndashlsquolsquomixed formrsquorsquo Lep lepidolite Zin zinnwaldite and Pol-FeMg-containing polylithionite) OIZ IIZa IIZb and Cc as in Fig 2
974 A M R Neiva
eschweizerbart_xxx
F contents tend to increase and the (AlIV thorn AlVI) AlVI
contents and KRb ratio tend to decrease from muscoviteto lepidolite (Table 1 Fig 7) This sequence is consistentbut rarely in the Cc lepidolite is rimmed by muscovite (Fig3j) But in the OIZ the evolution stops in lsquolsquomixed formrsquorsquoparticularly shown by the large range of the KRb ratiowhich mainly overlaps that of lepidolite from this zone(Fig 7) because this lepidolite is an Al-poorer mica whereasthe others are Al-richer micas (Fig 4)
In the OIZ the lepidolite has more Si Licalc and F andless (AlIV thorn AlVI) Ti Fe2thorn Mn Mg and Zn than zinn-waldite (Table 1) but it has larger ranges of Rb and KRbratio than zinnwaldite (Fig 7) The FeMg-containingpolylithionite is the richest mica in Si Licalc and thepoorest in (AlIV thorn AlVI) (Table 1) But at this zone scalethe polylithionite has Rb Cs contents and KRb ratiowithin the ranges for lepidolite and close to those of zinn-waldite (Fig 7)
Fig 6 Variation diagrams of micas from selected zoned crystals from the zones of the Namivo granitic pegmatite Mozambique to showtheir relationships lith musc lithian muscovite OIZ IIZa IIZb and Cc an in Fig 2
Silicate and oxide minerals from a zoned granitic pegmatite 975
eschweizerbart_xxx
From the OIZ to IIZa IIZb and Cc muscovite and lithianmuscovite generally show increases in the Si Licalc F and Rbcontents and decreases in the Fe2thorn and Mg contents and KRb ratio but the Mg content is very low in these micas fromthe IIZa IIZb and Cc (Table 1 Fig 7a) The lsquolsquomixed formrsquorsquoshows increases in the Si Licalc F Rb Cs contents anddecreases in the (AlIV thorn AlVI) and Mg contents and KRbratio but the Mg content is very low in this mica from theIIZb and Cc (Table 1 Fig 7b c) The lepidolite shows anincrease in the Si Licalc F Rb and Cs contents and a decreasein the KRb ratio from the IIZa to the IIZb and Cc (Table 1Fig 7d e) Furthermore the lepidolite from the OIZ has thelowest (AlIV thorn AlVI) AlVI and OH contents the highest SiFe2thorn Licalcand F contents and KRb ratio and the lowest Rband Cs contents compared to lepidolite from the other zones(Table 1 Fig 7d e)
5 Feldspars
Selected chemical analyses of albite and K-feldspar fromfive zones of the Namivo granitic pegmatite are given inTable 2 Strontium is the most abundant trace element inalbite (eg Cerny 1994) Anorthite and Sr contents and SrCa ratio of albite decrease from the WZ to the Cc (Fig 8Table 2) Rubidium is the most abundant trace element inK-feldspar followed by Cs in IIZa IIZb and Cc In gen-eral K Rb and Cs contents of K-feldspar increase and KRb and KCs values decrease from the WZ to the Cc (Table2 Fig 9)
The program SOLVCALC 20 (Wen amp Nekvasil 1994)using the Margules model Fuhrman amp Lindsley (1988) wasapplied for the purpose of thermometry The pairing ofplagioclase cores with the K-feldspars average of eachsample was used to estimate the crystallization temperaturesof primary magmatic feldspars They are 405 C (WZ)406ndash340 C (OIZ) 390ndash335 C (IIZa) 347ndash306 C (IIZb)and 333ndash289 C (Cc) at 3 kbar The metamorphic environ-ment of rare-element-Li granitic pegmatites is one of lowpressure 2ndash4 kbar (Cerny amp Ercit 2005) In general thedifference between the maximum and minimum calculatedtemperatures at 2 3 and 4 kbar for the same feldspar pairfrom the Namivo pegmatite is lower than 40 C The tem-perature decreases from the wall zone (WZ) to the core(Cc) A similar temperature behavior of feldspars wasfound in the pegmatite-aplite dike USA (Morgan ampLondon 1999)
6 Other silicates
Tourmaline of schorl composition was only found inthe OIZ (Table 2) because there was not enough Feand Mg for schorl to precipitate in the other zonesSpodumene only occurs in the Cc and its compositionis nearly pure (Table 2)
7 Columbite-tantalite
Representative chemical analyses of columbitendashtantalitefrom the Namivo granitic pegmatite are given in Table 3and plotted in the columbite quadrilateral (Fig 10a)Most crystals are unzoned but zoned crystals with dar-ker and lighter zones in BSE images are from the Cc Thelighter zone of columbite-(Mn) has higher Ta contentTa(Ta thorn Nb) and Mn(Mn thorn Fe) values and lower Nbcontent than the darker zone (Fig 10a b) The crystals ofthe columbitendashtantalite minerals are low in W Sn and Tiimpurities (Table 3)
The main trend starts from the columbite-(Mn) of theOIZ towards the more Mn-enriched and slightly Ta-enriched columbite-(Mn) from the IIZa and Cc The high-est Ta(Ta thorn Nb) values belong to the lighter zone ofcolumbite-(Mn) with Mn(Mn thorn Fe) frac14 10 from the CcThe richest columbite-(Mn) in Ta(TathornNb) and composi-tions of tantalite-(Fe) and tantalite-(Mn) were only foundin the OIZ (Fig 10a) and are associated with lepidolite andpolylithionite (Fig 3c)
8 Gahnite
Gahnite was rarely found in the OIZ and shows a darkerzone that partially surrounds a lighter zone in a BSE image(Fig 11a) The darker zone has a higher Zn content andlower Sn Ti Nb Ta Mn contents and SnZn value than thelighter zone (Table 4 Fig 11b c) These gahnite composi-tions fall within the igneous field of Batchelor amp Kinnaird(1984) The darker zone is closer in composition to thepure gahnite (Zn8Al16O32) than the lighter zone whichcontains up to 0983 apfu Sn 0195 apfu Ti 1029 apfutotal Fe2thorn 0101 apfu Mn (Table 4) and consequently hasa composition distinct from nigerite In general both thedarker and lighter zones have higher Sn Ti and Fe contentsthan gahnite from the granitic pegmatites of Nigeria(Batchelor amp Kinnaird 1984) Arga northern Portugal(Gomes et al 1995) and Cabanas northern Portugal(Neiva amp Champness 1997) Borborema province north-eastern Brazil (Soares et al 2007) The Zn=Fe2thornt values ofthe darker and lighter zones of gahnite from Namivo arelower than those reported in Neiva amp Champness (1997)and Soares et al (2007)
9 Discussion and conclusions
91 Evolution of micas in the zoned pegmatite
In general individual mica crystals show varying patternsand compositional zoning involving several elementsmainly Si AlVI (AlIV thorn AlVI) Fe2thorn Mn (Fe2thornthorn Mn thornMg) Licalc Rb Cs F and OH and the KRb ratioProgressively zoned crystals from the IIZa show grada-tional contacts between a lithian muscovite core and a
976 A M R Neiva
eschweizerbart_xxx
lsquolsquomixed formrsquorsquo rim (Figs 3e 6e f) and the zoning patternscorrespond to fractionation trends and probably reflect adrop in temperature during the crystallization of the grani-tic pegmatite melt Progressively zoned crystals also occurin OIZ IIZb and Cc Some crystals are reversely zonedwith a) a lsquolsquomixed formrsquorsquo core and a lithian muscovite rimfrom the OIZ (Figs 3d d1 6d) b) a core consisting oflsquolsquomixed formrsquorsquo and lepidolite and a rim of muscovite andlithian muscovite from the IIZa (Figs 3f f1 6g h) c) alepidolite core and a muscovite and lithian muscovite rimfrom the Cc (Figs 3j 6o p) which may be explained bythe hypothesis of oscillations in the compositions of themelt from which they grew alternating between an Li-enriched boundary layer and a bulk melt that is less frac-tionated The muscovite evolved to lithian muscovite inIIZa and Cc (Figs 3f 6g h 3j 6o p) Replacements (Figs3a 6a b 3c 6c 3i 6m n Table 1) occur in OIZ and Ccand overgrowths (Figs 3b g 6i j k 3h 6l Table 1) occurin OIZ and IIZb as found in BSE images
Muscovite evolved to lithian muscovite as observed inOIZ IIZa IIZb and Cc (Figs 3f 6g h 3j 6o p Table 1)Lithian muscovite evolved to lsquolsquomixed formrsquorsquo in OIZ IIZaIIZb and Cc (Figs 3e 6e f Table 1) and lsquolsquomixed formrsquorsquoevolved to lepidolite in IIZa IIZb and Cc (Figs 3f f1 6gh 3h 6l Table 1) All these evolutions are due to fractionalcrystallization
In the OIZ lepidolite has more Si Licalcand F butsimilar KRb to that of zinnwaldite and replaces it (Figs
3a 6a b 7d Table 1) An FeMg-containing polylithionitehas higher Si Licalcand Rb contents and a smaller KRbratio than the lepidolite that it replaces (Figs 3c 6c Table1) and a continuous chemical evolution from lepidolite topolylithionite is shown
The trends for major and trace elements of micas withineach zone are difficult to define due to some partial over-lapping but a progressive evolution from muscovite to lithianmuscovite lsquolsquomixed formrsquorsquo and lepidolite in IIZa IIZb and Ccis mainly shown by an increase in the Si Licalc F Rb and Cscontents and a decrease in the KRb ratio and this is simi-larly shown in the OIZ from muscovite to lsquolsquomixed formrsquorsquo(Table 1 Fig 7) In the OIZ Si and Licalccontents increaseprogressively from zinnwaldite to lepidolite and FeMg-containing polylithionite but a gap occurs between zinnwal-dite and lepidolite (Table 1 Fig 4) whereas a continuousevolution from lepidolite to polylithionite is observed TheKRb ratios of zinnwaldite and polylithionite are within therange of that of lepidolite (Fig 7d e)
Each Al-richer mica (muscovite lithian muscovite andlsquolsquomixed formrsquorsquo) exhibits an evolution from the OIZ to theIIZa and then to the IIZb and Cc particularly shown by anincrease in the Si Licalc F and Rb contents and adecrease in the KRb ratio but also an increase in theCs content in the lsquolsquomixed formrsquorsquo (Table 1 Fig 7) Theseelements and ratio have been used as petrogenetic indi-cators of evolution in micas from pegmatites (eg Cernyet al 2005 Roda Robles et al 2006 2007 Vieira et al
Fig 7 Plot of some variation diagrams of micas from the OIZ IIZa IIZb and Cc of the Namivo granitic pegmatite Mozambique showingthat the Rb2O and Cs2O contents increase and the KRb ratio decreases for micas from the OIZ to the Cc OIZ IIZa IIZb and Cc as in Fig 2
Silicate and oxide minerals from a zoned granitic pegmatite 977
eschweizerbart_xxx
Tab
le2
R
epre
sen
tati
ve
elec
tro
nm
icro
pro
be
anal
yse
sin
wt
o
ffe
ldsp
ars
sch
orl
and
spo
du
men
efr
om
the
Nam
ivo
gra
nit
icp
egm
atit
eM
oza
mb
iqu
e
Alb
ite
K-f
eld
spar
Sch
orl
Sp
od
um
ene
Zo
nes
WZ
OIZ
IIZ
aII
Zb
Cc
Zo
nes
WZ
OIZ
IIZ
aII
Zb
Cc
Zo
nes
OIZ
Zo
ne
Cc
SiO
26
75
76
78
86
87
06
84
76
84
1S
iO2
65
10
65
55
65
46
64
96
64
72
SiO
23
52
0S
iO2
64
65
TiO
20
02
mdash0
02
mdashmdash
TiO
2mdash
00
1mdash
mdashmdash
TiO
20
35
Al 2
O3
27
20
Al 2
O3
20
25
19
74
19
67
19
88
19
97
Al 2
O3
18
96
18
23
18
31
18
24
18
05
B2O
3
10
28
Fe 2
O3
00
6F
e 2O
3mdash
mdashmdash
mdash0
10
Fe 2
O3
mdash0
02
mdash0
03
mdashA
l 2O
33
17
2M
nO
01
3M
nO
00
6mdash
mdashmdash
mdashM
nO
mdash0
03
00
3mdash
mdashF
eO1
35
2M
gO
01
8M
gO
mdashmdash
mdashmdash
mdashM
gO
00
10
01
00
5mdash
mdashM
nO
03
3N
a 2O
01
9C
aO1
04
08
00
56
03
70
32
CaO
00
10
01
00
60
01
00
2M
gO
22
8L
i 2O
8
05
Na 2
O1
06
11
12
01
12
11
13
41
13
4N
a 2O
06
50
58
04
10
59
03
8C
aO0
23
To
tal
10
04
6K
2O
00
50
17
00
60
14
01
0K
2O
14
72
14
75
15
67
15
01
15
74
Li 2
O
02
2S
rO0
72
05
00
24
01
1mdash
Rb
2O
00
90
20
03
00
59
09
0N
a 2O
22
8S
i1
99
7P
2O
50
01
00
4mdash
mdashmdash
Cs 2
O
00
6
00
60
09
01
80
20
K2O
00
1A
lIV0
00
3T
ota
l1
00
33
10
03
31
00
46
10
03
11
00
24
P2O
5mdash
00
3mdash
mdashmdash
H2O
3
18
P2
00
To
tal
99
60
99
48
10
03
89
96
11
00
01
F0
78
AlV
I0
98
7S
rC
a(w
t)0
81
07
40
50
03
50
Cl
mdashF
e3thorn
00
01
KR
b(w
t)153
68
48
23
16
Sum
1003
8P
09
9S
i1
18
23
11
87
91
19
58
11
93
21
19
21
KC
s(w
t)4
07
20
41
63
73
69
O
F0
33
Li
10
00
P0
00
10
00
6mdash
mdashmdash
To
tal
10
00
5M
n0
00
3T
i0
00
3mdash
00
03
mdashmdash
Si
11
98
61
20
88
12
04
11
20
45
12
03
3M
g0
00
8A
l4
17
64
07
14
03
54
08
34
10
1P
mdash0
00
5mdash
mdashmdash
TS
i5
95
2N
a0
01
2F
e3thorn
mdashmdash
mdashmdash
00
13
Ti
mdash0
00
1mdash
mdashmdash
Al
00
48
P1
02
Mn
00
09
mdashmdash
mdashmdash
Al
41
14
39
62
39
70
39
86
39
55
B3
00
0M
gmdash
mdashmdash
mdashmdash
Fe3thorn
mdash0
00
3mdash
00
04
mdashZ
Al
60
00
Ca
01
95
01
50
01
04
00
69
00
60
Mn
mdash0
00
50
00
5mdash
mdashY
Al
02
74
Sr
00
73
00
51
00
24
00
11
mdashM
g0
00
30
00
30
01
4mdash
mdashT
i0
04
5N
a3
59
93
80
03
78
33
83
23
83
1C
a0
00
20
00
20
01
20
00
20
00
4M
g0
57
5K
00
11
00
38
00
13
00
31
00
22
Na
02
32
02
07
01
46
02
12
01
37
Mn
00
47
K3
45
73
47
03
67
73
55
03
73
3F
e2thorn
19
12
Z1
60
01
59
61
60
01
60
11
60
4R
b0
01
10
02
40
03
50
07
00
10
8L
i0
14
8X
38
94
04
39
33
94
39
1C
s0
00
20
00
50
00
70
01
40
01
6P
Y3
00
0m
ole
s
XC
a0
04
2A
n5
13
82
71
71
5Z
16
10
16
06
16
01
16
03
15
99
Na
07
47
Ab
94
69
53
97
09
75
97
9X
37
13
72
39
03
85
40
0K
00
02
Or
03
09
03
08
06
mo
les
amp
02
09
An
01
01
03
01
01
Ab
63
56
38
56
35
OH
35
83
Or
93
69
43
95
99
43
96
4F
04
17
Cl
mdash
WZ
ndashw
allzo
ne
OIZ
ndasho
ute
rin
term
edia
tezo
ne
IIZ
aan
dII
Zb
ndashin
ner
inte
rmed
iate
zon
esC
cndash
core
asin
Fig
2B
aOis
bel
ow
the
det
ecti
on
lim
itin
bo
thfe
ldsp
ars
Cs 2
Ofrac14
00
3w
tin
the
K-
feld
spar
fro
mth
eW
Z
mdashN
ot
det
ecte
d
Nu
mb
ero
fio
ns
on
the
bas
iso
f3
2o
xy
gen
sfo
ral
bit
ean
dK
-fel
dsp
ar
31
anio
ns
(O
OH
F
)fo
rsc
ho
rlan
d6
ox
yg
ens
for
spo
du
men
e
-A
mo
un
tin
ferr
edfr
om
con
sid
erat
ion
so
fst
oic
hio
met
ry
978 A M R Neiva
eschweizerbart_xxx
2011) Lepidolite from the OIZ is an Al-poorer mica (Fig4) and has the highest Si Licalcand F contents (Table 1)indicating that an evolution cannot be shown from thislepidolite to lepidolites from the other zones which areAl-richer micas (Fig 4) However there is a regulardecrease in the KRb ratio and a progressive increase inthe Rb and Cs contents from lepidolite of the OIZ tolepidolite of IIZa IIZb and Cc (Fig 7) which indicatesthat the KRb ratio and Rb and Cs contents must not beconsidered alone to show fractional crystallization in
lepidolites particularly if some are Al-richer micas andothers Al-poorer micas The high Licalcand F contents oflepidolite from the OIZ did not decrease its KRb ratioSuch an effect is considered to have taken place in lepi-dolite (an Al-richer mica) from the wall zone of the Tancopegmatite Manitoba Canada (Van Lichtervelde et al2008) An evolution from the lepidolite of the IIZa to thatof the Cc is generally shown by the increasing Si LicalcF Rb Cs contents and a decrease in the KRb ratio (Table1 Fig 7)
At the scale of crystals the pegmatite zones and alsothose from the OIZ to the Cc of the Namivo granitic pegma-tite Al-richer micas show fractionation because theyformed from the fractionation of an Li-rich pegmatite melt
The Al-poorer micas zinnwaldite lepidolite and FeMg-containing polylithionite only occur in the OIZ (Fig 4)Polylithionite is the mica richest in Si and Licalc and lepi-dolite from this zone is the richest in Si Licalcand F (Fig 4Table 1) The high Li contents of these micas reflect aconsiderably higher D(Li) at low temperature (Icenhoweramp London 1995) These Li-rich micas may have crystal-lized from an undercooled melt This hypothesis does notimply high Rb and Cs contents and low KRb ratios Thisagrees with the fact that these micas from the OIZ havesimilar Rb and Cs contents and KRb ratios to those of Al-richer micas (muscovite lithian muscovite and lsquolsquomixedformrsquorsquo) from the same pegmatite zone (Fig 7) Howeverthe lepidolite from the wall zone of the Tanco pegmatiteCanada of a similar origin has a low KRb ratio which isattributed to the complexly interrelated structural compo-nents of this lepidolite (Van Lichtervelde et al 2008) TheLi-rich micas from the OIZ may also represent disequili-brium These two hypotheses are considered the best forthese micas of primary magmatic origin
Another hypothesis was also considered They may havecrystallized in boundary layers which concentrate Li andF But this mechanism was suggested for the most fractio-nated tourmaline enriched in Li and F from the core of the
Fig 8 Plot of albite compositions from all zones of the Namivo granitic pegmatite Mozambique showing that the anorthite content of albitedecreases from the WZ to the Cc WZ OIZ IIZa IIZb and Cc as in Fig 2
Fig 9 The Rb vs Cs diagram of K-feldspar from all zones of theNamivo granitic pegmatite Mozambique showing that the Rb andCs contents of K-feldspar increase from the WZ to the Cc WZ OIZIIZa IIZb and Cc as in Fig 2
Silicate and oxide minerals from a zoned granitic pegmatite 979
eschweizerbart_xxx
Little Three pegmatite dike USA (Morgan amp London1999) and the micas enriched in Li and F from theNamivo pegmatite belonging to the OIZ Furthermore ina boundary layer melt that became enriched in Li and F theKRb ratio of micas decreases strongly (Van Lichterveldeet al 2008) which was not found in these micas from theOIZ (Fig 7d) Nor can they have resulted from the crystal-lization of a late melt that would have reacted with the OIZbecause these micas are among those containing the high-est KRb values (Fig 7d)
92 The importance of feldspars micas andcolumbitendashtantalite compositions to the Namivogranitic pegmatite evolution
The trace elements Rb and Cs and the KRb and KCs ratioshave been used to show the evolution of K-feldspar inpegmatites (eg Cerny 1994 Cerny et al 2005 RodaRobles et al 2005) The Rb and Cs contents increase andthe KRb and KCs ratios of K-feldspar decrease from theWZ to the Cc (Fig 9 Table 2) reflecting the growth of K-feldspar from an increasingly fractionated melt withouthaving grown from or having been chemically modifiedby an aqueous fluid as in the Swamp pegmatite section atthe Little Three Mine USA (London et al 2012) Thecrystallization of K-feldspar from an exsolved aqueousfluid from melt will reverse the magmatic fractionation ofRb Cs KRb and KCs because Rb and especially Cs areso much more compatible in vapor that both Rb and Csremain in the fluid phase (London et al 2012) The feldsparsolvus pairs in the Namivo pegmatite record magmaticcrystallization temperatures that decrease from WZ to CcAlbite shows a decrease in the Ca Sr contents and SrCaratio from the WZ to the Cc (Fig 8 Table 2) Therefore thefeldspars and also Al-richer micas as already explainedshow fractionation in this zoned pegmatite
In general lepidolite from the Namivo pegmatite hassimilar Rb2O and Cs2O contents and KRb (wt) values tothose of lepidolite from the Rozna and Dobra Voda lepi-dolite-subtype pegmatites in the Czech Republic (Cernyet al 1995) but lower Rb2O and Cs2O contents thanlepidolite from the lepidolite-subtype pegmatite at RedCross Lake Manitoba Canada (Cerny et al 2012a) K-feldspar from the Namivo pegmatite also has lower Rb2O
Table 3 Representative electron microprobe analyses in wt of columbitendashtantalite from the Namivo granitic pegmatite Mozambique
Outer Intermediate Zone - OIZ Inner Intermediate Zone - IIZa
Core - Cc
D L L
WO3 022 059 079 113 101 351 050 007Ta2O5 5487 5123 2503 3186 2888 2519 3127 4542Nb2O5 2537 3000 5483 4635 5113 5144 4911 3686SnO2 008 015 024 049 020 026 017 012TiO2 263 161 136 254 202 145 125 016FeO 860 710 665 471 236 068 mdash mdashMnO 793 952 1099 1304 1400 1725 1748 1718Total 9970 10020 9989 10012 9960 9978 9978 9981W 0004 0011 0013 0019 0016 0057 0008 0001Ta 1065 0975 0422 0552 0495 0430 0543 0847Nb 0819 0949 1538 1336 1456 1460 1418 1143Sn 0002 0004 0006 0012 0005 0007 0004 0003Ti 0141 0085 0063 0122 0096 0068 0060 0008Fe 0513 0416 0345 0251 0124 0036 mdash mdashMn 0479 0564 0578 0704 0747 0917 0945 0998P
3023 3004 2965 2996 2939 2975 2978 3000Mn(Mn thorn Fe) 048 058 063 074 086 096 100 100Ta(Ta thorn Nb) 057 051 022 029 025 023 028 043Classification tant-(Fe) tant-(Mn) col-(Mn) col-(Mn) col-(Mn) col-(Mn) col-(Mn) col-(Mn)
D ndash darker L ndash lighter zones mdash Not detected tant-tantalite col-columbite Cation formula on the basis of 6 atoms of oxygen
Fig 10 Compositions of columbitendashtantalite from the Namivogranitic pegmatite Mozambique in the columbite quadrilateralshowing that Mn(Mn thorn Fe) of columbite-(Mn) increases from theOIZ to the Cc and the richest columbite-(Mn) in Ta(Ta thorn Nb)tantalite-(Fe) and tantalite-(Mn) only occur in the OIZ OIZ IIZaand Cc as in Fig 2
980 A M R Neiva
eschweizerbart_xxx
and Cs2O contents than K-feldspar from the lepidolite-subtype pegmatite at Red Cross Lake The Rb2O andCs2O contents of primary and late K-feldspar of this peg-matite at Red Cross Lake attained unprecedented levels(Cerny et al 2012a) The lowest KRb (wt) values ofmuscovite lithian muscovite lsquolsquomixed formrsquorsquo and lepido-lite from the IIZb and Cc (Fig 7) and K-feldspar (KRb frac1414) from the Cc compare well with those found in theseminerals from the AC6frac143 lepidolite-subtype pegmatitefrom Greer Lake (Cerny et al 2005) and some of themost fractionated pegmatites worldwide which belong tothe petalite-subtype (eg Tanco Manitoba Cerny 2005Cerny et al 1998 Varutrask Sweden Cerny et al 2005)but muscovite lithian muscovite and lepidolite from theIIZb and Cc have lower Rb2O and Cs2O contents than thesemicas from the Tanco pegmatite (Cerny 2005a VanLichtervelde et al 2008) K-feldspar also has lower
contents of these oxides than the most evolved K-feldsparfrom the Tanco pegmatite (Cerny 2005a) The magmaticfractionation was strong from the WZ to IIZb and Cc of theNamivo lepidolite-subtype pegmatite
The compositional trend of columbite-(Mn) from the OIZto Cc of the Namivo granitic lepidolite-subtype pegmatite(Fig 10) is identical to that of columbite-group mineralsfrom the lepidolite-subtype complex granitic pegmatitesfrom the Dobra Voda in the Moldanubicum CzechRepublic (Novak amp Cerny 1998) and the HimalayaDistrict southern California (shown in Cerny et al 2004)Experimental data for the Fe-Mn pair (Linnen amp Cuney2005) suggest an increase in Fe with fractional crystalliza-tion which is not observed in nature Other phases seem tocontrol the bahavior of Fe and Mn in the melt eg thecrystallization of tourmaline causes a rapid increase of theMnFe in the melt (Van Lichtervelde et al 2006) When thecrystallization of tourmaline stopped the columbitendashtantaliteminerals showed a constant MnFe indicating that the Fe andMn contents in the melt remained constant Schorl onlyoccurs in the OIZ of the Namivo granitic pegmatite and itscrystallization cannot be responsible for the increase in theMnFe of the melt because Mn(Mn thorn Fe) of columbite-(Mn) increases progressively from the OIZ to the IIZa and Cc(Fig 10) Garnet zinnwaldite and gahnite containing Fe andMn also only occur in the OIZ and cannot also have causedthe increase of the MnFe in the melt The dominant Mnenrichment before Ta enrichment started in the columbitendash-tantalite composition from some granitic pegmatites isattributed to an increased alkali-fluoride activity at moderatemHF (Cerny et al 2004) and an increase in the activity offluorine (Martins et al 2011) Each Al-richer mica (musco-vite lithian muscovite and lsquolsquomixed formrsquorsquo) from the Namivogranitic pegmatite shows an increase in F content from theOIZ to the IIZa IIZb and Cc (Table 1) In general the Fcontent of lepidolite also increases from the IIZa to the IIZband Cc Therefore the extreme Fe-Mn fractionation beforeTa enrichment in columbite-(Mn) (Fig 10) may be due to anincrease in the activity of fluorine as a consequence offractional crystallization The increase in the Ta content ofcolumbite-(Mn) from the Namivo granitic pegmatite isattributed to fractional crystallization
The geochemical evolution of albite and K-feldsparfrom the WZ to the Cc Al-richer micas muscovite lithianmuscovite and lsquolsquomixed formrsquorsquo from the OIZ to the Cc andlepidolite from the IIZa to the Cc and columbite-(Mn) andalso beryl (Neiva amp Neiva 2005) from the OIZ to the Ccare caused by magma fractionation The pegmatite zonesare the product of primary crystallization from a volatile-rich silicate melt The pegmatite consolidated from the WZto the Cc The IIZb is one of the most evolved zones asalso suggested by the beryl composition (Neiva amp Neiva2005) and is the richest in lsquolsquomixed formrsquorsquo and lepidolite
The richest columbite-(Mn) in Ta(Ta thorn Nb) and com-positions of tantalite-(Fe) and tantalite-(Mn) only occur inthe OIZ (Fig 10a) associated with lepidolite and polythio-nite (Fig 3c) which may be due to the local depletion of Liand F in the melt which decreases the solubility of Ta andcauses Ta precipitation (Linnen 1998 Linnen amp Cuney
Fig 11 a Backscattered-electron image of a gahnite crystal with adarker zone partially surrounding a lighter zone from the OIZ of theNamivo granitic pegmatite b c Plot of gahnite compositions in theSn-Zn-Ti diagram (atomic proportions) showing a chemical distinc-tion between the lighter and darker zones OIZ as in Fig 2
Silicate and oxide minerals from a zoned granitic pegmatite 981
eschweizerbart_xxx
2005) At the Tanco pegmatite Ta oxides are also asso-ciated with lepidolite enriched in Li and F from the wallzone (Van Lichtervelde et al 2008)
93 Origin and evolution of the zoned graniticlepidolite-subtype pegmatite at Namivo
In general granitic pegmatites particularly those belong-ing to the rare-element class are accepted as having beenformed by the fractional crystallization of a granite melt(eg Cerny 1991a b 1992 Neiva et al 2008 2012 Roda-Robles et al 2012) But it also has been proposed thatpegmatites may be formed by partial melting of appropri-ate rock compositions (eg Nabelek et al 1992 Nabelekamp Russ-Nabelek 1992 Shearer et al 1992 Roda Robleset al 1999) The lepidolite-subtype pegmatites belong tothe LCT (lithium-cesium-tantalum) family (Cerny amp Ercit2005) They are derived by fractional crystallization of agranite magma (eg Cerny et al 2005 Neiva amp Ramos2010 Cerny et al 2012b) Experimental work by Londonet al (1989) and London (1990) using Macusani glass as astarting material equivalent to the bulk composition ofhighly fractionated rare-alkali-rich pegmatites underhighly evolved and hydrous but H2O undersaturatedmelt obtained the latest primary assemblage consisting
of an Li-rich mica thorn albite thorn quartz deposited directlyfrom the primary melt phase Other authors egZasedatelev (1974 1977) and Stewart (1978) argue thatlepidolite-bearing pegmatites are derived from direct ana-texis and Gordiyenko et al (1996) consider that they arederived from an undefined medium and the rare-elementmineralization is superimposed on preexisting barrenpegmatites
Lepidolite-subtype pegmatites may migrate a long wayfrom their parent granites because their volatile-rich highlyfluid pegmatite melts are stable at relatively low tempera-tures (eg Cerny et al 2005 Antunes et al 2013)Therefore the Namivo pegmatite is probably derived byfractional crystallization of an S-type granite magmawhich resulted from partial melting of metamorphosed juve-nile sediments containing micas that carry most of the traceelements that define the signature of the LCT pegmatites(eg Dahl et al 1993)
The two main models for the internal evolution of peg-matites that dominated for more than a century are a) thefractional crystallization of a flux-bearing granitic melt fromthe margins to the center of the pegmatite (Cameron et al1949) b) the interactions of an aqueous fluid with graniticmelt (Jahns amp Burnham 1969 Jahns 1982) The recentmodel of constitutional zone refining combines aspects ofboth models and invokes the formation of a flux-enriched
Table 4 Electron microprobe analyses in wt of zoned gahnite from the outer intermediate zone (OIZ) of the Namivo granitic pegmatiteMozambique
Darker Zone Lighter Zone
Mean s Range Mean s Range
SnO2 036 050 0ndash097 658 281 151ndash998TiO2 008 008 0ndash021 065 034 008ndash105Nb2O5 001 002 0ndash006 018 007 007ndash029Ta2O5 001 004 0ndash010 015 013 0ndash033ZnO 3998 123 3810ndash4109 3339 318 3004ndash3848FeO 367 048 331ndash442 433 065 306ndash498MnO 032 004 028ndash040 039 006 032ndash048MgO 003 004 0ndash010 ndash ndash ndashAl2O3 5507 050 5436ndash5572 5337 070 5257ndash5443SiO2 003 003 0ndash007 008 010 0ndash025Total 9956 9912n 8 8Sn 0035 0048 0ndash0095 0648 0278 0149ndash0983Ti 0015 0015 0ndash0038 0120 0064 0015ndash0195Nb ndash 0003 0ndash0006 0021 0009 0009ndash0037Ta ndash 0002 0ndash0006 0009 0009 0ndash0021Zn 7226 0182 6890ndash7382 6086 0568 5482ndash6965Fe2thornt 0752 0103 0675ndash0913 0894 0135 0628ndash1029Mn 0066 0008 0057ndash0083 0082 0013 0066ndash0101Mg 0010 0015 0ndash0037 ndash ndash ndashAl 15887 0052 15805ndash15954 15526 0170 15375ndash15853Si 0007 0008 0ndash0018 0019 0025 0ndash0062P
23998 23405Fe3thorn 0064 0230Fe2thorn 0686 0658SnZn 0005 0007 0ndash0014 0106 0052 0021ndash0179ZnFe2thornt 961 143 768ndash1093 681 190 536ndash1109
n number of analysis Cation formula based on 32 atoms of oxygen Fe2thornt total Fe2thorn estimated
982 A M R Neiva
eschweizerbart_xxx
boundary layer of silicate liquid in advance of a crystal-lization front (London 2008 London amp Morgan 2012)
Lepidolite-subtype pegmatites are generally scarce(Cerny et al 2005) particularly the zoned ones In thesymmetrically zoned lepidolite-subtype pegmatites ofRozna and Dobra Voda Czech Republic micas (Cernyet al 1995) tourmaline (Selway et al 1999) and colum-bite-group minerals (Novak amp Cerny 1998) evolve fromthe outermost zone to the innermost zone following thecrystallization sequence The same was found in tourma-line from the zoned Lastovicky Dolnı Bory and Raddovicelepidolite-subtype pegmatite dikes in the Czeck Republic(Selway et al 1999)
In general beryl (Neiva amp Neiva 2005) feldsparsmicas and columbite-(Mn) (in this paper) from theNamivo lepidolite-subtype pegmatite record the progres-sive chemical evolution of the pegmatite from the wallzone to the core These minerals were produced by crystal-lization from a silicate melt rather than an aqueous fluidphase The slow cooling of melt shown by the magmaticcrystallization temperatures of feldspars cannot explain theincrease in grain-size of minerals from the wall zone to thecore but fluxes will be necessary to promote the change oftexture particularly a flux-rich hydrosilicate liquidaccording to the experimental evidence (London 2009)The constitutional zone refining model will be the best forthis zoned pegmatite and probably for all lepidolite-sub-type pegmatites because this model also produces a higherfinal concentration of incompatible components in a smal-ler volume of rock than fractional crystallization does(Morgan amp London 1999)
The core margin at the Rozna pegmatite contains K-feld-spar and quartz and the core consists mainly of quartz but it issurrounded and penetrated by a quartz-bearing albitethorn lepi-dolite complex which contains several minerals At theDobra Voda pegmatite the center of the dike is occupiedby the lepidolite unit containing albite and other minerals(Cerny et al 1995) At the Namivo pegmatite the coremargin consists of quartz and beryl and the core containsmainly quartz and spodumene but also albite lepidolite andother minerals The last-unit assemblages of primary miner-als in most of the highly fractionated LCT pegmatites are richin albite and commonly contain lepidolite or spodumene andmost of the other rare phases These units represent the lastmost fractionated liquid that can be derived by fractionalcrystallization of a crustal melt (London 2008)
The Namivo granitic pegmatite shows a significant dis-tinction from the other zoned lepidolite-subtype pegmatitesand LCT pegmatites except the Tanco petalite-subtypepegmatite in Canada because the lepidolite richest in SiLi and F FeMg-containing polylithionite and associatedcolumbite-(Mn) with the highest Ta(Ta thorn Nb) ratio tanta-lite-(Fe) and tantalite-(Mn) only occur in the outer inter-mediate zone These minerals usually form late in theconsolidation of pegmatites The lepidolite and polylithio-nite are probably derived from the disequilibrium crystal-lization of an undercooled melt Tantalite may reflect a localdecrease in Li and F that caused Ta precipitation
This paper contributes to a better understanding of theorigin and evolution of the rare zoned lepidolite-subtypepegmatites and shows that although the pegmatite evolvedfrom the wall zone to the core it presents an unusualassociation of lepidolite polylithionite and tantalite in theouter intermediate zone
Acknowledgments Thanks are due to JM Cotelo Neivaand MB Dias for the samples and information providedand to MR Machado Leite and MF Guimaraes for theuse of the electron microprobe facilities at the LaboratorioNacional de Energia e Geologia (LNEG) PortugalFinancial support was provided by the PortugueseGovernment for the project Pest-OECTEUI00732011of the Geosciences Centre through the PortugueseFoundation for Science and Technology I would like tothank D London WB Simmons and the associated editorE Widom for their constructive reviews of this manuscriptand M Prieto for his editorial work
References
Alfonso P Melgarejo JC Yusta I Velasco F (2003)
Geochemistry of feldspars and muscovite in granitic pegmatite
from the Cap de Creus field Catalonia Spain Can Mineral 41
103ndash116
Antunes IMHR Neiva AMR Ramos JMF Silva PB
Silva MMVG Corfu F (2013) Petrogenetic links between
lepidolite-subtype aplite-pegmatite aplite veins and associated
granites at Segura (central Portugal) Chemie der Erde in press
httpdxdoiorg101016jchemer20121203
Batchelor RA amp Kinnaird JA (1984) Gahnite compositions
compared Mineral Mag 48 425ndash430
Beurlen H Da Silva MRR Thomas R Soares DR Olivier P
(2008) Nb-Ta-(Ti-Sn) oxide mineral chemistry as tracer of rare-
element granitic pegmatite fractionation in the Borborema pro-
vince Northeastern Brazil Miner Deposita 43 207ndash228
Cameron EN Jahns RH McNair AH Page LR (1949)
Internal structure of granitic pegmatites Econ Geol
Monograph 2 115 p
Cerny P (1991a) Fertile granites of Precambrian rare-element
pegmatite fields is geochemistry controlled by tectonic setting
or source lithologies Precambrian Res 51 429ndash468
mdash (1991b) Rare-element granite pegmatites I Anatomy and inter-
nal evolution of pegmatite deposits Geoscience Canada 18
49ndash67
mdash (1992) Geochemical and petrogenetic features of mineralization
in rare-element granitic pegmatites in the light of current
research Applied Geochemistry 7 393ndash416
mdash (1994) Evolution of feldspars in granitic pegmatites in
lsquolsquoFeldspars and their Reactionsrsquorsquo I Parsons ed NATO
Advanced Study Institute Series C421 501ndash539
mdash (2005) The Tanco rare-element pegmatite deposit Manitoba
regional context internal anatomy and global comparisons in
lsquolsquoRare-element Geochemistry and Mineral Depositsrsquorsquo RL
Linnen amp IM Samson eds Geochemical Association of
Canada Short Course Notes St Catherines 17 127ndash158
Silicate and oxide minerals from a zoned granitic pegmatite 983
eschweizerbart_xxx
Cerny P amp Ercit TS (2005) The classification of granitic pegma-
tites revisited Can Mineral 43 2005ndash2026
Cerny P Meintzer RE Andersen AJ (1985) Extreme fractiona-
tion in rare-element granitic pegmatites selected examples of
data and mechanisms Can Mineral 23 381ndash421
Cerny P Goad BE Hawthorne FC Chapmann R (1986)
Fractionation trends of the Nb- and Ta-bearing oxide minerals
in the Greer Lake pegmatite granite and its pegmatite aureole
southeastern Manitoba Am Mineral 71 501ndash517
Cerny P Stanek J Novak M Baadsgaard H Rieder M
Ottolini L Kavalova M Chapman R (1995) Geochemical
and structural evolution of micas in the Rozna amp Dobra Voda
pegmatites Czech Republic Mineral Petrol 55 177ndash201
Cerny P Ercit TS Vanstone PJ (1998) Mineralogy and petrol-
ogy of the Tanco rare-element pegmatite deposit southeastern
Manitoba International Mineralogical Association 17th General
Meeting Toronto Field Guidebook B6
Cerny P Chapman R Ferreira K Smeds SA (2004)
Geochemistry of oxide minerals of Nb Ta Sn and Sb in
the Varutrask granitic pegmatite Sweden The case of an
lsquolsquoanomalousrsquorsquo columbitendashtantalite trend Am Mineral 89
505ndash518
Cerny P Masau M Goad BE Ferreira K (2005) The Greer
Lake leucogranite Manitoba and the origin of lepidolite-sub-
type granitic pegmatites Lithos 80 305ndash321
Cerny P Teertstra DK Chapman R Selway JB Hawthorne
FC Ferreira K Chackowsky LE Wang X-J Meintzer
RE (2012a) Extreme fractionation and deformation of the
leucogranite-pegmatite suite at Red Cross Lake Manitoba
Canada IV Mineralogy Can Mineral 50 1839ndash1875
Cerny P Halden NM Ferreira K Meintzer RE Brisbin WC
Chackowsky LE (2012b) Extreme fractionation and deforma-
tion of the leucogranite-pegmatite suite at Red Cross Lake
Manitoba Canada II Petrology of the leucogranites and peg-
matites Can Mineral 50 1807ndash1822
Dahl PS When DC Feldmann SG (1993) The systematics of
trace-element partitioning between coexisting muscovite and
biotite in metamorphic rocks from the Black Hills South
Dakota USA Geochim Cosmochim Acta 57 2487ndash2505
Dias MB amp Wilson WE (2000) The Alto Ligonha Pegmatites
Mozambique Mineral Record 31 459ndash497
Fleet ME (2003) Rock-Forming Minerals vol 3A Sheet silicates
micas The Geological Society London second edition chap 6
Lithium micas 651ndash690
Foord EE Cerny P Jackson LL Sherman DM Eby RK
(1995) Mineralogical and geochemical evolutions of micas
from miarolitic pegmatites of the anorogenic pikes-Peak
Batholith Colorado Mineral Petrol 55 1ndash26
Foster MD (1960) Interpretation of the composition of lithium
micas US Geol Surv Prof Paper 354-E 115ndash147
Fuhrman ML amp Lindsley DK (1988) Ternary-feldspar modeling
and thermometry Am Mineral 73 201ndash215
Gomes CL Castro P Alves C (1995) Caracterizacao das espi-
nelas zincıferas e do par ganite-nigerite no campo aplito-
pegmatıtico da Serra de Arga-Minho N de Portugal IV
Congresso Nacional de Geologia Resumos Alargados
Universidade do Porto Mem 4 629ndash633
Gordiyenko VV Ilyina AN Timochina LA Badamina EB
Stanek J (1996) Geochemical model of evolution of a pegma-
tite-forming ore-magmatic system of western Moravia Proc
Russ Mineral Soc 125 38ndash48 (in Russian)
Icenhower JP amp London D (1995) An experimental study for
element partitioning between biotite muscovite and coexisting
peraluminous granitic melt at 200 MPa (H2O) Am Mineral 80
1229ndash1251
Jahns RH (1982) Internal evolution of pegmatite bodies in lsquolsquoGranitic
Pegmatites in science and industryrsquorsquo P Cerny ed Mineralogical
Association of Canada Short Course Handbook 8 293ndash327
Jahns RH amp Burnham CW (1969) Experimental studies of
pegmatite genesis I A model for the derivation and crystal-
lization of granitic pegmatites Econ Geol 64 843ndash864
Jolliff BL Papike JJ Shearer CK (1987) Fractionation trends
in mica and tourmaline as indicators of pegmatite internal evo-
lution Bob Ingersoll pegmatite Black Hills South Dakota
USA GeochimCosmochim Acta 51 519ndash534
Kile DE amp Foord EE (1998) Micas from the Pikes Peak bath-
olith and its cogenetic granitic pegmatites Colorado optical
properties composition and correlation with pegmatite evolu-
tion Can Mineral 36 463ndash482
Linnen RL (1998) The solubility of Nb-Ta-Zr-Hf-W in granitic
melts with Li and Li thorn F constraints for mineralization in rare
metal granites and pegmatites Econ Geol 93 1013ndash1025
Linnen RL amp Cuney M (2005) Granite-related rare-element
deposits and experimental constraints on Ta-Nb-W-Sn-Zr-Hf
mineralization in lsquolsquoRare-element geochemistry and mineral
depositsrsquorsquo RL Linnen amp IM Samson eds Geochemical
Association of Canada Short Course Notes 17 45ndash68
London D (1990) Internal differentiation of rare-element pegmatites
a synthesis of recent research in lsquolsquoOre Bearing Granite Systems
Petrogenesis and Mineralizing Processesrsquorsquo HJ Stein amp JL
Hannah eds Geol Soc America Special Paper 246 35ndash50
mdash (2008) Pegmatites The Canadian Mineralogist Special
Publication 10 347 p
mdash (2009) The origin of primary textures in granitic pegmatites
Can Mineral 47 697ndash724
London D amp Morgan GB VI (2012) The pegmatite puzzle
Elements 8 263ndash268
London D Morgan GB VI Hervig RL (1989) Vapor-under-
saturated experiments in the system macusanite-H2O at 200
MPa and the internal differentiation of granitic pegmatites
Contrib Mineral Petrol 102 1ndash17
London D Morgan GB VI Paul KA Guttery BM (2012)
Internal evolution of miarolitic granitic pegmatites at the Little
Three mine Ramona California USA Can Mineral 50
1025ndash1054
Martins T Lima A Simmons WB Folster AU Noronha F
(2011) Geochemical fractionation of Nb-Ta oxides in Li-bear-
ing pegmatites from the Barroso-Alvao pegmatite field northern
Portugal Can Mineral 49 777ndash791
Monier G Charoy B Cuney M Ohnenstetter D Robert JL
(1987) Evolution spatiale et temporelle de la composition des
micas du granite albitique a topaze-lepidolite de Beauvoir
Geologie De La France 2ndash3 179ndash188
Monier G amp Robert JL (1986) Evolution of the miscibility gap
between muscovite and biotite solid solutions with increasing
lithium content an experimental study in the systems
K2OndashLi2OndashMgOndashAl2O3ndashSiO2ndashH2OndashHF at 600 C 2 kbar
PH2O comparison with natural lithium micas Mineral Mag
50 641ndash651
Morgan GBVI amp London D (1999) Crystallization of the little
three layered pegmatite-aplite dike Ramona District California
Contrib Mineral Petrol 136 310ndash330
984 A M R Neiva
eschweizerbart_xxx
Nabelek PI amp Russ-Nabelek C (1992) The generation and crys-
tallization conditions of the Proterozoic Harney Peak
Leucrogranite Black Hills South Dakota USA petrologic and
geochemical constraints Contrib Mineral Petrol 110
173ndash191
Nabelek PI Russ-Nabelek C Haeussler GT (1992) Stable
isotope evidence for the petrogenesis and fluid evolution in
the Proterozoic Harney Peak leucogranite Black Hills
South Dakota Geochim Cosmochim Acta 56 403ndash417
Neiva AMR amp Champness PE (1997) Nigerite and gahnite from
the granitic pegmatite veins of Cabanas Ponte de Lima northern
Portugal N Jb Mineral Mh 9 385ndash409
Neiva AMR Gomes MEP Ramos JMF Silva PB (2008)
Geochemistry of granitic aplite-pegmatite sills and their miner-
als from Arcozelo da Serra area (Gouveia central Portugal)
Eur J Mineral 20 465ndash485
Neiva AMR amp Neiva JMC (2005) Beryl from the granitic
pegmatite at Namivo Alto Ligonha Mozambique N Jb
Mineral Abh 181 173ndash182
Neiva AMR amp Ramos JMF (2010) Geochemistry of granitic
aplite-pegmatite sills and petrogenetic links with granites
Guarda-Belmonte area central Portugal Eur J Mineral 22
837ndash854
Neiva AMR Silva PB Ramos JMF (2012) Geochemistry of
granitic aplite-pegmatite veins and sills and their minerals from the
Sabugal area central Portugal N Jb Mineral Abh 189 49ndash74
Novak M amp Cerny P (1998) Niobium-tantalum oxide minerals
from complex granitic pegmatites in the Moldanubicum Czech
Republic primary versus secondary compositional trends Can
Mineral 36 659ndash672
Pesquera Perez A Torres-Ruiz J Gil PP Velilla N (1999)
Chemistry and genetic implications of tourmaline and Li-F-Cs
micas from the Valdeflores (Caceres Spain) Am Mineral 84
55ndash69
Rieder M Cavazzini G DrsquoYakonov YuS Frank-Kamenetskii
VA Gottardi G Guggenheim S Koval PV Muller G
Neiva AMR Radoslovich EW Robert J-L Sassi FP
Takeda H Weiss Z Wones DR (1999) Nomenclature of the
micas Mineral Mag 63 267ndash279
Roda Robles E Pesquera Perez A Velasco Roldan F Fontan F
(1999) The granitic pegmatites of the Fregeneda area
(Salamanca Spain) characteristics and petrogenesis Mineral
Mag 63 535ndash558
Roda Robles E Pesquera A Gil-Crespo PP Torres-Ruiz J
Fontan F (2005) Origin and internal evolution of the Li-F-
Be-P-bearing Pinilla de Fermoselle pegmatite (Central Iberian
Zone Zamora Spain) Am Mineral 90 1887ndash1899
Roda Robles E Pesquera Perez A Gil PP Torres-Ruiz J de
Parseval P (2006) Mineralogy and geochemistry of micas from
the Pinilla de Fermoselle pegmatite (Zamora Spain) Eur J
Mineral 18 369ndash377
Roda Robles E Keller P Pesquera Perez A Fontan F (2007)
Micas of the muscovite-lepidolite series from Karibib pegma-
tites Namibia Mineral Mag 71 41ndash62
Roda Robles E Pesquera A Gil-Crespo P Torres-Ruiz J
(2012) From granite to highly evolved pegmatite a case study
of the Pinilla de Fermoselle granite-pegmatite system (Zamora
Spain) Lithos 153 192ndash207
Selway JB Novak M Cerny P Hawthorne FC (1999)
Compositional evolution of tourmaline in lepidolite-subtype
pegmatites Eur J Mineral 11 569ndash584
Shearer CK Papike JJ Jolliff B (1992) Petrogenetic links
among granites and pegmatites in the Harney Peak rare-element
granite-pegmatite system Black Hills South Dakota Can
Mineral 30 785ndash809
Soares DR Hartmut B Ferreira ACM da Silva MRR
(2007) Chemical composition of gahnite and degree of peg-
matitic fractionation in the Borborema Pegmatitic Province
northeastern Brazil Anais Da Academ Bras Cien 79
395ndash404
Stewart DB (1978) Petrogenesis of lithium-rich pegmatites Am
Mineral 63 970ndash980
Tischendorff G Gattesmann B Forster H-J Trumbull RB
(1997) On Li-bearing micas estimating Li from electron
microprobe analyses and an improved diagram for graphical
representation Mineral Mag 61 809ndash834
Van Lichtervelde M Linnen RL Salvi S Beziat D (2006)
The role of metagabbro rafts on tantalum mineralization in the
Tanco granitic pegmatite Manitoba Can Mineral 44
625ndash644
Van Lichtervelde M Gregoire M Linnen RL Beziat D Salvi
S (2008) Trace element geochemistry by laser ablation ICP-
MS of micas associated with Ta mineralization in the Tanco
pegmatite Manitoba Canada Contrib Mineral Petrol 155
791ndash806
Vieira R Roda-Robles E Pesquera A Lima A (2011)
Chemical variation and significance of micas from the
Fregeneda-Almendra pegmatitic field (Central-Iberian Zone
Spain and Portugal) Am Mineral 96 637ndash645
Wen S amp Nekvasil H (1994) SOLVCALC an interactive gra-
phics program package for calculating ternary feldspar solvus
and two-feldspar geothermometry Comput Geosci 20
1025ndash1040
Wise MA (1995) Trace element chemistry of lithium-rich micas
from rare-element granitic pegmatites Mineral Petrol 55
203ndash215
Zasedatelev AM (1974) Possible accumulation of lithium in host
rocks of lithium pegmatite veins during old sedimentation pro-
cesses Doklady Acad Sci USSR Earth Sci Ser 218 196ndash198
(in Russian)
mdash (1977) Quantitative of metamorphic generation of rare-metal
pegmatites with lithium mineralization Doklady Acad Sci
USSR Earth Sci Ser 236 219ndash221 (in Russian)
Received 26 January 2013
Modified version received 21 May 2013
Accepted 23 July 2013
Silicate and oxide minerals from a zoned granitic pegmatite 985
eschweizerbart_xxx
diffuse reequilibration took place in any crystal as thecontacts between core and rim are sharp
In the Cc lithian muscovite is surrounded and pene-trated by lsquolsquomixed formrsquorsquo showing well defined contacts(Fig 3i) The lsquolsquomixed formrsquorsquo has higher Si Fe2thorn Mn(Fe2thornthorn Mn thorn Mg) Licalc Rb Cs F contents and lowerAlVI (AlIV thorn AlVI) Na OH contents and KRb ratio thanthe lithian muscovite (Table 1 Fig 6m n) and a composi-tional gap occurs between both micas suggesting thatlsquolsquomixed formrsquorsquo replaced lithian muscovite In rare crystalsa small lepidolite core is surrounded by a large muscoviterim containing K-feldspar inclusions The contact betweenthe core and rim is sharp (Fig 3j) A thin partial rim oflithian muscovite surrounds muscovite and the contact isgradual The muscovite rim has higher AlVI (AlIVthornAlVI)Na K OH contents and a greater KRb value and lower SiFe2thorn Mn Licalc Rb Cs and F contents than the lepidolitecore (Table 1 Fig 6o p) and a compositional gap occursbetween them (Fig 6o p) indicating that either muscoviteforms an overgrowth or it is reversely formed From themuscovite rim to the lithian muscovite rim the Si Licalc
Rb F contents increase whereas the AlVI (AlIV thorn AlVI)and OH contents and KRb ratio decrease (Table 1 Fig 6op) suggesting that muscovite evolved to lithian muscoviteas also found in IIZa and IIZb
44 Evolution of mica compositions within each zoneand from the outer intermediate zone to the core of theNamivo granitic pegmatite
The KRb ratio is taken as the best fractionation index inmicas (eg Cerny et al 1985 Foord et al 1995 Wise1995 Pesquera et al 1999 Roda Robles et al 2006 2007)It is hard to establish trends in the evolution of mica com-position from muscovite and lithian muscovite to lsquolsquomixedformrsquorsquo and lepidolite within each zone because the KRbratio shows some partial overlapping particularly betweenthe lithian muscovite and lsquolsquomixed formrsquorsquo and also betweenthe latter and lepidolite However an evolution from mus-covites to lepidolite (Al-richer mica Fig 4) is clearer (Fig7) In general in IIZa IIZb and Cc the Si Licalc Rb Cs and
Fig 5 The main substitutions in micas from the Namivo granitic pegmatite Mozambique a b SiIVthorn LiVI versus AlIVthornAlVI showing the 2SithornLi 3Altotal substitution mechanism operating in dioctahedral micas (Mu muscovite and Lith mu lithian muscovite) c d AlVI thornamp VI
versus LiVI (where amp represents a vacancy) and showing the 3LiVI AlVI thorn 2 amp VI substitution mechanism operating in trioctahedral micas(Mix f ndashlsquolsquomixed formrsquorsquo Lep lepidolite Zin zinnwaldite and Pol-FeMg-containing polylithionite) OIZ IIZa IIZb and Cc as in Fig 2
974 A M R Neiva
eschweizerbart_xxx
F contents tend to increase and the (AlIV thorn AlVI) AlVI
contents and KRb ratio tend to decrease from muscoviteto lepidolite (Table 1 Fig 7) This sequence is consistentbut rarely in the Cc lepidolite is rimmed by muscovite (Fig3j) But in the OIZ the evolution stops in lsquolsquomixed formrsquorsquoparticularly shown by the large range of the KRb ratiowhich mainly overlaps that of lepidolite from this zone(Fig 7) because this lepidolite is an Al-poorer mica whereasthe others are Al-richer micas (Fig 4)
In the OIZ the lepidolite has more Si Licalc and F andless (AlIV thorn AlVI) Ti Fe2thorn Mn Mg and Zn than zinn-waldite (Table 1) but it has larger ranges of Rb and KRbratio than zinnwaldite (Fig 7) The FeMg-containingpolylithionite is the richest mica in Si Licalc and thepoorest in (AlIV thorn AlVI) (Table 1) But at this zone scalethe polylithionite has Rb Cs contents and KRb ratiowithin the ranges for lepidolite and close to those of zinn-waldite (Fig 7)
Fig 6 Variation diagrams of micas from selected zoned crystals from the zones of the Namivo granitic pegmatite Mozambique to showtheir relationships lith musc lithian muscovite OIZ IIZa IIZb and Cc an in Fig 2
Silicate and oxide minerals from a zoned granitic pegmatite 975
eschweizerbart_xxx
From the OIZ to IIZa IIZb and Cc muscovite and lithianmuscovite generally show increases in the Si Licalc F and Rbcontents and decreases in the Fe2thorn and Mg contents and KRb ratio but the Mg content is very low in these micas fromthe IIZa IIZb and Cc (Table 1 Fig 7a) The lsquolsquomixed formrsquorsquoshows increases in the Si Licalc F Rb Cs contents anddecreases in the (AlIV thorn AlVI) and Mg contents and KRbratio but the Mg content is very low in this mica from theIIZb and Cc (Table 1 Fig 7b c) The lepidolite shows anincrease in the Si Licalc F Rb and Cs contents and a decreasein the KRb ratio from the IIZa to the IIZb and Cc (Table 1Fig 7d e) Furthermore the lepidolite from the OIZ has thelowest (AlIV thorn AlVI) AlVI and OH contents the highest SiFe2thorn Licalcand F contents and KRb ratio and the lowest Rband Cs contents compared to lepidolite from the other zones(Table 1 Fig 7d e)
5 Feldspars
Selected chemical analyses of albite and K-feldspar fromfive zones of the Namivo granitic pegmatite are given inTable 2 Strontium is the most abundant trace element inalbite (eg Cerny 1994) Anorthite and Sr contents and SrCa ratio of albite decrease from the WZ to the Cc (Fig 8Table 2) Rubidium is the most abundant trace element inK-feldspar followed by Cs in IIZa IIZb and Cc In gen-eral K Rb and Cs contents of K-feldspar increase and KRb and KCs values decrease from the WZ to the Cc (Table2 Fig 9)
The program SOLVCALC 20 (Wen amp Nekvasil 1994)using the Margules model Fuhrman amp Lindsley (1988) wasapplied for the purpose of thermometry The pairing ofplagioclase cores with the K-feldspars average of eachsample was used to estimate the crystallization temperaturesof primary magmatic feldspars They are 405 C (WZ)406ndash340 C (OIZ) 390ndash335 C (IIZa) 347ndash306 C (IIZb)and 333ndash289 C (Cc) at 3 kbar The metamorphic environ-ment of rare-element-Li granitic pegmatites is one of lowpressure 2ndash4 kbar (Cerny amp Ercit 2005) In general thedifference between the maximum and minimum calculatedtemperatures at 2 3 and 4 kbar for the same feldspar pairfrom the Namivo pegmatite is lower than 40 C The tem-perature decreases from the wall zone (WZ) to the core(Cc) A similar temperature behavior of feldspars wasfound in the pegmatite-aplite dike USA (Morgan ampLondon 1999)
6 Other silicates
Tourmaline of schorl composition was only found inthe OIZ (Table 2) because there was not enough Feand Mg for schorl to precipitate in the other zonesSpodumene only occurs in the Cc and its compositionis nearly pure (Table 2)
7 Columbite-tantalite
Representative chemical analyses of columbitendashtantalitefrom the Namivo granitic pegmatite are given in Table 3and plotted in the columbite quadrilateral (Fig 10a)Most crystals are unzoned but zoned crystals with dar-ker and lighter zones in BSE images are from the Cc Thelighter zone of columbite-(Mn) has higher Ta contentTa(Ta thorn Nb) and Mn(Mn thorn Fe) values and lower Nbcontent than the darker zone (Fig 10a b) The crystals ofthe columbitendashtantalite minerals are low in W Sn and Tiimpurities (Table 3)
The main trend starts from the columbite-(Mn) of theOIZ towards the more Mn-enriched and slightly Ta-enriched columbite-(Mn) from the IIZa and Cc The high-est Ta(Ta thorn Nb) values belong to the lighter zone ofcolumbite-(Mn) with Mn(Mn thorn Fe) frac14 10 from the CcThe richest columbite-(Mn) in Ta(TathornNb) and composi-tions of tantalite-(Fe) and tantalite-(Mn) were only foundin the OIZ (Fig 10a) and are associated with lepidolite andpolylithionite (Fig 3c)
8 Gahnite
Gahnite was rarely found in the OIZ and shows a darkerzone that partially surrounds a lighter zone in a BSE image(Fig 11a) The darker zone has a higher Zn content andlower Sn Ti Nb Ta Mn contents and SnZn value than thelighter zone (Table 4 Fig 11b c) These gahnite composi-tions fall within the igneous field of Batchelor amp Kinnaird(1984) The darker zone is closer in composition to thepure gahnite (Zn8Al16O32) than the lighter zone whichcontains up to 0983 apfu Sn 0195 apfu Ti 1029 apfutotal Fe2thorn 0101 apfu Mn (Table 4) and consequently hasa composition distinct from nigerite In general both thedarker and lighter zones have higher Sn Ti and Fe contentsthan gahnite from the granitic pegmatites of Nigeria(Batchelor amp Kinnaird 1984) Arga northern Portugal(Gomes et al 1995) and Cabanas northern Portugal(Neiva amp Champness 1997) Borborema province north-eastern Brazil (Soares et al 2007) The Zn=Fe2thornt values ofthe darker and lighter zones of gahnite from Namivo arelower than those reported in Neiva amp Champness (1997)and Soares et al (2007)
9 Discussion and conclusions
91 Evolution of micas in the zoned pegmatite
In general individual mica crystals show varying patternsand compositional zoning involving several elementsmainly Si AlVI (AlIV thorn AlVI) Fe2thorn Mn (Fe2thornthorn Mn thornMg) Licalc Rb Cs F and OH and the KRb ratioProgressively zoned crystals from the IIZa show grada-tional contacts between a lithian muscovite core and a
976 A M R Neiva
eschweizerbart_xxx
lsquolsquomixed formrsquorsquo rim (Figs 3e 6e f) and the zoning patternscorrespond to fractionation trends and probably reflect adrop in temperature during the crystallization of the grani-tic pegmatite melt Progressively zoned crystals also occurin OIZ IIZb and Cc Some crystals are reversely zonedwith a) a lsquolsquomixed formrsquorsquo core and a lithian muscovite rimfrom the OIZ (Figs 3d d1 6d) b) a core consisting oflsquolsquomixed formrsquorsquo and lepidolite and a rim of muscovite andlithian muscovite from the IIZa (Figs 3f f1 6g h) c) alepidolite core and a muscovite and lithian muscovite rimfrom the Cc (Figs 3j 6o p) which may be explained bythe hypothesis of oscillations in the compositions of themelt from which they grew alternating between an Li-enriched boundary layer and a bulk melt that is less frac-tionated The muscovite evolved to lithian muscovite inIIZa and Cc (Figs 3f 6g h 3j 6o p) Replacements (Figs3a 6a b 3c 6c 3i 6m n Table 1) occur in OIZ and Ccand overgrowths (Figs 3b g 6i j k 3h 6l Table 1) occurin OIZ and IIZb as found in BSE images
Muscovite evolved to lithian muscovite as observed inOIZ IIZa IIZb and Cc (Figs 3f 6g h 3j 6o p Table 1)Lithian muscovite evolved to lsquolsquomixed formrsquorsquo in OIZ IIZaIIZb and Cc (Figs 3e 6e f Table 1) and lsquolsquomixed formrsquorsquoevolved to lepidolite in IIZa IIZb and Cc (Figs 3f f1 6gh 3h 6l Table 1) All these evolutions are due to fractionalcrystallization
In the OIZ lepidolite has more Si Licalcand F butsimilar KRb to that of zinnwaldite and replaces it (Figs
3a 6a b 7d Table 1) An FeMg-containing polylithionitehas higher Si Licalcand Rb contents and a smaller KRbratio than the lepidolite that it replaces (Figs 3c 6c Table1) and a continuous chemical evolution from lepidolite topolylithionite is shown
The trends for major and trace elements of micas withineach zone are difficult to define due to some partial over-lapping but a progressive evolution from muscovite to lithianmuscovite lsquolsquomixed formrsquorsquo and lepidolite in IIZa IIZb and Ccis mainly shown by an increase in the Si Licalc F Rb and Cscontents and a decrease in the KRb ratio and this is simi-larly shown in the OIZ from muscovite to lsquolsquomixed formrsquorsquo(Table 1 Fig 7) In the OIZ Si and Licalccontents increaseprogressively from zinnwaldite to lepidolite and FeMg-containing polylithionite but a gap occurs between zinnwal-dite and lepidolite (Table 1 Fig 4) whereas a continuousevolution from lepidolite to polylithionite is observed TheKRb ratios of zinnwaldite and polylithionite are within therange of that of lepidolite (Fig 7d e)
Each Al-richer mica (muscovite lithian muscovite andlsquolsquomixed formrsquorsquo) exhibits an evolution from the OIZ to theIIZa and then to the IIZb and Cc particularly shown by anincrease in the Si Licalc F and Rb contents and adecrease in the KRb ratio but also an increase in theCs content in the lsquolsquomixed formrsquorsquo (Table 1 Fig 7) Theseelements and ratio have been used as petrogenetic indi-cators of evolution in micas from pegmatites (eg Cernyet al 2005 Roda Robles et al 2006 2007 Vieira et al
Fig 7 Plot of some variation diagrams of micas from the OIZ IIZa IIZb and Cc of the Namivo granitic pegmatite Mozambique showingthat the Rb2O and Cs2O contents increase and the KRb ratio decreases for micas from the OIZ to the Cc OIZ IIZa IIZb and Cc as in Fig 2
Silicate and oxide minerals from a zoned granitic pegmatite 977
eschweizerbart_xxx
Tab
le2
R
epre
sen
tati
ve
elec
tro
nm
icro
pro
be
anal
yse
sin
wt
o
ffe
ldsp
ars
sch
orl
and
spo
du
men
efr
om
the
Nam
ivo
gra
nit
icp
egm
atit
eM
oza
mb
iqu
e
Alb
ite
K-f
eld
spar
Sch
orl
Sp
od
um
ene
Zo
nes
WZ
OIZ
IIZ
aII
Zb
Cc
Zo
nes
WZ
OIZ
IIZ
aII
Zb
Cc
Zo
nes
OIZ
Zo
ne
Cc
SiO
26
75
76
78
86
87
06
84
76
84
1S
iO2
65
10
65
55
65
46
64
96
64
72
SiO
23
52
0S
iO2
64
65
TiO
20
02
mdash0
02
mdashmdash
TiO
2mdash
00
1mdash
mdashmdash
TiO
20
35
Al 2
O3
27
20
Al 2
O3
20
25
19
74
19
67
19
88
19
97
Al 2
O3
18
96
18
23
18
31
18
24
18
05
B2O
3
10
28
Fe 2
O3
00
6F
e 2O
3mdash
mdashmdash
mdash0
10
Fe 2
O3
mdash0
02
mdash0
03
mdashA
l 2O
33
17
2M
nO
01
3M
nO
00
6mdash
mdashmdash
mdashM
nO
mdash0
03
00
3mdash
mdashF
eO1
35
2M
gO
01
8M
gO
mdashmdash
mdashmdash
mdashM
gO
00
10
01
00
5mdash
mdashM
nO
03
3N
a 2O
01
9C
aO1
04
08
00
56
03
70
32
CaO
00
10
01
00
60
01
00
2M
gO
22
8L
i 2O
8
05
Na 2
O1
06
11
12
01
12
11
13
41
13
4N
a 2O
06
50
58
04
10
59
03
8C
aO0
23
To
tal
10
04
6K
2O
00
50
17
00
60
14
01
0K
2O
14
72
14
75
15
67
15
01
15
74
Li 2
O
02
2S
rO0
72
05
00
24
01
1mdash
Rb
2O
00
90
20
03
00
59
09
0N
a 2O
22
8S
i1
99
7P
2O
50
01
00
4mdash
mdashmdash
Cs 2
O
00
6
00
60
09
01
80
20
K2O
00
1A
lIV0
00
3T
ota
l1
00
33
10
03
31
00
46
10
03
11
00
24
P2O
5mdash
00
3mdash
mdashmdash
H2O
3
18
P2
00
To
tal
99
60
99
48
10
03
89
96
11
00
01
F0
78
AlV
I0
98
7S
rC
a(w
t)0
81
07
40
50
03
50
Cl
mdashF
e3thorn
00
01
KR
b(w
t)153
68
48
23
16
Sum
1003
8P
09
9S
i1
18
23
11
87
91
19
58
11
93
21
19
21
KC
s(w
t)4
07
20
41
63
73
69
O
F0
33
Li
10
00
P0
00
10
00
6mdash
mdashmdash
To
tal
10
00
5M
n0
00
3T
i0
00
3mdash
00
03
mdashmdash
Si
11
98
61
20
88
12
04
11
20
45
12
03
3M
g0
00
8A
l4
17
64
07
14
03
54
08
34
10
1P
mdash0
00
5mdash
mdashmdash
TS
i5
95
2N
a0
01
2F
e3thorn
mdashmdash
mdashmdash
00
13
Ti
mdash0
00
1mdash
mdashmdash
Al
00
48
P1
02
Mn
00
09
mdashmdash
mdashmdash
Al
41
14
39
62
39
70
39
86
39
55
B3
00
0M
gmdash
mdashmdash
mdashmdash
Fe3thorn
mdash0
00
3mdash
00
04
mdashZ
Al
60
00
Ca
01
95
01
50
01
04
00
69
00
60
Mn
mdash0
00
50
00
5mdash
mdashY
Al
02
74
Sr
00
73
00
51
00
24
00
11
mdashM
g0
00
30
00
30
01
4mdash
mdashT
i0
04
5N
a3
59
93
80
03
78
33
83
23
83
1C
a0
00
20
00
20
01
20
00
20
00
4M
g0
57
5K
00
11
00
38
00
13
00
31
00
22
Na
02
32
02
07
01
46
02
12
01
37
Mn
00
47
K3
45
73
47
03
67
73
55
03
73
3F
e2thorn
19
12
Z1
60
01
59
61
60
01
60
11
60
4R
b0
01
10
02
40
03
50
07
00
10
8L
i0
14
8X
38
94
04
39
33
94
39
1C
s0
00
20
00
50
00
70
01
40
01
6P
Y3
00
0m
ole
s
XC
a0
04
2A
n5
13
82
71
71
5Z
16
10
16
06
16
01
16
03
15
99
Na
07
47
Ab
94
69
53
97
09
75
97
9X
37
13
72
39
03
85
40
0K
00
02
Or
03
09
03
08
06
mo
les
amp
02
09
An
01
01
03
01
01
Ab
63
56
38
56
35
OH
35
83
Or
93
69
43
95
99
43
96
4F
04
17
Cl
mdash
WZ
ndashw
allzo
ne
OIZ
ndasho
ute
rin
term
edia
tezo
ne
IIZ
aan
dII
Zb
ndashin
ner
inte
rmed
iate
zon
esC
cndash
core
asin
Fig
2B
aOis
bel
ow
the
det
ecti
on
lim
itin
bo
thfe
ldsp
ars
Cs 2
Ofrac14
00
3w
tin
the
K-
feld
spar
fro
mth
eW
Z
mdashN
ot
det
ecte
d
Nu
mb
ero
fio
ns
on
the
bas
iso
f3
2o
xy
gen
sfo
ral
bit
ean
dK
-fel
dsp
ar
31
anio
ns
(O
OH
F
)fo
rsc
ho
rlan
d6
ox
yg
ens
for
spo
du
men
e
-A
mo
un
tin
ferr
edfr
om
con
sid
erat
ion
so
fst
oic
hio
met
ry
978 A M R Neiva
eschweizerbart_xxx
2011) Lepidolite from the OIZ is an Al-poorer mica (Fig4) and has the highest Si Licalcand F contents (Table 1)indicating that an evolution cannot be shown from thislepidolite to lepidolites from the other zones which areAl-richer micas (Fig 4) However there is a regulardecrease in the KRb ratio and a progressive increase inthe Rb and Cs contents from lepidolite of the OIZ tolepidolite of IIZa IIZb and Cc (Fig 7) which indicatesthat the KRb ratio and Rb and Cs contents must not beconsidered alone to show fractional crystallization in
lepidolites particularly if some are Al-richer micas andothers Al-poorer micas The high Licalcand F contents oflepidolite from the OIZ did not decrease its KRb ratioSuch an effect is considered to have taken place in lepi-dolite (an Al-richer mica) from the wall zone of the Tancopegmatite Manitoba Canada (Van Lichtervelde et al2008) An evolution from the lepidolite of the IIZa to thatof the Cc is generally shown by the increasing Si LicalcF Rb Cs contents and a decrease in the KRb ratio (Table1 Fig 7)
At the scale of crystals the pegmatite zones and alsothose from the OIZ to the Cc of the Namivo granitic pegma-tite Al-richer micas show fractionation because theyformed from the fractionation of an Li-rich pegmatite melt
The Al-poorer micas zinnwaldite lepidolite and FeMg-containing polylithionite only occur in the OIZ (Fig 4)Polylithionite is the mica richest in Si and Licalc and lepi-dolite from this zone is the richest in Si Licalcand F (Fig 4Table 1) The high Li contents of these micas reflect aconsiderably higher D(Li) at low temperature (Icenhoweramp London 1995) These Li-rich micas may have crystal-lized from an undercooled melt This hypothesis does notimply high Rb and Cs contents and low KRb ratios Thisagrees with the fact that these micas from the OIZ havesimilar Rb and Cs contents and KRb ratios to those of Al-richer micas (muscovite lithian muscovite and lsquolsquomixedformrsquorsquo) from the same pegmatite zone (Fig 7) Howeverthe lepidolite from the wall zone of the Tanco pegmatiteCanada of a similar origin has a low KRb ratio which isattributed to the complexly interrelated structural compo-nents of this lepidolite (Van Lichtervelde et al 2008) TheLi-rich micas from the OIZ may also represent disequili-brium These two hypotheses are considered the best forthese micas of primary magmatic origin
Another hypothesis was also considered They may havecrystallized in boundary layers which concentrate Li andF But this mechanism was suggested for the most fractio-nated tourmaline enriched in Li and F from the core of the
Fig 8 Plot of albite compositions from all zones of the Namivo granitic pegmatite Mozambique showing that the anorthite content of albitedecreases from the WZ to the Cc WZ OIZ IIZa IIZb and Cc as in Fig 2
Fig 9 The Rb vs Cs diagram of K-feldspar from all zones of theNamivo granitic pegmatite Mozambique showing that the Rb andCs contents of K-feldspar increase from the WZ to the Cc WZ OIZIIZa IIZb and Cc as in Fig 2
Silicate and oxide minerals from a zoned granitic pegmatite 979
eschweizerbart_xxx
Little Three pegmatite dike USA (Morgan amp London1999) and the micas enriched in Li and F from theNamivo pegmatite belonging to the OIZ Furthermore ina boundary layer melt that became enriched in Li and F theKRb ratio of micas decreases strongly (Van Lichterveldeet al 2008) which was not found in these micas from theOIZ (Fig 7d) Nor can they have resulted from the crystal-lization of a late melt that would have reacted with the OIZbecause these micas are among those containing the high-est KRb values (Fig 7d)
92 The importance of feldspars micas andcolumbitendashtantalite compositions to the Namivogranitic pegmatite evolution
The trace elements Rb and Cs and the KRb and KCs ratioshave been used to show the evolution of K-feldspar inpegmatites (eg Cerny 1994 Cerny et al 2005 RodaRobles et al 2005) The Rb and Cs contents increase andthe KRb and KCs ratios of K-feldspar decrease from theWZ to the Cc (Fig 9 Table 2) reflecting the growth of K-feldspar from an increasingly fractionated melt withouthaving grown from or having been chemically modifiedby an aqueous fluid as in the Swamp pegmatite section atthe Little Three Mine USA (London et al 2012) Thecrystallization of K-feldspar from an exsolved aqueousfluid from melt will reverse the magmatic fractionation ofRb Cs KRb and KCs because Rb and especially Cs areso much more compatible in vapor that both Rb and Csremain in the fluid phase (London et al 2012) The feldsparsolvus pairs in the Namivo pegmatite record magmaticcrystallization temperatures that decrease from WZ to CcAlbite shows a decrease in the Ca Sr contents and SrCaratio from the WZ to the Cc (Fig 8 Table 2) Therefore thefeldspars and also Al-richer micas as already explainedshow fractionation in this zoned pegmatite
In general lepidolite from the Namivo pegmatite hassimilar Rb2O and Cs2O contents and KRb (wt) values tothose of lepidolite from the Rozna and Dobra Voda lepi-dolite-subtype pegmatites in the Czech Republic (Cernyet al 1995) but lower Rb2O and Cs2O contents thanlepidolite from the lepidolite-subtype pegmatite at RedCross Lake Manitoba Canada (Cerny et al 2012a) K-feldspar from the Namivo pegmatite also has lower Rb2O
Table 3 Representative electron microprobe analyses in wt of columbitendashtantalite from the Namivo granitic pegmatite Mozambique
Outer Intermediate Zone - OIZ Inner Intermediate Zone - IIZa
Core - Cc
D L L
WO3 022 059 079 113 101 351 050 007Ta2O5 5487 5123 2503 3186 2888 2519 3127 4542Nb2O5 2537 3000 5483 4635 5113 5144 4911 3686SnO2 008 015 024 049 020 026 017 012TiO2 263 161 136 254 202 145 125 016FeO 860 710 665 471 236 068 mdash mdashMnO 793 952 1099 1304 1400 1725 1748 1718Total 9970 10020 9989 10012 9960 9978 9978 9981W 0004 0011 0013 0019 0016 0057 0008 0001Ta 1065 0975 0422 0552 0495 0430 0543 0847Nb 0819 0949 1538 1336 1456 1460 1418 1143Sn 0002 0004 0006 0012 0005 0007 0004 0003Ti 0141 0085 0063 0122 0096 0068 0060 0008Fe 0513 0416 0345 0251 0124 0036 mdash mdashMn 0479 0564 0578 0704 0747 0917 0945 0998P
3023 3004 2965 2996 2939 2975 2978 3000Mn(Mn thorn Fe) 048 058 063 074 086 096 100 100Ta(Ta thorn Nb) 057 051 022 029 025 023 028 043Classification tant-(Fe) tant-(Mn) col-(Mn) col-(Mn) col-(Mn) col-(Mn) col-(Mn) col-(Mn)
D ndash darker L ndash lighter zones mdash Not detected tant-tantalite col-columbite Cation formula on the basis of 6 atoms of oxygen
Fig 10 Compositions of columbitendashtantalite from the Namivogranitic pegmatite Mozambique in the columbite quadrilateralshowing that Mn(Mn thorn Fe) of columbite-(Mn) increases from theOIZ to the Cc and the richest columbite-(Mn) in Ta(Ta thorn Nb)tantalite-(Fe) and tantalite-(Mn) only occur in the OIZ OIZ IIZaand Cc as in Fig 2
980 A M R Neiva
eschweizerbart_xxx
and Cs2O contents than K-feldspar from the lepidolite-subtype pegmatite at Red Cross Lake The Rb2O andCs2O contents of primary and late K-feldspar of this peg-matite at Red Cross Lake attained unprecedented levels(Cerny et al 2012a) The lowest KRb (wt) values ofmuscovite lithian muscovite lsquolsquomixed formrsquorsquo and lepido-lite from the IIZb and Cc (Fig 7) and K-feldspar (KRb frac1414) from the Cc compare well with those found in theseminerals from the AC6frac143 lepidolite-subtype pegmatitefrom Greer Lake (Cerny et al 2005) and some of themost fractionated pegmatites worldwide which belong tothe petalite-subtype (eg Tanco Manitoba Cerny 2005Cerny et al 1998 Varutrask Sweden Cerny et al 2005)but muscovite lithian muscovite and lepidolite from theIIZb and Cc have lower Rb2O and Cs2O contents than thesemicas from the Tanco pegmatite (Cerny 2005a VanLichtervelde et al 2008) K-feldspar also has lower
contents of these oxides than the most evolved K-feldsparfrom the Tanco pegmatite (Cerny 2005a) The magmaticfractionation was strong from the WZ to IIZb and Cc of theNamivo lepidolite-subtype pegmatite
The compositional trend of columbite-(Mn) from the OIZto Cc of the Namivo granitic lepidolite-subtype pegmatite(Fig 10) is identical to that of columbite-group mineralsfrom the lepidolite-subtype complex granitic pegmatitesfrom the Dobra Voda in the Moldanubicum CzechRepublic (Novak amp Cerny 1998) and the HimalayaDistrict southern California (shown in Cerny et al 2004)Experimental data for the Fe-Mn pair (Linnen amp Cuney2005) suggest an increase in Fe with fractional crystalliza-tion which is not observed in nature Other phases seem tocontrol the bahavior of Fe and Mn in the melt eg thecrystallization of tourmaline causes a rapid increase of theMnFe in the melt (Van Lichtervelde et al 2006) When thecrystallization of tourmaline stopped the columbitendashtantaliteminerals showed a constant MnFe indicating that the Fe andMn contents in the melt remained constant Schorl onlyoccurs in the OIZ of the Namivo granitic pegmatite and itscrystallization cannot be responsible for the increase in theMnFe of the melt because Mn(Mn thorn Fe) of columbite-(Mn) increases progressively from the OIZ to the IIZa and Cc(Fig 10) Garnet zinnwaldite and gahnite containing Fe andMn also only occur in the OIZ and cannot also have causedthe increase of the MnFe in the melt The dominant Mnenrichment before Ta enrichment started in the columbitendash-tantalite composition from some granitic pegmatites isattributed to an increased alkali-fluoride activity at moderatemHF (Cerny et al 2004) and an increase in the activity offluorine (Martins et al 2011) Each Al-richer mica (musco-vite lithian muscovite and lsquolsquomixed formrsquorsquo) from the Namivogranitic pegmatite shows an increase in F content from theOIZ to the IIZa IIZb and Cc (Table 1) In general the Fcontent of lepidolite also increases from the IIZa to the IIZband Cc Therefore the extreme Fe-Mn fractionation beforeTa enrichment in columbite-(Mn) (Fig 10) may be due to anincrease in the activity of fluorine as a consequence offractional crystallization The increase in the Ta content ofcolumbite-(Mn) from the Namivo granitic pegmatite isattributed to fractional crystallization
The geochemical evolution of albite and K-feldsparfrom the WZ to the Cc Al-richer micas muscovite lithianmuscovite and lsquolsquomixed formrsquorsquo from the OIZ to the Cc andlepidolite from the IIZa to the Cc and columbite-(Mn) andalso beryl (Neiva amp Neiva 2005) from the OIZ to the Ccare caused by magma fractionation The pegmatite zonesare the product of primary crystallization from a volatile-rich silicate melt The pegmatite consolidated from the WZto the Cc The IIZb is one of the most evolved zones asalso suggested by the beryl composition (Neiva amp Neiva2005) and is the richest in lsquolsquomixed formrsquorsquo and lepidolite
The richest columbite-(Mn) in Ta(Ta thorn Nb) and com-positions of tantalite-(Fe) and tantalite-(Mn) only occur inthe OIZ (Fig 10a) associated with lepidolite and polythio-nite (Fig 3c) which may be due to the local depletion of Liand F in the melt which decreases the solubility of Ta andcauses Ta precipitation (Linnen 1998 Linnen amp Cuney
Fig 11 a Backscattered-electron image of a gahnite crystal with adarker zone partially surrounding a lighter zone from the OIZ of theNamivo granitic pegmatite b c Plot of gahnite compositions in theSn-Zn-Ti diagram (atomic proportions) showing a chemical distinc-tion between the lighter and darker zones OIZ as in Fig 2
Silicate and oxide minerals from a zoned granitic pegmatite 981
eschweizerbart_xxx
2005) At the Tanco pegmatite Ta oxides are also asso-ciated with lepidolite enriched in Li and F from the wallzone (Van Lichtervelde et al 2008)
93 Origin and evolution of the zoned graniticlepidolite-subtype pegmatite at Namivo
In general granitic pegmatites particularly those belong-ing to the rare-element class are accepted as having beenformed by the fractional crystallization of a granite melt(eg Cerny 1991a b 1992 Neiva et al 2008 2012 Roda-Robles et al 2012) But it also has been proposed thatpegmatites may be formed by partial melting of appropri-ate rock compositions (eg Nabelek et al 1992 Nabelekamp Russ-Nabelek 1992 Shearer et al 1992 Roda Robleset al 1999) The lepidolite-subtype pegmatites belong tothe LCT (lithium-cesium-tantalum) family (Cerny amp Ercit2005) They are derived by fractional crystallization of agranite magma (eg Cerny et al 2005 Neiva amp Ramos2010 Cerny et al 2012b) Experimental work by Londonet al (1989) and London (1990) using Macusani glass as astarting material equivalent to the bulk composition ofhighly fractionated rare-alkali-rich pegmatites underhighly evolved and hydrous but H2O undersaturatedmelt obtained the latest primary assemblage consisting
of an Li-rich mica thorn albite thorn quartz deposited directlyfrom the primary melt phase Other authors egZasedatelev (1974 1977) and Stewart (1978) argue thatlepidolite-bearing pegmatites are derived from direct ana-texis and Gordiyenko et al (1996) consider that they arederived from an undefined medium and the rare-elementmineralization is superimposed on preexisting barrenpegmatites
Lepidolite-subtype pegmatites may migrate a long wayfrom their parent granites because their volatile-rich highlyfluid pegmatite melts are stable at relatively low tempera-tures (eg Cerny et al 2005 Antunes et al 2013)Therefore the Namivo pegmatite is probably derived byfractional crystallization of an S-type granite magmawhich resulted from partial melting of metamorphosed juve-nile sediments containing micas that carry most of the traceelements that define the signature of the LCT pegmatites(eg Dahl et al 1993)
The two main models for the internal evolution of peg-matites that dominated for more than a century are a) thefractional crystallization of a flux-bearing granitic melt fromthe margins to the center of the pegmatite (Cameron et al1949) b) the interactions of an aqueous fluid with graniticmelt (Jahns amp Burnham 1969 Jahns 1982) The recentmodel of constitutional zone refining combines aspects ofboth models and invokes the formation of a flux-enriched
Table 4 Electron microprobe analyses in wt of zoned gahnite from the outer intermediate zone (OIZ) of the Namivo granitic pegmatiteMozambique
Darker Zone Lighter Zone
Mean s Range Mean s Range
SnO2 036 050 0ndash097 658 281 151ndash998TiO2 008 008 0ndash021 065 034 008ndash105Nb2O5 001 002 0ndash006 018 007 007ndash029Ta2O5 001 004 0ndash010 015 013 0ndash033ZnO 3998 123 3810ndash4109 3339 318 3004ndash3848FeO 367 048 331ndash442 433 065 306ndash498MnO 032 004 028ndash040 039 006 032ndash048MgO 003 004 0ndash010 ndash ndash ndashAl2O3 5507 050 5436ndash5572 5337 070 5257ndash5443SiO2 003 003 0ndash007 008 010 0ndash025Total 9956 9912n 8 8Sn 0035 0048 0ndash0095 0648 0278 0149ndash0983Ti 0015 0015 0ndash0038 0120 0064 0015ndash0195Nb ndash 0003 0ndash0006 0021 0009 0009ndash0037Ta ndash 0002 0ndash0006 0009 0009 0ndash0021Zn 7226 0182 6890ndash7382 6086 0568 5482ndash6965Fe2thornt 0752 0103 0675ndash0913 0894 0135 0628ndash1029Mn 0066 0008 0057ndash0083 0082 0013 0066ndash0101Mg 0010 0015 0ndash0037 ndash ndash ndashAl 15887 0052 15805ndash15954 15526 0170 15375ndash15853Si 0007 0008 0ndash0018 0019 0025 0ndash0062P
23998 23405Fe3thorn 0064 0230Fe2thorn 0686 0658SnZn 0005 0007 0ndash0014 0106 0052 0021ndash0179ZnFe2thornt 961 143 768ndash1093 681 190 536ndash1109
n number of analysis Cation formula based on 32 atoms of oxygen Fe2thornt total Fe2thorn estimated
982 A M R Neiva
eschweizerbart_xxx
boundary layer of silicate liquid in advance of a crystal-lization front (London 2008 London amp Morgan 2012)
Lepidolite-subtype pegmatites are generally scarce(Cerny et al 2005) particularly the zoned ones In thesymmetrically zoned lepidolite-subtype pegmatites ofRozna and Dobra Voda Czech Republic micas (Cernyet al 1995) tourmaline (Selway et al 1999) and colum-bite-group minerals (Novak amp Cerny 1998) evolve fromthe outermost zone to the innermost zone following thecrystallization sequence The same was found in tourma-line from the zoned Lastovicky Dolnı Bory and Raddovicelepidolite-subtype pegmatite dikes in the Czeck Republic(Selway et al 1999)
In general beryl (Neiva amp Neiva 2005) feldsparsmicas and columbite-(Mn) (in this paper) from theNamivo lepidolite-subtype pegmatite record the progres-sive chemical evolution of the pegmatite from the wallzone to the core These minerals were produced by crystal-lization from a silicate melt rather than an aqueous fluidphase The slow cooling of melt shown by the magmaticcrystallization temperatures of feldspars cannot explain theincrease in grain-size of minerals from the wall zone to thecore but fluxes will be necessary to promote the change oftexture particularly a flux-rich hydrosilicate liquidaccording to the experimental evidence (London 2009)The constitutional zone refining model will be the best forthis zoned pegmatite and probably for all lepidolite-sub-type pegmatites because this model also produces a higherfinal concentration of incompatible components in a smal-ler volume of rock than fractional crystallization does(Morgan amp London 1999)
The core margin at the Rozna pegmatite contains K-feld-spar and quartz and the core consists mainly of quartz but it issurrounded and penetrated by a quartz-bearing albitethorn lepi-dolite complex which contains several minerals At theDobra Voda pegmatite the center of the dike is occupiedby the lepidolite unit containing albite and other minerals(Cerny et al 1995) At the Namivo pegmatite the coremargin consists of quartz and beryl and the core containsmainly quartz and spodumene but also albite lepidolite andother minerals The last-unit assemblages of primary miner-als in most of the highly fractionated LCT pegmatites are richin albite and commonly contain lepidolite or spodumene andmost of the other rare phases These units represent the lastmost fractionated liquid that can be derived by fractionalcrystallization of a crustal melt (London 2008)
The Namivo granitic pegmatite shows a significant dis-tinction from the other zoned lepidolite-subtype pegmatitesand LCT pegmatites except the Tanco petalite-subtypepegmatite in Canada because the lepidolite richest in SiLi and F FeMg-containing polylithionite and associatedcolumbite-(Mn) with the highest Ta(Ta thorn Nb) ratio tanta-lite-(Fe) and tantalite-(Mn) only occur in the outer inter-mediate zone These minerals usually form late in theconsolidation of pegmatites The lepidolite and polylithio-nite are probably derived from the disequilibrium crystal-lization of an undercooled melt Tantalite may reflect a localdecrease in Li and F that caused Ta precipitation
This paper contributes to a better understanding of theorigin and evolution of the rare zoned lepidolite-subtypepegmatites and shows that although the pegmatite evolvedfrom the wall zone to the core it presents an unusualassociation of lepidolite polylithionite and tantalite in theouter intermediate zone
Acknowledgments Thanks are due to JM Cotelo Neivaand MB Dias for the samples and information providedand to MR Machado Leite and MF Guimaraes for theuse of the electron microprobe facilities at the LaboratorioNacional de Energia e Geologia (LNEG) PortugalFinancial support was provided by the PortugueseGovernment for the project Pest-OECTEUI00732011of the Geosciences Centre through the PortugueseFoundation for Science and Technology I would like tothank D London WB Simmons and the associated editorE Widom for their constructive reviews of this manuscriptand M Prieto for his editorial work
References
Alfonso P Melgarejo JC Yusta I Velasco F (2003)
Geochemistry of feldspars and muscovite in granitic pegmatite
from the Cap de Creus field Catalonia Spain Can Mineral 41
103ndash116
Antunes IMHR Neiva AMR Ramos JMF Silva PB
Silva MMVG Corfu F (2013) Petrogenetic links between
lepidolite-subtype aplite-pegmatite aplite veins and associated
granites at Segura (central Portugal) Chemie der Erde in press
httpdxdoiorg101016jchemer20121203
Batchelor RA amp Kinnaird JA (1984) Gahnite compositions
compared Mineral Mag 48 425ndash430
Beurlen H Da Silva MRR Thomas R Soares DR Olivier P
(2008) Nb-Ta-(Ti-Sn) oxide mineral chemistry as tracer of rare-
element granitic pegmatite fractionation in the Borborema pro-
vince Northeastern Brazil Miner Deposita 43 207ndash228
Cameron EN Jahns RH McNair AH Page LR (1949)
Internal structure of granitic pegmatites Econ Geol
Monograph 2 115 p
Cerny P (1991a) Fertile granites of Precambrian rare-element
pegmatite fields is geochemistry controlled by tectonic setting
or source lithologies Precambrian Res 51 429ndash468
mdash (1991b) Rare-element granite pegmatites I Anatomy and inter-
nal evolution of pegmatite deposits Geoscience Canada 18
49ndash67
mdash (1992) Geochemical and petrogenetic features of mineralization
in rare-element granitic pegmatites in the light of current
research Applied Geochemistry 7 393ndash416
mdash (1994) Evolution of feldspars in granitic pegmatites in
lsquolsquoFeldspars and their Reactionsrsquorsquo I Parsons ed NATO
Advanced Study Institute Series C421 501ndash539
mdash (2005) The Tanco rare-element pegmatite deposit Manitoba
regional context internal anatomy and global comparisons in
lsquolsquoRare-element Geochemistry and Mineral Depositsrsquorsquo RL
Linnen amp IM Samson eds Geochemical Association of
Canada Short Course Notes St Catherines 17 127ndash158
Silicate and oxide minerals from a zoned granitic pegmatite 983
eschweizerbart_xxx
Cerny P amp Ercit TS (2005) The classification of granitic pegma-
tites revisited Can Mineral 43 2005ndash2026
Cerny P Meintzer RE Andersen AJ (1985) Extreme fractiona-
tion in rare-element granitic pegmatites selected examples of
data and mechanisms Can Mineral 23 381ndash421
Cerny P Goad BE Hawthorne FC Chapmann R (1986)
Fractionation trends of the Nb- and Ta-bearing oxide minerals
in the Greer Lake pegmatite granite and its pegmatite aureole
southeastern Manitoba Am Mineral 71 501ndash517
Cerny P Stanek J Novak M Baadsgaard H Rieder M
Ottolini L Kavalova M Chapman R (1995) Geochemical
and structural evolution of micas in the Rozna amp Dobra Voda
pegmatites Czech Republic Mineral Petrol 55 177ndash201
Cerny P Ercit TS Vanstone PJ (1998) Mineralogy and petrol-
ogy of the Tanco rare-element pegmatite deposit southeastern
Manitoba International Mineralogical Association 17th General
Meeting Toronto Field Guidebook B6
Cerny P Chapman R Ferreira K Smeds SA (2004)
Geochemistry of oxide minerals of Nb Ta Sn and Sb in
the Varutrask granitic pegmatite Sweden The case of an
lsquolsquoanomalousrsquorsquo columbitendashtantalite trend Am Mineral 89
505ndash518
Cerny P Masau M Goad BE Ferreira K (2005) The Greer
Lake leucogranite Manitoba and the origin of lepidolite-sub-
type granitic pegmatites Lithos 80 305ndash321
Cerny P Teertstra DK Chapman R Selway JB Hawthorne
FC Ferreira K Chackowsky LE Wang X-J Meintzer
RE (2012a) Extreme fractionation and deformation of the
leucogranite-pegmatite suite at Red Cross Lake Manitoba
Canada IV Mineralogy Can Mineral 50 1839ndash1875
Cerny P Halden NM Ferreira K Meintzer RE Brisbin WC
Chackowsky LE (2012b) Extreme fractionation and deforma-
tion of the leucogranite-pegmatite suite at Red Cross Lake
Manitoba Canada II Petrology of the leucogranites and peg-
matites Can Mineral 50 1807ndash1822
Dahl PS When DC Feldmann SG (1993) The systematics of
trace-element partitioning between coexisting muscovite and
biotite in metamorphic rocks from the Black Hills South
Dakota USA Geochim Cosmochim Acta 57 2487ndash2505
Dias MB amp Wilson WE (2000) The Alto Ligonha Pegmatites
Mozambique Mineral Record 31 459ndash497
Fleet ME (2003) Rock-Forming Minerals vol 3A Sheet silicates
micas The Geological Society London second edition chap 6
Lithium micas 651ndash690
Foord EE Cerny P Jackson LL Sherman DM Eby RK
(1995) Mineralogical and geochemical evolutions of micas
from miarolitic pegmatites of the anorogenic pikes-Peak
Batholith Colorado Mineral Petrol 55 1ndash26
Foster MD (1960) Interpretation of the composition of lithium
micas US Geol Surv Prof Paper 354-E 115ndash147
Fuhrman ML amp Lindsley DK (1988) Ternary-feldspar modeling
and thermometry Am Mineral 73 201ndash215
Gomes CL Castro P Alves C (1995) Caracterizacao das espi-
nelas zincıferas e do par ganite-nigerite no campo aplito-
pegmatıtico da Serra de Arga-Minho N de Portugal IV
Congresso Nacional de Geologia Resumos Alargados
Universidade do Porto Mem 4 629ndash633
Gordiyenko VV Ilyina AN Timochina LA Badamina EB
Stanek J (1996) Geochemical model of evolution of a pegma-
tite-forming ore-magmatic system of western Moravia Proc
Russ Mineral Soc 125 38ndash48 (in Russian)
Icenhower JP amp London D (1995) An experimental study for
element partitioning between biotite muscovite and coexisting
peraluminous granitic melt at 200 MPa (H2O) Am Mineral 80
1229ndash1251
Jahns RH (1982) Internal evolution of pegmatite bodies in lsquolsquoGranitic
Pegmatites in science and industryrsquorsquo P Cerny ed Mineralogical
Association of Canada Short Course Handbook 8 293ndash327
Jahns RH amp Burnham CW (1969) Experimental studies of
pegmatite genesis I A model for the derivation and crystal-
lization of granitic pegmatites Econ Geol 64 843ndash864
Jolliff BL Papike JJ Shearer CK (1987) Fractionation trends
in mica and tourmaline as indicators of pegmatite internal evo-
lution Bob Ingersoll pegmatite Black Hills South Dakota
USA GeochimCosmochim Acta 51 519ndash534
Kile DE amp Foord EE (1998) Micas from the Pikes Peak bath-
olith and its cogenetic granitic pegmatites Colorado optical
properties composition and correlation with pegmatite evolu-
tion Can Mineral 36 463ndash482
Linnen RL (1998) The solubility of Nb-Ta-Zr-Hf-W in granitic
melts with Li and Li thorn F constraints for mineralization in rare
metal granites and pegmatites Econ Geol 93 1013ndash1025
Linnen RL amp Cuney M (2005) Granite-related rare-element
deposits and experimental constraints on Ta-Nb-W-Sn-Zr-Hf
mineralization in lsquolsquoRare-element geochemistry and mineral
depositsrsquorsquo RL Linnen amp IM Samson eds Geochemical
Association of Canada Short Course Notes 17 45ndash68
London D (1990) Internal differentiation of rare-element pegmatites
a synthesis of recent research in lsquolsquoOre Bearing Granite Systems
Petrogenesis and Mineralizing Processesrsquorsquo HJ Stein amp JL
Hannah eds Geol Soc America Special Paper 246 35ndash50
mdash (2008) Pegmatites The Canadian Mineralogist Special
Publication 10 347 p
mdash (2009) The origin of primary textures in granitic pegmatites
Can Mineral 47 697ndash724
London D amp Morgan GB VI (2012) The pegmatite puzzle
Elements 8 263ndash268
London D Morgan GB VI Hervig RL (1989) Vapor-under-
saturated experiments in the system macusanite-H2O at 200
MPa and the internal differentiation of granitic pegmatites
Contrib Mineral Petrol 102 1ndash17
London D Morgan GB VI Paul KA Guttery BM (2012)
Internal evolution of miarolitic granitic pegmatites at the Little
Three mine Ramona California USA Can Mineral 50
1025ndash1054
Martins T Lima A Simmons WB Folster AU Noronha F
(2011) Geochemical fractionation of Nb-Ta oxides in Li-bear-
ing pegmatites from the Barroso-Alvao pegmatite field northern
Portugal Can Mineral 49 777ndash791
Monier G Charoy B Cuney M Ohnenstetter D Robert JL
(1987) Evolution spatiale et temporelle de la composition des
micas du granite albitique a topaze-lepidolite de Beauvoir
Geologie De La France 2ndash3 179ndash188
Monier G amp Robert JL (1986) Evolution of the miscibility gap
between muscovite and biotite solid solutions with increasing
lithium content an experimental study in the systems
K2OndashLi2OndashMgOndashAl2O3ndashSiO2ndashH2OndashHF at 600 C 2 kbar
PH2O comparison with natural lithium micas Mineral Mag
50 641ndash651
Morgan GBVI amp London D (1999) Crystallization of the little
three layered pegmatite-aplite dike Ramona District California
Contrib Mineral Petrol 136 310ndash330
984 A M R Neiva
eschweizerbart_xxx
Nabelek PI amp Russ-Nabelek C (1992) The generation and crys-
tallization conditions of the Proterozoic Harney Peak
Leucrogranite Black Hills South Dakota USA petrologic and
geochemical constraints Contrib Mineral Petrol 110
173ndash191
Nabelek PI Russ-Nabelek C Haeussler GT (1992) Stable
isotope evidence for the petrogenesis and fluid evolution in
the Proterozoic Harney Peak leucogranite Black Hills
South Dakota Geochim Cosmochim Acta 56 403ndash417
Neiva AMR amp Champness PE (1997) Nigerite and gahnite from
the granitic pegmatite veins of Cabanas Ponte de Lima northern
Portugal N Jb Mineral Mh 9 385ndash409
Neiva AMR Gomes MEP Ramos JMF Silva PB (2008)
Geochemistry of granitic aplite-pegmatite sills and their miner-
als from Arcozelo da Serra area (Gouveia central Portugal)
Eur J Mineral 20 465ndash485
Neiva AMR amp Neiva JMC (2005) Beryl from the granitic
pegmatite at Namivo Alto Ligonha Mozambique N Jb
Mineral Abh 181 173ndash182
Neiva AMR amp Ramos JMF (2010) Geochemistry of granitic
aplite-pegmatite sills and petrogenetic links with granites
Guarda-Belmonte area central Portugal Eur J Mineral 22
837ndash854
Neiva AMR Silva PB Ramos JMF (2012) Geochemistry of
granitic aplite-pegmatite veins and sills and their minerals from the
Sabugal area central Portugal N Jb Mineral Abh 189 49ndash74
Novak M amp Cerny P (1998) Niobium-tantalum oxide minerals
from complex granitic pegmatites in the Moldanubicum Czech
Republic primary versus secondary compositional trends Can
Mineral 36 659ndash672
Pesquera Perez A Torres-Ruiz J Gil PP Velilla N (1999)
Chemistry and genetic implications of tourmaline and Li-F-Cs
micas from the Valdeflores (Caceres Spain) Am Mineral 84
55ndash69
Rieder M Cavazzini G DrsquoYakonov YuS Frank-Kamenetskii
VA Gottardi G Guggenheim S Koval PV Muller G
Neiva AMR Radoslovich EW Robert J-L Sassi FP
Takeda H Weiss Z Wones DR (1999) Nomenclature of the
micas Mineral Mag 63 267ndash279
Roda Robles E Pesquera Perez A Velasco Roldan F Fontan F
(1999) The granitic pegmatites of the Fregeneda area
(Salamanca Spain) characteristics and petrogenesis Mineral
Mag 63 535ndash558
Roda Robles E Pesquera A Gil-Crespo PP Torres-Ruiz J
Fontan F (2005) Origin and internal evolution of the Li-F-
Be-P-bearing Pinilla de Fermoselle pegmatite (Central Iberian
Zone Zamora Spain) Am Mineral 90 1887ndash1899
Roda Robles E Pesquera Perez A Gil PP Torres-Ruiz J de
Parseval P (2006) Mineralogy and geochemistry of micas from
the Pinilla de Fermoselle pegmatite (Zamora Spain) Eur J
Mineral 18 369ndash377
Roda Robles E Keller P Pesquera Perez A Fontan F (2007)
Micas of the muscovite-lepidolite series from Karibib pegma-
tites Namibia Mineral Mag 71 41ndash62
Roda Robles E Pesquera A Gil-Crespo P Torres-Ruiz J
(2012) From granite to highly evolved pegmatite a case study
of the Pinilla de Fermoselle granite-pegmatite system (Zamora
Spain) Lithos 153 192ndash207
Selway JB Novak M Cerny P Hawthorne FC (1999)
Compositional evolution of tourmaline in lepidolite-subtype
pegmatites Eur J Mineral 11 569ndash584
Shearer CK Papike JJ Jolliff B (1992) Petrogenetic links
among granites and pegmatites in the Harney Peak rare-element
granite-pegmatite system Black Hills South Dakota Can
Mineral 30 785ndash809
Soares DR Hartmut B Ferreira ACM da Silva MRR
(2007) Chemical composition of gahnite and degree of peg-
matitic fractionation in the Borborema Pegmatitic Province
northeastern Brazil Anais Da Academ Bras Cien 79
395ndash404
Stewart DB (1978) Petrogenesis of lithium-rich pegmatites Am
Mineral 63 970ndash980
Tischendorff G Gattesmann B Forster H-J Trumbull RB
(1997) On Li-bearing micas estimating Li from electron
microprobe analyses and an improved diagram for graphical
representation Mineral Mag 61 809ndash834
Van Lichtervelde M Linnen RL Salvi S Beziat D (2006)
The role of metagabbro rafts on tantalum mineralization in the
Tanco granitic pegmatite Manitoba Can Mineral 44
625ndash644
Van Lichtervelde M Gregoire M Linnen RL Beziat D Salvi
S (2008) Trace element geochemistry by laser ablation ICP-
MS of micas associated with Ta mineralization in the Tanco
pegmatite Manitoba Canada Contrib Mineral Petrol 155
791ndash806
Vieira R Roda-Robles E Pesquera A Lima A (2011)
Chemical variation and significance of micas from the
Fregeneda-Almendra pegmatitic field (Central-Iberian Zone
Spain and Portugal) Am Mineral 96 637ndash645
Wen S amp Nekvasil H (1994) SOLVCALC an interactive gra-
phics program package for calculating ternary feldspar solvus
and two-feldspar geothermometry Comput Geosci 20
1025ndash1040
Wise MA (1995) Trace element chemistry of lithium-rich micas
from rare-element granitic pegmatites Mineral Petrol 55
203ndash215
Zasedatelev AM (1974) Possible accumulation of lithium in host
rocks of lithium pegmatite veins during old sedimentation pro-
cesses Doklady Acad Sci USSR Earth Sci Ser 218 196ndash198
(in Russian)
mdash (1977) Quantitative of metamorphic generation of rare-metal
pegmatites with lithium mineralization Doklady Acad Sci
USSR Earth Sci Ser 236 219ndash221 (in Russian)
Received 26 January 2013
Modified version received 21 May 2013
Accepted 23 July 2013
Silicate and oxide minerals from a zoned granitic pegmatite 985
eschweizerbart_xxx
F contents tend to increase and the (AlIV thorn AlVI) AlVI
contents and KRb ratio tend to decrease from muscoviteto lepidolite (Table 1 Fig 7) This sequence is consistentbut rarely in the Cc lepidolite is rimmed by muscovite (Fig3j) But in the OIZ the evolution stops in lsquolsquomixed formrsquorsquoparticularly shown by the large range of the KRb ratiowhich mainly overlaps that of lepidolite from this zone(Fig 7) because this lepidolite is an Al-poorer mica whereasthe others are Al-richer micas (Fig 4)
In the OIZ the lepidolite has more Si Licalc and F andless (AlIV thorn AlVI) Ti Fe2thorn Mn Mg and Zn than zinn-waldite (Table 1) but it has larger ranges of Rb and KRbratio than zinnwaldite (Fig 7) The FeMg-containingpolylithionite is the richest mica in Si Licalc and thepoorest in (AlIV thorn AlVI) (Table 1) But at this zone scalethe polylithionite has Rb Cs contents and KRb ratiowithin the ranges for lepidolite and close to those of zinn-waldite (Fig 7)
Fig 6 Variation diagrams of micas from selected zoned crystals from the zones of the Namivo granitic pegmatite Mozambique to showtheir relationships lith musc lithian muscovite OIZ IIZa IIZb and Cc an in Fig 2
Silicate and oxide minerals from a zoned granitic pegmatite 975
eschweizerbart_xxx
From the OIZ to IIZa IIZb and Cc muscovite and lithianmuscovite generally show increases in the Si Licalc F and Rbcontents and decreases in the Fe2thorn and Mg contents and KRb ratio but the Mg content is very low in these micas fromthe IIZa IIZb and Cc (Table 1 Fig 7a) The lsquolsquomixed formrsquorsquoshows increases in the Si Licalc F Rb Cs contents anddecreases in the (AlIV thorn AlVI) and Mg contents and KRbratio but the Mg content is very low in this mica from theIIZb and Cc (Table 1 Fig 7b c) The lepidolite shows anincrease in the Si Licalc F Rb and Cs contents and a decreasein the KRb ratio from the IIZa to the IIZb and Cc (Table 1Fig 7d e) Furthermore the lepidolite from the OIZ has thelowest (AlIV thorn AlVI) AlVI and OH contents the highest SiFe2thorn Licalcand F contents and KRb ratio and the lowest Rband Cs contents compared to lepidolite from the other zones(Table 1 Fig 7d e)
5 Feldspars
Selected chemical analyses of albite and K-feldspar fromfive zones of the Namivo granitic pegmatite are given inTable 2 Strontium is the most abundant trace element inalbite (eg Cerny 1994) Anorthite and Sr contents and SrCa ratio of albite decrease from the WZ to the Cc (Fig 8Table 2) Rubidium is the most abundant trace element inK-feldspar followed by Cs in IIZa IIZb and Cc In gen-eral K Rb and Cs contents of K-feldspar increase and KRb and KCs values decrease from the WZ to the Cc (Table2 Fig 9)
The program SOLVCALC 20 (Wen amp Nekvasil 1994)using the Margules model Fuhrman amp Lindsley (1988) wasapplied for the purpose of thermometry The pairing ofplagioclase cores with the K-feldspars average of eachsample was used to estimate the crystallization temperaturesof primary magmatic feldspars They are 405 C (WZ)406ndash340 C (OIZ) 390ndash335 C (IIZa) 347ndash306 C (IIZb)and 333ndash289 C (Cc) at 3 kbar The metamorphic environ-ment of rare-element-Li granitic pegmatites is one of lowpressure 2ndash4 kbar (Cerny amp Ercit 2005) In general thedifference between the maximum and minimum calculatedtemperatures at 2 3 and 4 kbar for the same feldspar pairfrom the Namivo pegmatite is lower than 40 C The tem-perature decreases from the wall zone (WZ) to the core(Cc) A similar temperature behavior of feldspars wasfound in the pegmatite-aplite dike USA (Morgan ampLondon 1999)
6 Other silicates
Tourmaline of schorl composition was only found inthe OIZ (Table 2) because there was not enough Feand Mg for schorl to precipitate in the other zonesSpodumene only occurs in the Cc and its compositionis nearly pure (Table 2)
7 Columbite-tantalite
Representative chemical analyses of columbitendashtantalitefrom the Namivo granitic pegmatite are given in Table 3and plotted in the columbite quadrilateral (Fig 10a)Most crystals are unzoned but zoned crystals with dar-ker and lighter zones in BSE images are from the Cc Thelighter zone of columbite-(Mn) has higher Ta contentTa(Ta thorn Nb) and Mn(Mn thorn Fe) values and lower Nbcontent than the darker zone (Fig 10a b) The crystals ofthe columbitendashtantalite minerals are low in W Sn and Tiimpurities (Table 3)
The main trend starts from the columbite-(Mn) of theOIZ towards the more Mn-enriched and slightly Ta-enriched columbite-(Mn) from the IIZa and Cc The high-est Ta(Ta thorn Nb) values belong to the lighter zone ofcolumbite-(Mn) with Mn(Mn thorn Fe) frac14 10 from the CcThe richest columbite-(Mn) in Ta(TathornNb) and composi-tions of tantalite-(Fe) and tantalite-(Mn) were only foundin the OIZ (Fig 10a) and are associated with lepidolite andpolylithionite (Fig 3c)
8 Gahnite
Gahnite was rarely found in the OIZ and shows a darkerzone that partially surrounds a lighter zone in a BSE image(Fig 11a) The darker zone has a higher Zn content andlower Sn Ti Nb Ta Mn contents and SnZn value than thelighter zone (Table 4 Fig 11b c) These gahnite composi-tions fall within the igneous field of Batchelor amp Kinnaird(1984) The darker zone is closer in composition to thepure gahnite (Zn8Al16O32) than the lighter zone whichcontains up to 0983 apfu Sn 0195 apfu Ti 1029 apfutotal Fe2thorn 0101 apfu Mn (Table 4) and consequently hasa composition distinct from nigerite In general both thedarker and lighter zones have higher Sn Ti and Fe contentsthan gahnite from the granitic pegmatites of Nigeria(Batchelor amp Kinnaird 1984) Arga northern Portugal(Gomes et al 1995) and Cabanas northern Portugal(Neiva amp Champness 1997) Borborema province north-eastern Brazil (Soares et al 2007) The Zn=Fe2thornt values ofthe darker and lighter zones of gahnite from Namivo arelower than those reported in Neiva amp Champness (1997)and Soares et al (2007)
9 Discussion and conclusions
91 Evolution of micas in the zoned pegmatite
In general individual mica crystals show varying patternsand compositional zoning involving several elementsmainly Si AlVI (AlIV thorn AlVI) Fe2thorn Mn (Fe2thornthorn Mn thornMg) Licalc Rb Cs F and OH and the KRb ratioProgressively zoned crystals from the IIZa show grada-tional contacts between a lithian muscovite core and a
976 A M R Neiva
eschweizerbart_xxx
lsquolsquomixed formrsquorsquo rim (Figs 3e 6e f) and the zoning patternscorrespond to fractionation trends and probably reflect adrop in temperature during the crystallization of the grani-tic pegmatite melt Progressively zoned crystals also occurin OIZ IIZb and Cc Some crystals are reversely zonedwith a) a lsquolsquomixed formrsquorsquo core and a lithian muscovite rimfrom the OIZ (Figs 3d d1 6d) b) a core consisting oflsquolsquomixed formrsquorsquo and lepidolite and a rim of muscovite andlithian muscovite from the IIZa (Figs 3f f1 6g h) c) alepidolite core and a muscovite and lithian muscovite rimfrom the Cc (Figs 3j 6o p) which may be explained bythe hypothesis of oscillations in the compositions of themelt from which they grew alternating between an Li-enriched boundary layer and a bulk melt that is less frac-tionated The muscovite evolved to lithian muscovite inIIZa and Cc (Figs 3f 6g h 3j 6o p) Replacements (Figs3a 6a b 3c 6c 3i 6m n Table 1) occur in OIZ and Ccand overgrowths (Figs 3b g 6i j k 3h 6l Table 1) occurin OIZ and IIZb as found in BSE images
Muscovite evolved to lithian muscovite as observed inOIZ IIZa IIZb and Cc (Figs 3f 6g h 3j 6o p Table 1)Lithian muscovite evolved to lsquolsquomixed formrsquorsquo in OIZ IIZaIIZb and Cc (Figs 3e 6e f Table 1) and lsquolsquomixed formrsquorsquoevolved to lepidolite in IIZa IIZb and Cc (Figs 3f f1 6gh 3h 6l Table 1) All these evolutions are due to fractionalcrystallization
In the OIZ lepidolite has more Si Licalcand F butsimilar KRb to that of zinnwaldite and replaces it (Figs
3a 6a b 7d Table 1) An FeMg-containing polylithionitehas higher Si Licalcand Rb contents and a smaller KRbratio than the lepidolite that it replaces (Figs 3c 6c Table1) and a continuous chemical evolution from lepidolite topolylithionite is shown
The trends for major and trace elements of micas withineach zone are difficult to define due to some partial over-lapping but a progressive evolution from muscovite to lithianmuscovite lsquolsquomixed formrsquorsquo and lepidolite in IIZa IIZb and Ccis mainly shown by an increase in the Si Licalc F Rb and Cscontents and a decrease in the KRb ratio and this is simi-larly shown in the OIZ from muscovite to lsquolsquomixed formrsquorsquo(Table 1 Fig 7) In the OIZ Si and Licalccontents increaseprogressively from zinnwaldite to lepidolite and FeMg-containing polylithionite but a gap occurs between zinnwal-dite and lepidolite (Table 1 Fig 4) whereas a continuousevolution from lepidolite to polylithionite is observed TheKRb ratios of zinnwaldite and polylithionite are within therange of that of lepidolite (Fig 7d e)
Each Al-richer mica (muscovite lithian muscovite andlsquolsquomixed formrsquorsquo) exhibits an evolution from the OIZ to theIIZa and then to the IIZb and Cc particularly shown by anincrease in the Si Licalc F and Rb contents and adecrease in the KRb ratio but also an increase in theCs content in the lsquolsquomixed formrsquorsquo (Table 1 Fig 7) Theseelements and ratio have been used as petrogenetic indi-cators of evolution in micas from pegmatites (eg Cernyet al 2005 Roda Robles et al 2006 2007 Vieira et al
Fig 7 Plot of some variation diagrams of micas from the OIZ IIZa IIZb and Cc of the Namivo granitic pegmatite Mozambique showingthat the Rb2O and Cs2O contents increase and the KRb ratio decreases for micas from the OIZ to the Cc OIZ IIZa IIZb and Cc as in Fig 2
Silicate and oxide minerals from a zoned granitic pegmatite 977
eschweizerbart_xxx
Tab
le2
R
epre
sen
tati
ve
elec
tro
nm
icro
pro
be
anal
yse
sin
wt
o
ffe
ldsp
ars
sch
orl
and
spo
du
men
efr
om
the
Nam
ivo
gra
nit
icp
egm
atit
eM
oza
mb
iqu
e
Alb
ite
K-f
eld
spar
Sch
orl
Sp
od
um
ene
Zo
nes
WZ
OIZ
IIZ
aII
Zb
Cc
Zo
nes
WZ
OIZ
IIZ
aII
Zb
Cc
Zo
nes
OIZ
Zo
ne
Cc
SiO
26
75
76
78
86
87
06
84
76
84
1S
iO2
65
10
65
55
65
46
64
96
64
72
SiO
23
52
0S
iO2
64
65
TiO
20
02
mdash0
02
mdashmdash
TiO
2mdash
00
1mdash
mdashmdash
TiO
20
35
Al 2
O3
27
20
Al 2
O3
20
25
19
74
19
67
19
88
19
97
Al 2
O3
18
96
18
23
18
31
18
24
18
05
B2O
3
10
28
Fe 2
O3
00
6F
e 2O
3mdash
mdashmdash
mdash0
10
Fe 2
O3
mdash0
02
mdash0
03
mdashA
l 2O
33
17
2M
nO
01
3M
nO
00
6mdash
mdashmdash
mdashM
nO
mdash0
03
00
3mdash
mdashF
eO1
35
2M
gO
01
8M
gO
mdashmdash
mdashmdash
mdashM
gO
00
10
01
00
5mdash
mdashM
nO
03
3N
a 2O
01
9C
aO1
04
08
00
56
03
70
32
CaO
00
10
01
00
60
01
00
2M
gO
22
8L
i 2O
8
05
Na 2
O1
06
11
12
01
12
11
13
41
13
4N
a 2O
06
50
58
04
10
59
03
8C
aO0
23
To
tal
10
04
6K
2O
00
50
17
00
60
14
01
0K
2O
14
72
14
75
15
67
15
01
15
74
Li 2
O
02
2S
rO0
72
05
00
24
01
1mdash
Rb
2O
00
90
20
03
00
59
09
0N
a 2O
22
8S
i1
99
7P
2O
50
01
00
4mdash
mdashmdash
Cs 2
O
00
6
00
60
09
01
80
20
K2O
00
1A
lIV0
00
3T
ota
l1
00
33
10
03
31
00
46
10
03
11
00
24
P2O
5mdash
00
3mdash
mdashmdash
H2O
3
18
P2
00
To
tal
99
60
99
48
10
03
89
96
11
00
01
F0
78
AlV
I0
98
7S
rC
a(w
t)0
81
07
40
50
03
50
Cl
mdashF
e3thorn
00
01
KR
b(w
t)153
68
48
23
16
Sum
1003
8P
09
9S
i1
18
23
11
87
91
19
58
11
93
21
19
21
KC
s(w
t)4
07
20
41
63
73
69
O
F0
33
Li
10
00
P0
00
10
00
6mdash
mdashmdash
To
tal
10
00
5M
n0
00
3T
i0
00
3mdash
00
03
mdashmdash
Si
11
98
61
20
88
12
04
11
20
45
12
03
3M
g0
00
8A
l4
17
64
07
14
03
54
08
34
10
1P
mdash0
00
5mdash
mdashmdash
TS
i5
95
2N
a0
01
2F
e3thorn
mdashmdash
mdashmdash
00
13
Ti
mdash0
00
1mdash
mdashmdash
Al
00
48
P1
02
Mn
00
09
mdashmdash
mdashmdash
Al
41
14
39
62
39
70
39
86
39
55
B3
00
0M
gmdash
mdashmdash
mdashmdash
Fe3thorn
mdash0
00
3mdash
00
04
mdashZ
Al
60
00
Ca
01
95
01
50
01
04
00
69
00
60
Mn
mdash0
00
50
00
5mdash
mdashY
Al
02
74
Sr
00
73
00
51
00
24
00
11
mdashM
g0
00
30
00
30
01
4mdash
mdashT
i0
04
5N
a3
59
93
80
03
78
33
83
23
83
1C
a0
00
20
00
20
01
20
00
20
00
4M
g0
57
5K
00
11
00
38
00
13
00
31
00
22
Na
02
32
02
07
01
46
02
12
01
37
Mn
00
47
K3
45
73
47
03
67
73
55
03
73
3F
e2thorn
19
12
Z1
60
01
59
61
60
01
60
11
60
4R
b0
01
10
02
40
03
50
07
00
10
8L
i0
14
8X
38
94
04
39
33
94
39
1C
s0
00
20
00
50
00
70
01
40
01
6P
Y3
00
0m
ole
s
XC
a0
04
2A
n5
13
82
71
71
5Z
16
10
16
06
16
01
16
03
15
99
Na
07
47
Ab
94
69
53
97
09
75
97
9X
37
13
72
39
03
85
40
0K
00
02
Or
03
09
03
08
06
mo
les
amp
02
09
An
01
01
03
01
01
Ab
63
56
38
56
35
OH
35
83
Or
93
69
43
95
99
43
96
4F
04
17
Cl
mdash
WZ
ndashw
allzo
ne
OIZ
ndasho
ute
rin
term
edia
tezo
ne
IIZ
aan
dII
Zb
ndashin
ner
inte
rmed
iate
zon
esC
cndash
core
asin
Fig
2B
aOis
bel
ow
the
det
ecti
on
lim
itin
bo
thfe
ldsp
ars
Cs 2
Ofrac14
00
3w
tin
the
K-
feld
spar
fro
mth
eW
Z
mdashN
ot
det
ecte
d
Nu
mb
ero
fio
ns
on
the
bas
iso
f3
2o
xy
gen
sfo
ral
bit
ean
dK
-fel
dsp
ar
31
anio
ns
(O
OH
F
)fo
rsc
ho
rlan
d6
ox
yg
ens
for
spo
du
men
e
-A
mo
un
tin
ferr
edfr
om
con
sid
erat
ion
so
fst
oic
hio
met
ry
978 A M R Neiva
eschweizerbart_xxx
2011) Lepidolite from the OIZ is an Al-poorer mica (Fig4) and has the highest Si Licalcand F contents (Table 1)indicating that an evolution cannot be shown from thislepidolite to lepidolites from the other zones which areAl-richer micas (Fig 4) However there is a regulardecrease in the KRb ratio and a progressive increase inthe Rb and Cs contents from lepidolite of the OIZ tolepidolite of IIZa IIZb and Cc (Fig 7) which indicatesthat the KRb ratio and Rb and Cs contents must not beconsidered alone to show fractional crystallization in
lepidolites particularly if some are Al-richer micas andothers Al-poorer micas The high Licalcand F contents oflepidolite from the OIZ did not decrease its KRb ratioSuch an effect is considered to have taken place in lepi-dolite (an Al-richer mica) from the wall zone of the Tancopegmatite Manitoba Canada (Van Lichtervelde et al2008) An evolution from the lepidolite of the IIZa to thatof the Cc is generally shown by the increasing Si LicalcF Rb Cs contents and a decrease in the KRb ratio (Table1 Fig 7)
At the scale of crystals the pegmatite zones and alsothose from the OIZ to the Cc of the Namivo granitic pegma-tite Al-richer micas show fractionation because theyformed from the fractionation of an Li-rich pegmatite melt
The Al-poorer micas zinnwaldite lepidolite and FeMg-containing polylithionite only occur in the OIZ (Fig 4)Polylithionite is the mica richest in Si and Licalc and lepi-dolite from this zone is the richest in Si Licalcand F (Fig 4Table 1) The high Li contents of these micas reflect aconsiderably higher D(Li) at low temperature (Icenhoweramp London 1995) These Li-rich micas may have crystal-lized from an undercooled melt This hypothesis does notimply high Rb and Cs contents and low KRb ratios Thisagrees with the fact that these micas from the OIZ havesimilar Rb and Cs contents and KRb ratios to those of Al-richer micas (muscovite lithian muscovite and lsquolsquomixedformrsquorsquo) from the same pegmatite zone (Fig 7) Howeverthe lepidolite from the wall zone of the Tanco pegmatiteCanada of a similar origin has a low KRb ratio which isattributed to the complexly interrelated structural compo-nents of this lepidolite (Van Lichtervelde et al 2008) TheLi-rich micas from the OIZ may also represent disequili-brium These two hypotheses are considered the best forthese micas of primary magmatic origin
Another hypothesis was also considered They may havecrystallized in boundary layers which concentrate Li andF But this mechanism was suggested for the most fractio-nated tourmaline enriched in Li and F from the core of the
Fig 8 Plot of albite compositions from all zones of the Namivo granitic pegmatite Mozambique showing that the anorthite content of albitedecreases from the WZ to the Cc WZ OIZ IIZa IIZb and Cc as in Fig 2
Fig 9 The Rb vs Cs diagram of K-feldspar from all zones of theNamivo granitic pegmatite Mozambique showing that the Rb andCs contents of K-feldspar increase from the WZ to the Cc WZ OIZIIZa IIZb and Cc as in Fig 2
Silicate and oxide minerals from a zoned granitic pegmatite 979
eschweizerbart_xxx
Little Three pegmatite dike USA (Morgan amp London1999) and the micas enriched in Li and F from theNamivo pegmatite belonging to the OIZ Furthermore ina boundary layer melt that became enriched in Li and F theKRb ratio of micas decreases strongly (Van Lichterveldeet al 2008) which was not found in these micas from theOIZ (Fig 7d) Nor can they have resulted from the crystal-lization of a late melt that would have reacted with the OIZbecause these micas are among those containing the high-est KRb values (Fig 7d)
92 The importance of feldspars micas andcolumbitendashtantalite compositions to the Namivogranitic pegmatite evolution
The trace elements Rb and Cs and the KRb and KCs ratioshave been used to show the evolution of K-feldspar inpegmatites (eg Cerny 1994 Cerny et al 2005 RodaRobles et al 2005) The Rb and Cs contents increase andthe KRb and KCs ratios of K-feldspar decrease from theWZ to the Cc (Fig 9 Table 2) reflecting the growth of K-feldspar from an increasingly fractionated melt withouthaving grown from or having been chemically modifiedby an aqueous fluid as in the Swamp pegmatite section atthe Little Three Mine USA (London et al 2012) Thecrystallization of K-feldspar from an exsolved aqueousfluid from melt will reverse the magmatic fractionation ofRb Cs KRb and KCs because Rb and especially Cs areso much more compatible in vapor that both Rb and Csremain in the fluid phase (London et al 2012) The feldsparsolvus pairs in the Namivo pegmatite record magmaticcrystallization temperatures that decrease from WZ to CcAlbite shows a decrease in the Ca Sr contents and SrCaratio from the WZ to the Cc (Fig 8 Table 2) Therefore thefeldspars and also Al-richer micas as already explainedshow fractionation in this zoned pegmatite
In general lepidolite from the Namivo pegmatite hassimilar Rb2O and Cs2O contents and KRb (wt) values tothose of lepidolite from the Rozna and Dobra Voda lepi-dolite-subtype pegmatites in the Czech Republic (Cernyet al 1995) but lower Rb2O and Cs2O contents thanlepidolite from the lepidolite-subtype pegmatite at RedCross Lake Manitoba Canada (Cerny et al 2012a) K-feldspar from the Namivo pegmatite also has lower Rb2O
Table 3 Representative electron microprobe analyses in wt of columbitendashtantalite from the Namivo granitic pegmatite Mozambique
Outer Intermediate Zone - OIZ Inner Intermediate Zone - IIZa
Core - Cc
D L L
WO3 022 059 079 113 101 351 050 007Ta2O5 5487 5123 2503 3186 2888 2519 3127 4542Nb2O5 2537 3000 5483 4635 5113 5144 4911 3686SnO2 008 015 024 049 020 026 017 012TiO2 263 161 136 254 202 145 125 016FeO 860 710 665 471 236 068 mdash mdashMnO 793 952 1099 1304 1400 1725 1748 1718Total 9970 10020 9989 10012 9960 9978 9978 9981W 0004 0011 0013 0019 0016 0057 0008 0001Ta 1065 0975 0422 0552 0495 0430 0543 0847Nb 0819 0949 1538 1336 1456 1460 1418 1143Sn 0002 0004 0006 0012 0005 0007 0004 0003Ti 0141 0085 0063 0122 0096 0068 0060 0008Fe 0513 0416 0345 0251 0124 0036 mdash mdashMn 0479 0564 0578 0704 0747 0917 0945 0998P
3023 3004 2965 2996 2939 2975 2978 3000Mn(Mn thorn Fe) 048 058 063 074 086 096 100 100Ta(Ta thorn Nb) 057 051 022 029 025 023 028 043Classification tant-(Fe) tant-(Mn) col-(Mn) col-(Mn) col-(Mn) col-(Mn) col-(Mn) col-(Mn)
D ndash darker L ndash lighter zones mdash Not detected tant-tantalite col-columbite Cation formula on the basis of 6 atoms of oxygen
Fig 10 Compositions of columbitendashtantalite from the Namivogranitic pegmatite Mozambique in the columbite quadrilateralshowing that Mn(Mn thorn Fe) of columbite-(Mn) increases from theOIZ to the Cc and the richest columbite-(Mn) in Ta(Ta thorn Nb)tantalite-(Fe) and tantalite-(Mn) only occur in the OIZ OIZ IIZaand Cc as in Fig 2
980 A M R Neiva
eschweizerbart_xxx
and Cs2O contents than K-feldspar from the lepidolite-subtype pegmatite at Red Cross Lake The Rb2O andCs2O contents of primary and late K-feldspar of this peg-matite at Red Cross Lake attained unprecedented levels(Cerny et al 2012a) The lowest KRb (wt) values ofmuscovite lithian muscovite lsquolsquomixed formrsquorsquo and lepido-lite from the IIZb and Cc (Fig 7) and K-feldspar (KRb frac1414) from the Cc compare well with those found in theseminerals from the AC6frac143 lepidolite-subtype pegmatitefrom Greer Lake (Cerny et al 2005) and some of themost fractionated pegmatites worldwide which belong tothe petalite-subtype (eg Tanco Manitoba Cerny 2005Cerny et al 1998 Varutrask Sweden Cerny et al 2005)but muscovite lithian muscovite and lepidolite from theIIZb and Cc have lower Rb2O and Cs2O contents than thesemicas from the Tanco pegmatite (Cerny 2005a VanLichtervelde et al 2008) K-feldspar also has lower
contents of these oxides than the most evolved K-feldsparfrom the Tanco pegmatite (Cerny 2005a) The magmaticfractionation was strong from the WZ to IIZb and Cc of theNamivo lepidolite-subtype pegmatite
The compositional trend of columbite-(Mn) from the OIZto Cc of the Namivo granitic lepidolite-subtype pegmatite(Fig 10) is identical to that of columbite-group mineralsfrom the lepidolite-subtype complex granitic pegmatitesfrom the Dobra Voda in the Moldanubicum CzechRepublic (Novak amp Cerny 1998) and the HimalayaDistrict southern California (shown in Cerny et al 2004)Experimental data for the Fe-Mn pair (Linnen amp Cuney2005) suggest an increase in Fe with fractional crystalliza-tion which is not observed in nature Other phases seem tocontrol the bahavior of Fe and Mn in the melt eg thecrystallization of tourmaline causes a rapid increase of theMnFe in the melt (Van Lichtervelde et al 2006) When thecrystallization of tourmaline stopped the columbitendashtantaliteminerals showed a constant MnFe indicating that the Fe andMn contents in the melt remained constant Schorl onlyoccurs in the OIZ of the Namivo granitic pegmatite and itscrystallization cannot be responsible for the increase in theMnFe of the melt because Mn(Mn thorn Fe) of columbite-(Mn) increases progressively from the OIZ to the IIZa and Cc(Fig 10) Garnet zinnwaldite and gahnite containing Fe andMn also only occur in the OIZ and cannot also have causedthe increase of the MnFe in the melt The dominant Mnenrichment before Ta enrichment started in the columbitendash-tantalite composition from some granitic pegmatites isattributed to an increased alkali-fluoride activity at moderatemHF (Cerny et al 2004) and an increase in the activity offluorine (Martins et al 2011) Each Al-richer mica (musco-vite lithian muscovite and lsquolsquomixed formrsquorsquo) from the Namivogranitic pegmatite shows an increase in F content from theOIZ to the IIZa IIZb and Cc (Table 1) In general the Fcontent of lepidolite also increases from the IIZa to the IIZband Cc Therefore the extreme Fe-Mn fractionation beforeTa enrichment in columbite-(Mn) (Fig 10) may be due to anincrease in the activity of fluorine as a consequence offractional crystallization The increase in the Ta content ofcolumbite-(Mn) from the Namivo granitic pegmatite isattributed to fractional crystallization
The geochemical evolution of albite and K-feldsparfrom the WZ to the Cc Al-richer micas muscovite lithianmuscovite and lsquolsquomixed formrsquorsquo from the OIZ to the Cc andlepidolite from the IIZa to the Cc and columbite-(Mn) andalso beryl (Neiva amp Neiva 2005) from the OIZ to the Ccare caused by magma fractionation The pegmatite zonesare the product of primary crystallization from a volatile-rich silicate melt The pegmatite consolidated from the WZto the Cc The IIZb is one of the most evolved zones asalso suggested by the beryl composition (Neiva amp Neiva2005) and is the richest in lsquolsquomixed formrsquorsquo and lepidolite
The richest columbite-(Mn) in Ta(Ta thorn Nb) and com-positions of tantalite-(Fe) and tantalite-(Mn) only occur inthe OIZ (Fig 10a) associated with lepidolite and polythio-nite (Fig 3c) which may be due to the local depletion of Liand F in the melt which decreases the solubility of Ta andcauses Ta precipitation (Linnen 1998 Linnen amp Cuney
Fig 11 a Backscattered-electron image of a gahnite crystal with adarker zone partially surrounding a lighter zone from the OIZ of theNamivo granitic pegmatite b c Plot of gahnite compositions in theSn-Zn-Ti diagram (atomic proportions) showing a chemical distinc-tion between the lighter and darker zones OIZ as in Fig 2
Silicate and oxide minerals from a zoned granitic pegmatite 981
eschweizerbart_xxx
2005) At the Tanco pegmatite Ta oxides are also asso-ciated with lepidolite enriched in Li and F from the wallzone (Van Lichtervelde et al 2008)
93 Origin and evolution of the zoned graniticlepidolite-subtype pegmatite at Namivo
In general granitic pegmatites particularly those belong-ing to the rare-element class are accepted as having beenformed by the fractional crystallization of a granite melt(eg Cerny 1991a b 1992 Neiva et al 2008 2012 Roda-Robles et al 2012) But it also has been proposed thatpegmatites may be formed by partial melting of appropri-ate rock compositions (eg Nabelek et al 1992 Nabelekamp Russ-Nabelek 1992 Shearer et al 1992 Roda Robleset al 1999) The lepidolite-subtype pegmatites belong tothe LCT (lithium-cesium-tantalum) family (Cerny amp Ercit2005) They are derived by fractional crystallization of agranite magma (eg Cerny et al 2005 Neiva amp Ramos2010 Cerny et al 2012b) Experimental work by Londonet al (1989) and London (1990) using Macusani glass as astarting material equivalent to the bulk composition ofhighly fractionated rare-alkali-rich pegmatites underhighly evolved and hydrous but H2O undersaturatedmelt obtained the latest primary assemblage consisting
of an Li-rich mica thorn albite thorn quartz deposited directlyfrom the primary melt phase Other authors egZasedatelev (1974 1977) and Stewart (1978) argue thatlepidolite-bearing pegmatites are derived from direct ana-texis and Gordiyenko et al (1996) consider that they arederived from an undefined medium and the rare-elementmineralization is superimposed on preexisting barrenpegmatites
Lepidolite-subtype pegmatites may migrate a long wayfrom their parent granites because their volatile-rich highlyfluid pegmatite melts are stable at relatively low tempera-tures (eg Cerny et al 2005 Antunes et al 2013)Therefore the Namivo pegmatite is probably derived byfractional crystallization of an S-type granite magmawhich resulted from partial melting of metamorphosed juve-nile sediments containing micas that carry most of the traceelements that define the signature of the LCT pegmatites(eg Dahl et al 1993)
The two main models for the internal evolution of peg-matites that dominated for more than a century are a) thefractional crystallization of a flux-bearing granitic melt fromthe margins to the center of the pegmatite (Cameron et al1949) b) the interactions of an aqueous fluid with graniticmelt (Jahns amp Burnham 1969 Jahns 1982) The recentmodel of constitutional zone refining combines aspects ofboth models and invokes the formation of a flux-enriched
Table 4 Electron microprobe analyses in wt of zoned gahnite from the outer intermediate zone (OIZ) of the Namivo granitic pegmatiteMozambique
Darker Zone Lighter Zone
Mean s Range Mean s Range
SnO2 036 050 0ndash097 658 281 151ndash998TiO2 008 008 0ndash021 065 034 008ndash105Nb2O5 001 002 0ndash006 018 007 007ndash029Ta2O5 001 004 0ndash010 015 013 0ndash033ZnO 3998 123 3810ndash4109 3339 318 3004ndash3848FeO 367 048 331ndash442 433 065 306ndash498MnO 032 004 028ndash040 039 006 032ndash048MgO 003 004 0ndash010 ndash ndash ndashAl2O3 5507 050 5436ndash5572 5337 070 5257ndash5443SiO2 003 003 0ndash007 008 010 0ndash025Total 9956 9912n 8 8Sn 0035 0048 0ndash0095 0648 0278 0149ndash0983Ti 0015 0015 0ndash0038 0120 0064 0015ndash0195Nb ndash 0003 0ndash0006 0021 0009 0009ndash0037Ta ndash 0002 0ndash0006 0009 0009 0ndash0021Zn 7226 0182 6890ndash7382 6086 0568 5482ndash6965Fe2thornt 0752 0103 0675ndash0913 0894 0135 0628ndash1029Mn 0066 0008 0057ndash0083 0082 0013 0066ndash0101Mg 0010 0015 0ndash0037 ndash ndash ndashAl 15887 0052 15805ndash15954 15526 0170 15375ndash15853Si 0007 0008 0ndash0018 0019 0025 0ndash0062P
23998 23405Fe3thorn 0064 0230Fe2thorn 0686 0658SnZn 0005 0007 0ndash0014 0106 0052 0021ndash0179ZnFe2thornt 961 143 768ndash1093 681 190 536ndash1109
n number of analysis Cation formula based on 32 atoms of oxygen Fe2thornt total Fe2thorn estimated
982 A M R Neiva
eschweizerbart_xxx
boundary layer of silicate liquid in advance of a crystal-lization front (London 2008 London amp Morgan 2012)
Lepidolite-subtype pegmatites are generally scarce(Cerny et al 2005) particularly the zoned ones In thesymmetrically zoned lepidolite-subtype pegmatites ofRozna and Dobra Voda Czech Republic micas (Cernyet al 1995) tourmaline (Selway et al 1999) and colum-bite-group minerals (Novak amp Cerny 1998) evolve fromthe outermost zone to the innermost zone following thecrystallization sequence The same was found in tourma-line from the zoned Lastovicky Dolnı Bory and Raddovicelepidolite-subtype pegmatite dikes in the Czeck Republic(Selway et al 1999)
In general beryl (Neiva amp Neiva 2005) feldsparsmicas and columbite-(Mn) (in this paper) from theNamivo lepidolite-subtype pegmatite record the progres-sive chemical evolution of the pegmatite from the wallzone to the core These minerals were produced by crystal-lization from a silicate melt rather than an aqueous fluidphase The slow cooling of melt shown by the magmaticcrystallization temperatures of feldspars cannot explain theincrease in grain-size of minerals from the wall zone to thecore but fluxes will be necessary to promote the change oftexture particularly a flux-rich hydrosilicate liquidaccording to the experimental evidence (London 2009)The constitutional zone refining model will be the best forthis zoned pegmatite and probably for all lepidolite-sub-type pegmatites because this model also produces a higherfinal concentration of incompatible components in a smal-ler volume of rock than fractional crystallization does(Morgan amp London 1999)
The core margin at the Rozna pegmatite contains K-feld-spar and quartz and the core consists mainly of quartz but it issurrounded and penetrated by a quartz-bearing albitethorn lepi-dolite complex which contains several minerals At theDobra Voda pegmatite the center of the dike is occupiedby the lepidolite unit containing albite and other minerals(Cerny et al 1995) At the Namivo pegmatite the coremargin consists of quartz and beryl and the core containsmainly quartz and spodumene but also albite lepidolite andother minerals The last-unit assemblages of primary miner-als in most of the highly fractionated LCT pegmatites are richin albite and commonly contain lepidolite or spodumene andmost of the other rare phases These units represent the lastmost fractionated liquid that can be derived by fractionalcrystallization of a crustal melt (London 2008)
The Namivo granitic pegmatite shows a significant dis-tinction from the other zoned lepidolite-subtype pegmatitesand LCT pegmatites except the Tanco petalite-subtypepegmatite in Canada because the lepidolite richest in SiLi and F FeMg-containing polylithionite and associatedcolumbite-(Mn) with the highest Ta(Ta thorn Nb) ratio tanta-lite-(Fe) and tantalite-(Mn) only occur in the outer inter-mediate zone These minerals usually form late in theconsolidation of pegmatites The lepidolite and polylithio-nite are probably derived from the disequilibrium crystal-lization of an undercooled melt Tantalite may reflect a localdecrease in Li and F that caused Ta precipitation
This paper contributes to a better understanding of theorigin and evolution of the rare zoned lepidolite-subtypepegmatites and shows that although the pegmatite evolvedfrom the wall zone to the core it presents an unusualassociation of lepidolite polylithionite and tantalite in theouter intermediate zone
Acknowledgments Thanks are due to JM Cotelo Neivaand MB Dias for the samples and information providedand to MR Machado Leite and MF Guimaraes for theuse of the electron microprobe facilities at the LaboratorioNacional de Energia e Geologia (LNEG) PortugalFinancial support was provided by the PortugueseGovernment for the project Pest-OECTEUI00732011of the Geosciences Centre through the PortugueseFoundation for Science and Technology I would like tothank D London WB Simmons and the associated editorE Widom for their constructive reviews of this manuscriptand M Prieto for his editorial work
References
Alfonso P Melgarejo JC Yusta I Velasco F (2003)
Geochemistry of feldspars and muscovite in granitic pegmatite
from the Cap de Creus field Catalonia Spain Can Mineral 41
103ndash116
Antunes IMHR Neiva AMR Ramos JMF Silva PB
Silva MMVG Corfu F (2013) Petrogenetic links between
lepidolite-subtype aplite-pegmatite aplite veins and associated
granites at Segura (central Portugal) Chemie der Erde in press
httpdxdoiorg101016jchemer20121203
Batchelor RA amp Kinnaird JA (1984) Gahnite compositions
compared Mineral Mag 48 425ndash430
Beurlen H Da Silva MRR Thomas R Soares DR Olivier P
(2008) Nb-Ta-(Ti-Sn) oxide mineral chemistry as tracer of rare-
element granitic pegmatite fractionation in the Borborema pro-
vince Northeastern Brazil Miner Deposita 43 207ndash228
Cameron EN Jahns RH McNair AH Page LR (1949)
Internal structure of granitic pegmatites Econ Geol
Monograph 2 115 p
Cerny P (1991a) Fertile granites of Precambrian rare-element
pegmatite fields is geochemistry controlled by tectonic setting
or source lithologies Precambrian Res 51 429ndash468
mdash (1991b) Rare-element granite pegmatites I Anatomy and inter-
nal evolution of pegmatite deposits Geoscience Canada 18
49ndash67
mdash (1992) Geochemical and petrogenetic features of mineralization
in rare-element granitic pegmatites in the light of current
research Applied Geochemistry 7 393ndash416
mdash (1994) Evolution of feldspars in granitic pegmatites in
lsquolsquoFeldspars and their Reactionsrsquorsquo I Parsons ed NATO
Advanced Study Institute Series C421 501ndash539
mdash (2005) The Tanco rare-element pegmatite deposit Manitoba
regional context internal anatomy and global comparisons in
lsquolsquoRare-element Geochemistry and Mineral Depositsrsquorsquo RL
Linnen amp IM Samson eds Geochemical Association of
Canada Short Course Notes St Catherines 17 127ndash158
Silicate and oxide minerals from a zoned granitic pegmatite 983
eschweizerbart_xxx
Cerny P amp Ercit TS (2005) The classification of granitic pegma-
tites revisited Can Mineral 43 2005ndash2026
Cerny P Meintzer RE Andersen AJ (1985) Extreme fractiona-
tion in rare-element granitic pegmatites selected examples of
data and mechanisms Can Mineral 23 381ndash421
Cerny P Goad BE Hawthorne FC Chapmann R (1986)
Fractionation trends of the Nb- and Ta-bearing oxide minerals
in the Greer Lake pegmatite granite and its pegmatite aureole
southeastern Manitoba Am Mineral 71 501ndash517
Cerny P Stanek J Novak M Baadsgaard H Rieder M
Ottolini L Kavalova M Chapman R (1995) Geochemical
and structural evolution of micas in the Rozna amp Dobra Voda
pegmatites Czech Republic Mineral Petrol 55 177ndash201
Cerny P Ercit TS Vanstone PJ (1998) Mineralogy and petrol-
ogy of the Tanco rare-element pegmatite deposit southeastern
Manitoba International Mineralogical Association 17th General
Meeting Toronto Field Guidebook B6
Cerny P Chapman R Ferreira K Smeds SA (2004)
Geochemistry of oxide minerals of Nb Ta Sn and Sb in
the Varutrask granitic pegmatite Sweden The case of an
lsquolsquoanomalousrsquorsquo columbitendashtantalite trend Am Mineral 89
505ndash518
Cerny P Masau M Goad BE Ferreira K (2005) The Greer
Lake leucogranite Manitoba and the origin of lepidolite-sub-
type granitic pegmatites Lithos 80 305ndash321
Cerny P Teertstra DK Chapman R Selway JB Hawthorne
FC Ferreira K Chackowsky LE Wang X-J Meintzer
RE (2012a) Extreme fractionation and deformation of the
leucogranite-pegmatite suite at Red Cross Lake Manitoba
Canada IV Mineralogy Can Mineral 50 1839ndash1875
Cerny P Halden NM Ferreira K Meintzer RE Brisbin WC
Chackowsky LE (2012b) Extreme fractionation and deforma-
tion of the leucogranite-pegmatite suite at Red Cross Lake
Manitoba Canada II Petrology of the leucogranites and peg-
matites Can Mineral 50 1807ndash1822
Dahl PS When DC Feldmann SG (1993) The systematics of
trace-element partitioning between coexisting muscovite and
biotite in metamorphic rocks from the Black Hills South
Dakota USA Geochim Cosmochim Acta 57 2487ndash2505
Dias MB amp Wilson WE (2000) The Alto Ligonha Pegmatites
Mozambique Mineral Record 31 459ndash497
Fleet ME (2003) Rock-Forming Minerals vol 3A Sheet silicates
micas The Geological Society London second edition chap 6
Lithium micas 651ndash690
Foord EE Cerny P Jackson LL Sherman DM Eby RK
(1995) Mineralogical and geochemical evolutions of micas
from miarolitic pegmatites of the anorogenic pikes-Peak
Batholith Colorado Mineral Petrol 55 1ndash26
Foster MD (1960) Interpretation of the composition of lithium
micas US Geol Surv Prof Paper 354-E 115ndash147
Fuhrman ML amp Lindsley DK (1988) Ternary-feldspar modeling
and thermometry Am Mineral 73 201ndash215
Gomes CL Castro P Alves C (1995) Caracterizacao das espi-
nelas zincıferas e do par ganite-nigerite no campo aplito-
pegmatıtico da Serra de Arga-Minho N de Portugal IV
Congresso Nacional de Geologia Resumos Alargados
Universidade do Porto Mem 4 629ndash633
Gordiyenko VV Ilyina AN Timochina LA Badamina EB
Stanek J (1996) Geochemical model of evolution of a pegma-
tite-forming ore-magmatic system of western Moravia Proc
Russ Mineral Soc 125 38ndash48 (in Russian)
Icenhower JP amp London D (1995) An experimental study for
element partitioning between biotite muscovite and coexisting
peraluminous granitic melt at 200 MPa (H2O) Am Mineral 80
1229ndash1251
Jahns RH (1982) Internal evolution of pegmatite bodies in lsquolsquoGranitic
Pegmatites in science and industryrsquorsquo P Cerny ed Mineralogical
Association of Canada Short Course Handbook 8 293ndash327
Jahns RH amp Burnham CW (1969) Experimental studies of
pegmatite genesis I A model for the derivation and crystal-
lization of granitic pegmatites Econ Geol 64 843ndash864
Jolliff BL Papike JJ Shearer CK (1987) Fractionation trends
in mica and tourmaline as indicators of pegmatite internal evo-
lution Bob Ingersoll pegmatite Black Hills South Dakota
USA GeochimCosmochim Acta 51 519ndash534
Kile DE amp Foord EE (1998) Micas from the Pikes Peak bath-
olith and its cogenetic granitic pegmatites Colorado optical
properties composition and correlation with pegmatite evolu-
tion Can Mineral 36 463ndash482
Linnen RL (1998) The solubility of Nb-Ta-Zr-Hf-W in granitic
melts with Li and Li thorn F constraints for mineralization in rare
metal granites and pegmatites Econ Geol 93 1013ndash1025
Linnen RL amp Cuney M (2005) Granite-related rare-element
deposits and experimental constraints on Ta-Nb-W-Sn-Zr-Hf
mineralization in lsquolsquoRare-element geochemistry and mineral
depositsrsquorsquo RL Linnen amp IM Samson eds Geochemical
Association of Canada Short Course Notes 17 45ndash68
London D (1990) Internal differentiation of rare-element pegmatites
a synthesis of recent research in lsquolsquoOre Bearing Granite Systems
Petrogenesis and Mineralizing Processesrsquorsquo HJ Stein amp JL
Hannah eds Geol Soc America Special Paper 246 35ndash50
mdash (2008) Pegmatites The Canadian Mineralogist Special
Publication 10 347 p
mdash (2009) The origin of primary textures in granitic pegmatites
Can Mineral 47 697ndash724
London D amp Morgan GB VI (2012) The pegmatite puzzle
Elements 8 263ndash268
London D Morgan GB VI Hervig RL (1989) Vapor-under-
saturated experiments in the system macusanite-H2O at 200
MPa and the internal differentiation of granitic pegmatites
Contrib Mineral Petrol 102 1ndash17
London D Morgan GB VI Paul KA Guttery BM (2012)
Internal evolution of miarolitic granitic pegmatites at the Little
Three mine Ramona California USA Can Mineral 50
1025ndash1054
Martins T Lima A Simmons WB Folster AU Noronha F
(2011) Geochemical fractionation of Nb-Ta oxides in Li-bear-
ing pegmatites from the Barroso-Alvao pegmatite field northern
Portugal Can Mineral 49 777ndash791
Monier G Charoy B Cuney M Ohnenstetter D Robert JL
(1987) Evolution spatiale et temporelle de la composition des
micas du granite albitique a topaze-lepidolite de Beauvoir
Geologie De La France 2ndash3 179ndash188
Monier G amp Robert JL (1986) Evolution of the miscibility gap
between muscovite and biotite solid solutions with increasing
lithium content an experimental study in the systems
K2OndashLi2OndashMgOndashAl2O3ndashSiO2ndashH2OndashHF at 600 C 2 kbar
PH2O comparison with natural lithium micas Mineral Mag
50 641ndash651
Morgan GBVI amp London D (1999) Crystallization of the little
three layered pegmatite-aplite dike Ramona District California
Contrib Mineral Petrol 136 310ndash330
984 A M R Neiva
eschweizerbart_xxx
Nabelek PI amp Russ-Nabelek C (1992) The generation and crys-
tallization conditions of the Proterozoic Harney Peak
Leucrogranite Black Hills South Dakota USA petrologic and
geochemical constraints Contrib Mineral Petrol 110
173ndash191
Nabelek PI Russ-Nabelek C Haeussler GT (1992) Stable
isotope evidence for the petrogenesis and fluid evolution in
the Proterozoic Harney Peak leucogranite Black Hills
South Dakota Geochim Cosmochim Acta 56 403ndash417
Neiva AMR amp Champness PE (1997) Nigerite and gahnite from
the granitic pegmatite veins of Cabanas Ponte de Lima northern
Portugal N Jb Mineral Mh 9 385ndash409
Neiva AMR Gomes MEP Ramos JMF Silva PB (2008)
Geochemistry of granitic aplite-pegmatite sills and their miner-
als from Arcozelo da Serra area (Gouveia central Portugal)
Eur J Mineral 20 465ndash485
Neiva AMR amp Neiva JMC (2005) Beryl from the granitic
pegmatite at Namivo Alto Ligonha Mozambique N Jb
Mineral Abh 181 173ndash182
Neiva AMR amp Ramos JMF (2010) Geochemistry of granitic
aplite-pegmatite sills and petrogenetic links with granites
Guarda-Belmonte area central Portugal Eur J Mineral 22
837ndash854
Neiva AMR Silva PB Ramos JMF (2012) Geochemistry of
granitic aplite-pegmatite veins and sills and their minerals from the
Sabugal area central Portugal N Jb Mineral Abh 189 49ndash74
Novak M amp Cerny P (1998) Niobium-tantalum oxide minerals
from complex granitic pegmatites in the Moldanubicum Czech
Republic primary versus secondary compositional trends Can
Mineral 36 659ndash672
Pesquera Perez A Torres-Ruiz J Gil PP Velilla N (1999)
Chemistry and genetic implications of tourmaline and Li-F-Cs
micas from the Valdeflores (Caceres Spain) Am Mineral 84
55ndash69
Rieder M Cavazzini G DrsquoYakonov YuS Frank-Kamenetskii
VA Gottardi G Guggenheim S Koval PV Muller G
Neiva AMR Radoslovich EW Robert J-L Sassi FP
Takeda H Weiss Z Wones DR (1999) Nomenclature of the
micas Mineral Mag 63 267ndash279
Roda Robles E Pesquera Perez A Velasco Roldan F Fontan F
(1999) The granitic pegmatites of the Fregeneda area
(Salamanca Spain) characteristics and petrogenesis Mineral
Mag 63 535ndash558
Roda Robles E Pesquera A Gil-Crespo PP Torres-Ruiz J
Fontan F (2005) Origin and internal evolution of the Li-F-
Be-P-bearing Pinilla de Fermoselle pegmatite (Central Iberian
Zone Zamora Spain) Am Mineral 90 1887ndash1899
Roda Robles E Pesquera Perez A Gil PP Torres-Ruiz J de
Parseval P (2006) Mineralogy and geochemistry of micas from
the Pinilla de Fermoselle pegmatite (Zamora Spain) Eur J
Mineral 18 369ndash377
Roda Robles E Keller P Pesquera Perez A Fontan F (2007)
Micas of the muscovite-lepidolite series from Karibib pegma-
tites Namibia Mineral Mag 71 41ndash62
Roda Robles E Pesquera A Gil-Crespo P Torres-Ruiz J
(2012) From granite to highly evolved pegmatite a case study
of the Pinilla de Fermoselle granite-pegmatite system (Zamora
Spain) Lithos 153 192ndash207
Selway JB Novak M Cerny P Hawthorne FC (1999)
Compositional evolution of tourmaline in lepidolite-subtype
pegmatites Eur J Mineral 11 569ndash584
Shearer CK Papike JJ Jolliff B (1992) Petrogenetic links
among granites and pegmatites in the Harney Peak rare-element
granite-pegmatite system Black Hills South Dakota Can
Mineral 30 785ndash809
Soares DR Hartmut B Ferreira ACM da Silva MRR
(2007) Chemical composition of gahnite and degree of peg-
matitic fractionation in the Borborema Pegmatitic Province
northeastern Brazil Anais Da Academ Bras Cien 79
395ndash404
Stewart DB (1978) Petrogenesis of lithium-rich pegmatites Am
Mineral 63 970ndash980
Tischendorff G Gattesmann B Forster H-J Trumbull RB
(1997) On Li-bearing micas estimating Li from electron
microprobe analyses and an improved diagram for graphical
representation Mineral Mag 61 809ndash834
Van Lichtervelde M Linnen RL Salvi S Beziat D (2006)
The role of metagabbro rafts on tantalum mineralization in the
Tanco granitic pegmatite Manitoba Can Mineral 44
625ndash644
Van Lichtervelde M Gregoire M Linnen RL Beziat D Salvi
S (2008) Trace element geochemistry by laser ablation ICP-
MS of micas associated with Ta mineralization in the Tanco
pegmatite Manitoba Canada Contrib Mineral Petrol 155
791ndash806
Vieira R Roda-Robles E Pesquera A Lima A (2011)
Chemical variation and significance of micas from the
Fregeneda-Almendra pegmatitic field (Central-Iberian Zone
Spain and Portugal) Am Mineral 96 637ndash645
Wen S amp Nekvasil H (1994) SOLVCALC an interactive gra-
phics program package for calculating ternary feldspar solvus
and two-feldspar geothermometry Comput Geosci 20
1025ndash1040
Wise MA (1995) Trace element chemistry of lithium-rich micas
from rare-element granitic pegmatites Mineral Petrol 55
203ndash215
Zasedatelev AM (1974) Possible accumulation of lithium in host
rocks of lithium pegmatite veins during old sedimentation pro-
cesses Doklady Acad Sci USSR Earth Sci Ser 218 196ndash198
(in Russian)
mdash (1977) Quantitative of metamorphic generation of rare-metal
pegmatites with lithium mineralization Doklady Acad Sci
USSR Earth Sci Ser 236 219ndash221 (in Russian)
Received 26 January 2013
Modified version received 21 May 2013
Accepted 23 July 2013
Silicate and oxide minerals from a zoned granitic pegmatite 985
eschweizerbart_xxx
From the OIZ to IIZa IIZb and Cc muscovite and lithianmuscovite generally show increases in the Si Licalc F and Rbcontents and decreases in the Fe2thorn and Mg contents and KRb ratio but the Mg content is very low in these micas fromthe IIZa IIZb and Cc (Table 1 Fig 7a) The lsquolsquomixed formrsquorsquoshows increases in the Si Licalc F Rb Cs contents anddecreases in the (AlIV thorn AlVI) and Mg contents and KRbratio but the Mg content is very low in this mica from theIIZb and Cc (Table 1 Fig 7b c) The lepidolite shows anincrease in the Si Licalc F Rb and Cs contents and a decreasein the KRb ratio from the IIZa to the IIZb and Cc (Table 1Fig 7d e) Furthermore the lepidolite from the OIZ has thelowest (AlIV thorn AlVI) AlVI and OH contents the highest SiFe2thorn Licalcand F contents and KRb ratio and the lowest Rband Cs contents compared to lepidolite from the other zones(Table 1 Fig 7d e)
5 Feldspars
Selected chemical analyses of albite and K-feldspar fromfive zones of the Namivo granitic pegmatite are given inTable 2 Strontium is the most abundant trace element inalbite (eg Cerny 1994) Anorthite and Sr contents and SrCa ratio of albite decrease from the WZ to the Cc (Fig 8Table 2) Rubidium is the most abundant trace element inK-feldspar followed by Cs in IIZa IIZb and Cc In gen-eral K Rb and Cs contents of K-feldspar increase and KRb and KCs values decrease from the WZ to the Cc (Table2 Fig 9)
The program SOLVCALC 20 (Wen amp Nekvasil 1994)using the Margules model Fuhrman amp Lindsley (1988) wasapplied for the purpose of thermometry The pairing ofplagioclase cores with the K-feldspars average of eachsample was used to estimate the crystallization temperaturesof primary magmatic feldspars They are 405 C (WZ)406ndash340 C (OIZ) 390ndash335 C (IIZa) 347ndash306 C (IIZb)and 333ndash289 C (Cc) at 3 kbar The metamorphic environ-ment of rare-element-Li granitic pegmatites is one of lowpressure 2ndash4 kbar (Cerny amp Ercit 2005) In general thedifference between the maximum and minimum calculatedtemperatures at 2 3 and 4 kbar for the same feldspar pairfrom the Namivo pegmatite is lower than 40 C The tem-perature decreases from the wall zone (WZ) to the core(Cc) A similar temperature behavior of feldspars wasfound in the pegmatite-aplite dike USA (Morgan ampLondon 1999)
6 Other silicates
Tourmaline of schorl composition was only found inthe OIZ (Table 2) because there was not enough Feand Mg for schorl to precipitate in the other zonesSpodumene only occurs in the Cc and its compositionis nearly pure (Table 2)
7 Columbite-tantalite
Representative chemical analyses of columbitendashtantalitefrom the Namivo granitic pegmatite are given in Table 3and plotted in the columbite quadrilateral (Fig 10a)Most crystals are unzoned but zoned crystals with dar-ker and lighter zones in BSE images are from the Cc Thelighter zone of columbite-(Mn) has higher Ta contentTa(Ta thorn Nb) and Mn(Mn thorn Fe) values and lower Nbcontent than the darker zone (Fig 10a b) The crystals ofthe columbitendashtantalite minerals are low in W Sn and Tiimpurities (Table 3)
The main trend starts from the columbite-(Mn) of theOIZ towards the more Mn-enriched and slightly Ta-enriched columbite-(Mn) from the IIZa and Cc The high-est Ta(Ta thorn Nb) values belong to the lighter zone ofcolumbite-(Mn) with Mn(Mn thorn Fe) frac14 10 from the CcThe richest columbite-(Mn) in Ta(TathornNb) and composi-tions of tantalite-(Fe) and tantalite-(Mn) were only foundin the OIZ (Fig 10a) and are associated with lepidolite andpolylithionite (Fig 3c)
8 Gahnite
Gahnite was rarely found in the OIZ and shows a darkerzone that partially surrounds a lighter zone in a BSE image(Fig 11a) The darker zone has a higher Zn content andlower Sn Ti Nb Ta Mn contents and SnZn value than thelighter zone (Table 4 Fig 11b c) These gahnite composi-tions fall within the igneous field of Batchelor amp Kinnaird(1984) The darker zone is closer in composition to thepure gahnite (Zn8Al16O32) than the lighter zone whichcontains up to 0983 apfu Sn 0195 apfu Ti 1029 apfutotal Fe2thorn 0101 apfu Mn (Table 4) and consequently hasa composition distinct from nigerite In general both thedarker and lighter zones have higher Sn Ti and Fe contentsthan gahnite from the granitic pegmatites of Nigeria(Batchelor amp Kinnaird 1984) Arga northern Portugal(Gomes et al 1995) and Cabanas northern Portugal(Neiva amp Champness 1997) Borborema province north-eastern Brazil (Soares et al 2007) The Zn=Fe2thornt values ofthe darker and lighter zones of gahnite from Namivo arelower than those reported in Neiva amp Champness (1997)and Soares et al (2007)
9 Discussion and conclusions
91 Evolution of micas in the zoned pegmatite
In general individual mica crystals show varying patternsand compositional zoning involving several elementsmainly Si AlVI (AlIV thorn AlVI) Fe2thorn Mn (Fe2thornthorn Mn thornMg) Licalc Rb Cs F and OH and the KRb ratioProgressively zoned crystals from the IIZa show grada-tional contacts between a lithian muscovite core and a
976 A M R Neiva
eschweizerbart_xxx
lsquolsquomixed formrsquorsquo rim (Figs 3e 6e f) and the zoning patternscorrespond to fractionation trends and probably reflect adrop in temperature during the crystallization of the grani-tic pegmatite melt Progressively zoned crystals also occurin OIZ IIZb and Cc Some crystals are reversely zonedwith a) a lsquolsquomixed formrsquorsquo core and a lithian muscovite rimfrom the OIZ (Figs 3d d1 6d) b) a core consisting oflsquolsquomixed formrsquorsquo and lepidolite and a rim of muscovite andlithian muscovite from the IIZa (Figs 3f f1 6g h) c) alepidolite core and a muscovite and lithian muscovite rimfrom the Cc (Figs 3j 6o p) which may be explained bythe hypothesis of oscillations in the compositions of themelt from which they grew alternating between an Li-enriched boundary layer and a bulk melt that is less frac-tionated The muscovite evolved to lithian muscovite inIIZa and Cc (Figs 3f 6g h 3j 6o p) Replacements (Figs3a 6a b 3c 6c 3i 6m n Table 1) occur in OIZ and Ccand overgrowths (Figs 3b g 6i j k 3h 6l Table 1) occurin OIZ and IIZb as found in BSE images
Muscovite evolved to lithian muscovite as observed inOIZ IIZa IIZb and Cc (Figs 3f 6g h 3j 6o p Table 1)Lithian muscovite evolved to lsquolsquomixed formrsquorsquo in OIZ IIZaIIZb and Cc (Figs 3e 6e f Table 1) and lsquolsquomixed formrsquorsquoevolved to lepidolite in IIZa IIZb and Cc (Figs 3f f1 6gh 3h 6l Table 1) All these evolutions are due to fractionalcrystallization
In the OIZ lepidolite has more Si Licalcand F butsimilar KRb to that of zinnwaldite and replaces it (Figs
3a 6a b 7d Table 1) An FeMg-containing polylithionitehas higher Si Licalcand Rb contents and a smaller KRbratio than the lepidolite that it replaces (Figs 3c 6c Table1) and a continuous chemical evolution from lepidolite topolylithionite is shown
The trends for major and trace elements of micas withineach zone are difficult to define due to some partial over-lapping but a progressive evolution from muscovite to lithianmuscovite lsquolsquomixed formrsquorsquo and lepidolite in IIZa IIZb and Ccis mainly shown by an increase in the Si Licalc F Rb and Cscontents and a decrease in the KRb ratio and this is simi-larly shown in the OIZ from muscovite to lsquolsquomixed formrsquorsquo(Table 1 Fig 7) In the OIZ Si and Licalccontents increaseprogressively from zinnwaldite to lepidolite and FeMg-containing polylithionite but a gap occurs between zinnwal-dite and lepidolite (Table 1 Fig 4) whereas a continuousevolution from lepidolite to polylithionite is observed TheKRb ratios of zinnwaldite and polylithionite are within therange of that of lepidolite (Fig 7d e)
Each Al-richer mica (muscovite lithian muscovite andlsquolsquomixed formrsquorsquo) exhibits an evolution from the OIZ to theIIZa and then to the IIZb and Cc particularly shown by anincrease in the Si Licalc F and Rb contents and adecrease in the KRb ratio but also an increase in theCs content in the lsquolsquomixed formrsquorsquo (Table 1 Fig 7) Theseelements and ratio have been used as petrogenetic indi-cators of evolution in micas from pegmatites (eg Cernyet al 2005 Roda Robles et al 2006 2007 Vieira et al
Fig 7 Plot of some variation diagrams of micas from the OIZ IIZa IIZb and Cc of the Namivo granitic pegmatite Mozambique showingthat the Rb2O and Cs2O contents increase and the KRb ratio decreases for micas from the OIZ to the Cc OIZ IIZa IIZb and Cc as in Fig 2
Silicate and oxide minerals from a zoned granitic pegmatite 977
eschweizerbart_xxx
Tab
le2
R
epre
sen
tati
ve
elec
tro
nm
icro
pro
be
anal
yse
sin
wt
o
ffe
ldsp
ars
sch
orl
and
spo
du
men
efr
om
the
Nam
ivo
gra
nit
icp
egm
atit
eM
oza
mb
iqu
e
Alb
ite
K-f
eld
spar
Sch
orl
Sp
od
um
ene
Zo
nes
WZ
OIZ
IIZ
aII
Zb
Cc
Zo
nes
WZ
OIZ
IIZ
aII
Zb
Cc
Zo
nes
OIZ
Zo
ne
Cc
SiO
26
75
76
78
86
87
06
84
76
84
1S
iO2
65
10
65
55
65
46
64
96
64
72
SiO
23
52
0S
iO2
64
65
TiO
20
02
mdash0
02
mdashmdash
TiO
2mdash
00
1mdash
mdashmdash
TiO
20
35
Al 2
O3
27
20
Al 2
O3
20
25
19
74
19
67
19
88
19
97
Al 2
O3
18
96
18
23
18
31
18
24
18
05
B2O
3
10
28
Fe 2
O3
00
6F
e 2O
3mdash
mdashmdash
mdash0
10
Fe 2
O3
mdash0
02
mdash0
03
mdashA
l 2O
33
17
2M
nO
01
3M
nO
00
6mdash
mdashmdash
mdashM
nO
mdash0
03
00
3mdash
mdashF
eO1
35
2M
gO
01
8M
gO
mdashmdash
mdashmdash
mdashM
gO
00
10
01
00
5mdash
mdashM
nO
03
3N
a 2O
01
9C
aO1
04
08
00
56
03
70
32
CaO
00
10
01
00
60
01
00
2M
gO
22
8L
i 2O
8
05
Na 2
O1
06
11
12
01
12
11
13
41
13
4N
a 2O
06
50
58
04
10
59
03
8C
aO0
23
To
tal
10
04
6K
2O
00
50
17
00
60
14
01
0K
2O
14
72
14
75
15
67
15
01
15
74
Li 2
O
02
2S
rO0
72
05
00
24
01
1mdash
Rb
2O
00
90
20
03
00
59
09
0N
a 2O
22
8S
i1
99
7P
2O
50
01
00
4mdash
mdashmdash
Cs 2
O
00
6
00
60
09
01
80
20
K2O
00
1A
lIV0
00
3T
ota
l1
00
33
10
03
31
00
46
10
03
11
00
24
P2O
5mdash
00
3mdash
mdashmdash
H2O
3
18
P2
00
To
tal
99
60
99
48
10
03
89
96
11
00
01
F0
78
AlV
I0
98
7S
rC
a(w
t)0
81
07
40
50
03
50
Cl
mdashF
e3thorn
00
01
KR
b(w
t)153
68
48
23
16
Sum
1003
8P
09
9S
i1
18
23
11
87
91
19
58
11
93
21
19
21
KC
s(w
t)4
07
20
41
63
73
69
O
F0
33
Li
10
00
P0
00
10
00
6mdash
mdashmdash
To
tal
10
00
5M
n0
00
3T
i0
00
3mdash
00
03
mdashmdash
Si
11
98
61
20
88
12
04
11
20
45
12
03
3M
g0
00
8A
l4
17
64
07
14
03
54
08
34
10
1P
mdash0
00
5mdash
mdashmdash
TS
i5
95
2N
a0
01
2F
e3thorn
mdashmdash
mdashmdash
00
13
Ti
mdash0
00
1mdash
mdashmdash
Al
00
48
P1
02
Mn
00
09
mdashmdash
mdashmdash
Al
41
14
39
62
39
70
39
86
39
55
B3
00
0M
gmdash
mdashmdash
mdashmdash
Fe3thorn
mdash0
00
3mdash
00
04
mdashZ
Al
60
00
Ca
01
95
01
50
01
04
00
69
00
60
Mn
mdash0
00
50
00
5mdash
mdashY
Al
02
74
Sr
00
73
00
51
00
24
00
11
mdashM
g0
00
30
00
30
01
4mdash
mdashT
i0
04
5N
a3
59
93
80
03
78
33
83
23
83
1C
a0
00
20
00
20
01
20
00
20
00
4M
g0
57
5K
00
11
00
38
00
13
00
31
00
22
Na
02
32
02
07
01
46
02
12
01
37
Mn
00
47
K3
45
73
47
03
67
73
55
03
73
3F
e2thorn
19
12
Z1
60
01
59
61
60
01
60
11
60
4R
b0
01
10
02
40
03
50
07
00
10
8L
i0
14
8X
38
94
04
39
33
94
39
1C
s0
00
20
00
50
00
70
01
40
01
6P
Y3
00
0m
ole
s
XC
a0
04
2A
n5
13
82
71
71
5Z
16
10
16
06
16
01
16
03
15
99
Na
07
47
Ab
94
69
53
97
09
75
97
9X
37
13
72
39
03
85
40
0K
00
02
Or
03
09
03
08
06
mo
les
amp
02
09
An
01
01
03
01
01
Ab
63
56
38
56
35
OH
35
83
Or
93
69
43
95
99
43
96
4F
04
17
Cl
mdash
WZ
ndashw
allzo
ne
OIZ
ndasho
ute
rin
term
edia
tezo
ne
IIZ
aan
dII
Zb
ndashin
ner
inte
rmed
iate
zon
esC
cndash
core
asin
Fig
2B
aOis
bel
ow
the
det
ecti
on
lim
itin
bo
thfe
ldsp
ars
Cs 2
Ofrac14
00
3w
tin
the
K-
feld
spar
fro
mth
eW
Z
mdashN
ot
det
ecte
d
Nu
mb
ero
fio
ns
on
the
bas
iso
f3
2o
xy
gen
sfo
ral
bit
ean
dK
-fel
dsp
ar
31
anio
ns
(O
OH
F
)fo
rsc
ho
rlan
d6
ox
yg
ens
for
spo
du
men
e
-A
mo
un
tin
ferr
edfr
om
con
sid
erat
ion
so
fst
oic
hio
met
ry
978 A M R Neiva
eschweizerbart_xxx
2011) Lepidolite from the OIZ is an Al-poorer mica (Fig4) and has the highest Si Licalcand F contents (Table 1)indicating that an evolution cannot be shown from thislepidolite to lepidolites from the other zones which areAl-richer micas (Fig 4) However there is a regulardecrease in the KRb ratio and a progressive increase inthe Rb and Cs contents from lepidolite of the OIZ tolepidolite of IIZa IIZb and Cc (Fig 7) which indicatesthat the KRb ratio and Rb and Cs contents must not beconsidered alone to show fractional crystallization in
lepidolites particularly if some are Al-richer micas andothers Al-poorer micas The high Licalcand F contents oflepidolite from the OIZ did not decrease its KRb ratioSuch an effect is considered to have taken place in lepi-dolite (an Al-richer mica) from the wall zone of the Tancopegmatite Manitoba Canada (Van Lichtervelde et al2008) An evolution from the lepidolite of the IIZa to thatof the Cc is generally shown by the increasing Si LicalcF Rb Cs contents and a decrease in the KRb ratio (Table1 Fig 7)
At the scale of crystals the pegmatite zones and alsothose from the OIZ to the Cc of the Namivo granitic pegma-tite Al-richer micas show fractionation because theyformed from the fractionation of an Li-rich pegmatite melt
The Al-poorer micas zinnwaldite lepidolite and FeMg-containing polylithionite only occur in the OIZ (Fig 4)Polylithionite is the mica richest in Si and Licalc and lepi-dolite from this zone is the richest in Si Licalcand F (Fig 4Table 1) The high Li contents of these micas reflect aconsiderably higher D(Li) at low temperature (Icenhoweramp London 1995) These Li-rich micas may have crystal-lized from an undercooled melt This hypothesis does notimply high Rb and Cs contents and low KRb ratios Thisagrees with the fact that these micas from the OIZ havesimilar Rb and Cs contents and KRb ratios to those of Al-richer micas (muscovite lithian muscovite and lsquolsquomixedformrsquorsquo) from the same pegmatite zone (Fig 7) Howeverthe lepidolite from the wall zone of the Tanco pegmatiteCanada of a similar origin has a low KRb ratio which isattributed to the complexly interrelated structural compo-nents of this lepidolite (Van Lichtervelde et al 2008) TheLi-rich micas from the OIZ may also represent disequili-brium These two hypotheses are considered the best forthese micas of primary magmatic origin
Another hypothesis was also considered They may havecrystallized in boundary layers which concentrate Li andF But this mechanism was suggested for the most fractio-nated tourmaline enriched in Li and F from the core of the
Fig 8 Plot of albite compositions from all zones of the Namivo granitic pegmatite Mozambique showing that the anorthite content of albitedecreases from the WZ to the Cc WZ OIZ IIZa IIZb and Cc as in Fig 2
Fig 9 The Rb vs Cs diagram of K-feldspar from all zones of theNamivo granitic pegmatite Mozambique showing that the Rb andCs contents of K-feldspar increase from the WZ to the Cc WZ OIZIIZa IIZb and Cc as in Fig 2
Silicate and oxide minerals from a zoned granitic pegmatite 979
eschweizerbart_xxx
Little Three pegmatite dike USA (Morgan amp London1999) and the micas enriched in Li and F from theNamivo pegmatite belonging to the OIZ Furthermore ina boundary layer melt that became enriched in Li and F theKRb ratio of micas decreases strongly (Van Lichterveldeet al 2008) which was not found in these micas from theOIZ (Fig 7d) Nor can they have resulted from the crystal-lization of a late melt that would have reacted with the OIZbecause these micas are among those containing the high-est KRb values (Fig 7d)
92 The importance of feldspars micas andcolumbitendashtantalite compositions to the Namivogranitic pegmatite evolution
The trace elements Rb and Cs and the KRb and KCs ratioshave been used to show the evolution of K-feldspar inpegmatites (eg Cerny 1994 Cerny et al 2005 RodaRobles et al 2005) The Rb and Cs contents increase andthe KRb and KCs ratios of K-feldspar decrease from theWZ to the Cc (Fig 9 Table 2) reflecting the growth of K-feldspar from an increasingly fractionated melt withouthaving grown from or having been chemically modifiedby an aqueous fluid as in the Swamp pegmatite section atthe Little Three Mine USA (London et al 2012) Thecrystallization of K-feldspar from an exsolved aqueousfluid from melt will reverse the magmatic fractionation ofRb Cs KRb and KCs because Rb and especially Cs areso much more compatible in vapor that both Rb and Csremain in the fluid phase (London et al 2012) The feldsparsolvus pairs in the Namivo pegmatite record magmaticcrystallization temperatures that decrease from WZ to CcAlbite shows a decrease in the Ca Sr contents and SrCaratio from the WZ to the Cc (Fig 8 Table 2) Therefore thefeldspars and also Al-richer micas as already explainedshow fractionation in this zoned pegmatite
In general lepidolite from the Namivo pegmatite hassimilar Rb2O and Cs2O contents and KRb (wt) values tothose of lepidolite from the Rozna and Dobra Voda lepi-dolite-subtype pegmatites in the Czech Republic (Cernyet al 1995) but lower Rb2O and Cs2O contents thanlepidolite from the lepidolite-subtype pegmatite at RedCross Lake Manitoba Canada (Cerny et al 2012a) K-feldspar from the Namivo pegmatite also has lower Rb2O
Table 3 Representative electron microprobe analyses in wt of columbitendashtantalite from the Namivo granitic pegmatite Mozambique
Outer Intermediate Zone - OIZ Inner Intermediate Zone - IIZa
Core - Cc
D L L
WO3 022 059 079 113 101 351 050 007Ta2O5 5487 5123 2503 3186 2888 2519 3127 4542Nb2O5 2537 3000 5483 4635 5113 5144 4911 3686SnO2 008 015 024 049 020 026 017 012TiO2 263 161 136 254 202 145 125 016FeO 860 710 665 471 236 068 mdash mdashMnO 793 952 1099 1304 1400 1725 1748 1718Total 9970 10020 9989 10012 9960 9978 9978 9981W 0004 0011 0013 0019 0016 0057 0008 0001Ta 1065 0975 0422 0552 0495 0430 0543 0847Nb 0819 0949 1538 1336 1456 1460 1418 1143Sn 0002 0004 0006 0012 0005 0007 0004 0003Ti 0141 0085 0063 0122 0096 0068 0060 0008Fe 0513 0416 0345 0251 0124 0036 mdash mdashMn 0479 0564 0578 0704 0747 0917 0945 0998P
3023 3004 2965 2996 2939 2975 2978 3000Mn(Mn thorn Fe) 048 058 063 074 086 096 100 100Ta(Ta thorn Nb) 057 051 022 029 025 023 028 043Classification tant-(Fe) tant-(Mn) col-(Mn) col-(Mn) col-(Mn) col-(Mn) col-(Mn) col-(Mn)
D ndash darker L ndash lighter zones mdash Not detected tant-tantalite col-columbite Cation formula on the basis of 6 atoms of oxygen
Fig 10 Compositions of columbitendashtantalite from the Namivogranitic pegmatite Mozambique in the columbite quadrilateralshowing that Mn(Mn thorn Fe) of columbite-(Mn) increases from theOIZ to the Cc and the richest columbite-(Mn) in Ta(Ta thorn Nb)tantalite-(Fe) and tantalite-(Mn) only occur in the OIZ OIZ IIZaand Cc as in Fig 2
980 A M R Neiva
eschweizerbart_xxx
and Cs2O contents than K-feldspar from the lepidolite-subtype pegmatite at Red Cross Lake The Rb2O andCs2O contents of primary and late K-feldspar of this peg-matite at Red Cross Lake attained unprecedented levels(Cerny et al 2012a) The lowest KRb (wt) values ofmuscovite lithian muscovite lsquolsquomixed formrsquorsquo and lepido-lite from the IIZb and Cc (Fig 7) and K-feldspar (KRb frac1414) from the Cc compare well with those found in theseminerals from the AC6frac143 lepidolite-subtype pegmatitefrom Greer Lake (Cerny et al 2005) and some of themost fractionated pegmatites worldwide which belong tothe petalite-subtype (eg Tanco Manitoba Cerny 2005Cerny et al 1998 Varutrask Sweden Cerny et al 2005)but muscovite lithian muscovite and lepidolite from theIIZb and Cc have lower Rb2O and Cs2O contents than thesemicas from the Tanco pegmatite (Cerny 2005a VanLichtervelde et al 2008) K-feldspar also has lower
contents of these oxides than the most evolved K-feldsparfrom the Tanco pegmatite (Cerny 2005a) The magmaticfractionation was strong from the WZ to IIZb and Cc of theNamivo lepidolite-subtype pegmatite
The compositional trend of columbite-(Mn) from the OIZto Cc of the Namivo granitic lepidolite-subtype pegmatite(Fig 10) is identical to that of columbite-group mineralsfrom the lepidolite-subtype complex granitic pegmatitesfrom the Dobra Voda in the Moldanubicum CzechRepublic (Novak amp Cerny 1998) and the HimalayaDistrict southern California (shown in Cerny et al 2004)Experimental data for the Fe-Mn pair (Linnen amp Cuney2005) suggest an increase in Fe with fractional crystalliza-tion which is not observed in nature Other phases seem tocontrol the bahavior of Fe and Mn in the melt eg thecrystallization of tourmaline causes a rapid increase of theMnFe in the melt (Van Lichtervelde et al 2006) When thecrystallization of tourmaline stopped the columbitendashtantaliteminerals showed a constant MnFe indicating that the Fe andMn contents in the melt remained constant Schorl onlyoccurs in the OIZ of the Namivo granitic pegmatite and itscrystallization cannot be responsible for the increase in theMnFe of the melt because Mn(Mn thorn Fe) of columbite-(Mn) increases progressively from the OIZ to the IIZa and Cc(Fig 10) Garnet zinnwaldite and gahnite containing Fe andMn also only occur in the OIZ and cannot also have causedthe increase of the MnFe in the melt The dominant Mnenrichment before Ta enrichment started in the columbitendash-tantalite composition from some granitic pegmatites isattributed to an increased alkali-fluoride activity at moderatemHF (Cerny et al 2004) and an increase in the activity offluorine (Martins et al 2011) Each Al-richer mica (musco-vite lithian muscovite and lsquolsquomixed formrsquorsquo) from the Namivogranitic pegmatite shows an increase in F content from theOIZ to the IIZa IIZb and Cc (Table 1) In general the Fcontent of lepidolite also increases from the IIZa to the IIZband Cc Therefore the extreme Fe-Mn fractionation beforeTa enrichment in columbite-(Mn) (Fig 10) may be due to anincrease in the activity of fluorine as a consequence offractional crystallization The increase in the Ta content ofcolumbite-(Mn) from the Namivo granitic pegmatite isattributed to fractional crystallization
The geochemical evolution of albite and K-feldsparfrom the WZ to the Cc Al-richer micas muscovite lithianmuscovite and lsquolsquomixed formrsquorsquo from the OIZ to the Cc andlepidolite from the IIZa to the Cc and columbite-(Mn) andalso beryl (Neiva amp Neiva 2005) from the OIZ to the Ccare caused by magma fractionation The pegmatite zonesare the product of primary crystallization from a volatile-rich silicate melt The pegmatite consolidated from the WZto the Cc The IIZb is one of the most evolved zones asalso suggested by the beryl composition (Neiva amp Neiva2005) and is the richest in lsquolsquomixed formrsquorsquo and lepidolite
The richest columbite-(Mn) in Ta(Ta thorn Nb) and com-positions of tantalite-(Fe) and tantalite-(Mn) only occur inthe OIZ (Fig 10a) associated with lepidolite and polythio-nite (Fig 3c) which may be due to the local depletion of Liand F in the melt which decreases the solubility of Ta andcauses Ta precipitation (Linnen 1998 Linnen amp Cuney
Fig 11 a Backscattered-electron image of a gahnite crystal with adarker zone partially surrounding a lighter zone from the OIZ of theNamivo granitic pegmatite b c Plot of gahnite compositions in theSn-Zn-Ti diagram (atomic proportions) showing a chemical distinc-tion between the lighter and darker zones OIZ as in Fig 2
Silicate and oxide minerals from a zoned granitic pegmatite 981
eschweizerbart_xxx
2005) At the Tanco pegmatite Ta oxides are also asso-ciated with lepidolite enriched in Li and F from the wallzone (Van Lichtervelde et al 2008)
93 Origin and evolution of the zoned graniticlepidolite-subtype pegmatite at Namivo
In general granitic pegmatites particularly those belong-ing to the rare-element class are accepted as having beenformed by the fractional crystallization of a granite melt(eg Cerny 1991a b 1992 Neiva et al 2008 2012 Roda-Robles et al 2012) But it also has been proposed thatpegmatites may be formed by partial melting of appropri-ate rock compositions (eg Nabelek et al 1992 Nabelekamp Russ-Nabelek 1992 Shearer et al 1992 Roda Robleset al 1999) The lepidolite-subtype pegmatites belong tothe LCT (lithium-cesium-tantalum) family (Cerny amp Ercit2005) They are derived by fractional crystallization of agranite magma (eg Cerny et al 2005 Neiva amp Ramos2010 Cerny et al 2012b) Experimental work by Londonet al (1989) and London (1990) using Macusani glass as astarting material equivalent to the bulk composition ofhighly fractionated rare-alkali-rich pegmatites underhighly evolved and hydrous but H2O undersaturatedmelt obtained the latest primary assemblage consisting
of an Li-rich mica thorn albite thorn quartz deposited directlyfrom the primary melt phase Other authors egZasedatelev (1974 1977) and Stewart (1978) argue thatlepidolite-bearing pegmatites are derived from direct ana-texis and Gordiyenko et al (1996) consider that they arederived from an undefined medium and the rare-elementmineralization is superimposed on preexisting barrenpegmatites
Lepidolite-subtype pegmatites may migrate a long wayfrom their parent granites because their volatile-rich highlyfluid pegmatite melts are stable at relatively low tempera-tures (eg Cerny et al 2005 Antunes et al 2013)Therefore the Namivo pegmatite is probably derived byfractional crystallization of an S-type granite magmawhich resulted from partial melting of metamorphosed juve-nile sediments containing micas that carry most of the traceelements that define the signature of the LCT pegmatites(eg Dahl et al 1993)
The two main models for the internal evolution of peg-matites that dominated for more than a century are a) thefractional crystallization of a flux-bearing granitic melt fromthe margins to the center of the pegmatite (Cameron et al1949) b) the interactions of an aqueous fluid with graniticmelt (Jahns amp Burnham 1969 Jahns 1982) The recentmodel of constitutional zone refining combines aspects ofboth models and invokes the formation of a flux-enriched
Table 4 Electron microprobe analyses in wt of zoned gahnite from the outer intermediate zone (OIZ) of the Namivo granitic pegmatiteMozambique
Darker Zone Lighter Zone
Mean s Range Mean s Range
SnO2 036 050 0ndash097 658 281 151ndash998TiO2 008 008 0ndash021 065 034 008ndash105Nb2O5 001 002 0ndash006 018 007 007ndash029Ta2O5 001 004 0ndash010 015 013 0ndash033ZnO 3998 123 3810ndash4109 3339 318 3004ndash3848FeO 367 048 331ndash442 433 065 306ndash498MnO 032 004 028ndash040 039 006 032ndash048MgO 003 004 0ndash010 ndash ndash ndashAl2O3 5507 050 5436ndash5572 5337 070 5257ndash5443SiO2 003 003 0ndash007 008 010 0ndash025Total 9956 9912n 8 8Sn 0035 0048 0ndash0095 0648 0278 0149ndash0983Ti 0015 0015 0ndash0038 0120 0064 0015ndash0195Nb ndash 0003 0ndash0006 0021 0009 0009ndash0037Ta ndash 0002 0ndash0006 0009 0009 0ndash0021Zn 7226 0182 6890ndash7382 6086 0568 5482ndash6965Fe2thornt 0752 0103 0675ndash0913 0894 0135 0628ndash1029Mn 0066 0008 0057ndash0083 0082 0013 0066ndash0101Mg 0010 0015 0ndash0037 ndash ndash ndashAl 15887 0052 15805ndash15954 15526 0170 15375ndash15853Si 0007 0008 0ndash0018 0019 0025 0ndash0062P
23998 23405Fe3thorn 0064 0230Fe2thorn 0686 0658SnZn 0005 0007 0ndash0014 0106 0052 0021ndash0179ZnFe2thornt 961 143 768ndash1093 681 190 536ndash1109
n number of analysis Cation formula based on 32 atoms of oxygen Fe2thornt total Fe2thorn estimated
982 A M R Neiva
eschweizerbart_xxx
boundary layer of silicate liquid in advance of a crystal-lization front (London 2008 London amp Morgan 2012)
Lepidolite-subtype pegmatites are generally scarce(Cerny et al 2005) particularly the zoned ones In thesymmetrically zoned lepidolite-subtype pegmatites ofRozna and Dobra Voda Czech Republic micas (Cernyet al 1995) tourmaline (Selway et al 1999) and colum-bite-group minerals (Novak amp Cerny 1998) evolve fromthe outermost zone to the innermost zone following thecrystallization sequence The same was found in tourma-line from the zoned Lastovicky Dolnı Bory and Raddovicelepidolite-subtype pegmatite dikes in the Czeck Republic(Selway et al 1999)
In general beryl (Neiva amp Neiva 2005) feldsparsmicas and columbite-(Mn) (in this paper) from theNamivo lepidolite-subtype pegmatite record the progres-sive chemical evolution of the pegmatite from the wallzone to the core These minerals were produced by crystal-lization from a silicate melt rather than an aqueous fluidphase The slow cooling of melt shown by the magmaticcrystallization temperatures of feldspars cannot explain theincrease in grain-size of minerals from the wall zone to thecore but fluxes will be necessary to promote the change oftexture particularly a flux-rich hydrosilicate liquidaccording to the experimental evidence (London 2009)The constitutional zone refining model will be the best forthis zoned pegmatite and probably for all lepidolite-sub-type pegmatites because this model also produces a higherfinal concentration of incompatible components in a smal-ler volume of rock than fractional crystallization does(Morgan amp London 1999)
The core margin at the Rozna pegmatite contains K-feld-spar and quartz and the core consists mainly of quartz but it issurrounded and penetrated by a quartz-bearing albitethorn lepi-dolite complex which contains several minerals At theDobra Voda pegmatite the center of the dike is occupiedby the lepidolite unit containing albite and other minerals(Cerny et al 1995) At the Namivo pegmatite the coremargin consists of quartz and beryl and the core containsmainly quartz and spodumene but also albite lepidolite andother minerals The last-unit assemblages of primary miner-als in most of the highly fractionated LCT pegmatites are richin albite and commonly contain lepidolite or spodumene andmost of the other rare phases These units represent the lastmost fractionated liquid that can be derived by fractionalcrystallization of a crustal melt (London 2008)
The Namivo granitic pegmatite shows a significant dis-tinction from the other zoned lepidolite-subtype pegmatitesand LCT pegmatites except the Tanco petalite-subtypepegmatite in Canada because the lepidolite richest in SiLi and F FeMg-containing polylithionite and associatedcolumbite-(Mn) with the highest Ta(Ta thorn Nb) ratio tanta-lite-(Fe) and tantalite-(Mn) only occur in the outer inter-mediate zone These minerals usually form late in theconsolidation of pegmatites The lepidolite and polylithio-nite are probably derived from the disequilibrium crystal-lization of an undercooled melt Tantalite may reflect a localdecrease in Li and F that caused Ta precipitation
This paper contributes to a better understanding of theorigin and evolution of the rare zoned lepidolite-subtypepegmatites and shows that although the pegmatite evolvedfrom the wall zone to the core it presents an unusualassociation of lepidolite polylithionite and tantalite in theouter intermediate zone
Acknowledgments Thanks are due to JM Cotelo Neivaand MB Dias for the samples and information providedand to MR Machado Leite and MF Guimaraes for theuse of the electron microprobe facilities at the LaboratorioNacional de Energia e Geologia (LNEG) PortugalFinancial support was provided by the PortugueseGovernment for the project Pest-OECTEUI00732011of the Geosciences Centre through the PortugueseFoundation for Science and Technology I would like tothank D London WB Simmons and the associated editorE Widom for their constructive reviews of this manuscriptand M Prieto for his editorial work
References
Alfonso P Melgarejo JC Yusta I Velasco F (2003)
Geochemistry of feldspars and muscovite in granitic pegmatite
from the Cap de Creus field Catalonia Spain Can Mineral 41
103ndash116
Antunes IMHR Neiva AMR Ramos JMF Silva PB
Silva MMVG Corfu F (2013) Petrogenetic links between
lepidolite-subtype aplite-pegmatite aplite veins and associated
granites at Segura (central Portugal) Chemie der Erde in press
httpdxdoiorg101016jchemer20121203
Batchelor RA amp Kinnaird JA (1984) Gahnite compositions
compared Mineral Mag 48 425ndash430
Beurlen H Da Silva MRR Thomas R Soares DR Olivier P
(2008) Nb-Ta-(Ti-Sn) oxide mineral chemistry as tracer of rare-
element granitic pegmatite fractionation in the Borborema pro-
vince Northeastern Brazil Miner Deposita 43 207ndash228
Cameron EN Jahns RH McNair AH Page LR (1949)
Internal structure of granitic pegmatites Econ Geol
Monograph 2 115 p
Cerny P (1991a) Fertile granites of Precambrian rare-element
pegmatite fields is geochemistry controlled by tectonic setting
or source lithologies Precambrian Res 51 429ndash468
mdash (1991b) Rare-element granite pegmatites I Anatomy and inter-
nal evolution of pegmatite deposits Geoscience Canada 18
49ndash67
mdash (1992) Geochemical and petrogenetic features of mineralization
in rare-element granitic pegmatites in the light of current
research Applied Geochemistry 7 393ndash416
mdash (1994) Evolution of feldspars in granitic pegmatites in
lsquolsquoFeldspars and their Reactionsrsquorsquo I Parsons ed NATO
Advanced Study Institute Series C421 501ndash539
mdash (2005) The Tanco rare-element pegmatite deposit Manitoba
regional context internal anatomy and global comparisons in
lsquolsquoRare-element Geochemistry and Mineral Depositsrsquorsquo RL
Linnen amp IM Samson eds Geochemical Association of
Canada Short Course Notes St Catherines 17 127ndash158
Silicate and oxide minerals from a zoned granitic pegmatite 983
eschweizerbart_xxx
Cerny P amp Ercit TS (2005) The classification of granitic pegma-
tites revisited Can Mineral 43 2005ndash2026
Cerny P Meintzer RE Andersen AJ (1985) Extreme fractiona-
tion in rare-element granitic pegmatites selected examples of
data and mechanisms Can Mineral 23 381ndash421
Cerny P Goad BE Hawthorne FC Chapmann R (1986)
Fractionation trends of the Nb- and Ta-bearing oxide minerals
in the Greer Lake pegmatite granite and its pegmatite aureole
southeastern Manitoba Am Mineral 71 501ndash517
Cerny P Stanek J Novak M Baadsgaard H Rieder M
Ottolini L Kavalova M Chapman R (1995) Geochemical
and structural evolution of micas in the Rozna amp Dobra Voda
pegmatites Czech Republic Mineral Petrol 55 177ndash201
Cerny P Ercit TS Vanstone PJ (1998) Mineralogy and petrol-
ogy of the Tanco rare-element pegmatite deposit southeastern
Manitoba International Mineralogical Association 17th General
Meeting Toronto Field Guidebook B6
Cerny P Chapman R Ferreira K Smeds SA (2004)
Geochemistry of oxide minerals of Nb Ta Sn and Sb in
the Varutrask granitic pegmatite Sweden The case of an
lsquolsquoanomalousrsquorsquo columbitendashtantalite trend Am Mineral 89
505ndash518
Cerny P Masau M Goad BE Ferreira K (2005) The Greer
Lake leucogranite Manitoba and the origin of lepidolite-sub-
type granitic pegmatites Lithos 80 305ndash321
Cerny P Teertstra DK Chapman R Selway JB Hawthorne
FC Ferreira K Chackowsky LE Wang X-J Meintzer
RE (2012a) Extreme fractionation and deformation of the
leucogranite-pegmatite suite at Red Cross Lake Manitoba
Canada IV Mineralogy Can Mineral 50 1839ndash1875
Cerny P Halden NM Ferreira K Meintzer RE Brisbin WC
Chackowsky LE (2012b) Extreme fractionation and deforma-
tion of the leucogranite-pegmatite suite at Red Cross Lake
Manitoba Canada II Petrology of the leucogranites and peg-
matites Can Mineral 50 1807ndash1822
Dahl PS When DC Feldmann SG (1993) The systematics of
trace-element partitioning between coexisting muscovite and
biotite in metamorphic rocks from the Black Hills South
Dakota USA Geochim Cosmochim Acta 57 2487ndash2505
Dias MB amp Wilson WE (2000) The Alto Ligonha Pegmatites
Mozambique Mineral Record 31 459ndash497
Fleet ME (2003) Rock-Forming Minerals vol 3A Sheet silicates
micas The Geological Society London second edition chap 6
Lithium micas 651ndash690
Foord EE Cerny P Jackson LL Sherman DM Eby RK
(1995) Mineralogical and geochemical evolutions of micas
from miarolitic pegmatites of the anorogenic pikes-Peak
Batholith Colorado Mineral Petrol 55 1ndash26
Foster MD (1960) Interpretation of the composition of lithium
micas US Geol Surv Prof Paper 354-E 115ndash147
Fuhrman ML amp Lindsley DK (1988) Ternary-feldspar modeling
and thermometry Am Mineral 73 201ndash215
Gomes CL Castro P Alves C (1995) Caracterizacao das espi-
nelas zincıferas e do par ganite-nigerite no campo aplito-
pegmatıtico da Serra de Arga-Minho N de Portugal IV
Congresso Nacional de Geologia Resumos Alargados
Universidade do Porto Mem 4 629ndash633
Gordiyenko VV Ilyina AN Timochina LA Badamina EB
Stanek J (1996) Geochemical model of evolution of a pegma-
tite-forming ore-magmatic system of western Moravia Proc
Russ Mineral Soc 125 38ndash48 (in Russian)
Icenhower JP amp London D (1995) An experimental study for
element partitioning between biotite muscovite and coexisting
peraluminous granitic melt at 200 MPa (H2O) Am Mineral 80
1229ndash1251
Jahns RH (1982) Internal evolution of pegmatite bodies in lsquolsquoGranitic
Pegmatites in science and industryrsquorsquo P Cerny ed Mineralogical
Association of Canada Short Course Handbook 8 293ndash327
Jahns RH amp Burnham CW (1969) Experimental studies of
pegmatite genesis I A model for the derivation and crystal-
lization of granitic pegmatites Econ Geol 64 843ndash864
Jolliff BL Papike JJ Shearer CK (1987) Fractionation trends
in mica and tourmaline as indicators of pegmatite internal evo-
lution Bob Ingersoll pegmatite Black Hills South Dakota
USA GeochimCosmochim Acta 51 519ndash534
Kile DE amp Foord EE (1998) Micas from the Pikes Peak bath-
olith and its cogenetic granitic pegmatites Colorado optical
properties composition and correlation with pegmatite evolu-
tion Can Mineral 36 463ndash482
Linnen RL (1998) The solubility of Nb-Ta-Zr-Hf-W in granitic
melts with Li and Li thorn F constraints for mineralization in rare
metal granites and pegmatites Econ Geol 93 1013ndash1025
Linnen RL amp Cuney M (2005) Granite-related rare-element
deposits and experimental constraints on Ta-Nb-W-Sn-Zr-Hf
mineralization in lsquolsquoRare-element geochemistry and mineral
depositsrsquorsquo RL Linnen amp IM Samson eds Geochemical
Association of Canada Short Course Notes 17 45ndash68
London D (1990) Internal differentiation of rare-element pegmatites
a synthesis of recent research in lsquolsquoOre Bearing Granite Systems
Petrogenesis and Mineralizing Processesrsquorsquo HJ Stein amp JL
Hannah eds Geol Soc America Special Paper 246 35ndash50
mdash (2008) Pegmatites The Canadian Mineralogist Special
Publication 10 347 p
mdash (2009) The origin of primary textures in granitic pegmatites
Can Mineral 47 697ndash724
London D amp Morgan GB VI (2012) The pegmatite puzzle
Elements 8 263ndash268
London D Morgan GB VI Hervig RL (1989) Vapor-under-
saturated experiments in the system macusanite-H2O at 200
MPa and the internal differentiation of granitic pegmatites
Contrib Mineral Petrol 102 1ndash17
London D Morgan GB VI Paul KA Guttery BM (2012)
Internal evolution of miarolitic granitic pegmatites at the Little
Three mine Ramona California USA Can Mineral 50
1025ndash1054
Martins T Lima A Simmons WB Folster AU Noronha F
(2011) Geochemical fractionation of Nb-Ta oxides in Li-bear-
ing pegmatites from the Barroso-Alvao pegmatite field northern
Portugal Can Mineral 49 777ndash791
Monier G Charoy B Cuney M Ohnenstetter D Robert JL
(1987) Evolution spatiale et temporelle de la composition des
micas du granite albitique a topaze-lepidolite de Beauvoir
Geologie De La France 2ndash3 179ndash188
Monier G amp Robert JL (1986) Evolution of the miscibility gap
between muscovite and biotite solid solutions with increasing
lithium content an experimental study in the systems
K2OndashLi2OndashMgOndashAl2O3ndashSiO2ndashH2OndashHF at 600 C 2 kbar
PH2O comparison with natural lithium micas Mineral Mag
50 641ndash651
Morgan GBVI amp London D (1999) Crystallization of the little
three layered pegmatite-aplite dike Ramona District California
Contrib Mineral Petrol 136 310ndash330
984 A M R Neiva
eschweizerbart_xxx
Nabelek PI amp Russ-Nabelek C (1992) The generation and crys-
tallization conditions of the Proterozoic Harney Peak
Leucrogranite Black Hills South Dakota USA petrologic and
geochemical constraints Contrib Mineral Petrol 110
173ndash191
Nabelek PI Russ-Nabelek C Haeussler GT (1992) Stable
isotope evidence for the petrogenesis and fluid evolution in
the Proterozoic Harney Peak leucogranite Black Hills
South Dakota Geochim Cosmochim Acta 56 403ndash417
Neiva AMR amp Champness PE (1997) Nigerite and gahnite from
the granitic pegmatite veins of Cabanas Ponte de Lima northern
Portugal N Jb Mineral Mh 9 385ndash409
Neiva AMR Gomes MEP Ramos JMF Silva PB (2008)
Geochemistry of granitic aplite-pegmatite sills and their miner-
als from Arcozelo da Serra area (Gouveia central Portugal)
Eur J Mineral 20 465ndash485
Neiva AMR amp Neiva JMC (2005) Beryl from the granitic
pegmatite at Namivo Alto Ligonha Mozambique N Jb
Mineral Abh 181 173ndash182
Neiva AMR amp Ramos JMF (2010) Geochemistry of granitic
aplite-pegmatite sills and petrogenetic links with granites
Guarda-Belmonte area central Portugal Eur J Mineral 22
837ndash854
Neiva AMR Silva PB Ramos JMF (2012) Geochemistry of
granitic aplite-pegmatite veins and sills and their minerals from the
Sabugal area central Portugal N Jb Mineral Abh 189 49ndash74
Novak M amp Cerny P (1998) Niobium-tantalum oxide minerals
from complex granitic pegmatites in the Moldanubicum Czech
Republic primary versus secondary compositional trends Can
Mineral 36 659ndash672
Pesquera Perez A Torres-Ruiz J Gil PP Velilla N (1999)
Chemistry and genetic implications of tourmaline and Li-F-Cs
micas from the Valdeflores (Caceres Spain) Am Mineral 84
55ndash69
Rieder M Cavazzini G DrsquoYakonov YuS Frank-Kamenetskii
VA Gottardi G Guggenheim S Koval PV Muller G
Neiva AMR Radoslovich EW Robert J-L Sassi FP
Takeda H Weiss Z Wones DR (1999) Nomenclature of the
micas Mineral Mag 63 267ndash279
Roda Robles E Pesquera Perez A Velasco Roldan F Fontan F
(1999) The granitic pegmatites of the Fregeneda area
(Salamanca Spain) characteristics and petrogenesis Mineral
Mag 63 535ndash558
Roda Robles E Pesquera A Gil-Crespo PP Torres-Ruiz J
Fontan F (2005) Origin and internal evolution of the Li-F-
Be-P-bearing Pinilla de Fermoselle pegmatite (Central Iberian
Zone Zamora Spain) Am Mineral 90 1887ndash1899
Roda Robles E Pesquera Perez A Gil PP Torres-Ruiz J de
Parseval P (2006) Mineralogy and geochemistry of micas from
the Pinilla de Fermoselle pegmatite (Zamora Spain) Eur J
Mineral 18 369ndash377
Roda Robles E Keller P Pesquera Perez A Fontan F (2007)
Micas of the muscovite-lepidolite series from Karibib pegma-
tites Namibia Mineral Mag 71 41ndash62
Roda Robles E Pesquera A Gil-Crespo P Torres-Ruiz J
(2012) From granite to highly evolved pegmatite a case study
of the Pinilla de Fermoselle granite-pegmatite system (Zamora
Spain) Lithos 153 192ndash207
Selway JB Novak M Cerny P Hawthorne FC (1999)
Compositional evolution of tourmaline in lepidolite-subtype
pegmatites Eur J Mineral 11 569ndash584
Shearer CK Papike JJ Jolliff B (1992) Petrogenetic links
among granites and pegmatites in the Harney Peak rare-element
granite-pegmatite system Black Hills South Dakota Can
Mineral 30 785ndash809
Soares DR Hartmut B Ferreira ACM da Silva MRR
(2007) Chemical composition of gahnite and degree of peg-
matitic fractionation in the Borborema Pegmatitic Province
northeastern Brazil Anais Da Academ Bras Cien 79
395ndash404
Stewart DB (1978) Petrogenesis of lithium-rich pegmatites Am
Mineral 63 970ndash980
Tischendorff G Gattesmann B Forster H-J Trumbull RB
(1997) On Li-bearing micas estimating Li from electron
microprobe analyses and an improved diagram for graphical
representation Mineral Mag 61 809ndash834
Van Lichtervelde M Linnen RL Salvi S Beziat D (2006)
The role of metagabbro rafts on tantalum mineralization in the
Tanco granitic pegmatite Manitoba Can Mineral 44
625ndash644
Van Lichtervelde M Gregoire M Linnen RL Beziat D Salvi
S (2008) Trace element geochemistry by laser ablation ICP-
MS of micas associated with Ta mineralization in the Tanco
pegmatite Manitoba Canada Contrib Mineral Petrol 155
791ndash806
Vieira R Roda-Robles E Pesquera A Lima A (2011)
Chemical variation and significance of micas from the
Fregeneda-Almendra pegmatitic field (Central-Iberian Zone
Spain and Portugal) Am Mineral 96 637ndash645
Wen S amp Nekvasil H (1994) SOLVCALC an interactive gra-
phics program package for calculating ternary feldspar solvus
and two-feldspar geothermometry Comput Geosci 20
1025ndash1040
Wise MA (1995) Trace element chemistry of lithium-rich micas
from rare-element granitic pegmatites Mineral Petrol 55
203ndash215
Zasedatelev AM (1974) Possible accumulation of lithium in host
rocks of lithium pegmatite veins during old sedimentation pro-
cesses Doklady Acad Sci USSR Earth Sci Ser 218 196ndash198
(in Russian)
mdash (1977) Quantitative of metamorphic generation of rare-metal
pegmatites with lithium mineralization Doklady Acad Sci
USSR Earth Sci Ser 236 219ndash221 (in Russian)
Received 26 January 2013
Modified version received 21 May 2013
Accepted 23 July 2013
Silicate and oxide minerals from a zoned granitic pegmatite 985
eschweizerbart_xxx
lsquolsquomixed formrsquorsquo rim (Figs 3e 6e f) and the zoning patternscorrespond to fractionation trends and probably reflect adrop in temperature during the crystallization of the grani-tic pegmatite melt Progressively zoned crystals also occurin OIZ IIZb and Cc Some crystals are reversely zonedwith a) a lsquolsquomixed formrsquorsquo core and a lithian muscovite rimfrom the OIZ (Figs 3d d1 6d) b) a core consisting oflsquolsquomixed formrsquorsquo and lepidolite and a rim of muscovite andlithian muscovite from the IIZa (Figs 3f f1 6g h) c) alepidolite core and a muscovite and lithian muscovite rimfrom the Cc (Figs 3j 6o p) which may be explained bythe hypothesis of oscillations in the compositions of themelt from which they grew alternating between an Li-enriched boundary layer and a bulk melt that is less frac-tionated The muscovite evolved to lithian muscovite inIIZa and Cc (Figs 3f 6g h 3j 6o p) Replacements (Figs3a 6a b 3c 6c 3i 6m n Table 1) occur in OIZ and Ccand overgrowths (Figs 3b g 6i j k 3h 6l Table 1) occurin OIZ and IIZb as found in BSE images
Muscovite evolved to lithian muscovite as observed inOIZ IIZa IIZb and Cc (Figs 3f 6g h 3j 6o p Table 1)Lithian muscovite evolved to lsquolsquomixed formrsquorsquo in OIZ IIZaIIZb and Cc (Figs 3e 6e f Table 1) and lsquolsquomixed formrsquorsquoevolved to lepidolite in IIZa IIZb and Cc (Figs 3f f1 6gh 3h 6l Table 1) All these evolutions are due to fractionalcrystallization
In the OIZ lepidolite has more Si Licalcand F butsimilar KRb to that of zinnwaldite and replaces it (Figs
3a 6a b 7d Table 1) An FeMg-containing polylithionitehas higher Si Licalcand Rb contents and a smaller KRbratio than the lepidolite that it replaces (Figs 3c 6c Table1) and a continuous chemical evolution from lepidolite topolylithionite is shown
The trends for major and trace elements of micas withineach zone are difficult to define due to some partial over-lapping but a progressive evolution from muscovite to lithianmuscovite lsquolsquomixed formrsquorsquo and lepidolite in IIZa IIZb and Ccis mainly shown by an increase in the Si Licalc F Rb and Cscontents and a decrease in the KRb ratio and this is simi-larly shown in the OIZ from muscovite to lsquolsquomixed formrsquorsquo(Table 1 Fig 7) In the OIZ Si and Licalccontents increaseprogressively from zinnwaldite to lepidolite and FeMg-containing polylithionite but a gap occurs between zinnwal-dite and lepidolite (Table 1 Fig 4) whereas a continuousevolution from lepidolite to polylithionite is observed TheKRb ratios of zinnwaldite and polylithionite are within therange of that of lepidolite (Fig 7d e)
Each Al-richer mica (muscovite lithian muscovite andlsquolsquomixed formrsquorsquo) exhibits an evolution from the OIZ to theIIZa and then to the IIZb and Cc particularly shown by anincrease in the Si Licalc F and Rb contents and adecrease in the KRb ratio but also an increase in theCs content in the lsquolsquomixed formrsquorsquo (Table 1 Fig 7) Theseelements and ratio have been used as petrogenetic indi-cators of evolution in micas from pegmatites (eg Cernyet al 2005 Roda Robles et al 2006 2007 Vieira et al
Fig 7 Plot of some variation diagrams of micas from the OIZ IIZa IIZb and Cc of the Namivo granitic pegmatite Mozambique showingthat the Rb2O and Cs2O contents increase and the KRb ratio decreases for micas from the OIZ to the Cc OIZ IIZa IIZb and Cc as in Fig 2
Silicate and oxide minerals from a zoned granitic pegmatite 977
eschweizerbart_xxx
Tab
le2
R
epre
sen
tati
ve
elec
tro
nm
icro
pro
be
anal
yse
sin
wt
o
ffe
ldsp
ars
sch
orl
and
spo
du
men
efr
om
the
Nam
ivo
gra
nit
icp
egm
atit
eM
oza
mb
iqu
e
Alb
ite
K-f
eld
spar
Sch
orl
Sp
od
um
ene
Zo
nes
WZ
OIZ
IIZ
aII
Zb
Cc
Zo
nes
WZ
OIZ
IIZ
aII
Zb
Cc
Zo
nes
OIZ
Zo
ne
Cc
SiO
26
75
76
78
86
87
06
84
76
84
1S
iO2
65
10
65
55
65
46
64
96
64
72
SiO
23
52
0S
iO2
64
65
TiO
20
02
mdash0
02
mdashmdash
TiO
2mdash
00
1mdash
mdashmdash
TiO
20
35
Al 2
O3
27
20
Al 2
O3
20
25
19
74
19
67
19
88
19
97
Al 2
O3
18
96
18
23
18
31
18
24
18
05
B2O
3
10
28
Fe 2
O3
00
6F
e 2O
3mdash
mdashmdash
mdash0
10
Fe 2
O3
mdash0
02
mdash0
03
mdashA
l 2O
33
17
2M
nO
01
3M
nO
00
6mdash
mdashmdash
mdashM
nO
mdash0
03
00
3mdash
mdashF
eO1
35
2M
gO
01
8M
gO
mdashmdash
mdashmdash
mdashM
gO
00
10
01
00
5mdash
mdashM
nO
03
3N
a 2O
01
9C
aO1
04
08
00
56
03
70
32
CaO
00
10
01
00
60
01
00
2M
gO
22
8L
i 2O
8
05
Na 2
O1
06
11
12
01
12
11
13
41
13
4N
a 2O
06
50
58
04
10
59
03
8C
aO0
23
To
tal
10
04
6K
2O
00
50
17
00
60
14
01
0K
2O
14
72
14
75
15
67
15
01
15
74
Li 2
O
02
2S
rO0
72
05
00
24
01
1mdash
Rb
2O
00
90
20
03
00
59
09
0N
a 2O
22
8S
i1
99
7P
2O
50
01
00
4mdash
mdashmdash
Cs 2
O
00
6
00
60
09
01
80
20
K2O
00
1A
lIV0
00
3T
ota
l1
00
33
10
03
31
00
46
10
03
11
00
24
P2O
5mdash
00
3mdash
mdashmdash
H2O
3
18
P2
00
To
tal
99
60
99
48
10
03
89
96
11
00
01
F0
78
AlV
I0
98
7S
rC
a(w
t)0
81
07
40
50
03
50
Cl
mdashF
e3thorn
00
01
KR
b(w
t)153
68
48
23
16
Sum
1003
8P
09
9S
i1
18
23
11
87
91
19
58
11
93
21
19
21
KC
s(w
t)4
07
20
41
63
73
69
O
F0
33
Li
10
00
P0
00
10
00
6mdash
mdashmdash
To
tal
10
00
5M
n0
00
3T
i0
00
3mdash
00
03
mdashmdash
Si
11
98
61
20
88
12
04
11
20
45
12
03
3M
g0
00
8A
l4
17
64
07
14
03
54
08
34
10
1P
mdash0
00
5mdash
mdashmdash
TS
i5
95
2N
a0
01
2F
e3thorn
mdashmdash
mdashmdash
00
13
Ti
mdash0
00
1mdash
mdashmdash
Al
00
48
P1
02
Mn
00
09
mdashmdash
mdashmdash
Al
41
14
39
62
39
70
39
86
39
55
B3
00
0M
gmdash
mdashmdash
mdashmdash
Fe3thorn
mdash0
00
3mdash
00
04
mdashZ
Al
60
00
Ca
01
95
01
50
01
04
00
69
00
60
Mn
mdash0
00
50
00
5mdash
mdashY
Al
02
74
Sr
00
73
00
51
00
24
00
11
mdashM
g0
00
30
00
30
01
4mdash
mdashT
i0
04
5N
a3
59
93
80
03
78
33
83
23
83
1C
a0
00
20
00
20
01
20
00
20
00
4M
g0
57
5K
00
11
00
38
00
13
00
31
00
22
Na
02
32
02
07
01
46
02
12
01
37
Mn
00
47
K3
45
73
47
03
67
73
55
03
73
3F
e2thorn
19
12
Z1
60
01
59
61
60
01
60
11
60
4R
b0
01
10
02
40
03
50
07
00
10
8L
i0
14
8X
38
94
04
39
33
94
39
1C
s0
00
20
00
50
00
70
01
40
01
6P
Y3
00
0m
ole
s
XC
a0
04
2A
n5
13
82
71
71
5Z
16
10
16
06
16
01
16
03
15
99
Na
07
47
Ab
94
69
53
97
09
75
97
9X
37
13
72
39
03
85
40
0K
00
02
Or
03
09
03
08
06
mo
les
amp
02
09
An
01
01
03
01
01
Ab
63
56
38
56
35
OH
35
83
Or
93
69
43
95
99
43
96
4F
04
17
Cl
mdash
WZ
ndashw
allzo
ne
OIZ
ndasho
ute
rin
term
edia
tezo
ne
IIZ
aan
dII
Zb
ndashin
ner
inte
rmed
iate
zon
esC
cndash
core
asin
Fig
2B
aOis
bel
ow
the
det
ecti
on
lim
itin
bo
thfe
ldsp
ars
Cs 2
Ofrac14
00
3w
tin
the
K-
feld
spar
fro
mth
eW
Z
mdashN
ot
det
ecte
d
Nu
mb
ero
fio
ns
on
the
bas
iso
f3
2o
xy
gen
sfo
ral
bit
ean
dK
-fel
dsp
ar
31
anio
ns
(O
OH
F
)fo
rsc
ho
rlan
d6
ox
yg
ens
for
spo
du
men
e
-A
mo
un
tin
ferr
edfr
om
con
sid
erat
ion
so
fst
oic
hio
met
ry
978 A M R Neiva
eschweizerbart_xxx
2011) Lepidolite from the OIZ is an Al-poorer mica (Fig4) and has the highest Si Licalcand F contents (Table 1)indicating that an evolution cannot be shown from thislepidolite to lepidolites from the other zones which areAl-richer micas (Fig 4) However there is a regulardecrease in the KRb ratio and a progressive increase inthe Rb and Cs contents from lepidolite of the OIZ tolepidolite of IIZa IIZb and Cc (Fig 7) which indicatesthat the KRb ratio and Rb and Cs contents must not beconsidered alone to show fractional crystallization in
lepidolites particularly if some are Al-richer micas andothers Al-poorer micas The high Licalcand F contents oflepidolite from the OIZ did not decrease its KRb ratioSuch an effect is considered to have taken place in lepi-dolite (an Al-richer mica) from the wall zone of the Tancopegmatite Manitoba Canada (Van Lichtervelde et al2008) An evolution from the lepidolite of the IIZa to thatof the Cc is generally shown by the increasing Si LicalcF Rb Cs contents and a decrease in the KRb ratio (Table1 Fig 7)
At the scale of crystals the pegmatite zones and alsothose from the OIZ to the Cc of the Namivo granitic pegma-tite Al-richer micas show fractionation because theyformed from the fractionation of an Li-rich pegmatite melt
The Al-poorer micas zinnwaldite lepidolite and FeMg-containing polylithionite only occur in the OIZ (Fig 4)Polylithionite is the mica richest in Si and Licalc and lepi-dolite from this zone is the richest in Si Licalcand F (Fig 4Table 1) The high Li contents of these micas reflect aconsiderably higher D(Li) at low temperature (Icenhoweramp London 1995) These Li-rich micas may have crystal-lized from an undercooled melt This hypothesis does notimply high Rb and Cs contents and low KRb ratios Thisagrees with the fact that these micas from the OIZ havesimilar Rb and Cs contents and KRb ratios to those of Al-richer micas (muscovite lithian muscovite and lsquolsquomixedformrsquorsquo) from the same pegmatite zone (Fig 7) Howeverthe lepidolite from the wall zone of the Tanco pegmatiteCanada of a similar origin has a low KRb ratio which isattributed to the complexly interrelated structural compo-nents of this lepidolite (Van Lichtervelde et al 2008) TheLi-rich micas from the OIZ may also represent disequili-brium These two hypotheses are considered the best forthese micas of primary magmatic origin
Another hypothesis was also considered They may havecrystallized in boundary layers which concentrate Li andF But this mechanism was suggested for the most fractio-nated tourmaline enriched in Li and F from the core of the
Fig 8 Plot of albite compositions from all zones of the Namivo granitic pegmatite Mozambique showing that the anorthite content of albitedecreases from the WZ to the Cc WZ OIZ IIZa IIZb and Cc as in Fig 2
Fig 9 The Rb vs Cs diagram of K-feldspar from all zones of theNamivo granitic pegmatite Mozambique showing that the Rb andCs contents of K-feldspar increase from the WZ to the Cc WZ OIZIIZa IIZb and Cc as in Fig 2
Silicate and oxide minerals from a zoned granitic pegmatite 979
eschweizerbart_xxx
Little Three pegmatite dike USA (Morgan amp London1999) and the micas enriched in Li and F from theNamivo pegmatite belonging to the OIZ Furthermore ina boundary layer melt that became enriched in Li and F theKRb ratio of micas decreases strongly (Van Lichterveldeet al 2008) which was not found in these micas from theOIZ (Fig 7d) Nor can they have resulted from the crystal-lization of a late melt that would have reacted with the OIZbecause these micas are among those containing the high-est KRb values (Fig 7d)
92 The importance of feldspars micas andcolumbitendashtantalite compositions to the Namivogranitic pegmatite evolution
The trace elements Rb and Cs and the KRb and KCs ratioshave been used to show the evolution of K-feldspar inpegmatites (eg Cerny 1994 Cerny et al 2005 RodaRobles et al 2005) The Rb and Cs contents increase andthe KRb and KCs ratios of K-feldspar decrease from theWZ to the Cc (Fig 9 Table 2) reflecting the growth of K-feldspar from an increasingly fractionated melt withouthaving grown from or having been chemically modifiedby an aqueous fluid as in the Swamp pegmatite section atthe Little Three Mine USA (London et al 2012) Thecrystallization of K-feldspar from an exsolved aqueousfluid from melt will reverse the magmatic fractionation ofRb Cs KRb and KCs because Rb and especially Cs areso much more compatible in vapor that both Rb and Csremain in the fluid phase (London et al 2012) The feldsparsolvus pairs in the Namivo pegmatite record magmaticcrystallization temperatures that decrease from WZ to CcAlbite shows a decrease in the Ca Sr contents and SrCaratio from the WZ to the Cc (Fig 8 Table 2) Therefore thefeldspars and also Al-richer micas as already explainedshow fractionation in this zoned pegmatite
In general lepidolite from the Namivo pegmatite hassimilar Rb2O and Cs2O contents and KRb (wt) values tothose of lepidolite from the Rozna and Dobra Voda lepi-dolite-subtype pegmatites in the Czech Republic (Cernyet al 1995) but lower Rb2O and Cs2O contents thanlepidolite from the lepidolite-subtype pegmatite at RedCross Lake Manitoba Canada (Cerny et al 2012a) K-feldspar from the Namivo pegmatite also has lower Rb2O
Table 3 Representative electron microprobe analyses in wt of columbitendashtantalite from the Namivo granitic pegmatite Mozambique
Outer Intermediate Zone - OIZ Inner Intermediate Zone - IIZa
Core - Cc
D L L
WO3 022 059 079 113 101 351 050 007Ta2O5 5487 5123 2503 3186 2888 2519 3127 4542Nb2O5 2537 3000 5483 4635 5113 5144 4911 3686SnO2 008 015 024 049 020 026 017 012TiO2 263 161 136 254 202 145 125 016FeO 860 710 665 471 236 068 mdash mdashMnO 793 952 1099 1304 1400 1725 1748 1718Total 9970 10020 9989 10012 9960 9978 9978 9981W 0004 0011 0013 0019 0016 0057 0008 0001Ta 1065 0975 0422 0552 0495 0430 0543 0847Nb 0819 0949 1538 1336 1456 1460 1418 1143Sn 0002 0004 0006 0012 0005 0007 0004 0003Ti 0141 0085 0063 0122 0096 0068 0060 0008Fe 0513 0416 0345 0251 0124 0036 mdash mdashMn 0479 0564 0578 0704 0747 0917 0945 0998P
3023 3004 2965 2996 2939 2975 2978 3000Mn(Mn thorn Fe) 048 058 063 074 086 096 100 100Ta(Ta thorn Nb) 057 051 022 029 025 023 028 043Classification tant-(Fe) tant-(Mn) col-(Mn) col-(Mn) col-(Mn) col-(Mn) col-(Mn) col-(Mn)
D ndash darker L ndash lighter zones mdash Not detected tant-tantalite col-columbite Cation formula on the basis of 6 atoms of oxygen
Fig 10 Compositions of columbitendashtantalite from the Namivogranitic pegmatite Mozambique in the columbite quadrilateralshowing that Mn(Mn thorn Fe) of columbite-(Mn) increases from theOIZ to the Cc and the richest columbite-(Mn) in Ta(Ta thorn Nb)tantalite-(Fe) and tantalite-(Mn) only occur in the OIZ OIZ IIZaand Cc as in Fig 2
980 A M R Neiva
eschweizerbart_xxx
and Cs2O contents than K-feldspar from the lepidolite-subtype pegmatite at Red Cross Lake The Rb2O andCs2O contents of primary and late K-feldspar of this peg-matite at Red Cross Lake attained unprecedented levels(Cerny et al 2012a) The lowest KRb (wt) values ofmuscovite lithian muscovite lsquolsquomixed formrsquorsquo and lepido-lite from the IIZb and Cc (Fig 7) and K-feldspar (KRb frac1414) from the Cc compare well with those found in theseminerals from the AC6frac143 lepidolite-subtype pegmatitefrom Greer Lake (Cerny et al 2005) and some of themost fractionated pegmatites worldwide which belong tothe petalite-subtype (eg Tanco Manitoba Cerny 2005Cerny et al 1998 Varutrask Sweden Cerny et al 2005)but muscovite lithian muscovite and lepidolite from theIIZb and Cc have lower Rb2O and Cs2O contents than thesemicas from the Tanco pegmatite (Cerny 2005a VanLichtervelde et al 2008) K-feldspar also has lower
contents of these oxides than the most evolved K-feldsparfrom the Tanco pegmatite (Cerny 2005a) The magmaticfractionation was strong from the WZ to IIZb and Cc of theNamivo lepidolite-subtype pegmatite
The compositional trend of columbite-(Mn) from the OIZto Cc of the Namivo granitic lepidolite-subtype pegmatite(Fig 10) is identical to that of columbite-group mineralsfrom the lepidolite-subtype complex granitic pegmatitesfrom the Dobra Voda in the Moldanubicum CzechRepublic (Novak amp Cerny 1998) and the HimalayaDistrict southern California (shown in Cerny et al 2004)Experimental data for the Fe-Mn pair (Linnen amp Cuney2005) suggest an increase in Fe with fractional crystalliza-tion which is not observed in nature Other phases seem tocontrol the bahavior of Fe and Mn in the melt eg thecrystallization of tourmaline causes a rapid increase of theMnFe in the melt (Van Lichtervelde et al 2006) When thecrystallization of tourmaline stopped the columbitendashtantaliteminerals showed a constant MnFe indicating that the Fe andMn contents in the melt remained constant Schorl onlyoccurs in the OIZ of the Namivo granitic pegmatite and itscrystallization cannot be responsible for the increase in theMnFe of the melt because Mn(Mn thorn Fe) of columbite-(Mn) increases progressively from the OIZ to the IIZa and Cc(Fig 10) Garnet zinnwaldite and gahnite containing Fe andMn also only occur in the OIZ and cannot also have causedthe increase of the MnFe in the melt The dominant Mnenrichment before Ta enrichment started in the columbitendash-tantalite composition from some granitic pegmatites isattributed to an increased alkali-fluoride activity at moderatemHF (Cerny et al 2004) and an increase in the activity offluorine (Martins et al 2011) Each Al-richer mica (musco-vite lithian muscovite and lsquolsquomixed formrsquorsquo) from the Namivogranitic pegmatite shows an increase in F content from theOIZ to the IIZa IIZb and Cc (Table 1) In general the Fcontent of lepidolite also increases from the IIZa to the IIZband Cc Therefore the extreme Fe-Mn fractionation beforeTa enrichment in columbite-(Mn) (Fig 10) may be due to anincrease in the activity of fluorine as a consequence offractional crystallization The increase in the Ta content ofcolumbite-(Mn) from the Namivo granitic pegmatite isattributed to fractional crystallization
The geochemical evolution of albite and K-feldsparfrom the WZ to the Cc Al-richer micas muscovite lithianmuscovite and lsquolsquomixed formrsquorsquo from the OIZ to the Cc andlepidolite from the IIZa to the Cc and columbite-(Mn) andalso beryl (Neiva amp Neiva 2005) from the OIZ to the Ccare caused by magma fractionation The pegmatite zonesare the product of primary crystallization from a volatile-rich silicate melt The pegmatite consolidated from the WZto the Cc The IIZb is one of the most evolved zones asalso suggested by the beryl composition (Neiva amp Neiva2005) and is the richest in lsquolsquomixed formrsquorsquo and lepidolite
The richest columbite-(Mn) in Ta(Ta thorn Nb) and com-positions of tantalite-(Fe) and tantalite-(Mn) only occur inthe OIZ (Fig 10a) associated with lepidolite and polythio-nite (Fig 3c) which may be due to the local depletion of Liand F in the melt which decreases the solubility of Ta andcauses Ta precipitation (Linnen 1998 Linnen amp Cuney
Fig 11 a Backscattered-electron image of a gahnite crystal with adarker zone partially surrounding a lighter zone from the OIZ of theNamivo granitic pegmatite b c Plot of gahnite compositions in theSn-Zn-Ti diagram (atomic proportions) showing a chemical distinc-tion between the lighter and darker zones OIZ as in Fig 2
Silicate and oxide minerals from a zoned granitic pegmatite 981
eschweizerbart_xxx
2005) At the Tanco pegmatite Ta oxides are also asso-ciated with lepidolite enriched in Li and F from the wallzone (Van Lichtervelde et al 2008)
93 Origin and evolution of the zoned graniticlepidolite-subtype pegmatite at Namivo
In general granitic pegmatites particularly those belong-ing to the rare-element class are accepted as having beenformed by the fractional crystallization of a granite melt(eg Cerny 1991a b 1992 Neiva et al 2008 2012 Roda-Robles et al 2012) But it also has been proposed thatpegmatites may be formed by partial melting of appropri-ate rock compositions (eg Nabelek et al 1992 Nabelekamp Russ-Nabelek 1992 Shearer et al 1992 Roda Robleset al 1999) The lepidolite-subtype pegmatites belong tothe LCT (lithium-cesium-tantalum) family (Cerny amp Ercit2005) They are derived by fractional crystallization of agranite magma (eg Cerny et al 2005 Neiva amp Ramos2010 Cerny et al 2012b) Experimental work by Londonet al (1989) and London (1990) using Macusani glass as astarting material equivalent to the bulk composition ofhighly fractionated rare-alkali-rich pegmatites underhighly evolved and hydrous but H2O undersaturatedmelt obtained the latest primary assemblage consisting
of an Li-rich mica thorn albite thorn quartz deposited directlyfrom the primary melt phase Other authors egZasedatelev (1974 1977) and Stewart (1978) argue thatlepidolite-bearing pegmatites are derived from direct ana-texis and Gordiyenko et al (1996) consider that they arederived from an undefined medium and the rare-elementmineralization is superimposed on preexisting barrenpegmatites
Lepidolite-subtype pegmatites may migrate a long wayfrom their parent granites because their volatile-rich highlyfluid pegmatite melts are stable at relatively low tempera-tures (eg Cerny et al 2005 Antunes et al 2013)Therefore the Namivo pegmatite is probably derived byfractional crystallization of an S-type granite magmawhich resulted from partial melting of metamorphosed juve-nile sediments containing micas that carry most of the traceelements that define the signature of the LCT pegmatites(eg Dahl et al 1993)
The two main models for the internal evolution of peg-matites that dominated for more than a century are a) thefractional crystallization of a flux-bearing granitic melt fromthe margins to the center of the pegmatite (Cameron et al1949) b) the interactions of an aqueous fluid with graniticmelt (Jahns amp Burnham 1969 Jahns 1982) The recentmodel of constitutional zone refining combines aspects ofboth models and invokes the formation of a flux-enriched
Table 4 Electron microprobe analyses in wt of zoned gahnite from the outer intermediate zone (OIZ) of the Namivo granitic pegmatiteMozambique
Darker Zone Lighter Zone
Mean s Range Mean s Range
SnO2 036 050 0ndash097 658 281 151ndash998TiO2 008 008 0ndash021 065 034 008ndash105Nb2O5 001 002 0ndash006 018 007 007ndash029Ta2O5 001 004 0ndash010 015 013 0ndash033ZnO 3998 123 3810ndash4109 3339 318 3004ndash3848FeO 367 048 331ndash442 433 065 306ndash498MnO 032 004 028ndash040 039 006 032ndash048MgO 003 004 0ndash010 ndash ndash ndashAl2O3 5507 050 5436ndash5572 5337 070 5257ndash5443SiO2 003 003 0ndash007 008 010 0ndash025Total 9956 9912n 8 8Sn 0035 0048 0ndash0095 0648 0278 0149ndash0983Ti 0015 0015 0ndash0038 0120 0064 0015ndash0195Nb ndash 0003 0ndash0006 0021 0009 0009ndash0037Ta ndash 0002 0ndash0006 0009 0009 0ndash0021Zn 7226 0182 6890ndash7382 6086 0568 5482ndash6965Fe2thornt 0752 0103 0675ndash0913 0894 0135 0628ndash1029Mn 0066 0008 0057ndash0083 0082 0013 0066ndash0101Mg 0010 0015 0ndash0037 ndash ndash ndashAl 15887 0052 15805ndash15954 15526 0170 15375ndash15853Si 0007 0008 0ndash0018 0019 0025 0ndash0062P
23998 23405Fe3thorn 0064 0230Fe2thorn 0686 0658SnZn 0005 0007 0ndash0014 0106 0052 0021ndash0179ZnFe2thornt 961 143 768ndash1093 681 190 536ndash1109
n number of analysis Cation formula based on 32 atoms of oxygen Fe2thornt total Fe2thorn estimated
982 A M R Neiva
eschweizerbart_xxx
boundary layer of silicate liquid in advance of a crystal-lization front (London 2008 London amp Morgan 2012)
Lepidolite-subtype pegmatites are generally scarce(Cerny et al 2005) particularly the zoned ones In thesymmetrically zoned lepidolite-subtype pegmatites ofRozna and Dobra Voda Czech Republic micas (Cernyet al 1995) tourmaline (Selway et al 1999) and colum-bite-group minerals (Novak amp Cerny 1998) evolve fromthe outermost zone to the innermost zone following thecrystallization sequence The same was found in tourma-line from the zoned Lastovicky Dolnı Bory and Raddovicelepidolite-subtype pegmatite dikes in the Czeck Republic(Selway et al 1999)
In general beryl (Neiva amp Neiva 2005) feldsparsmicas and columbite-(Mn) (in this paper) from theNamivo lepidolite-subtype pegmatite record the progres-sive chemical evolution of the pegmatite from the wallzone to the core These minerals were produced by crystal-lization from a silicate melt rather than an aqueous fluidphase The slow cooling of melt shown by the magmaticcrystallization temperatures of feldspars cannot explain theincrease in grain-size of minerals from the wall zone to thecore but fluxes will be necessary to promote the change oftexture particularly a flux-rich hydrosilicate liquidaccording to the experimental evidence (London 2009)The constitutional zone refining model will be the best forthis zoned pegmatite and probably for all lepidolite-sub-type pegmatites because this model also produces a higherfinal concentration of incompatible components in a smal-ler volume of rock than fractional crystallization does(Morgan amp London 1999)
The core margin at the Rozna pegmatite contains K-feld-spar and quartz and the core consists mainly of quartz but it issurrounded and penetrated by a quartz-bearing albitethorn lepi-dolite complex which contains several minerals At theDobra Voda pegmatite the center of the dike is occupiedby the lepidolite unit containing albite and other minerals(Cerny et al 1995) At the Namivo pegmatite the coremargin consists of quartz and beryl and the core containsmainly quartz and spodumene but also albite lepidolite andother minerals The last-unit assemblages of primary miner-als in most of the highly fractionated LCT pegmatites are richin albite and commonly contain lepidolite or spodumene andmost of the other rare phases These units represent the lastmost fractionated liquid that can be derived by fractionalcrystallization of a crustal melt (London 2008)
The Namivo granitic pegmatite shows a significant dis-tinction from the other zoned lepidolite-subtype pegmatitesand LCT pegmatites except the Tanco petalite-subtypepegmatite in Canada because the lepidolite richest in SiLi and F FeMg-containing polylithionite and associatedcolumbite-(Mn) with the highest Ta(Ta thorn Nb) ratio tanta-lite-(Fe) and tantalite-(Mn) only occur in the outer inter-mediate zone These minerals usually form late in theconsolidation of pegmatites The lepidolite and polylithio-nite are probably derived from the disequilibrium crystal-lization of an undercooled melt Tantalite may reflect a localdecrease in Li and F that caused Ta precipitation
This paper contributes to a better understanding of theorigin and evolution of the rare zoned lepidolite-subtypepegmatites and shows that although the pegmatite evolvedfrom the wall zone to the core it presents an unusualassociation of lepidolite polylithionite and tantalite in theouter intermediate zone
Acknowledgments Thanks are due to JM Cotelo Neivaand MB Dias for the samples and information providedand to MR Machado Leite and MF Guimaraes for theuse of the electron microprobe facilities at the LaboratorioNacional de Energia e Geologia (LNEG) PortugalFinancial support was provided by the PortugueseGovernment for the project Pest-OECTEUI00732011of the Geosciences Centre through the PortugueseFoundation for Science and Technology I would like tothank D London WB Simmons and the associated editorE Widom for their constructive reviews of this manuscriptand M Prieto for his editorial work
References
Alfonso P Melgarejo JC Yusta I Velasco F (2003)
Geochemistry of feldspars and muscovite in granitic pegmatite
from the Cap de Creus field Catalonia Spain Can Mineral 41
103ndash116
Antunes IMHR Neiva AMR Ramos JMF Silva PB
Silva MMVG Corfu F (2013) Petrogenetic links between
lepidolite-subtype aplite-pegmatite aplite veins and associated
granites at Segura (central Portugal) Chemie der Erde in press
httpdxdoiorg101016jchemer20121203
Batchelor RA amp Kinnaird JA (1984) Gahnite compositions
compared Mineral Mag 48 425ndash430
Beurlen H Da Silva MRR Thomas R Soares DR Olivier P
(2008) Nb-Ta-(Ti-Sn) oxide mineral chemistry as tracer of rare-
element granitic pegmatite fractionation in the Borborema pro-
vince Northeastern Brazil Miner Deposita 43 207ndash228
Cameron EN Jahns RH McNair AH Page LR (1949)
Internal structure of granitic pegmatites Econ Geol
Monograph 2 115 p
Cerny P (1991a) Fertile granites of Precambrian rare-element
pegmatite fields is geochemistry controlled by tectonic setting
or source lithologies Precambrian Res 51 429ndash468
mdash (1991b) Rare-element granite pegmatites I Anatomy and inter-
nal evolution of pegmatite deposits Geoscience Canada 18
49ndash67
mdash (1992) Geochemical and petrogenetic features of mineralization
in rare-element granitic pegmatites in the light of current
research Applied Geochemistry 7 393ndash416
mdash (1994) Evolution of feldspars in granitic pegmatites in
lsquolsquoFeldspars and their Reactionsrsquorsquo I Parsons ed NATO
Advanced Study Institute Series C421 501ndash539
mdash (2005) The Tanco rare-element pegmatite deposit Manitoba
regional context internal anatomy and global comparisons in
lsquolsquoRare-element Geochemistry and Mineral Depositsrsquorsquo RL
Linnen amp IM Samson eds Geochemical Association of
Canada Short Course Notes St Catherines 17 127ndash158
Silicate and oxide minerals from a zoned granitic pegmatite 983
eschweizerbart_xxx
Cerny P amp Ercit TS (2005) The classification of granitic pegma-
tites revisited Can Mineral 43 2005ndash2026
Cerny P Meintzer RE Andersen AJ (1985) Extreme fractiona-
tion in rare-element granitic pegmatites selected examples of
data and mechanisms Can Mineral 23 381ndash421
Cerny P Goad BE Hawthorne FC Chapmann R (1986)
Fractionation trends of the Nb- and Ta-bearing oxide minerals
in the Greer Lake pegmatite granite and its pegmatite aureole
southeastern Manitoba Am Mineral 71 501ndash517
Cerny P Stanek J Novak M Baadsgaard H Rieder M
Ottolini L Kavalova M Chapman R (1995) Geochemical
and structural evolution of micas in the Rozna amp Dobra Voda
pegmatites Czech Republic Mineral Petrol 55 177ndash201
Cerny P Ercit TS Vanstone PJ (1998) Mineralogy and petrol-
ogy of the Tanco rare-element pegmatite deposit southeastern
Manitoba International Mineralogical Association 17th General
Meeting Toronto Field Guidebook B6
Cerny P Chapman R Ferreira K Smeds SA (2004)
Geochemistry of oxide minerals of Nb Ta Sn and Sb in
the Varutrask granitic pegmatite Sweden The case of an
lsquolsquoanomalousrsquorsquo columbitendashtantalite trend Am Mineral 89
505ndash518
Cerny P Masau M Goad BE Ferreira K (2005) The Greer
Lake leucogranite Manitoba and the origin of lepidolite-sub-
type granitic pegmatites Lithos 80 305ndash321
Cerny P Teertstra DK Chapman R Selway JB Hawthorne
FC Ferreira K Chackowsky LE Wang X-J Meintzer
RE (2012a) Extreme fractionation and deformation of the
leucogranite-pegmatite suite at Red Cross Lake Manitoba
Canada IV Mineralogy Can Mineral 50 1839ndash1875
Cerny P Halden NM Ferreira K Meintzer RE Brisbin WC
Chackowsky LE (2012b) Extreme fractionation and deforma-
tion of the leucogranite-pegmatite suite at Red Cross Lake
Manitoba Canada II Petrology of the leucogranites and peg-
matites Can Mineral 50 1807ndash1822
Dahl PS When DC Feldmann SG (1993) The systematics of
trace-element partitioning between coexisting muscovite and
biotite in metamorphic rocks from the Black Hills South
Dakota USA Geochim Cosmochim Acta 57 2487ndash2505
Dias MB amp Wilson WE (2000) The Alto Ligonha Pegmatites
Mozambique Mineral Record 31 459ndash497
Fleet ME (2003) Rock-Forming Minerals vol 3A Sheet silicates
micas The Geological Society London second edition chap 6
Lithium micas 651ndash690
Foord EE Cerny P Jackson LL Sherman DM Eby RK
(1995) Mineralogical and geochemical evolutions of micas
from miarolitic pegmatites of the anorogenic pikes-Peak
Batholith Colorado Mineral Petrol 55 1ndash26
Foster MD (1960) Interpretation of the composition of lithium
micas US Geol Surv Prof Paper 354-E 115ndash147
Fuhrman ML amp Lindsley DK (1988) Ternary-feldspar modeling
and thermometry Am Mineral 73 201ndash215
Gomes CL Castro P Alves C (1995) Caracterizacao das espi-
nelas zincıferas e do par ganite-nigerite no campo aplito-
pegmatıtico da Serra de Arga-Minho N de Portugal IV
Congresso Nacional de Geologia Resumos Alargados
Universidade do Porto Mem 4 629ndash633
Gordiyenko VV Ilyina AN Timochina LA Badamina EB
Stanek J (1996) Geochemical model of evolution of a pegma-
tite-forming ore-magmatic system of western Moravia Proc
Russ Mineral Soc 125 38ndash48 (in Russian)
Icenhower JP amp London D (1995) An experimental study for
element partitioning between biotite muscovite and coexisting
peraluminous granitic melt at 200 MPa (H2O) Am Mineral 80
1229ndash1251
Jahns RH (1982) Internal evolution of pegmatite bodies in lsquolsquoGranitic
Pegmatites in science and industryrsquorsquo P Cerny ed Mineralogical
Association of Canada Short Course Handbook 8 293ndash327
Jahns RH amp Burnham CW (1969) Experimental studies of
pegmatite genesis I A model for the derivation and crystal-
lization of granitic pegmatites Econ Geol 64 843ndash864
Jolliff BL Papike JJ Shearer CK (1987) Fractionation trends
in mica and tourmaline as indicators of pegmatite internal evo-
lution Bob Ingersoll pegmatite Black Hills South Dakota
USA GeochimCosmochim Acta 51 519ndash534
Kile DE amp Foord EE (1998) Micas from the Pikes Peak bath-
olith and its cogenetic granitic pegmatites Colorado optical
properties composition and correlation with pegmatite evolu-
tion Can Mineral 36 463ndash482
Linnen RL (1998) The solubility of Nb-Ta-Zr-Hf-W in granitic
melts with Li and Li thorn F constraints for mineralization in rare
metal granites and pegmatites Econ Geol 93 1013ndash1025
Linnen RL amp Cuney M (2005) Granite-related rare-element
deposits and experimental constraints on Ta-Nb-W-Sn-Zr-Hf
mineralization in lsquolsquoRare-element geochemistry and mineral
depositsrsquorsquo RL Linnen amp IM Samson eds Geochemical
Association of Canada Short Course Notes 17 45ndash68
London D (1990) Internal differentiation of rare-element pegmatites
a synthesis of recent research in lsquolsquoOre Bearing Granite Systems
Petrogenesis and Mineralizing Processesrsquorsquo HJ Stein amp JL
Hannah eds Geol Soc America Special Paper 246 35ndash50
mdash (2008) Pegmatites The Canadian Mineralogist Special
Publication 10 347 p
mdash (2009) The origin of primary textures in granitic pegmatites
Can Mineral 47 697ndash724
London D amp Morgan GB VI (2012) The pegmatite puzzle
Elements 8 263ndash268
London D Morgan GB VI Hervig RL (1989) Vapor-under-
saturated experiments in the system macusanite-H2O at 200
MPa and the internal differentiation of granitic pegmatites
Contrib Mineral Petrol 102 1ndash17
London D Morgan GB VI Paul KA Guttery BM (2012)
Internal evolution of miarolitic granitic pegmatites at the Little
Three mine Ramona California USA Can Mineral 50
1025ndash1054
Martins T Lima A Simmons WB Folster AU Noronha F
(2011) Geochemical fractionation of Nb-Ta oxides in Li-bear-
ing pegmatites from the Barroso-Alvao pegmatite field northern
Portugal Can Mineral 49 777ndash791
Monier G Charoy B Cuney M Ohnenstetter D Robert JL
(1987) Evolution spatiale et temporelle de la composition des
micas du granite albitique a topaze-lepidolite de Beauvoir
Geologie De La France 2ndash3 179ndash188
Monier G amp Robert JL (1986) Evolution of the miscibility gap
between muscovite and biotite solid solutions with increasing
lithium content an experimental study in the systems
K2OndashLi2OndashMgOndashAl2O3ndashSiO2ndashH2OndashHF at 600 C 2 kbar
PH2O comparison with natural lithium micas Mineral Mag
50 641ndash651
Morgan GBVI amp London D (1999) Crystallization of the little
three layered pegmatite-aplite dike Ramona District California
Contrib Mineral Petrol 136 310ndash330
984 A M R Neiva
eschweizerbart_xxx
Nabelek PI amp Russ-Nabelek C (1992) The generation and crys-
tallization conditions of the Proterozoic Harney Peak
Leucrogranite Black Hills South Dakota USA petrologic and
geochemical constraints Contrib Mineral Petrol 110
173ndash191
Nabelek PI Russ-Nabelek C Haeussler GT (1992) Stable
isotope evidence for the petrogenesis and fluid evolution in
the Proterozoic Harney Peak leucogranite Black Hills
South Dakota Geochim Cosmochim Acta 56 403ndash417
Neiva AMR amp Champness PE (1997) Nigerite and gahnite from
the granitic pegmatite veins of Cabanas Ponte de Lima northern
Portugal N Jb Mineral Mh 9 385ndash409
Neiva AMR Gomes MEP Ramos JMF Silva PB (2008)
Geochemistry of granitic aplite-pegmatite sills and their miner-
als from Arcozelo da Serra area (Gouveia central Portugal)
Eur J Mineral 20 465ndash485
Neiva AMR amp Neiva JMC (2005) Beryl from the granitic
pegmatite at Namivo Alto Ligonha Mozambique N Jb
Mineral Abh 181 173ndash182
Neiva AMR amp Ramos JMF (2010) Geochemistry of granitic
aplite-pegmatite sills and petrogenetic links with granites
Guarda-Belmonte area central Portugal Eur J Mineral 22
837ndash854
Neiva AMR Silva PB Ramos JMF (2012) Geochemistry of
granitic aplite-pegmatite veins and sills and their minerals from the
Sabugal area central Portugal N Jb Mineral Abh 189 49ndash74
Novak M amp Cerny P (1998) Niobium-tantalum oxide minerals
from complex granitic pegmatites in the Moldanubicum Czech
Republic primary versus secondary compositional trends Can
Mineral 36 659ndash672
Pesquera Perez A Torres-Ruiz J Gil PP Velilla N (1999)
Chemistry and genetic implications of tourmaline and Li-F-Cs
micas from the Valdeflores (Caceres Spain) Am Mineral 84
55ndash69
Rieder M Cavazzini G DrsquoYakonov YuS Frank-Kamenetskii
VA Gottardi G Guggenheim S Koval PV Muller G
Neiva AMR Radoslovich EW Robert J-L Sassi FP
Takeda H Weiss Z Wones DR (1999) Nomenclature of the
micas Mineral Mag 63 267ndash279
Roda Robles E Pesquera Perez A Velasco Roldan F Fontan F
(1999) The granitic pegmatites of the Fregeneda area
(Salamanca Spain) characteristics and petrogenesis Mineral
Mag 63 535ndash558
Roda Robles E Pesquera A Gil-Crespo PP Torres-Ruiz J
Fontan F (2005) Origin and internal evolution of the Li-F-
Be-P-bearing Pinilla de Fermoselle pegmatite (Central Iberian
Zone Zamora Spain) Am Mineral 90 1887ndash1899
Roda Robles E Pesquera Perez A Gil PP Torres-Ruiz J de
Parseval P (2006) Mineralogy and geochemistry of micas from
the Pinilla de Fermoselle pegmatite (Zamora Spain) Eur J
Mineral 18 369ndash377
Roda Robles E Keller P Pesquera Perez A Fontan F (2007)
Micas of the muscovite-lepidolite series from Karibib pegma-
tites Namibia Mineral Mag 71 41ndash62
Roda Robles E Pesquera A Gil-Crespo P Torres-Ruiz J
(2012) From granite to highly evolved pegmatite a case study
of the Pinilla de Fermoselle granite-pegmatite system (Zamora
Spain) Lithos 153 192ndash207
Selway JB Novak M Cerny P Hawthorne FC (1999)
Compositional evolution of tourmaline in lepidolite-subtype
pegmatites Eur J Mineral 11 569ndash584
Shearer CK Papike JJ Jolliff B (1992) Petrogenetic links
among granites and pegmatites in the Harney Peak rare-element
granite-pegmatite system Black Hills South Dakota Can
Mineral 30 785ndash809
Soares DR Hartmut B Ferreira ACM da Silva MRR
(2007) Chemical composition of gahnite and degree of peg-
matitic fractionation in the Borborema Pegmatitic Province
northeastern Brazil Anais Da Academ Bras Cien 79
395ndash404
Stewart DB (1978) Petrogenesis of lithium-rich pegmatites Am
Mineral 63 970ndash980
Tischendorff G Gattesmann B Forster H-J Trumbull RB
(1997) On Li-bearing micas estimating Li from electron
microprobe analyses and an improved diagram for graphical
representation Mineral Mag 61 809ndash834
Van Lichtervelde M Linnen RL Salvi S Beziat D (2006)
The role of metagabbro rafts on tantalum mineralization in the
Tanco granitic pegmatite Manitoba Can Mineral 44
625ndash644
Van Lichtervelde M Gregoire M Linnen RL Beziat D Salvi
S (2008) Trace element geochemistry by laser ablation ICP-
MS of micas associated with Ta mineralization in the Tanco
pegmatite Manitoba Canada Contrib Mineral Petrol 155
791ndash806
Vieira R Roda-Robles E Pesquera A Lima A (2011)
Chemical variation and significance of micas from the
Fregeneda-Almendra pegmatitic field (Central-Iberian Zone
Spain and Portugal) Am Mineral 96 637ndash645
Wen S amp Nekvasil H (1994) SOLVCALC an interactive gra-
phics program package for calculating ternary feldspar solvus
and two-feldspar geothermometry Comput Geosci 20
1025ndash1040
Wise MA (1995) Trace element chemistry of lithium-rich micas
from rare-element granitic pegmatites Mineral Petrol 55
203ndash215
Zasedatelev AM (1974) Possible accumulation of lithium in host
rocks of lithium pegmatite veins during old sedimentation pro-
cesses Doklady Acad Sci USSR Earth Sci Ser 218 196ndash198
(in Russian)
mdash (1977) Quantitative of metamorphic generation of rare-metal
pegmatites with lithium mineralization Doklady Acad Sci
USSR Earth Sci Ser 236 219ndash221 (in Russian)
Received 26 January 2013
Modified version received 21 May 2013
Accepted 23 July 2013
Silicate and oxide minerals from a zoned granitic pegmatite 985
eschweizerbart_xxx
Tab
le2
R
epre
sen
tati
ve
elec
tro
nm
icro
pro
be
anal
yse
sin
wt
o
ffe
ldsp
ars
sch
orl
and
spo
du
men
efr
om
the
Nam
ivo
gra
nit
icp
egm
atit
eM
oza
mb
iqu
e
Alb
ite
K-f
eld
spar
Sch
orl
Sp
od
um
ene
Zo
nes
WZ
OIZ
IIZ
aII
Zb
Cc
Zo
nes
WZ
OIZ
IIZ
aII
Zb
Cc
Zo
nes
OIZ
Zo
ne
Cc
SiO
26
75
76
78
86
87
06
84
76
84
1S
iO2
65
10
65
55
65
46
64
96
64
72
SiO
23
52
0S
iO2
64
65
TiO
20
02
mdash0
02
mdashmdash
TiO
2mdash
00
1mdash
mdashmdash
TiO
20
35
Al 2
O3
27
20
Al 2
O3
20
25
19
74
19
67
19
88
19
97
Al 2
O3
18
96
18
23
18
31
18
24
18
05
B2O
3
10
28
Fe 2
O3
00
6F
e 2O
3mdash
mdashmdash
mdash0
10
Fe 2
O3
mdash0
02
mdash0
03
mdashA
l 2O
33
17
2M
nO
01
3M
nO
00
6mdash
mdashmdash
mdashM
nO
mdash0
03
00
3mdash
mdashF
eO1
35
2M
gO
01
8M
gO
mdashmdash
mdashmdash
mdashM
gO
00
10
01
00
5mdash
mdashM
nO
03
3N
a 2O
01
9C
aO1
04
08
00
56
03
70
32
CaO
00
10
01
00
60
01
00
2M
gO
22
8L
i 2O
8
05
Na 2
O1
06
11
12
01
12
11
13
41
13
4N
a 2O
06
50
58
04
10
59
03
8C
aO0
23
To
tal
10
04
6K
2O
00
50
17
00
60
14
01
0K
2O
14
72
14
75
15
67
15
01
15
74
Li 2
O
02
2S
rO0
72
05
00
24
01
1mdash
Rb
2O
00
90
20
03
00
59
09
0N
a 2O
22
8S
i1
99
7P
2O
50
01
00
4mdash
mdashmdash
Cs 2
O
00
6
00
60
09
01
80
20
K2O
00
1A
lIV0
00
3T
ota
l1
00
33
10
03
31
00
46
10
03
11
00
24
P2O
5mdash
00
3mdash
mdashmdash
H2O
3
18
P2
00
To
tal
99
60
99
48
10
03
89
96
11
00
01
F0
78
AlV
I0
98
7S
rC
a(w
t)0
81
07
40
50
03
50
Cl
mdashF
e3thorn
00
01
KR
b(w
t)153
68
48
23
16
Sum
1003
8P
09
9S
i1
18
23
11
87
91
19
58
11
93
21
19
21
KC
s(w
t)4
07
20
41
63
73
69
O
F0
33
Li
10
00
P0
00
10
00
6mdash
mdashmdash
To
tal
10
00
5M
n0
00
3T
i0
00
3mdash
00
03
mdashmdash
Si
11
98
61
20
88
12
04
11
20
45
12
03
3M
g0
00
8A
l4
17
64
07
14
03
54
08
34
10
1P
mdash0
00
5mdash
mdashmdash
TS
i5
95
2N
a0
01
2F
e3thorn
mdashmdash
mdashmdash
00
13
Ti
mdash0
00
1mdash
mdashmdash
Al
00
48
P1
02
Mn
00
09
mdashmdash
mdashmdash
Al
41
14
39
62
39
70
39
86
39
55
B3
00
0M
gmdash
mdashmdash
mdashmdash
Fe3thorn
mdash0
00
3mdash
00
04
mdashZ
Al
60
00
Ca
01
95
01
50
01
04
00
69
00
60
Mn
mdash0
00
50
00
5mdash
mdashY
Al
02
74
Sr
00
73
00
51
00
24
00
11
mdashM
g0
00
30
00
30
01
4mdash
mdashT
i0
04
5N
a3
59
93
80
03
78
33
83
23
83
1C
a0
00
20
00
20
01
20
00
20
00
4M
g0
57
5K
00
11
00
38
00
13
00
31
00
22
Na
02
32
02
07
01
46
02
12
01
37
Mn
00
47
K3
45
73
47
03
67
73
55
03
73
3F
e2thorn
19
12
Z1
60
01
59
61
60
01
60
11
60
4R
b0
01
10
02
40
03
50
07
00
10
8L
i0
14
8X
38
94
04
39
33
94
39
1C
s0
00
20
00
50
00
70
01
40
01
6P
Y3
00
0m
ole
s
XC
a0
04
2A
n5
13
82
71
71
5Z
16
10
16
06
16
01
16
03
15
99
Na
07
47
Ab
94
69
53
97
09
75
97
9X
37
13
72
39
03
85
40
0K
00
02
Or
03
09
03
08
06
mo
les
amp
02
09
An
01
01
03
01
01
Ab
63
56
38
56
35
OH
35
83
Or
93
69
43
95
99
43
96
4F
04
17
Cl
mdash
WZ
ndashw
allzo
ne
OIZ
ndasho
ute
rin
term
edia
tezo
ne
IIZ
aan
dII
Zb
ndashin
ner
inte
rmed
iate
zon
esC
cndash
core
asin
Fig
2B
aOis
bel
ow
the
det
ecti
on
lim
itin
bo
thfe
ldsp
ars
Cs 2
Ofrac14
00
3w
tin
the
K-
feld
spar
fro
mth
eW
Z
mdashN
ot
det
ecte
d
Nu
mb
ero
fio
ns
on
the
bas
iso
f3
2o
xy
gen
sfo
ral
bit
ean
dK
-fel
dsp
ar
31
anio
ns
(O
OH
F
)fo
rsc
ho
rlan
d6
ox
yg
ens
for
spo
du
men
e
-A
mo
un
tin
ferr
edfr
om
con
sid
erat
ion
so
fst
oic
hio
met
ry
978 A M R Neiva
eschweizerbart_xxx
2011) Lepidolite from the OIZ is an Al-poorer mica (Fig4) and has the highest Si Licalcand F contents (Table 1)indicating that an evolution cannot be shown from thislepidolite to lepidolites from the other zones which areAl-richer micas (Fig 4) However there is a regulardecrease in the KRb ratio and a progressive increase inthe Rb and Cs contents from lepidolite of the OIZ tolepidolite of IIZa IIZb and Cc (Fig 7) which indicatesthat the KRb ratio and Rb and Cs contents must not beconsidered alone to show fractional crystallization in
lepidolites particularly if some are Al-richer micas andothers Al-poorer micas The high Licalcand F contents oflepidolite from the OIZ did not decrease its KRb ratioSuch an effect is considered to have taken place in lepi-dolite (an Al-richer mica) from the wall zone of the Tancopegmatite Manitoba Canada (Van Lichtervelde et al2008) An evolution from the lepidolite of the IIZa to thatof the Cc is generally shown by the increasing Si LicalcF Rb Cs contents and a decrease in the KRb ratio (Table1 Fig 7)
At the scale of crystals the pegmatite zones and alsothose from the OIZ to the Cc of the Namivo granitic pegma-tite Al-richer micas show fractionation because theyformed from the fractionation of an Li-rich pegmatite melt
The Al-poorer micas zinnwaldite lepidolite and FeMg-containing polylithionite only occur in the OIZ (Fig 4)Polylithionite is the mica richest in Si and Licalc and lepi-dolite from this zone is the richest in Si Licalcand F (Fig 4Table 1) The high Li contents of these micas reflect aconsiderably higher D(Li) at low temperature (Icenhoweramp London 1995) These Li-rich micas may have crystal-lized from an undercooled melt This hypothesis does notimply high Rb and Cs contents and low KRb ratios Thisagrees with the fact that these micas from the OIZ havesimilar Rb and Cs contents and KRb ratios to those of Al-richer micas (muscovite lithian muscovite and lsquolsquomixedformrsquorsquo) from the same pegmatite zone (Fig 7) Howeverthe lepidolite from the wall zone of the Tanco pegmatiteCanada of a similar origin has a low KRb ratio which isattributed to the complexly interrelated structural compo-nents of this lepidolite (Van Lichtervelde et al 2008) TheLi-rich micas from the OIZ may also represent disequili-brium These two hypotheses are considered the best forthese micas of primary magmatic origin
Another hypothesis was also considered They may havecrystallized in boundary layers which concentrate Li andF But this mechanism was suggested for the most fractio-nated tourmaline enriched in Li and F from the core of the
Fig 8 Plot of albite compositions from all zones of the Namivo granitic pegmatite Mozambique showing that the anorthite content of albitedecreases from the WZ to the Cc WZ OIZ IIZa IIZb and Cc as in Fig 2
Fig 9 The Rb vs Cs diagram of K-feldspar from all zones of theNamivo granitic pegmatite Mozambique showing that the Rb andCs contents of K-feldspar increase from the WZ to the Cc WZ OIZIIZa IIZb and Cc as in Fig 2
Silicate and oxide minerals from a zoned granitic pegmatite 979
eschweizerbart_xxx
Little Three pegmatite dike USA (Morgan amp London1999) and the micas enriched in Li and F from theNamivo pegmatite belonging to the OIZ Furthermore ina boundary layer melt that became enriched in Li and F theKRb ratio of micas decreases strongly (Van Lichterveldeet al 2008) which was not found in these micas from theOIZ (Fig 7d) Nor can they have resulted from the crystal-lization of a late melt that would have reacted with the OIZbecause these micas are among those containing the high-est KRb values (Fig 7d)
92 The importance of feldspars micas andcolumbitendashtantalite compositions to the Namivogranitic pegmatite evolution
The trace elements Rb and Cs and the KRb and KCs ratioshave been used to show the evolution of K-feldspar inpegmatites (eg Cerny 1994 Cerny et al 2005 RodaRobles et al 2005) The Rb and Cs contents increase andthe KRb and KCs ratios of K-feldspar decrease from theWZ to the Cc (Fig 9 Table 2) reflecting the growth of K-feldspar from an increasingly fractionated melt withouthaving grown from or having been chemically modifiedby an aqueous fluid as in the Swamp pegmatite section atthe Little Three Mine USA (London et al 2012) Thecrystallization of K-feldspar from an exsolved aqueousfluid from melt will reverse the magmatic fractionation ofRb Cs KRb and KCs because Rb and especially Cs areso much more compatible in vapor that both Rb and Csremain in the fluid phase (London et al 2012) The feldsparsolvus pairs in the Namivo pegmatite record magmaticcrystallization temperatures that decrease from WZ to CcAlbite shows a decrease in the Ca Sr contents and SrCaratio from the WZ to the Cc (Fig 8 Table 2) Therefore thefeldspars and also Al-richer micas as already explainedshow fractionation in this zoned pegmatite
In general lepidolite from the Namivo pegmatite hassimilar Rb2O and Cs2O contents and KRb (wt) values tothose of lepidolite from the Rozna and Dobra Voda lepi-dolite-subtype pegmatites in the Czech Republic (Cernyet al 1995) but lower Rb2O and Cs2O contents thanlepidolite from the lepidolite-subtype pegmatite at RedCross Lake Manitoba Canada (Cerny et al 2012a) K-feldspar from the Namivo pegmatite also has lower Rb2O
Table 3 Representative electron microprobe analyses in wt of columbitendashtantalite from the Namivo granitic pegmatite Mozambique
Outer Intermediate Zone - OIZ Inner Intermediate Zone - IIZa
Core - Cc
D L L
WO3 022 059 079 113 101 351 050 007Ta2O5 5487 5123 2503 3186 2888 2519 3127 4542Nb2O5 2537 3000 5483 4635 5113 5144 4911 3686SnO2 008 015 024 049 020 026 017 012TiO2 263 161 136 254 202 145 125 016FeO 860 710 665 471 236 068 mdash mdashMnO 793 952 1099 1304 1400 1725 1748 1718Total 9970 10020 9989 10012 9960 9978 9978 9981W 0004 0011 0013 0019 0016 0057 0008 0001Ta 1065 0975 0422 0552 0495 0430 0543 0847Nb 0819 0949 1538 1336 1456 1460 1418 1143Sn 0002 0004 0006 0012 0005 0007 0004 0003Ti 0141 0085 0063 0122 0096 0068 0060 0008Fe 0513 0416 0345 0251 0124 0036 mdash mdashMn 0479 0564 0578 0704 0747 0917 0945 0998P
3023 3004 2965 2996 2939 2975 2978 3000Mn(Mn thorn Fe) 048 058 063 074 086 096 100 100Ta(Ta thorn Nb) 057 051 022 029 025 023 028 043Classification tant-(Fe) tant-(Mn) col-(Mn) col-(Mn) col-(Mn) col-(Mn) col-(Mn) col-(Mn)
D ndash darker L ndash lighter zones mdash Not detected tant-tantalite col-columbite Cation formula on the basis of 6 atoms of oxygen
Fig 10 Compositions of columbitendashtantalite from the Namivogranitic pegmatite Mozambique in the columbite quadrilateralshowing that Mn(Mn thorn Fe) of columbite-(Mn) increases from theOIZ to the Cc and the richest columbite-(Mn) in Ta(Ta thorn Nb)tantalite-(Fe) and tantalite-(Mn) only occur in the OIZ OIZ IIZaand Cc as in Fig 2
980 A M R Neiva
eschweizerbart_xxx
and Cs2O contents than K-feldspar from the lepidolite-subtype pegmatite at Red Cross Lake The Rb2O andCs2O contents of primary and late K-feldspar of this peg-matite at Red Cross Lake attained unprecedented levels(Cerny et al 2012a) The lowest KRb (wt) values ofmuscovite lithian muscovite lsquolsquomixed formrsquorsquo and lepido-lite from the IIZb and Cc (Fig 7) and K-feldspar (KRb frac1414) from the Cc compare well with those found in theseminerals from the AC6frac143 lepidolite-subtype pegmatitefrom Greer Lake (Cerny et al 2005) and some of themost fractionated pegmatites worldwide which belong tothe petalite-subtype (eg Tanco Manitoba Cerny 2005Cerny et al 1998 Varutrask Sweden Cerny et al 2005)but muscovite lithian muscovite and lepidolite from theIIZb and Cc have lower Rb2O and Cs2O contents than thesemicas from the Tanco pegmatite (Cerny 2005a VanLichtervelde et al 2008) K-feldspar also has lower
contents of these oxides than the most evolved K-feldsparfrom the Tanco pegmatite (Cerny 2005a) The magmaticfractionation was strong from the WZ to IIZb and Cc of theNamivo lepidolite-subtype pegmatite
The compositional trend of columbite-(Mn) from the OIZto Cc of the Namivo granitic lepidolite-subtype pegmatite(Fig 10) is identical to that of columbite-group mineralsfrom the lepidolite-subtype complex granitic pegmatitesfrom the Dobra Voda in the Moldanubicum CzechRepublic (Novak amp Cerny 1998) and the HimalayaDistrict southern California (shown in Cerny et al 2004)Experimental data for the Fe-Mn pair (Linnen amp Cuney2005) suggest an increase in Fe with fractional crystalliza-tion which is not observed in nature Other phases seem tocontrol the bahavior of Fe and Mn in the melt eg thecrystallization of tourmaline causes a rapid increase of theMnFe in the melt (Van Lichtervelde et al 2006) When thecrystallization of tourmaline stopped the columbitendashtantaliteminerals showed a constant MnFe indicating that the Fe andMn contents in the melt remained constant Schorl onlyoccurs in the OIZ of the Namivo granitic pegmatite and itscrystallization cannot be responsible for the increase in theMnFe of the melt because Mn(Mn thorn Fe) of columbite-(Mn) increases progressively from the OIZ to the IIZa and Cc(Fig 10) Garnet zinnwaldite and gahnite containing Fe andMn also only occur in the OIZ and cannot also have causedthe increase of the MnFe in the melt The dominant Mnenrichment before Ta enrichment started in the columbitendash-tantalite composition from some granitic pegmatites isattributed to an increased alkali-fluoride activity at moderatemHF (Cerny et al 2004) and an increase in the activity offluorine (Martins et al 2011) Each Al-richer mica (musco-vite lithian muscovite and lsquolsquomixed formrsquorsquo) from the Namivogranitic pegmatite shows an increase in F content from theOIZ to the IIZa IIZb and Cc (Table 1) In general the Fcontent of lepidolite also increases from the IIZa to the IIZband Cc Therefore the extreme Fe-Mn fractionation beforeTa enrichment in columbite-(Mn) (Fig 10) may be due to anincrease in the activity of fluorine as a consequence offractional crystallization The increase in the Ta content ofcolumbite-(Mn) from the Namivo granitic pegmatite isattributed to fractional crystallization
The geochemical evolution of albite and K-feldsparfrom the WZ to the Cc Al-richer micas muscovite lithianmuscovite and lsquolsquomixed formrsquorsquo from the OIZ to the Cc andlepidolite from the IIZa to the Cc and columbite-(Mn) andalso beryl (Neiva amp Neiva 2005) from the OIZ to the Ccare caused by magma fractionation The pegmatite zonesare the product of primary crystallization from a volatile-rich silicate melt The pegmatite consolidated from the WZto the Cc The IIZb is one of the most evolved zones asalso suggested by the beryl composition (Neiva amp Neiva2005) and is the richest in lsquolsquomixed formrsquorsquo and lepidolite
The richest columbite-(Mn) in Ta(Ta thorn Nb) and com-positions of tantalite-(Fe) and tantalite-(Mn) only occur inthe OIZ (Fig 10a) associated with lepidolite and polythio-nite (Fig 3c) which may be due to the local depletion of Liand F in the melt which decreases the solubility of Ta andcauses Ta precipitation (Linnen 1998 Linnen amp Cuney
Fig 11 a Backscattered-electron image of a gahnite crystal with adarker zone partially surrounding a lighter zone from the OIZ of theNamivo granitic pegmatite b c Plot of gahnite compositions in theSn-Zn-Ti diagram (atomic proportions) showing a chemical distinc-tion between the lighter and darker zones OIZ as in Fig 2
Silicate and oxide minerals from a zoned granitic pegmatite 981
eschweizerbart_xxx
2005) At the Tanco pegmatite Ta oxides are also asso-ciated with lepidolite enriched in Li and F from the wallzone (Van Lichtervelde et al 2008)
93 Origin and evolution of the zoned graniticlepidolite-subtype pegmatite at Namivo
In general granitic pegmatites particularly those belong-ing to the rare-element class are accepted as having beenformed by the fractional crystallization of a granite melt(eg Cerny 1991a b 1992 Neiva et al 2008 2012 Roda-Robles et al 2012) But it also has been proposed thatpegmatites may be formed by partial melting of appropri-ate rock compositions (eg Nabelek et al 1992 Nabelekamp Russ-Nabelek 1992 Shearer et al 1992 Roda Robleset al 1999) The lepidolite-subtype pegmatites belong tothe LCT (lithium-cesium-tantalum) family (Cerny amp Ercit2005) They are derived by fractional crystallization of agranite magma (eg Cerny et al 2005 Neiva amp Ramos2010 Cerny et al 2012b) Experimental work by Londonet al (1989) and London (1990) using Macusani glass as astarting material equivalent to the bulk composition ofhighly fractionated rare-alkali-rich pegmatites underhighly evolved and hydrous but H2O undersaturatedmelt obtained the latest primary assemblage consisting
of an Li-rich mica thorn albite thorn quartz deposited directlyfrom the primary melt phase Other authors egZasedatelev (1974 1977) and Stewart (1978) argue thatlepidolite-bearing pegmatites are derived from direct ana-texis and Gordiyenko et al (1996) consider that they arederived from an undefined medium and the rare-elementmineralization is superimposed on preexisting barrenpegmatites
Lepidolite-subtype pegmatites may migrate a long wayfrom their parent granites because their volatile-rich highlyfluid pegmatite melts are stable at relatively low tempera-tures (eg Cerny et al 2005 Antunes et al 2013)Therefore the Namivo pegmatite is probably derived byfractional crystallization of an S-type granite magmawhich resulted from partial melting of metamorphosed juve-nile sediments containing micas that carry most of the traceelements that define the signature of the LCT pegmatites(eg Dahl et al 1993)
The two main models for the internal evolution of peg-matites that dominated for more than a century are a) thefractional crystallization of a flux-bearing granitic melt fromthe margins to the center of the pegmatite (Cameron et al1949) b) the interactions of an aqueous fluid with graniticmelt (Jahns amp Burnham 1969 Jahns 1982) The recentmodel of constitutional zone refining combines aspects ofboth models and invokes the formation of a flux-enriched
Table 4 Electron microprobe analyses in wt of zoned gahnite from the outer intermediate zone (OIZ) of the Namivo granitic pegmatiteMozambique
Darker Zone Lighter Zone
Mean s Range Mean s Range
SnO2 036 050 0ndash097 658 281 151ndash998TiO2 008 008 0ndash021 065 034 008ndash105Nb2O5 001 002 0ndash006 018 007 007ndash029Ta2O5 001 004 0ndash010 015 013 0ndash033ZnO 3998 123 3810ndash4109 3339 318 3004ndash3848FeO 367 048 331ndash442 433 065 306ndash498MnO 032 004 028ndash040 039 006 032ndash048MgO 003 004 0ndash010 ndash ndash ndashAl2O3 5507 050 5436ndash5572 5337 070 5257ndash5443SiO2 003 003 0ndash007 008 010 0ndash025Total 9956 9912n 8 8Sn 0035 0048 0ndash0095 0648 0278 0149ndash0983Ti 0015 0015 0ndash0038 0120 0064 0015ndash0195Nb ndash 0003 0ndash0006 0021 0009 0009ndash0037Ta ndash 0002 0ndash0006 0009 0009 0ndash0021Zn 7226 0182 6890ndash7382 6086 0568 5482ndash6965Fe2thornt 0752 0103 0675ndash0913 0894 0135 0628ndash1029Mn 0066 0008 0057ndash0083 0082 0013 0066ndash0101Mg 0010 0015 0ndash0037 ndash ndash ndashAl 15887 0052 15805ndash15954 15526 0170 15375ndash15853Si 0007 0008 0ndash0018 0019 0025 0ndash0062P
23998 23405Fe3thorn 0064 0230Fe2thorn 0686 0658SnZn 0005 0007 0ndash0014 0106 0052 0021ndash0179ZnFe2thornt 961 143 768ndash1093 681 190 536ndash1109
n number of analysis Cation formula based on 32 atoms of oxygen Fe2thornt total Fe2thorn estimated
982 A M R Neiva
eschweizerbart_xxx
boundary layer of silicate liquid in advance of a crystal-lization front (London 2008 London amp Morgan 2012)
Lepidolite-subtype pegmatites are generally scarce(Cerny et al 2005) particularly the zoned ones In thesymmetrically zoned lepidolite-subtype pegmatites ofRozna and Dobra Voda Czech Republic micas (Cernyet al 1995) tourmaline (Selway et al 1999) and colum-bite-group minerals (Novak amp Cerny 1998) evolve fromthe outermost zone to the innermost zone following thecrystallization sequence The same was found in tourma-line from the zoned Lastovicky Dolnı Bory and Raddovicelepidolite-subtype pegmatite dikes in the Czeck Republic(Selway et al 1999)
In general beryl (Neiva amp Neiva 2005) feldsparsmicas and columbite-(Mn) (in this paper) from theNamivo lepidolite-subtype pegmatite record the progres-sive chemical evolution of the pegmatite from the wallzone to the core These minerals were produced by crystal-lization from a silicate melt rather than an aqueous fluidphase The slow cooling of melt shown by the magmaticcrystallization temperatures of feldspars cannot explain theincrease in grain-size of minerals from the wall zone to thecore but fluxes will be necessary to promote the change oftexture particularly a flux-rich hydrosilicate liquidaccording to the experimental evidence (London 2009)The constitutional zone refining model will be the best forthis zoned pegmatite and probably for all lepidolite-sub-type pegmatites because this model also produces a higherfinal concentration of incompatible components in a smal-ler volume of rock than fractional crystallization does(Morgan amp London 1999)
The core margin at the Rozna pegmatite contains K-feld-spar and quartz and the core consists mainly of quartz but it issurrounded and penetrated by a quartz-bearing albitethorn lepi-dolite complex which contains several minerals At theDobra Voda pegmatite the center of the dike is occupiedby the lepidolite unit containing albite and other minerals(Cerny et al 1995) At the Namivo pegmatite the coremargin consists of quartz and beryl and the core containsmainly quartz and spodumene but also albite lepidolite andother minerals The last-unit assemblages of primary miner-als in most of the highly fractionated LCT pegmatites are richin albite and commonly contain lepidolite or spodumene andmost of the other rare phases These units represent the lastmost fractionated liquid that can be derived by fractionalcrystallization of a crustal melt (London 2008)
The Namivo granitic pegmatite shows a significant dis-tinction from the other zoned lepidolite-subtype pegmatitesand LCT pegmatites except the Tanco petalite-subtypepegmatite in Canada because the lepidolite richest in SiLi and F FeMg-containing polylithionite and associatedcolumbite-(Mn) with the highest Ta(Ta thorn Nb) ratio tanta-lite-(Fe) and tantalite-(Mn) only occur in the outer inter-mediate zone These minerals usually form late in theconsolidation of pegmatites The lepidolite and polylithio-nite are probably derived from the disequilibrium crystal-lization of an undercooled melt Tantalite may reflect a localdecrease in Li and F that caused Ta precipitation
This paper contributes to a better understanding of theorigin and evolution of the rare zoned lepidolite-subtypepegmatites and shows that although the pegmatite evolvedfrom the wall zone to the core it presents an unusualassociation of lepidolite polylithionite and tantalite in theouter intermediate zone
Acknowledgments Thanks are due to JM Cotelo Neivaand MB Dias for the samples and information providedand to MR Machado Leite and MF Guimaraes for theuse of the electron microprobe facilities at the LaboratorioNacional de Energia e Geologia (LNEG) PortugalFinancial support was provided by the PortugueseGovernment for the project Pest-OECTEUI00732011of the Geosciences Centre through the PortugueseFoundation for Science and Technology I would like tothank D London WB Simmons and the associated editorE Widom for their constructive reviews of this manuscriptand M Prieto for his editorial work
References
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Geochemistry of feldspars and muscovite in granitic pegmatite
from the Cap de Creus field Catalonia Spain Can Mineral 41
103ndash116
Antunes IMHR Neiva AMR Ramos JMF Silva PB
Silva MMVG Corfu F (2013) Petrogenetic links between
lepidolite-subtype aplite-pegmatite aplite veins and associated
granites at Segura (central Portugal) Chemie der Erde in press
httpdxdoiorg101016jchemer20121203
Batchelor RA amp Kinnaird JA (1984) Gahnite compositions
compared Mineral Mag 48 425ndash430
Beurlen H Da Silva MRR Thomas R Soares DR Olivier P
(2008) Nb-Ta-(Ti-Sn) oxide mineral chemistry as tracer of rare-
element granitic pegmatite fractionation in the Borborema pro-
vince Northeastern Brazil Miner Deposita 43 207ndash228
Cameron EN Jahns RH McNair AH Page LR (1949)
Internal structure of granitic pegmatites Econ Geol
Monograph 2 115 p
Cerny P (1991a) Fertile granites of Precambrian rare-element
pegmatite fields is geochemistry controlled by tectonic setting
or source lithologies Precambrian Res 51 429ndash468
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nal evolution of pegmatite deposits Geoscience Canada 18
49ndash67
mdash (1992) Geochemical and petrogenetic features of mineralization
in rare-element granitic pegmatites in the light of current
research Applied Geochemistry 7 393ndash416
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lsquolsquoFeldspars and their Reactionsrsquorsquo I Parsons ed NATO
Advanced Study Institute Series C421 501ndash539
mdash (2005) The Tanco rare-element pegmatite deposit Manitoba
regional context internal anatomy and global comparisons in
lsquolsquoRare-element Geochemistry and Mineral Depositsrsquorsquo RL
Linnen amp IM Samson eds Geochemical Association of
Canada Short Course Notes St Catherines 17 127ndash158
Silicate and oxide minerals from a zoned granitic pegmatite 983
eschweizerbart_xxx
Cerny P amp Ercit TS (2005) The classification of granitic pegma-
tites revisited Can Mineral 43 2005ndash2026
Cerny P Meintzer RE Andersen AJ (1985) Extreme fractiona-
tion in rare-element granitic pegmatites selected examples of
data and mechanisms Can Mineral 23 381ndash421
Cerny P Goad BE Hawthorne FC Chapmann R (1986)
Fractionation trends of the Nb- and Ta-bearing oxide minerals
in the Greer Lake pegmatite granite and its pegmatite aureole
southeastern Manitoba Am Mineral 71 501ndash517
Cerny P Stanek J Novak M Baadsgaard H Rieder M
Ottolini L Kavalova M Chapman R (1995) Geochemical
and structural evolution of micas in the Rozna amp Dobra Voda
pegmatites Czech Republic Mineral Petrol 55 177ndash201
Cerny P Ercit TS Vanstone PJ (1998) Mineralogy and petrol-
ogy of the Tanco rare-element pegmatite deposit southeastern
Manitoba International Mineralogical Association 17th General
Meeting Toronto Field Guidebook B6
Cerny P Chapman R Ferreira K Smeds SA (2004)
Geochemistry of oxide minerals of Nb Ta Sn and Sb in
the Varutrask granitic pegmatite Sweden The case of an
lsquolsquoanomalousrsquorsquo columbitendashtantalite trend Am Mineral 89
505ndash518
Cerny P Masau M Goad BE Ferreira K (2005) The Greer
Lake leucogranite Manitoba and the origin of lepidolite-sub-
type granitic pegmatites Lithos 80 305ndash321
Cerny P Teertstra DK Chapman R Selway JB Hawthorne
FC Ferreira K Chackowsky LE Wang X-J Meintzer
RE (2012a) Extreme fractionation and deformation of the
leucogranite-pegmatite suite at Red Cross Lake Manitoba
Canada IV Mineralogy Can Mineral 50 1839ndash1875
Cerny P Halden NM Ferreira K Meintzer RE Brisbin WC
Chackowsky LE (2012b) Extreme fractionation and deforma-
tion of the leucogranite-pegmatite suite at Red Cross Lake
Manitoba Canada II Petrology of the leucogranites and peg-
matites Can Mineral 50 1807ndash1822
Dahl PS When DC Feldmann SG (1993) The systematics of
trace-element partitioning between coexisting muscovite and
biotite in metamorphic rocks from the Black Hills South
Dakota USA Geochim Cosmochim Acta 57 2487ndash2505
Dias MB amp Wilson WE (2000) The Alto Ligonha Pegmatites
Mozambique Mineral Record 31 459ndash497
Fleet ME (2003) Rock-Forming Minerals vol 3A Sheet silicates
micas The Geological Society London second edition chap 6
Lithium micas 651ndash690
Foord EE Cerny P Jackson LL Sherman DM Eby RK
(1995) Mineralogical and geochemical evolutions of micas
from miarolitic pegmatites of the anorogenic pikes-Peak
Batholith Colorado Mineral Petrol 55 1ndash26
Foster MD (1960) Interpretation of the composition of lithium
micas US Geol Surv Prof Paper 354-E 115ndash147
Fuhrman ML amp Lindsley DK (1988) Ternary-feldspar modeling
and thermometry Am Mineral 73 201ndash215
Gomes CL Castro P Alves C (1995) Caracterizacao das espi-
nelas zincıferas e do par ganite-nigerite no campo aplito-
pegmatıtico da Serra de Arga-Minho N de Portugal IV
Congresso Nacional de Geologia Resumos Alargados
Universidade do Porto Mem 4 629ndash633
Gordiyenko VV Ilyina AN Timochina LA Badamina EB
Stanek J (1996) Geochemical model of evolution of a pegma-
tite-forming ore-magmatic system of western Moravia Proc
Russ Mineral Soc 125 38ndash48 (in Russian)
Icenhower JP amp London D (1995) An experimental study for
element partitioning between biotite muscovite and coexisting
peraluminous granitic melt at 200 MPa (H2O) Am Mineral 80
1229ndash1251
Jahns RH (1982) Internal evolution of pegmatite bodies in lsquolsquoGranitic
Pegmatites in science and industryrsquorsquo P Cerny ed Mineralogical
Association of Canada Short Course Handbook 8 293ndash327
Jahns RH amp Burnham CW (1969) Experimental studies of
pegmatite genesis I A model for the derivation and crystal-
lization of granitic pegmatites Econ Geol 64 843ndash864
Jolliff BL Papike JJ Shearer CK (1987) Fractionation trends
in mica and tourmaline as indicators of pegmatite internal evo-
lution Bob Ingersoll pegmatite Black Hills South Dakota
USA GeochimCosmochim Acta 51 519ndash534
Kile DE amp Foord EE (1998) Micas from the Pikes Peak bath-
olith and its cogenetic granitic pegmatites Colorado optical
properties composition and correlation with pegmatite evolu-
tion Can Mineral 36 463ndash482
Linnen RL (1998) The solubility of Nb-Ta-Zr-Hf-W in granitic
melts with Li and Li thorn F constraints for mineralization in rare
metal granites and pegmatites Econ Geol 93 1013ndash1025
Linnen RL amp Cuney M (2005) Granite-related rare-element
deposits and experimental constraints on Ta-Nb-W-Sn-Zr-Hf
mineralization in lsquolsquoRare-element geochemistry and mineral
depositsrsquorsquo RL Linnen amp IM Samson eds Geochemical
Association of Canada Short Course Notes 17 45ndash68
London D (1990) Internal differentiation of rare-element pegmatites
a synthesis of recent research in lsquolsquoOre Bearing Granite Systems
Petrogenesis and Mineralizing Processesrsquorsquo HJ Stein amp JL
Hannah eds Geol Soc America Special Paper 246 35ndash50
mdash (2008) Pegmatites The Canadian Mineralogist Special
Publication 10 347 p
mdash (2009) The origin of primary textures in granitic pegmatites
Can Mineral 47 697ndash724
London D amp Morgan GB VI (2012) The pegmatite puzzle
Elements 8 263ndash268
London D Morgan GB VI Hervig RL (1989) Vapor-under-
saturated experiments in the system macusanite-H2O at 200
MPa and the internal differentiation of granitic pegmatites
Contrib Mineral Petrol 102 1ndash17
London D Morgan GB VI Paul KA Guttery BM (2012)
Internal evolution of miarolitic granitic pegmatites at the Little
Three mine Ramona California USA Can Mineral 50
1025ndash1054
Martins T Lima A Simmons WB Folster AU Noronha F
(2011) Geochemical fractionation of Nb-Ta oxides in Li-bear-
ing pegmatites from the Barroso-Alvao pegmatite field northern
Portugal Can Mineral 49 777ndash791
Monier G Charoy B Cuney M Ohnenstetter D Robert JL
(1987) Evolution spatiale et temporelle de la composition des
micas du granite albitique a topaze-lepidolite de Beauvoir
Geologie De La France 2ndash3 179ndash188
Monier G amp Robert JL (1986) Evolution of the miscibility gap
between muscovite and biotite solid solutions with increasing
lithium content an experimental study in the systems
K2OndashLi2OndashMgOndashAl2O3ndashSiO2ndashH2OndashHF at 600 C 2 kbar
PH2O comparison with natural lithium micas Mineral Mag
50 641ndash651
Morgan GBVI amp London D (1999) Crystallization of the little
three layered pegmatite-aplite dike Ramona District California
Contrib Mineral Petrol 136 310ndash330
984 A M R Neiva
eschweizerbart_xxx
Nabelek PI amp Russ-Nabelek C (1992) The generation and crys-
tallization conditions of the Proterozoic Harney Peak
Leucrogranite Black Hills South Dakota USA petrologic and
geochemical constraints Contrib Mineral Petrol 110
173ndash191
Nabelek PI Russ-Nabelek C Haeussler GT (1992) Stable
isotope evidence for the petrogenesis and fluid evolution in
the Proterozoic Harney Peak leucogranite Black Hills
South Dakota Geochim Cosmochim Acta 56 403ndash417
Neiva AMR amp Champness PE (1997) Nigerite and gahnite from
the granitic pegmatite veins of Cabanas Ponte de Lima northern
Portugal N Jb Mineral Mh 9 385ndash409
Neiva AMR Gomes MEP Ramos JMF Silva PB (2008)
Geochemistry of granitic aplite-pegmatite sills and their miner-
als from Arcozelo da Serra area (Gouveia central Portugal)
Eur J Mineral 20 465ndash485
Neiva AMR amp Neiva JMC (2005) Beryl from the granitic
pegmatite at Namivo Alto Ligonha Mozambique N Jb
Mineral Abh 181 173ndash182
Neiva AMR amp Ramos JMF (2010) Geochemistry of granitic
aplite-pegmatite sills and petrogenetic links with granites
Guarda-Belmonte area central Portugal Eur J Mineral 22
837ndash854
Neiva AMR Silva PB Ramos JMF (2012) Geochemistry of
granitic aplite-pegmatite veins and sills and their minerals from the
Sabugal area central Portugal N Jb Mineral Abh 189 49ndash74
Novak M amp Cerny P (1998) Niobium-tantalum oxide minerals
from complex granitic pegmatites in the Moldanubicum Czech
Republic primary versus secondary compositional trends Can
Mineral 36 659ndash672
Pesquera Perez A Torres-Ruiz J Gil PP Velilla N (1999)
Chemistry and genetic implications of tourmaline and Li-F-Cs
micas from the Valdeflores (Caceres Spain) Am Mineral 84
55ndash69
Rieder M Cavazzini G DrsquoYakonov YuS Frank-Kamenetskii
VA Gottardi G Guggenheim S Koval PV Muller G
Neiva AMR Radoslovich EW Robert J-L Sassi FP
Takeda H Weiss Z Wones DR (1999) Nomenclature of the
micas Mineral Mag 63 267ndash279
Roda Robles E Pesquera Perez A Velasco Roldan F Fontan F
(1999) The granitic pegmatites of the Fregeneda area
(Salamanca Spain) characteristics and petrogenesis Mineral
Mag 63 535ndash558
Roda Robles E Pesquera A Gil-Crespo PP Torres-Ruiz J
Fontan F (2005) Origin and internal evolution of the Li-F-
Be-P-bearing Pinilla de Fermoselle pegmatite (Central Iberian
Zone Zamora Spain) Am Mineral 90 1887ndash1899
Roda Robles E Pesquera Perez A Gil PP Torres-Ruiz J de
Parseval P (2006) Mineralogy and geochemistry of micas from
the Pinilla de Fermoselle pegmatite (Zamora Spain) Eur J
Mineral 18 369ndash377
Roda Robles E Keller P Pesquera Perez A Fontan F (2007)
Micas of the muscovite-lepidolite series from Karibib pegma-
tites Namibia Mineral Mag 71 41ndash62
Roda Robles E Pesquera A Gil-Crespo P Torres-Ruiz J
(2012) From granite to highly evolved pegmatite a case study
of the Pinilla de Fermoselle granite-pegmatite system (Zamora
Spain) Lithos 153 192ndash207
Selway JB Novak M Cerny P Hawthorne FC (1999)
Compositional evolution of tourmaline in lepidolite-subtype
pegmatites Eur J Mineral 11 569ndash584
Shearer CK Papike JJ Jolliff B (1992) Petrogenetic links
among granites and pegmatites in the Harney Peak rare-element
granite-pegmatite system Black Hills South Dakota Can
Mineral 30 785ndash809
Soares DR Hartmut B Ferreira ACM da Silva MRR
(2007) Chemical composition of gahnite and degree of peg-
matitic fractionation in the Borborema Pegmatitic Province
northeastern Brazil Anais Da Academ Bras Cien 79
395ndash404
Stewart DB (1978) Petrogenesis of lithium-rich pegmatites Am
Mineral 63 970ndash980
Tischendorff G Gattesmann B Forster H-J Trumbull RB
(1997) On Li-bearing micas estimating Li from electron
microprobe analyses and an improved diagram for graphical
representation Mineral Mag 61 809ndash834
Van Lichtervelde M Linnen RL Salvi S Beziat D (2006)
The role of metagabbro rafts on tantalum mineralization in the
Tanco granitic pegmatite Manitoba Can Mineral 44
625ndash644
Van Lichtervelde M Gregoire M Linnen RL Beziat D Salvi
S (2008) Trace element geochemistry by laser ablation ICP-
MS of micas associated with Ta mineralization in the Tanco
pegmatite Manitoba Canada Contrib Mineral Petrol 155
791ndash806
Vieira R Roda-Robles E Pesquera A Lima A (2011)
Chemical variation and significance of micas from the
Fregeneda-Almendra pegmatitic field (Central-Iberian Zone
Spain and Portugal) Am Mineral 96 637ndash645
Wen S amp Nekvasil H (1994) SOLVCALC an interactive gra-
phics program package for calculating ternary feldspar solvus
and two-feldspar geothermometry Comput Geosci 20
1025ndash1040
Wise MA (1995) Trace element chemistry of lithium-rich micas
from rare-element granitic pegmatites Mineral Petrol 55
203ndash215
Zasedatelev AM (1974) Possible accumulation of lithium in host
rocks of lithium pegmatite veins during old sedimentation pro-
cesses Doklady Acad Sci USSR Earth Sci Ser 218 196ndash198
(in Russian)
mdash (1977) Quantitative of metamorphic generation of rare-metal
pegmatites with lithium mineralization Doklady Acad Sci
USSR Earth Sci Ser 236 219ndash221 (in Russian)
Received 26 January 2013
Modified version received 21 May 2013
Accepted 23 July 2013
Silicate and oxide minerals from a zoned granitic pegmatite 985
eschweizerbart_xxx
2011) Lepidolite from the OIZ is an Al-poorer mica (Fig4) and has the highest Si Licalcand F contents (Table 1)indicating that an evolution cannot be shown from thislepidolite to lepidolites from the other zones which areAl-richer micas (Fig 4) However there is a regulardecrease in the KRb ratio and a progressive increase inthe Rb and Cs contents from lepidolite of the OIZ tolepidolite of IIZa IIZb and Cc (Fig 7) which indicatesthat the KRb ratio and Rb and Cs contents must not beconsidered alone to show fractional crystallization in
lepidolites particularly if some are Al-richer micas andothers Al-poorer micas The high Licalcand F contents oflepidolite from the OIZ did not decrease its KRb ratioSuch an effect is considered to have taken place in lepi-dolite (an Al-richer mica) from the wall zone of the Tancopegmatite Manitoba Canada (Van Lichtervelde et al2008) An evolution from the lepidolite of the IIZa to thatof the Cc is generally shown by the increasing Si LicalcF Rb Cs contents and a decrease in the KRb ratio (Table1 Fig 7)
At the scale of crystals the pegmatite zones and alsothose from the OIZ to the Cc of the Namivo granitic pegma-tite Al-richer micas show fractionation because theyformed from the fractionation of an Li-rich pegmatite melt
The Al-poorer micas zinnwaldite lepidolite and FeMg-containing polylithionite only occur in the OIZ (Fig 4)Polylithionite is the mica richest in Si and Licalc and lepi-dolite from this zone is the richest in Si Licalcand F (Fig 4Table 1) The high Li contents of these micas reflect aconsiderably higher D(Li) at low temperature (Icenhoweramp London 1995) These Li-rich micas may have crystal-lized from an undercooled melt This hypothesis does notimply high Rb and Cs contents and low KRb ratios Thisagrees with the fact that these micas from the OIZ havesimilar Rb and Cs contents and KRb ratios to those of Al-richer micas (muscovite lithian muscovite and lsquolsquomixedformrsquorsquo) from the same pegmatite zone (Fig 7) Howeverthe lepidolite from the wall zone of the Tanco pegmatiteCanada of a similar origin has a low KRb ratio which isattributed to the complexly interrelated structural compo-nents of this lepidolite (Van Lichtervelde et al 2008) TheLi-rich micas from the OIZ may also represent disequili-brium These two hypotheses are considered the best forthese micas of primary magmatic origin
Another hypothesis was also considered They may havecrystallized in boundary layers which concentrate Li andF But this mechanism was suggested for the most fractio-nated tourmaline enriched in Li and F from the core of the
Fig 8 Plot of albite compositions from all zones of the Namivo granitic pegmatite Mozambique showing that the anorthite content of albitedecreases from the WZ to the Cc WZ OIZ IIZa IIZb and Cc as in Fig 2
Fig 9 The Rb vs Cs diagram of K-feldspar from all zones of theNamivo granitic pegmatite Mozambique showing that the Rb andCs contents of K-feldspar increase from the WZ to the Cc WZ OIZIIZa IIZb and Cc as in Fig 2
Silicate and oxide minerals from a zoned granitic pegmatite 979
eschweizerbart_xxx
Little Three pegmatite dike USA (Morgan amp London1999) and the micas enriched in Li and F from theNamivo pegmatite belonging to the OIZ Furthermore ina boundary layer melt that became enriched in Li and F theKRb ratio of micas decreases strongly (Van Lichterveldeet al 2008) which was not found in these micas from theOIZ (Fig 7d) Nor can they have resulted from the crystal-lization of a late melt that would have reacted with the OIZbecause these micas are among those containing the high-est KRb values (Fig 7d)
92 The importance of feldspars micas andcolumbitendashtantalite compositions to the Namivogranitic pegmatite evolution
The trace elements Rb and Cs and the KRb and KCs ratioshave been used to show the evolution of K-feldspar inpegmatites (eg Cerny 1994 Cerny et al 2005 RodaRobles et al 2005) The Rb and Cs contents increase andthe KRb and KCs ratios of K-feldspar decrease from theWZ to the Cc (Fig 9 Table 2) reflecting the growth of K-feldspar from an increasingly fractionated melt withouthaving grown from or having been chemically modifiedby an aqueous fluid as in the Swamp pegmatite section atthe Little Three Mine USA (London et al 2012) Thecrystallization of K-feldspar from an exsolved aqueousfluid from melt will reverse the magmatic fractionation ofRb Cs KRb and KCs because Rb and especially Cs areso much more compatible in vapor that both Rb and Csremain in the fluid phase (London et al 2012) The feldsparsolvus pairs in the Namivo pegmatite record magmaticcrystallization temperatures that decrease from WZ to CcAlbite shows a decrease in the Ca Sr contents and SrCaratio from the WZ to the Cc (Fig 8 Table 2) Therefore thefeldspars and also Al-richer micas as already explainedshow fractionation in this zoned pegmatite
In general lepidolite from the Namivo pegmatite hassimilar Rb2O and Cs2O contents and KRb (wt) values tothose of lepidolite from the Rozna and Dobra Voda lepi-dolite-subtype pegmatites in the Czech Republic (Cernyet al 1995) but lower Rb2O and Cs2O contents thanlepidolite from the lepidolite-subtype pegmatite at RedCross Lake Manitoba Canada (Cerny et al 2012a) K-feldspar from the Namivo pegmatite also has lower Rb2O
Table 3 Representative electron microprobe analyses in wt of columbitendashtantalite from the Namivo granitic pegmatite Mozambique
Outer Intermediate Zone - OIZ Inner Intermediate Zone - IIZa
Core - Cc
D L L
WO3 022 059 079 113 101 351 050 007Ta2O5 5487 5123 2503 3186 2888 2519 3127 4542Nb2O5 2537 3000 5483 4635 5113 5144 4911 3686SnO2 008 015 024 049 020 026 017 012TiO2 263 161 136 254 202 145 125 016FeO 860 710 665 471 236 068 mdash mdashMnO 793 952 1099 1304 1400 1725 1748 1718Total 9970 10020 9989 10012 9960 9978 9978 9981W 0004 0011 0013 0019 0016 0057 0008 0001Ta 1065 0975 0422 0552 0495 0430 0543 0847Nb 0819 0949 1538 1336 1456 1460 1418 1143Sn 0002 0004 0006 0012 0005 0007 0004 0003Ti 0141 0085 0063 0122 0096 0068 0060 0008Fe 0513 0416 0345 0251 0124 0036 mdash mdashMn 0479 0564 0578 0704 0747 0917 0945 0998P
3023 3004 2965 2996 2939 2975 2978 3000Mn(Mn thorn Fe) 048 058 063 074 086 096 100 100Ta(Ta thorn Nb) 057 051 022 029 025 023 028 043Classification tant-(Fe) tant-(Mn) col-(Mn) col-(Mn) col-(Mn) col-(Mn) col-(Mn) col-(Mn)
D ndash darker L ndash lighter zones mdash Not detected tant-tantalite col-columbite Cation formula on the basis of 6 atoms of oxygen
Fig 10 Compositions of columbitendashtantalite from the Namivogranitic pegmatite Mozambique in the columbite quadrilateralshowing that Mn(Mn thorn Fe) of columbite-(Mn) increases from theOIZ to the Cc and the richest columbite-(Mn) in Ta(Ta thorn Nb)tantalite-(Fe) and tantalite-(Mn) only occur in the OIZ OIZ IIZaand Cc as in Fig 2
980 A M R Neiva
eschweizerbart_xxx
and Cs2O contents than K-feldspar from the lepidolite-subtype pegmatite at Red Cross Lake The Rb2O andCs2O contents of primary and late K-feldspar of this peg-matite at Red Cross Lake attained unprecedented levels(Cerny et al 2012a) The lowest KRb (wt) values ofmuscovite lithian muscovite lsquolsquomixed formrsquorsquo and lepido-lite from the IIZb and Cc (Fig 7) and K-feldspar (KRb frac1414) from the Cc compare well with those found in theseminerals from the AC6frac143 lepidolite-subtype pegmatitefrom Greer Lake (Cerny et al 2005) and some of themost fractionated pegmatites worldwide which belong tothe petalite-subtype (eg Tanco Manitoba Cerny 2005Cerny et al 1998 Varutrask Sweden Cerny et al 2005)but muscovite lithian muscovite and lepidolite from theIIZb and Cc have lower Rb2O and Cs2O contents than thesemicas from the Tanco pegmatite (Cerny 2005a VanLichtervelde et al 2008) K-feldspar also has lower
contents of these oxides than the most evolved K-feldsparfrom the Tanco pegmatite (Cerny 2005a) The magmaticfractionation was strong from the WZ to IIZb and Cc of theNamivo lepidolite-subtype pegmatite
The compositional trend of columbite-(Mn) from the OIZto Cc of the Namivo granitic lepidolite-subtype pegmatite(Fig 10) is identical to that of columbite-group mineralsfrom the lepidolite-subtype complex granitic pegmatitesfrom the Dobra Voda in the Moldanubicum CzechRepublic (Novak amp Cerny 1998) and the HimalayaDistrict southern California (shown in Cerny et al 2004)Experimental data for the Fe-Mn pair (Linnen amp Cuney2005) suggest an increase in Fe with fractional crystalliza-tion which is not observed in nature Other phases seem tocontrol the bahavior of Fe and Mn in the melt eg thecrystallization of tourmaline causes a rapid increase of theMnFe in the melt (Van Lichtervelde et al 2006) When thecrystallization of tourmaline stopped the columbitendashtantaliteminerals showed a constant MnFe indicating that the Fe andMn contents in the melt remained constant Schorl onlyoccurs in the OIZ of the Namivo granitic pegmatite and itscrystallization cannot be responsible for the increase in theMnFe of the melt because Mn(Mn thorn Fe) of columbite-(Mn) increases progressively from the OIZ to the IIZa and Cc(Fig 10) Garnet zinnwaldite and gahnite containing Fe andMn also only occur in the OIZ and cannot also have causedthe increase of the MnFe in the melt The dominant Mnenrichment before Ta enrichment started in the columbitendash-tantalite composition from some granitic pegmatites isattributed to an increased alkali-fluoride activity at moderatemHF (Cerny et al 2004) and an increase in the activity offluorine (Martins et al 2011) Each Al-richer mica (musco-vite lithian muscovite and lsquolsquomixed formrsquorsquo) from the Namivogranitic pegmatite shows an increase in F content from theOIZ to the IIZa IIZb and Cc (Table 1) In general the Fcontent of lepidolite also increases from the IIZa to the IIZband Cc Therefore the extreme Fe-Mn fractionation beforeTa enrichment in columbite-(Mn) (Fig 10) may be due to anincrease in the activity of fluorine as a consequence offractional crystallization The increase in the Ta content ofcolumbite-(Mn) from the Namivo granitic pegmatite isattributed to fractional crystallization
The geochemical evolution of albite and K-feldsparfrom the WZ to the Cc Al-richer micas muscovite lithianmuscovite and lsquolsquomixed formrsquorsquo from the OIZ to the Cc andlepidolite from the IIZa to the Cc and columbite-(Mn) andalso beryl (Neiva amp Neiva 2005) from the OIZ to the Ccare caused by magma fractionation The pegmatite zonesare the product of primary crystallization from a volatile-rich silicate melt The pegmatite consolidated from the WZto the Cc The IIZb is one of the most evolved zones asalso suggested by the beryl composition (Neiva amp Neiva2005) and is the richest in lsquolsquomixed formrsquorsquo and lepidolite
The richest columbite-(Mn) in Ta(Ta thorn Nb) and com-positions of tantalite-(Fe) and tantalite-(Mn) only occur inthe OIZ (Fig 10a) associated with lepidolite and polythio-nite (Fig 3c) which may be due to the local depletion of Liand F in the melt which decreases the solubility of Ta andcauses Ta precipitation (Linnen 1998 Linnen amp Cuney
Fig 11 a Backscattered-electron image of a gahnite crystal with adarker zone partially surrounding a lighter zone from the OIZ of theNamivo granitic pegmatite b c Plot of gahnite compositions in theSn-Zn-Ti diagram (atomic proportions) showing a chemical distinc-tion between the lighter and darker zones OIZ as in Fig 2
Silicate and oxide minerals from a zoned granitic pegmatite 981
eschweizerbart_xxx
2005) At the Tanco pegmatite Ta oxides are also asso-ciated with lepidolite enriched in Li and F from the wallzone (Van Lichtervelde et al 2008)
93 Origin and evolution of the zoned graniticlepidolite-subtype pegmatite at Namivo
In general granitic pegmatites particularly those belong-ing to the rare-element class are accepted as having beenformed by the fractional crystallization of a granite melt(eg Cerny 1991a b 1992 Neiva et al 2008 2012 Roda-Robles et al 2012) But it also has been proposed thatpegmatites may be formed by partial melting of appropri-ate rock compositions (eg Nabelek et al 1992 Nabelekamp Russ-Nabelek 1992 Shearer et al 1992 Roda Robleset al 1999) The lepidolite-subtype pegmatites belong tothe LCT (lithium-cesium-tantalum) family (Cerny amp Ercit2005) They are derived by fractional crystallization of agranite magma (eg Cerny et al 2005 Neiva amp Ramos2010 Cerny et al 2012b) Experimental work by Londonet al (1989) and London (1990) using Macusani glass as astarting material equivalent to the bulk composition ofhighly fractionated rare-alkali-rich pegmatites underhighly evolved and hydrous but H2O undersaturatedmelt obtained the latest primary assemblage consisting
of an Li-rich mica thorn albite thorn quartz deposited directlyfrom the primary melt phase Other authors egZasedatelev (1974 1977) and Stewart (1978) argue thatlepidolite-bearing pegmatites are derived from direct ana-texis and Gordiyenko et al (1996) consider that they arederived from an undefined medium and the rare-elementmineralization is superimposed on preexisting barrenpegmatites
Lepidolite-subtype pegmatites may migrate a long wayfrom their parent granites because their volatile-rich highlyfluid pegmatite melts are stable at relatively low tempera-tures (eg Cerny et al 2005 Antunes et al 2013)Therefore the Namivo pegmatite is probably derived byfractional crystallization of an S-type granite magmawhich resulted from partial melting of metamorphosed juve-nile sediments containing micas that carry most of the traceelements that define the signature of the LCT pegmatites(eg Dahl et al 1993)
The two main models for the internal evolution of peg-matites that dominated for more than a century are a) thefractional crystallization of a flux-bearing granitic melt fromthe margins to the center of the pegmatite (Cameron et al1949) b) the interactions of an aqueous fluid with graniticmelt (Jahns amp Burnham 1969 Jahns 1982) The recentmodel of constitutional zone refining combines aspects ofboth models and invokes the formation of a flux-enriched
Table 4 Electron microprobe analyses in wt of zoned gahnite from the outer intermediate zone (OIZ) of the Namivo granitic pegmatiteMozambique
Darker Zone Lighter Zone
Mean s Range Mean s Range
SnO2 036 050 0ndash097 658 281 151ndash998TiO2 008 008 0ndash021 065 034 008ndash105Nb2O5 001 002 0ndash006 018 007 007ndash029Ta2O5 001 004 0ndash010 015 013 0ndash033ZnO 3998 123 3810ndash4109 3339 318 3004ndash3848FeO 367 048 331ndash442 433 065 306ndash498MnO 032 004 028ndash040 039 006 032ndash048MgO 003 004 0ndash010 ndash ndash ndashAl2O3 5507 050 5436ndash5572 5337 070 5257ndash5443SiO2 003 003 0ndash007 008 010 0ndash025Total 9956 9912n 8 8Sn 0035 0048 0ndash0095 0648 0278 0149ndash0983Ti 0015 0015 0ndash0038 0120 0064 0015ndash0195Nb ndash 0003 0ndash0006 0021 0009 0009ndash0037Ta ndash 0002 0ndash0006 0009 0009 0ndash0021Zn 7226 0182 6890ndash7382 6086 0568 5482ndash6965Fe2thornt 0752 0103 0675ndash0913 0894 0135 0628ndash1029Mn 0066 0008 0057ndash0083 0082 0013 0066ndash0101Mg 0010 0015 0ndash0037 ndash ndash ndashAl 15887 0052 15805ndash15954 15526 0170 15375ndash15853Si 0007 0008 0ndash0018 0019 0025 0ndash0062P
23998 23405Fe3thorn 0064 0230Fe2thorn 0686 0658SnZn 0005 0007 0ndash0014 0106 0052 0021ndash0179ZnFe2thornt 961 143 768ndash1093 681 190 536ndash1109
n number of analysis Cation formula based on 32 atoms of oxygen Fe2thornt total Fe2thorn estimated
982 A M R Neiva
eschweizerbart_xxx
boundary layer of silicate liquid in advance of a crystal-lization front (London 2008 London amp Morgan 2012)
Lepidolite-subtype pegmatites are generally scarce(Cerny et al 2005) particularly the zoned ones In thesymmetrically zoned lepidolite-subtype pegmatites ofRozna and Dobra Voda Czech Republic micas (Cernyet al 1995) tourmaline (Selway et al 1999) and colum-bite-group minerals (Novak amp Cerny 1998) evolve fromthe outermost zone to the innermost zone following thecrystallization sequence The same was found in tourma-line from the zoned Lastovicky Dolnı Bory and Raddovicelepidolite-subtype pegmatite dikes in the Czeck Republic(Selway et al 1999)
In general beryl (Neiva amp Neiva 2005) feldsparsmicas and columbite-(Mn) (in this paper) from theNamivo lepidolite-subtype pegmatite record the progres-sive chemical evolution of the pegmatite from the wallzone to the core These minerals were produced by crystal-lization from a silicate melt rather than an aqueous fluidphase The slow cooling of melt shown by the magmaticcrystallization temperatures of feldspars cannot explain theincrease in grain-size of minerals from the wall zone to thecore but fluxes will be necessary to promote the change oftexture particularly a flux-rich hydrosilicate liquidaccording to the experimental evidence (London 2009)The constitutional zone refining model will be the best forthis zoned pegmatite and probably for all lepidolite-sub-type pegmatites because this model also produces a higherfinal concentration of incompatible components in a smal-ler volume of rock than fractional crystallization does(Morgan amp London 1999)
The core margin at the Rozna pegmatite contains K-feld-spar and quartz and the core consists mainly of quartz but it issurrounded and penetrated by a quartz-bearing albitethorn lepi-dolite complex which contains several minerals At theDobra Voda pegmatite the center of the dike is occupiedby the lepidolite unit containing albite and other minerals(Cerny et al 1995) At the Namivo pegmatite the coremargin consists of quartz and beryl and the core containsmainly quartz and spodumene but also albite lepidolite andother minerals The last-unit assemblages of primary miner-als in most of the highly fractionated LCT pegmatites are richin albite and commonly contain lepidolite or spodumene andmost of the other rare phases These units represent the lastmost fractionated liquid that can be derived by fractionalcrystallization of a crustal melt (London 2008)
The Namivo granitic pegmatite shows a significant dis-tinction from the other zoned lepidolite-subtype pegmatitesand LCT pegmatites except the Tanco petalite-subtypepegmatite in Canada because the lepidolite richest in SiLi and F FeMg-containing polylithionite and associatedcolumbite-(Mn) with the highest Ta(Ta thorn Nb) ratio tanta-lite-(Fe) and tantalite-(Mn) only occur in the outer inter-mediate zone These minerals usually form late in theconsolidation of pegmatites The lepidolite and polylithio-nite are probably derived from the disequilibrium crystal-lization of an undercooled melt Tantalite may reflect a localdecrease in Li and F that caused Ta precipitation
This paper contributes to a better understanding of theorigin and evolution of the rare zoned lepidolite-subtypepegmatites and shows that although the pegmatite evolvedfrom the wall zone to the core it presents an unusualassociation of lepidolite polylithionite and tantalite in theouter intermediate zone
Acknowledgments Thanks are due to JM Cotelo Neivaand MB Dias for the samples and information providedand to MR Machado Leite and MF Guimaraes for theuse of the electron microprobe facilities at the LaboratorioNacional de Energia e Geologia (LNEG) PortugalFinancial support was provided by the PortugueseGovernment for the project Pest-OECTEUI00732011of the Geosciences Centre through the PortugueseFoundation for Science and Technology I would like tothank D London WB Simmons and the associated editorE Widom for their constructive reviews of this manuscriptand M Prieto for his editorial work
References
Alfonso P Melgarejo JC Yusta I Velasco F (2003)
Geochemistry of feldspars and muscovite in granitic pegmatite
from the Cap de Creus field Catalonia Spain Can Mineral 41
103ndash116
Antunes IMHR Neiva AMR Ramos JMF Silva PB
Silva MMVG Corfu F (2013) Petrogenetic links between
lepidolite-subtype aplite-pegmatite aplite veins and associated
granites at Segura (central Portugal) Chemie der Erde in press
httpdxdoiorg101016jchemer20121203
Batchelor RA amp Kinnaird JA (1984) Gahnite compositions
compared Mineral Mag 48 425ndash430
Beurlen H Da Silva MRR Thomas R Soares DR Olivier P
(2008) Nb-Ta-(Ti-Sn) oxide mineral chemistry as tracer of rare-
element granitic pegmatite fractionation in the Borborema pro-
vince Northeastern Brazil Miner Deposita 43 207ndash228
Cameron EN Jahns RH McNair AH Page LR (1949)
Internal structure of granitic pegmatites Econ Geol
Monograph 2 115 p
Cerny P (1991a) Fertile granites of Precambrian rare-element
pegmatite fields is geochemistry controlled by tectonic setting
or source lithologies Precambrian Res 51 429ndash468
mdash (1991b) Rare-element granite pegmatites I Anatomy and inter-
nal evolution of pegmatite deposits Geoscience Canada 18
49ndash67
mdash (1992) Geochemical and petrogenetic features of mineralization
in rare-element granitic pegmatites in the light of current
research Applied Geochemistry 7 393ndash416
mdash (1994) Evolution of feldspars in granitic pegmatites in
lsquolsquoFeldspars and their Reactionsrsquorsquo I Parsons ed NATO
Advanced Study Institute Series C421 501ndash539
mdash (2005) The Tanco rare-element pegmatite deposit Manitoba
regional context internal anatomy and global comparisons in
lsquolsquoRare-element Geochemistry and Mineral Depositsrsquorsquo RL
Linnen amp IM Samson eds Geochemical Association of
Canada Short Course Notes St Catherines 17 127ndash158
Silicate and oxide minerals from a zoned granitic pegmatite 983
eschweizerbart_xxx
Cerny P amp Ercit TS (2005) The classification of granitic pegma-
tites revisited Can Mineral 43 2005ndash2026
Cerny P Meintzer RE Andersen AJ (1985) Extreme fractiona-
tion in rare-element granitic pegmatites selected examples of
data and mechanisms Can Mineral 23 381ndash421
Cerny P Goad BE Hawthorne FC Chapmann R (1986)
Fractionation trends of the Nb- and Ta-bearing oxide minerals
in the Greer Lake pegmatite granite and its pegmatite aureole
southeastern Manitoba Am Mineral 71 501ndash517
Cerny P Stanek J Novak M Baadsgaard H Rieder M
Ottolini L Kavalova M Chapman R (1995) Geochemical
and structural evolution of micas in the Rozna amp Dobra Voda
pegmatites Czech Republic Mineral Petrol 55 177ndash201
Cerny P Ercit TS Vanstone PJ (1998) Mineralogy and petrol-
ogy of the Tanco rare-element pegmatite deposit southeastern
Manitoba International Mineralogical Association 17th General
Meeting Toronto Field Guidebook B6
Cerny P Chapman R Ferreira K Smeds SA (2004)
Geochemistry of oxide minerals of Nb Ta Sn and Sb in
the Varutrask granitic pegmatite Sweden The case of an
lsquolsquoanomalousrsquorsquo columbitendashtantalite trend Am Mineral 89
505ndash518
Cerny P Masau M Goad BE Ferreira K (2005) The Greer
Lake leucogranite Manitoba and the origin of lepidolite-sub-
type granitic pegmatites Lithos 80 305ndash321
Cerny P Teertstra DK Chapman R Selway JB Hawthorne
FC Ferreira K Chackowsky LE Wang X-J Meintzer
RE (2012a) Extreme fractionation and deformation of the
leucogranite-pegmatite suite at Red Cross Lake Manitoba
Canada IV Mineralogy Can Mineral 50 1839ndash1875
Cerny P Halden NM Ferreira K Meintzer RE Brisbin WC
Chackowsky LE (2012b) Extreme fractionation and deforma-
tion of the leucogranite-pegmatite suite at Red Cross Lake
Manitoba Canada II Petrology of the leucogranites and peg-
matites Can Mineral 50 1807ndash1822
Dahl PS When DC Feldmann SG (1993) The systematics of
trace-element partitioning between coexisting muscovite and
biotite in metamorphic rocks from the Black Hills South
Dakota USA Geochim Cosmochim Acta 57 2487ndash2505
Dias MB amp Wilson WE (2000) The Alto Ligonha Pegmatites
Mozambique Mineral Record 31 459ndash497
Fleet ME (2003) Rock-Forming Minerals vol 3A Sheet silicates
micas The Geological Society London second edition chap 6
Lithium micas 651ndash690
Foord EE Cerny P Jackson LL Sherman DM Eby RK
(1995) Mineralogical and geochemical evolutions of micas
from miarolitic pegmatites of the anorogenic pikes-Peak
Batholith Colorado Mineral Petrol 55 1ndash26
Foster MD (1960) Interpretation of the composition of lithium
micas US Geol Surv Prof Paper 354-E 115ndash147
Fuhrman ML amp Lindsley DK (1988) Ternary-feldspar modeling
and thermometry Am Mineral 73 201ndash215
Gomes CL Castro P Alves C (1995) Caracterizacao das espi-
nelas zincıferas e do par ganite-nigerite no campo aplito-
pegmatıtico da Serra de Arga-Minho N de Portugal IV
Congresso Nacional de Geologia Resumos Alargados
Universidade do Porto Mem 4 629ndash633
Gordiyenko VV Ilyina AN Timochina LA Badamina EB
Stanek J (1996) Geochemical model of evolution of a pegma-
tite-forming ore-magmatic system of western Moravia Proc
Russ Mineral Soc 125 38ndash48 (in Russian)
Icenhower JP amp London D (1995) An experimental study for
element partitioning between biotite muscovite and coexisting
peraluminous granitic melt at 200 MPa (H2O) Am Mineral 80
1229ndash1251
Jahns RH (1982) Internal evolution of pegmatite bodies in lsquolsquoGranitic
Pegmatites in science and industryrsquorsquo P Cerny ed Mineralogical
Association of Canada Short Course Handbook 8 293ndash327
Jahns RH amp Burnham CW (1969) Experimental studies of
pegmatite genesis I A model for the derivation and crystal-
lization of granitic pegmatites Econ Geol 64 843ndash864
Jolliff BL Papike JJ Shearer CK (1987) Fractionation trends
in mica and tourmaline as indicators of pegmatite internal evo-
lution Bob Ingersoll pegmatite Black Hills South Dakota
USA GeochimCosmochim Acta 51 519ndash534
Kile DE amp Foord EE (1998) Micas from the Pikes Peak bath-
olith and its cogenetic granitic pegmatites Colorado optical
properties composition and correlation with pegmatite evolu-
tion Can Mineral 36 463ndash482
Linnen RL (1998) The solubility of Nb-Ta-Zr-Hf-W in granitic
melts with Li and Li thorn F constraints for mineralization in rare
metal granites and pegmatites Econ Geol 93 1013ndash1025
Linnen RL amp Cuney M (2005) Granite-related rare-element
deposits and experimental constraints on Ta-Nb-W-Sn-Zr-Hf
mineralization in lsquolsquoRare-element geochemistry and mineral
depositsrsquorsquo RL Linnen amp IM Samson eds Geochemical
Association of Canada Short Course Notes 17 45ndash68
London D (1990) Internal differentiation of rare-element pegmatites
a synthesis of recent research in lsquolsquoOre Bearing Granite Systems
Petrogenesis and Mineralizing Processesrsquorsquo HJ Stein amp JL
Hannah eds Geol Soc America Special Paper 246 35ndash50
mdash (2008) Pegmatites The Canadian Mineralogist Special
Publication 10 347 p
mdash (2009) The origin of primary textures in granitic pegmatites
Can Mineral 47 697ndash724
London D amp Morgan GB VI (2012) The pegmatite puzzle
Elements 8 263ndash268
London D Morgan GB VI Hervig RL (1989) Vapor-under-
saturated experiments in the system macusanite-H2O at 200
MPa and the internal differentiation of granitic pegmatites
Contrib Mineral Petrol 102 1ndash17
London D Morgan GB VI Paul KA Guttery BM (2012)
Internal evolution of miarolitic granitic pegmatites at the Little
Three mine Ramona California USA Can Mineral 50
1025ndash1054
Martins T Lima A Simmons WB Folster AU Noronha F
(2011) Geochemical fractionation of Nb-Ta oxides in Li-bear-
ing pegmatites from the Barroso-Alvao pegmatite field northern
Portugal Can Mineral 49 777ndash791
Monier G Charoy B Cuney M Ohnenstetter D Robert JL
(1987) Evolution spatiale et temporelle de la composition des
micas du granite albitique a topaze-lepidolite de Beauvoir
Geologie De La France 2ndash3 179ndash188
Monier G amp Robert JL (1986) Evolution of the miscibility gap
between muscovite and biotite solid solutions with increasing
lithium content an experimental study in the systems
K2OndashLi2OndashMgOndashAl2O3ndashSiO2ndashH2OndashHF at 600 C 2 kbar
PH2O comparison with natural lithium micas Mineral Mag
50 641ndash651
Morgan GBVI amp London D (1999) Crystallization of the little
three layered pegmatite-aplite dike Ramona District California
Contrib Mineral Petrol 136 310ndash330
984 A M R Neiva
eschweizerbart_xxx
Nabelek PI amp Russ-Nabelek C (1992) The generation and crys-
tallization conditions of the Proterozoic Harney Peak
Leucrogranite Black Hills South Dakota USA petrologic and
geochemical constraints Contrib Mineral Petrol 110
173ndash191
Nabelek PI Russ-Nabelek C Haeussler GT (1992) Stable
isotope evidence for the petrogenesis and fluid evolution in
the Proterozoic Harney Peak leucogranite Black Hills
South Dakota Geochim Cosmochim Acta 56 403ndash417
Neiva AMR amp Champness PE (1997) Nigerite and gahnite from
the granitic pegmatite veins of Cabanas Ponte de Lima northern
Portugal N Jb Mineral Mh 9 385ndash409
Neiva AMR Gomes MEP Ramos JMF Silva PB (2008)
Geochemistry of granitic aplite-pegmatite sills and their miner-
als from Arcozelo da Serra area (Gouveia central Portugal)
Eur J Mineral 20 465ndash485
Neiva AMR amp Neiva JMC (2005) Beryl from the granitic
pegmatite at Namivo Alto Ligonha Mozambique N Jb
Mineral Abh 181 173ndash182
Neiva AMR amp Ramos JMF (2010) Geochemistry of granitic
aplite-pegmatite sills and petrogenetic links with granites
Guarda-Belmonte area central Portugal Eur J Mineral 22
837ndash854
Neiva AMR Silva PB Ramos JMF (2012) Geochemistry of
granitic aplite-pegmatite veins and sills and their minerals from the
Sabugal area central Portugal N Jb Mineral Abh 189 49ndash74
Novak M amp Cerny P (1998) Niobium-tantalum oxide minerals
from complex granitic pegmatites in the Moldanubicum Czech
Republic primary versus secondary compositional trends Can
Mineral 36 659ndash672
Pesquera Perez A Torres-Ruiz J Gil PP Velilla N (1999)
Chemistry and genetic implications of tourmaline and Li-F-Cs
micas from the Valdeflores (Caceres Spain) Am Mineral 84
55ndash69
Rieder M Cavazzini G DrsquoYakonov YuS Frank-Kamenetskii
VA Gottardi G Guggenheim S Koval PV Muller G
Neiva AMR Radoslovich EW Robert J-L Sassi FP
Takeda H Weiss Z Wones DR (1999) Nomenclature of the
micas Mineral Mag 63 267ndash279
Roda Robles E Pesquera Perez A Velasco Roldan F Fontan F
(1999) The granitic pegmatites of the Fregeneda area
(Salamanca Spain) characteristics and petrogenesis Mineral
Mag 63 535ndash558
Roda Robles E Pesquera A Gil-Crespo PP Torres-Ruiz J
Fontan F (2005) Origin and internal evolution of the Li-F-
Be-P-bearing Pinilla de Fermoselle pegmatite (Central Iberian
Zone Zamora Spain) Am Mineral 90 1887ndash1899
Roda Robles E Pesquera Perez A Gil PP Torres-Ruiz J de
Parseval P (2006) Mineralogy and geochemistry of micas from
the Pinilla de Fermoselle pegmatite (Zamora Spain) Eur J
Mineral 18 369ndash377
Roda Robles E Keller P Pesquera Perez A Fontan F (2007)
Micas of the muscovite-lepidolite series from Karibib pegma-
tites Namibia Mineral Mag 71 41ndash62
Roda Robles E Pesquera A Gil-Crespo P Torres-Ruiz J
(2012) From granite to highly evolved pegmatite a case study
of the Pinilla de Fermoselle granite-pegmatite system (Zamora
Spain) Lithos 153 192ndash207
Selway JB Novak M Cerny P Hawthorne FC (1999)
Compositional evolution of tourmaline in lepidolite-subtype
pegmatites Eur J Mineral 11 569ndash584
Shearer CK Papike JJ Jolliff B (1992) Petrogenetic links
among granites and pegmatites in the Harney Peak rare-element
granite-pegmatite system Black Hills South Dakota Can
Mineral 30 785ndash809
Soares DR Hartmut B Ferreira ACM da Silva MRR
(2007) Chemical composition of gahnite and degree of peg-
matitic fractionation in the Borborema Pegmatitic Province
northeastern Brazil Anais Da Academ Bras Cien 79
395ndash404
Stewart DB (1978) Petrogenesis of lithium-rich pegmatites Am
Mineral 63 970ndash980
Tischendorff G Gattesmann B Forster H-J Trumbull RB
(1997) On Li-bearing micas estimating Li from electron
microprobe analyses and an improved diagram for graphical
representation Mineral Mag 61 809ndash834
Van Lichtervelde M Linnen RL Salvi S Beziat D (2006)
The role of metagabbro rafts on tantalum mineralization in the
Tanco granitic pegmatite Manitoba Can Mineral 44
625ndash644
Van Lichtervelde M Gregoire M Linnen RL Beziat D Salvi
S (2008) Trace element geochemistry by laser ablation ICP-
MS of micas associated with Ta mineralization in the Tanco
pegmatite Manitoba Canada Contrib Mineral Petrol 155
791ndash806
Vieira R Roda-Robles E Pesquera A Lima A (2011)
Chemical variation and significance of micas from the
Fregeneda-Almendra pegmatitic field (Central-Iberian Zone
Spain and Portugal) Am Mineral 96 637ndash645
Wen S amp Nekvasil H (1994) SOLVCALC an interactive gra-
phics program package for calculating ternary feldspar solvus
and two-feldspar geothermometry Comput Geosci 20
1025ndash1040
Wise MA (1995) Trace element chemistry of lithium-rich micas
from rare-element granitic pegmatites Mineral Petrol 55
203ndash215
Zasedatelev AM (1974) Possible accumulation of lithium in host
rocks of lithium pegmatite veins during old sedimentation pro-
cesses Doklady Acad Sci USSR Earth Sci Ser 218 196ndash198
(in Russian)
mdash (1977) Quantitative of metamorphic generation of rare-metal
pegmatites with lithium mineralization Doklady Acad Sci
USSR Earth Sci Ser 236 219ndash221 (in Russian)
Received 26 January 2013
Modified version received 21 May 2013
Accepted 23 July 2013
Silicate and oxide minerals from a zoned granitic pegmatite 985
eschweizerbart_xxx
Little Three pegmatite dike USA (Morgan amp London1999) and the micas enriched in Li and F from theNamivo pegmatite belonging to the OIZ Furthermore ina boundary layer melt that became enriched in Li and F theKRb ratio of micas decreases strongly (Van Lichterveldeet al 2008) which was not found in these micas from theOIZ (Fig 7d) Nor can they have resulted from the crystal-lization of a late melt that would have reacted with the OIZbecause these micas are among those containing the high-est KRb values (Fig 7d)
92 The importance of feldspars micas andcolumbitendashtantalite compositions to the Namivogranitic pegmatite evolution
The trace elements Rb and Cs and the KRb and KCs ratioshave been used to show the evolution of K-feldspar inpegmatites (eg Cerny 1994 Cerny et al 2005 RodaRobles et al 2005) The Rb and Cs contents increase andthe KRb and KCs ratios of K-feldspar decrease from theWZ to the Cc (Fig 9 Table 2) reflecting the growth of K-feldspar from an increasingly fractionated melt withouthaving grown from or having been chemically modifiedby an aqueous fluid as in the Swamp pegmatite section atthe Little Three Mine USA (London et al 2012) Thecrystallization of K-feldspar from an exsolved aqueousfluid from melt will reverse the magmatic fractionation ofRb Cs KRb and KCs because Rb and especially Cs areso much more compatible in vapor that both Rb and Csremain in the fluid phase (London et al 2012) The feldsparsolvus pairs in the Namivo pegmatite record magmaticcrystallization temperatures that decrease from WZ to CcAlbite shows a decrease in the Ca Sr contents and SrCaratio from the WZ to the Cc (Fig 8 Table 2) Therefore thefeldspars and also Al-richer micas as already explainedshow fractionation in this zoned pegmatite
In general lepidolite from the Namivo pegmatite hassimilar Rb2O and Cs2O contents and KRb (wt) values tothose of lepidolite from the Rozna and Dobra Voda lepi-dolite-subtype pegmatites in the Czech Republic (Cernyet al 1995) but lower Rb2O and Cs2O contents thanlepidolite from the lepidolite-subtype pegmatite at RedCross Lake Manitoba Canada (Cerny et al 2012a) K-feldspar from the Namivo pegmatite also has lower Rb2O
Table 3 Representative electron microprobe analyses in wt of columbitendashtantalite from the Namivo granitic pegmatite Mozambique
Outer Intermediate Zone - OIZ Inner Intermediate Zone - IIZa
Core - Cc
D L L
WO3 022 059 079 113 101 351 050 007Ta2O5 5487 5123 2503 3186 2888 2519 3127 4542Nb2O5 2537 3000 5483 4635 5113 5144 4911 3686SnO2 008 015 024 049 020 026 017 012TiO2 263 161 136 254 202 145 125 016FeO 860 710 665 471 236 068 mdash mdashMnO 793 952 1099 1304 1400 1725 1748 1718Total 9970 10020 9989 10012 9960 9978 9978 9981W 0004 0011 0013 0019 0016 0057 0008 0001Ta 1065 0975 0422 0552 0495 0430 0543 0847Nb 0819 0949 1538 1336 1456 1460 1418 1143Sn 0002 0004 0006 0012 0005 0007 0004 0003Ti 0141 0085 0063 0122 0096 0068 0060 0008Fe 0513 0416 0345 0251 0124 0036 mdash mdashMn 0479 0564 0578 0704 0747 0917 0945 0998P
3023 3004 2965 2996 2939 2975 2978 3000Mn(Mn thorn Fe) 048 058 063 074 086 096 100 100Ta(Ta thorn Nb) 057 051 022 029 025 023 028 043Classification tant-(Fe) tant-(Mn) col-(Mn) col-(Mn) col-(Mn) col-(Mn) col-(Mn) col-(Mn)
D ndash darker L ndash lighter zones mdash Not detected tant-tantalite col-columbite Cation formula on the basis of 6 atoms of oxygen
Fig 10 Compositions of columbitendashtantalite from the Namivogranitic pegmatite Mozambique in the columbite quadrilateralshowing that Mn(Mn thorn Fe) of columbite-(Mn) increases from theOIZ to the Cc and the richest columbite-(Mn) in Ta(Ta thorn Nb)tantalite-(Fe) and tantalite-(Mn) only occur in the OIZ OIZ IIZaand Cc as in Fig 2
980 A M R Neiva
eschweizerbart_xxx
and Cs2O contents than K-feldspar from the lepidolite-subtype pegmatite at Red Cross Lake The Rb2O andCs2O contents of primary and late K-feldspar of this peg-matite at Red Cross Lake attained unprecedented levels(Cerny et al 2012a) The lowest KRb (wt) values ofmuscovite lithian muscovite lsquolsquomixed formrsquorsquo and lepido-lite from the IIZb and Cc (Fig 7) and K-feldspar (KRb frac1414) from the Cc compare well with those found in theseminerals from the AC6frac143 lepidolite-subtype pegmatitefrom Greer Lake (Cerny et al 2005) and some of themost fractionated pegmatites worldwide which belong tothe petalite-subtype (eg Tanco Manitoba Cerny 2005Cerny et al 1998 Varutrask Sweden Cerny et al 2005)but muscovite lithian muscovite and lepidolite from theIIZb and Cc have lower Rb2O and Cs2O contents than thesemicas from the Tanco pegmatite (Cerny 2005a VanLichtervelde et al 2008) K-feldspar also has lower
contents of these oxides than the most evolved K-feldsparfrom the Tanco pegmatite (Cerny 2005a) The magmaticfractionation was strong from the WZ to IIZb and Cc of theNamivo lepidolite-subtype pegmatite
The compositional trend of columbite-(Mn) from the OIZto Cc of the Namivo granitic lepidolite-subtype pegmatite(Fig 10) is identical to that of columbite-group mineralsfrom the lepidolite-subtype complex granitic pegmatitesfrom the Dobra Voda in the Moldanubicum CzechRepublic (Novak amp Cerny 1998) and the HimalayaDistrict southern California (shown in Cerny et al 2004)Experimental data for the Fe-Mn pair (Linnen amp Cuney2005) suggest an increase in Fe with fractional crystalliza-tion which is not observed in nature Other phases seem tocontrol the bahavior of Fe and Mn in the melt eg thecrystallization of tourmaline causes a rapid increase of theMnFe in the melt (Van Lichtervelde et al 2006) When thecrystallization of tourmaline stopped the columbitendashtantaliteminerals showed a constant MnFe indicating that the Fe andMn contents in the melt remained constant Schorl onlyoccurs in the OIZ of the Namivo granitic pegmatite and itscrystallization cannot be responsible for the increase in theMnFe of the melt because Mn(Mn thorn Fe) of columbite-(Mn) increases progressively from the OIZ to the IIZa and Cc(Fig 10) Garnet zinnwaldite and gahnite containing Fe andMn also only occur in the OIZ and cannot also have causedthe increase of the MnFe in the melt The dominant Mnenrichment before Ta enrichment started in the columbitendash-tantalite composition from some granitic pegmatites isattributed to an increased alkali-fluoride activity at moderatemHF (Cerny et al 2004) and an increase in the activity offluorine (Martins et al 2011) Each Al-richer mica (musco-vite lithian muscovite and lsquolsquomixed formrsquorsquo) from the Namivogranitic pegmatite shows an increase in F content from theOIZ to the IIZa IIZb and Cc (Table 1) In general the Fcontent of lepidolite also increases from the IIZa to the IIZband Cc Therefore the extreme Fe-Mn fractionation beforeTa enrichment in columbite-(Mn) (Fig 10) may be due to anincrease in the activity of fluorine as a consequence offractional crystallization The increase in the Ta content ofcolumbite-(Mn) from the Namivo granitic pegmatite isattributed to fractional crystallization
The geochemical evolution of albite and K-feldsparfrom the WZ to the Cc Al-richer micas muscovite lithianmuscovite and lsquolsquomixed formrsquorsquo from the OIZ to the Cc andlepidolite from the IIZa to the Cc and columbite-(Mn) andalso beryl (Neiva amp Neiva 2005) from the OIZ to the Ccare caused by magma fractionation The pegmatite zonesare the product of primary crystallization from a volatile-rich silicate melt The pegmatite consolidated from the WZto the Cc The IIZb is one of the most evolved zones asalso suggested by the beryl composition (Neiva amp Neiva2005) and is the richest in lsquolsquomixed formrsquorsquo and lepidolite
The richest columbite-(Mn) in Ta(Ta thorn Nb) and com-positions of tantalite-(Fe) and tantalite-(Mn) only occur inthe OIZ (Fig 10a) associated with lepidolite and polythio-nite (Fig 3c) which may be due to the local depletion of Liand F in the melt which decreases the solubility of Ta andcauses Ta precipitation (Linnen 1998 Linnen amp Cuney
Fig 11 a Backscattered-electron image of a gahnite crystal with adarker zone partially surrounding a lighter zone from the OIZ of theNamivo granitic pegmatite b c Plot of gahnite compositions in theSn-Zn-Ti diagram (atomic proportions) showing a chemical distinc-tion between the lighter and darker zones OIZ as in Fig 2
Silicate and oxide minerals from a zoned granitic pegmatite 981
eschweizerbart_xxx
2005) At the Tanco pegmatite Ta oxides are also asso-ciated with lepidolite enriched in Li and F from the wallzone (Van Lichtervelde et al 2008)
93 Origin and evolution of the zoned graniticlepidolite-subtype pegmatite at Namivo
In general granitic pegmatites particularly those belong-ing to the rare-element class are accepted as having beenformed by the fractional crystallization of a granite melt(eg Cerny 1991a b 1992 Neiva et al 2008 2012 Roda-Robles et al 2012) But it also has been proposed thatpegmatites may be formed by partial melting of appropri-ate rock compositions (eg Nabelek et al 1992 Nabelekamp Russ-Nabelek 1992 Shearer et al 1992 Roda Robleset al 1999) The lepidolite-subtype pegmatites belong tothe LCT (lithium-cesium-tantalum) family (Cerny amp Ercit2005) They are derived by fractional crystallization of agranite magma (eg Cerny et al 2005 Neiva amp Ramos2010 Cerny et al 2012b) Experimental work by Londonet al (1989) and London (1990) using Macusani glass as astarting material equivalent to the bulk composition ofhighly fractionated rare-alkali-rich pegmatites underhighly evolved and hydrous but H2O undersaturatedmelt obtained the latest primary assemblage consisting
of an Li-rich mica thorn albite thorn quartz deposited directlyfrom the primary melt phase Other authors egZasedatelev (1974 1977) and Stewart (1978) argue thatlepidolite-bearing pegmatites are derived from direct ana-texis and Gordiyenko et al (1996) consider that they arederived from an undefined medium and the rare-elementmineralization is superimposed on preexisting barrenpegmatites
Lepidolite-subtype pegmatites may migrate a long wayfrom their parent granites because their volatile-rich highlyfluid pegmatite melts are stable at relatively low tempera-tures (eg Cerny et al 2005 Antunes et al 2013)Therefore the Namivo pegmatite is probably derived byfractional crystallization of an S-type granite magmawhich resulted from partial melting of metamorphosed juve-nile sediments containing micas that carry most of the traceelements that define the signature of the LCT pegmatites(eg Dahl et al 1993)
The two main models for the internal evolution of peg-matites that dominated for more than a century are a) thefractional crystallization of a flux-bearing granitic melt fromthe margins to the center of the pegmatite (Cameron et al1949) b) the interactions of an aqueous fluid with graniticmelt (Jahns amp Burnham 1969 Jahns 1982) The recentmodel of constitutional zone refining combines aspects ofboth models and invokes the formation of a flux-enriched
Table 4 Electron microprobe analyses in wt of zoned gahnite from the outer intermediate zone (OIZ) of the Namivo granitic pegmatiteMozambique
Darker Zone Lighter Zone
Mean s Range Mean s Range
SnO2 036 050 0ndash097 658 281 151ndash998TiO2 008 008 0ndash021 065 034 008ndash105Nb2O5 001 002 0ndash006 018 007 007ndash029Ta2O5 001 004 0ndash010 015 013 0ndash033ZnO 3998 123 3810ndash4109 3339 318 3004ndash3848FeO 367 048 331ndash442 433 065 306ndash498MnO 032 004 028ndash040 039 006 032ndash048MgO 003 004 0ndash010 ndash ndash ndashAl2O3 5507 050 5436ndash5572 5337 070 5257ndash5443SiO2 003 003 0ndash007 008 010 0ndash025Total 9956 9912n 8 8Sn 0035 0048 0ndash0095 0648 0278 0149ndash0983Ti 0015 0015 0ndash0038 0120 0064 0015ndash0195Nb ndash 0003 0ndash0006 0021 0009 0009ndash0037Ta ndash 0002 0ndash0006 0009 0009 0ndash0021Zn 7226 0182 6890ndash7382 6086 0568 5482ndash6965Fe2thornt 0752 0103 0675ndash0913 0894 0135 0628ndash1029Mn 0066 0008 0057ndash0083 0082 0013 0066ndash0101Mg 0010 0015 0ndash0037 ndash ndash ndashAl 15887 0052 15805ndash15954 15526 0170 15375ndash15853Si 0007 0008 0ndash0018 0019 0025 0ndash0062P
23998 23405Fe3thorn 0064 0230Fe2thorn 0686 0658SnZn 0005 0007 0ndash0014 0106 0052 0021ndash0179ZnFe2thornt 961 143 768ndash1093 681 190 536ndash1109
n number of analysis Cation formula based on 32 atoms of oxygen Fe2thornt total Fe2thorn estimated
982 A M R Neiva
eschweizerbart_xxx
boundary layer of silicate liquid in advance of a crystal-lization front (London 2008 London amp Morgan 2012)
Lepidolite-subtype pegmatites are generally scarce(Cerny et al 2005) particularly the zoned ones In thesymmetrically zoned lepidolite-subtype pegmatites ofRozna and Dobra Voda Czech Republic micas (Cernyet al 1995) tourmaline (Selway et al 1999) and colum-bite-group minerals (Novak amp Cerny 1998) evolve fromthe outermost zone to the innermost zone following thecrystallization sequence The same was found in tourma-line from the zoned Lastovicky Dolnı Bory and Raddovicelepidolite-subtype pegmatite dikes in the Czeck Republic(Selway et al 1999)
In general beryl (Neiva amp Neiva 2005) feldsparsmicas and columbite-(Mn) (in this paper) from theNamivo lepidolite-subtype pegmatite record the progres-sive chemical evolution of the pegmatite from the wallzone to the core These minerals were produced by crystal-lization from a silicate melt rather than an aqueous fluidphase The slow cooling of melt shown by the magmaticcrystallization temperatures of feldspars cannot explain theincrease in grain-size of minerals from the wall zone to thecore but fluxes will be necessary to promote the change oftexture particularly a flux-rich hydrosilicate liquidaccording to the experimental evidence (London 2009)The constitutional zone refining model will be the best forthis zoned pegmatite and probably for all lepidolite-sub-type pegmatites because this model also produces a higherfinal concentration of incompatible components in a smal-ler volume of rock than fractional crystallization does(Morgan amp London 1999)
The core margin at the Rozna pegmatite contains K-feld-spar and quartz and the core consists mainly of quartz but it issurrounded and penetrated by a quartz-bearing albitethorn lepi-dolite complex which contains several minerals At theDobra Voda pegmatite the center of the dike is occupiedby the lepidolite unit containing albite and other minerals(Cerny et al 1995) At the Namivo pegmatite the coremargin consists of quartz and beryl and the core containsmainly quartz and spodumene but also albite lepidolite andother minerals The last-unit assemblages of primary miner-als in most of the highly fractionated LCT pegmatites are richin albite and commonly contain lepidolite or spodumene andmost of the other rare phases These units represent the lastmost fractionated liquid that can be derived by fractionalcrystallization of a crustal melt (London 2008)
The Namivo granitic pegmatite shows a significant dis-tinction from the other zoned lepidolite-subtype pegmatitesand LCT pegmatites except the Tanco petalite-subtypepegmatite in Canada because the lepidolite richest in SiLi and F FeMg-containing polylithionite and associatedcolumbite-(Mn) with the highest Ta(Ta thorn Nb) ratio tanta-lite-(Fe) and tantalite-(Mn) only occur in the outer inter-mediate zone These minerals usually form late in theconsolidation of pegmatites The lepidolite and polylithio-nite are probably derived from the disequilibrium crystal-lization of an undercooled melt Tantalite may reflect a localdecrease in Li and F that caused Ta precipitation
This paper contributes to a better understanding of theorigin and evolution of the rare zoned lepidolite-subtypepegmatites and shows that although the pegmatite evolvedfrom the wall zone to the core it presents an unusualassociation of lepidolite polylithionite and tantalite in theouter intermediate zone
Acknowledgments Thanks are due to JM Cotelo Neivaand MB Dias for the samples and information providedand to MR Machado Leite and MF Guimaraes for theuse of the electron microprobe facilities at the LaboratorioNacional de Energia e Geologia (LNEG) PortugalFinancial support was provided by the PortugueseGovernment for the project Pest-OECTEUI00732011of the Geosciences Centre through the PortugueseFoundation for Science and Technology I would like tothank D London WB Simmons and the associated editorE Widom for their constructive reviews of this manuscriptand M Prieto for his editorial work
References
Alfonso P Melgarejo JC Yusta I Velasco F (2003)
Geochemistry of feldspars and muscovite in granitic pegmatite
from the Cap de Creus field Catalonia Spain Can Mineral 41
103ndash116
Antunes IMHR Neiva AMR Ramos JMF Silva PB
Silva MMVG Corfu F (2013) Petrogenetic links between
lepidolite-subtype aplite-pegmatite aplite veins and associated
granites at Segura (central Portugal) Chemie der Erde in press
httpdxdoiorg101016jchemer20121203
Batchelor RA amp Kinnaird JA (1984) Gahnite compositions
compared Mineral Mag 48 425ndash430
Beurlen H Da Silva MRR Thomas R Soares DR Olivier P
(2008) Nb-Ta-(Ti-Sn) oxide mineral chemistry as tracer of rare-
element granitic pegmatite fractionation in the Borborema pro-
vince Northeastern Brazil Miner Deposita 43 207ndash228
Cameron EN Jahns RH McNair AH Page LR (1949)
Internal structure of granitic pegmatites Econ Geol
Monograph 2 115 p
Cerny P (1991a) Fertile granites of Precambrian rare-element
pegmatite fields is geochemistry controlled by tectonic setting
or source lithologies Precambrian Res 51 429ndash468
mdash (1991b) Rare-element granite pegmatites I Anatomy and inter-
nal evolution of pegmatite deposits Geoscience Canada 18
49ndash67
mdash (1992) Geochemical and petrogenetic features of mineralization
in rare-element granitic pegmatites in the light of current
research Applied Geochemistry 7 393ndash416
mdash (1994) Evolution of feldspars in granitic pegmatites in
lsquolsquoFeldspars and their Reactionsrsquorsquo I Parsons ed NATO
Advanced Study Institute Series C421 501ndash539
mdash (2005) The Tanco rare-element pegmatite deposit Manitoba
regional context internal anatomy and global comparisons in
lsquolsquoRare-element Geochemistry and Mineral Depositsrsquorsquo RL
Linnen amp IM Samson eds Geochemical Association of
Canada Short Course Notes St Catherines 17 127ndash158
Silicate and oxide minerals from a zoned granitic pegmatite 983
eschweizerbart_xxx
Cerny P amp Ercit TS (2005) The classification of granitic pegma-
tites revisited Can Mineral 43 2005ndash2026
Cerny P Meintzer RE Andersen AJ (1985) Extreme fractiona-
tion in rare-element granitic pegmatites selected examples of
data and mechanisms Can Mineral 23 381ndash421
Cerny P Goad BE Hawthorne FC Chapmann R (1986)
Fractionation trends of the Nb- and Ta-bearing oxide minerals
in the Greer Lake pegmatite granite and its pegmatite aureole
southeastern Manitoba Am Mineral 71 501ndash517
Cerny P Stanek J Novak M Baadsgaard H Rieder M
Ottolini L Kavalova M Chapman R (1995) Geochemical
and structural evolution of micas in the Rozna amp Dobra Voda
pegmatites Czech Republic Mineral Petrol 55 177ndash201
Cerny P Ercit TS Vanstone PJ (1998) Mineralogy and petrol-
ogy of the Tanco rare-element pegmatite deposit southeastern
Manitoba International Mineralogical Association 17th General
Meeting Toronto Field Guidebook B6
Cerny P Chapman R Ferreira K Smeds SA (2004)
Geochemistry of oxide minerals of Nb Ta Sn and Sb in
the Varutrask granitic pegmatite Sweden The case of an
lsquolsquoanomalousrsquorsquo columbitendashtantalite trend Am Mineral 89
505ndash518
Cerny P Masau M Goad BE Ferreira K (2005) The Greer
Lake leucogranite Manitoba and the origin of lepidolite-sub-
type granitic pegmatites Lithos 80 305ndash321
Cerny P Teertstra DK Chapman R Selway JB Hawthorne
FC Ferreira K Chackowsky LE Wang X-J Meintzer
RE (2012a) Extreme fractionation and deformation of the
leucogranite-pegmatite suite at Red Cross Lake Manitoba
Canada IV Mineralogy Can Mineral 50 1839ndash1875
Cerny P Halden NM Ferreira K Meintzer RE Brisbin WC
Chackowsky LE (2012b) Extreme fractionation and deforma-
tion of the leucogranite-pegmatite suite at Red Cross Lake
Manitoba Canada II Petrology of the leucogranites and peg-
matites Can Mineral 50 1807ndash1822
Dahl PS When DC Feldmann SG (1993) The systematics of
trace-element partitioning between coexisting muscovite and
biotite in metamorphic rocks from the Black Hills South
Dakota USA Geochim Cosmochim Acta 57 2487ndash2505
Dias MB amp Wilson WE (2000) The Alto Ligonha Pegmatites
Mozambique Mineral Record 31 459ndash497
Fleet ME (2003) Rock-Forming Minerals vol 3A Sheet silicates
micas The Geological Society London second edition chap 6
Lithium micas 651ndash690
Foord EE Cerny P Jackson LL Sherman DM Eby RK
(1995) Mineralogical and geochemical evolutions of micas
from miarolitic pegmatites of the anorogenic pikes-Peak
Batholith Colorado Mineral Petrol 55 1ndash26
Foster MD (1960) Interpretation of the composition of lithium
micas US Geol Surv Prof Paper 354-E 115ndash147
Fuhrman ML amp Lindsley DK (1988) Ternary-feldspar modeling
and thermometry Am Mineral 73 201ndash215
Gomes CL Castro P Alves C (1995) Caracterizacao das espi-
nelas zincıferas e do par ganite-nigerite no campo aplito-
pegmatıtico da Serra de Arga-Minho N de Portugal IV
Congresso Nacional de Geologia Resumos Alargados
Universidade do Porto Mem 4 629ndash633
Gordiyenko VV Ilyina AN Timochina LA Badamina EB
Stanek J (1996) Geochemical model of evolution of a pegma-
tite-forming ore-magmatic system of western Moravia Proc
Russ Mineral Soc 125 38ndash48 (in Russian)
Icenhower JP amp London D (1995) An experimental study for
element partitioning between biotite muscovite and coexisting
peraluminous granitic melt at 200 MPa (H2O) Am Mineral 80
1229ndash1251
Jahns RH (1982) Internal evolution of pegmatite bodies in lsquolsquoGranitic
Pegmatites in science and industryrsquorsquo P Cerny ed Mineralogical
Association of Canada Short Course Handbook 8 293ndash327
Jahns RH amp Burnham CW (1969) Experimental studies of
pegmatite genesis I A model for the derivation and crystal-
lization of granitic pegmatites Econ Geol 64 843ndash864
Jolliff BL Papike JJ Shearer CK (1987) Fractionation trends
in mica and tourmaline as indicators of pegmatite internal evo-
lution Bob Ingersoll pegmatite Black Hills South Dakota
USA GeochimCosmochim Acta 51 519ndash534
Kile DE amp Foord EE (1998) Micas from the Pikes Peak bath-
olith and its cogenetic granitic pegmatites Colorado optical
properties composition and correlation with pegmatite evolu-
tion Can Mineral 36 463ndash482
Linnen RL (1998) The solubility of Nb-Ta-Zr-Hf-W in granitic
melts with Li and Li thorn F constraints for mineralization in rare
metal granites and pegmatites Econ Geol 93 1013ndash1025
Linnen RL amp Cuney M (2005) Granite-related rare-element
deposits and experimental constraints on Ta-Nb-W-Sn-Zr-Hf
mineralization in lsquolsquoRare-element geochemistry and mineral
depositsrsquorsquo RL Linnen amp IM Samson eds Geochemical
Association of Canada Short Course Notes 17 45ndash68
London D (1990) Internal differentiation of rare-element pegmatites
a synthesis of recent research in lsquolsquoOre Bearing Granite Systems
Petrogenesis and Mineralizing Processesrsquorsquo HJ Stein amp JL
Hannah eds Geol Soc America Special Paper 246 35ndash50
mdash (2008) Pegmatites The Canadian Mineralogist Special
Publication 10 347 p
mdash (2009) The origin of primary textures in granitic pegmatites
Can Mineral 47 697ndash724
London D amp Morgan GB VI (2012) The pegmatite puzzle
Elements 8 263ndash268
London D Morgan GB VI Hervig RL (1989) Vapor-under-
saturated experiments in the system macusanite-H2O at 200
MPa and the internal differentiation of granitic pegmatites
Contrib Mineral Petrol 102 1ndash17
London D Morgan GB VI Paul KA Guttery BM (2012)
Internal evolution of miarolitic granitic pegmatites at the Little
Three mine Ramona California USA Can Mineral 50
1025ndash1054
Martins T Lima A Simmons WB Folster AU Noronha F
(2011) Geochemical fractionation of Nb-Ta oxides in Li-bear-
ing pegmatites from the Barroso-Alvao pegmatite field northern
Portugal Can Mineral 49 777ndash791
Monier G Charoy B Cuney M Ohnenstetter D Robert JL
(1987) Evolution spatiale et temporelle de la composition des
micas du granite albitique a topaze-lepidolite de Beauvoir
Geologie De La France 2ndash3 179ndash188
Monier G amp Robert JL (1986) Evolution of the miscibility gap
between muscovite and biotite solid solutions with increasing
lithium content an experimental study in the systems
K2OndashLi2OndashMgOndashAl2O3ndashSiO2ndashH2OndashHF at 600 C 2 kbar
PH2O comparison with natural lithium micas Mineral Mag
50 641ndash651
Morgan GBVI amp London D (1999) Crystallization of the little
three layered pegmatite-aplite dike Ramona District California
Contrib Mineral Petrol 136 310ndash330
984 A M R Neiva
eschweizerbart_xxx
Nabelek PI amp Russ-Nabelek C (1992) The generation and crys-
tallization conditions of the Proterozoic Harney Peak
Leucrogranite Black Hills South Dakota USA petrologic and
geochemical constraints Contrib Mineral Petrol 110
173ndash191
Nabelek PI Russ-Nabelek C Haeussler GT (1992) Stable
isotope evidence for the petrogenesis and fluid evolution in
the Proterozoic Harney Peak leucogranite Black Hills
South Dakota Geochim Cosmochim Acta 56 403ndash417
Neiva AMR amp Champness PE (1997) Nigerite and gahnite from
the granitic pegmatite veins of Cabanas Ponte de Lima northern
Portugal N Jb Mineral Mh 9 385ndash409
Neiva AMR Gomes MEP Ramos JMF Silva PB (2008)
Geochemistry of granitic aplite-pegmatite sills and their miner-
als from Arcozelo da Serra area (Gouveia central Portugal)
Eur J Mineral 20 465ndash485
Neiva AMR amp Neiva JMC (2005) Beryl from the granitic
pegmatite at Namivo Alto Ligonha Mozambique N Jb
Mineral Abh 181 173ndash182
Neiva AMR amp Ramos JMF (2010) Geochemistry of granitic
aplite-pegmatite sills and petrogenetic links with granites
Guarda-Belmonte area central Portugal Eur J Mineral 22
837ndash854
Neiva AMR Silva PB Ramos JMF (2012) Geochemistry of
granitic aplite-pegmatite veins and sills and their minerals from the
Sabugal area central Portugal N Jb Mineral Abh 189 49ndash74
Novak M amp Cerny P (1998) Niobium-tantalum oxide minerals
from complex granitic pegmatites in the Moldanubicum Czech
Republic primary versus secondary compositional trends Can
Mineral 36 659ndash672
Pesquera Perez A Torres-Ruiz J Gil PP Velilla N (1999)
Chemistry and genetic implications of tourmaline and Li-F-Cs
micas from the Valdeflores (Caceres Spain) Am Mineral 84
55ndash69
Rieder M Cavazzini G DrsquoYakonov YuS Frank-Kamenetskii
VA Gottardi G Guggenheim S Koval PV Muller G
Neiva AMR Radoslovich EW Robert J-L Sassi FP
Takeda H Weiss Z Wones DR (1999) Nomenclature of the
micas Mineral Mag 63 267ndash279
Roda Robles E Pesquera Perez A Velasco Roldan F Fontan F
(1999) The granitic pegmatites of the Fregeneda area
(Salamanca Spain) characteristics and petrogenesis Mineral
Mag 63 535ndash558
Roda Robles E Pesquera A Gil-Crespo PP Torres-Ruiz J
Fontan F (2005) Origin and internal evolution of the Li-F-
Be-P-bearing Pinilla de Fermoselle pegmatite (Central Iberian
Zone Zamora Spain) Am Mineral 90 1887ndash1899
Roda Robles E Pesquera Perez A Gil PP Torres-Ruiz J de
Parseval P (2006) Mineralogy and geochemistry of micas from
the Pinilla de Fermoselle pegmatite (Zamora Spain) Eur J
Mineral 18 369ndash377
Roda Robles E Keller P Pesquera Perez A Fontan F (2007)
Micas of the muscovite-lepidolite series from Karibib pegma-
tites Namibia Mineral Mag 71 41ndash62
Roda Robles E Pesquera A Gil-Crespo P Torres-Ruiz J
(2012) From granite to highly evolved pegmatite a case study
of the Pinilla de Fermoselle granite-pegmatite system (Zamora
Spain) Lithos 153 192ndash207
Selway JB Novak M Cerny P Hawthorne FC (1999)
Compositional evolution of tourmaline in lepidolite-subtype
pegmatites Eur J Mineral 11 569ndash584
Shearer CK Papike JJ Jolliff B (1992) Petrogenetic links
among granites and pegmatites in the Harney Peak rare-element
granite-pegmatite system Black Hills South Dakota Can
Mineral 30 785ndash809
Soares DR Hartmut B Ferreira ACM da Silva MRR
(2007) Chemical composition of gahnite and degree of peg-
matitic fractionation in the Borborema Pegmatitic Province
northeastern Brazil Anais Da Academ Bras Cien 79
395ndash404
Stewart DB (1978) Petrogenesis of lithium-rich pegmatites Am
Mineral 63 970ndash980
Tischendorff G Gattesmann B Forster H-J Trumbull RB
(1997) On Li-bearing micas estimating Li from electron
microprobe analyses and an improved diagram for graphical
representation Mineral Mag 61 809ndash834
Van Lichtervelde M Linnen RL Salvi S Beziat D (2006)
The role of metagabbro rafts on tantalum mineralization in the
Tanco granitic pegmatite Manitoba Can Mineral 44
625ndash644
Van Lichtervelde M Gregoire M Linnen RL Beziat D Salvi
S (2008) Trace element geochemistry by laser ablation ICP-
MS of micas associated with Ta mineralization in the Tanco
pegmatite Manitoba Canada Contrib Mineral Petrol 155
791ndash806
Vieira R Roda-Robles E Pesquera A Lima A (2011)
Chemical variation and significance of micas from the
Fregeneda-Almendra pegmatitic field (Central-Iberian Zone
Spain and Portugal) Am Mineral 96 637ndash645
Wen S amp Nekvasil H (1994) SOLVCALC an interactive gra-
phics program package for calculating ternary feldspar solvus
and two-feldspar geothermometry Comput Geosci 20
1025ndash1040
Wise MA (1995) Trace element chemistry of lithium-rich micas
from rare-element granitic pegmatites Mineral Petrol 55
203ndash215
Zasedatelev AM (1974) Possible accumulation of lithium in host
rocks of lithium pegmatite veins during old sedimentation pro-
cesses Doklady Acad Sci USSR Earth Sci Ser 218 196ndash198
(in Russian)
mdash (1977) Quantitative of metamorphic generation of rare-metal
pegmatites with lithium mineralization Doklady Acad Sci
USSR Earth Sci Ser 236 219ndash221 (in Russian)
Received 26 January 2013
Modified version received 21 May 2013
Accepted 23 July 2013
Silicate and oxide minerals from a zoned granitic pegmatite 985
eschweizerbart_xxx
and Cs2O contents than K-feldspar from the lepidolite-subtype pegmatite at Red Cross Lake The Rb2O andCs2O contents of primary and late K-feldspar of this peg-matite at Red Cross Lake attained unprecedented levels(Cerny et al 2012a) The lowest KRb (wt) values ofmuscovite lithian muscovite lsquolsquomixed formrsquorsquo and lepido-lite from the IIZb and Cc (Fig 7) and K-feldspar (KRb frac1414) from the Cc compare well with those found in theseminerals from the AC6frac143 lepidolite-subtype pegmatitefrom Greer Lake (Cerny et al 2005) and some of themost fractionated pegmatites worldwide which belong tothe petalite-subtype (eg Tanco Manitoba Cerny 2005Cerny et al 1998 Varutrask Sweden Cerny et al 2005)but muscovite lithian muscovite and lepidolite from theIIZb and Cc have lower Rb2O and Cs2O contents than thesemicas from the Tanco pegmatite (Cerny 2005a VanLichtervelde et al 2008) K-feldspar also has lower
contents of these oxides than the most evolved K-feldsparfrom the Tanco pegmatite (Cerny 2005a) The magmaticfractionation was strong from the WZ to IIZb and Cc of theNamivo lepidolite-subtype pegmatite
The compositional trend of columbite-(Mn) from the OIZto Cc of the Namivo granitic lepidolite-subtype pegmatite(Fig 10) is identical to that of columbite-group mineralsfrom the lepidolite-subtype complex granitic pegmatitesfrom the Dobra Voda in the Moldanubicum CzechRepublic (Novak amp Cerny 1998) and the HimalayaDistrict southern California (shown in Cerny et al 2004)Experimental data for the Fe-Mn pair (Linnen amp Cuney2005) suggest an increase in Fe with fractional crystalliza-tion which is not observed in nature Other phases seem tocontrol the bahavior of Fe and Mn in the melt eg thecrystallization of tourmaline causes a rapid increase of theMnFe in the melt (Van Lichtervelde et al 2006) When thecrystallization of tourmaline stopped the columbitendashtantaliteminerals showed a constant MnFe indicating that the Fe andMn contents in the melt remained constant Schorl onlyoccurs in the OIZ of the Namivo granitic pegmatite and itscrystallization cannot be responsible for the increase in theMnFe of the melt because Mn(Mn thorn Fe) of columbite-(Mn) increases progressively from the OIZ to the IIZa and Cc(Fig 10) Garnet zinnwaldite and gahnite containing Fe andMn also only occur in the OIZ and cannot also have causedthe increase of the MnFe in the melt The dominant Mnenrichment before Ta enrichment started in the columbitendash-tantalite composition from some granitic pegmatites isattributed to an increased alkali-fluoride activity at moderatemHF (Cerny et al 2004) and an increase in the activity offluorine (Martins et al 2011) Each Al-richer mica (musco-vite lithian muscovite and lsquolsquomixed formrsquorsquo) from the Namivogranitic pegmatite shows an increase in F content from theOIZ to the IIZa IIZb and Cc (Table 1) In general the Fcontent of lepidolite also increases from the IIZa to the IIZband Cc Therefore the extreme Fe-Mn fractionation beforeTa enrichment in columbite-(Mn) (Fig 10) may be due to anincrease in the activity of fluorine as a consequence offractional crystallization The increase in the Ta content ofcolumbite-(Mn) from the Namivo granitic pegmatite isattributed to fractional crystallization
The geochemical evolution of albite and K-feldsparfrom the WZ to the Cc Al-richer micas muscovite lithianmuscovite and lsquolsquomixed formrsquorsquo from the OIZ to the Cc andlepidolite from the IIZa to the Cc and columbite-(Mn) andalso beryl (Neiva amp Neiva 2005) from the OIZ to the Ccare caused by magma fractionation The pegmatite zonesare the product of primary crystallization from a volatile-rich silicate melt The pegmatite consolidated from the WZto the Cc The IIZb is one of the most evolved zones asalso suggested by the beryl composition (Neiva amp Neiva2005) and is the richest in lsquolsquomixed formrsquorsquo and lepidolite
The richest columbite-(Mn) in Ta(Ta thorn Nb) and com-positions of tantalite-(Fe) and tantalite-(Mn) only occur inthe OIZ (Fig 10a) associated with lepidolite and polythio-nite (Fig 3c) which may be due to the local depletion of Liand F in the melt which decreases the solubility of Ta andcauses Ta precipitation (Linnen 1998 Linnen amp Cuney
Fig 11 a Backscattered-electron image of a gahnite crystal with adarker zone partially surrounding a lighter zone from the OIZ of theNamivo granitic pegmatite b c Plot of gahnite compositions in theSn-Zn-Ti diagram (atomic proportions) showing a chemical distinc-tion between the lighter and darker zones OIZ as in Fig 2
Silicate and oxide minerals from a zoned granitic pegmatite 981
eschweizerbart_xxx
2005) At the Tanco pegmatite Ta oxides are also asso-ciated with lepidolite enriched in Li and F from the wallzone (Van Lichtervelde et al 2008)
93 Origin and evolution of the zoned graniticlepidolite-subtype pegmatite at Namivo
In general granitic pegmatites particularly those belong-ing to the rare-element class are accepted as having beenformed by the fractional crystallization of a granite melt(eg Cerny 1991a b 1992 Neiva et al 2008 2012 Roda-Robles et al 2012) But it also has been proposed thatpegmatites may be formed by partial melting of appropri-ate rock compositions (eg Nabelek et al 1992 Nabelekamp Russ-Nabelek 1992 Shearer et al 1992 Roda Robleset al 1999) The lepidolite-subtype pegmatites belong tothe LCT (lithium-cesium-tantalum) family (Cerny amp Ercit2005) They are derived by fractional crystallization of agranite magma (eg Cerny et al 2005 Neiva amp Ramos2010 Cerny et al 2012b) Experimental work by Londonet al (1989) and London (1990) using Macusani glass as astarting material equivalent to the bulk composition ofhighly fractionated rare-alkali-rich pegmatites underhighly evolved and hydrous but H2O undersaturatedmelt obtained the latest primary assemblage consisting
of an Li-rich mica thorn albite thorn quartz deposited directlyfrom the primary melt phase Other authors egZasedatelev (1974 1977) and Stewart (1978) argue thatlepidolite-bearing pegmatites are derived from direct ana-texis and Gordiyenko et al (1996) consider that they arederived from an undefined medium and the rare-elementmineralization is superimposed on preexisting barrenpegmatites
Lepidolite-subtype pegmatites may migrate a long wayfrom their parent granites because their volatile-rich highlyfluid pegmatite melts are stable at relatively low tempera-tures (eg Cerny et al 2005 Antunes et al 2013)Therefore the Namivo pegmatite is probably derived byfractional crystallization of an S-type granite magmawhich resulted from partial melting of metamorphosed juve-nile sediments containing micas that carry most of the traceelements that define the signature of the LCT pegmatites(eg Dahl et al 1993)
The two main models for the internal evolution of peg-matites that dominated for more than a century are a) thefractional crystallization of a flux-bearing granitic melt fromthe margins to the center of the pegmatite (Cameron et al1949) b) the interactions of an aqueous fluid with graniticmelt (Jahns amp Burnham 1969 Jahns 1982) The recentmodel of constitutional zone refining combines aspects ofboth models and invokes the formation of a flux-enriched
Table 4 Electron microprobe analyses in wt of zoned gahnite from the outer intermediate zone (OIZ) of the Namivo granitic pegmatiteMozambique
Darker Zone Lighter Zone
Mean s Range Mean s Range
SnO2 036 050 0ndash097 658 281 151ndash998TiO2 008 008 0ndash021 065 034 008ndash105Nb2O5 001 002 0ndash006 018 007 007ndash029Ta2O5 001 004 0ndash010 015 013 0ndash033ZnO 3998 123 3810ndash4109 3339 318 3004ndash3848FeO 367 048 331ndash442 433 065 306ndash498MnO 032 004 028ndash040 039 006 032ndash048MgO 003 004 0ndash010 ndash ndash ndashAl2O3 5507 050 5436ndash5572 5337 070 5257ndash5443SiO2 003 003 0ndash007 008 010 0ndash025Total 9956 9912n 8 8Sn 0035 0048 0ndash0095 0648 0278 0149ndash0983Ti 0015 0015 0ndash0038 0120 0064 0015ndash0195Nb ndash 0003 0ndash0006 0021 0009 0009ndash0037Ta ndash 0002 0ndash0006 0009 0009 0ndash0021Zn 7226 0182 6890ndash7382 6086 0568 5482ndash6965Fe2thornt 0752 0103 0675ndash0913 0894 0135 0628ndash1029Mn 0066 0008 0057ndash0083 0082 0013 0066ndash0101Mg 0010 0015 0ndash0037 ndash ndash ndashAl 15887 0052 15805ndash15954 15526 0170 15375ndash15853Si 0007 0008 0ndash0018 0019 0025 0ndash0062P
23998 23405Fe3thorn 0064 0230Fe2thorn 0686 0658SnZn 0005 0007 0ndash0014 0106 0052 0021ndash0179ZnFe2thornt 961 143 768ndash1093 681 190 536ndash1109
n number of analysis Cation formula based on 32 atoms of oxygen Fe2thornt total Fe2thorn estimated
982 A M R Neiva
eschweizerbart_xxx
boundary layer of silicate liquid in advance of a crystal-lization front (London 2008 London amp Morgan 2012)
Lepidolite-subtype pegmatites are generally scarce(Cerny et al 2005) particularly the zoned ones In thesymmetrically zoned lepidolite-subtype pegmatites ofRozna and Dobra Voda Czech Republic micas (Cernyet al 1995) tourmaline (Selway et al 1999) and colum-bite-group minerals (Novak amp Cerny 1998) evolve fromthe outermost zone to the innermost zone following thecrystallization sequence The same was found in tourma-line from the zoned Lastovicky Dolnı Bory and Raddovicelepidolite-subtype pegmatite dikes in the Czeck Republic(Selway et al 1999)
In general beryl (Neiva amp Neiva 2005) feldsparsmicas and columbite-(Mn) (in this paper) from theNamivo lepidolite-subtype pegmatite record the progres-sive chemical evolution of the pegmatite from the wallzone to the core These minerals were produced by crystal-lization from a silicate melt rather than an aqueous fluidphase The slow cooling of melt shown by the magmaticcrystallization temperatures of feldspars cannot explain theincrease in grain-size of minerals from the wall zone to thecore but fluxes will be necessary to promote the change oftexture particularly a flux-rich hydrosilicate liquidaccording to the experimental evidence (London 2009)The constitutional zone refining model will be the best forthis zoned pegmatite and probably for all lepidolite-sub-type pegmatites because this model also produces a higherfinal concentration of incompatible components in a smal-ler volume of rock than fractional crystallization does(Morgan amp London 1999)
The core margin at the Rozna pegmatite contains K-feld-spar and quartz and the core consists mainly of quartz but it issurrounded and penetrated by a quartz-bearing albitethorn lepi-dolite complex which contains several minerals At theDobra Voda pegmatite the center of the dike is occupiedby the lepidolite unit containing albite and other minerals(Cerny et al 1995) At the Namivo pegmatite the coremargin consists of quartz and beryl and the core containsmainly quartz and spodumene but also albite lepidolite andother minerals The last-unit assemblages of primary miner-als in most of the highly fractionated LCT pegmatites are richin albite and commonly contain lepidolite or spodumene andmost of the other rare phases These units represent the lastmost fractionated liquid that can be derived by fractionalcrystallization of a crustal melt (London 2008)
The Namivo granitic pegmatite shows a significant dis-tinction from the other zoned lepidolite-subtype pegmatitesand LCT pegmatites except the Tanco petalite-subtypepegmatite in Canada because the lepidolite richest in SiLi and F FeMg-containing polylithionite and associatedcolumbite-(Mn) with the highest Ta(Ta thorn Nb) ratio tanta-lite-(Fe) and tantalite-(Mn) only occur in the outer inter-mediate zone These minerals usually form late in theconsolidation of pegmatites The lepidolite and polylithio-nite are probably derived from the disequilibrium crystal-lization of an undercooled melt Tantalite may reflect a localdecrease in Li and F that caused Ta precipitation
This paper contributes to a better understanding of theorigin and evolution of the rare zoned lepidolite-subtypepegmatites and shows that although the pegmatite evolvedfrom the wall zone to the core it presents an unusualassociation of lepidolite polylithionite and tantalite in theouter intermediate zone
Acknowledgments Thanks are due to JM Cotelo Neivaand MB Dias for the samples and information providedand to MR Machado Leite and MF Guimaraes for theuse of the electron microprobe facilities at the LaboratorioNacional de Energia e Geologia (LNEG) PortugalFinancial support was provided by the PortugueseGovernment for the project Pest-OECTEUI00732011of the Geosciences Centre through the PortugueseFoundation for Science and Technology I would like tothank D London WB Simmons and the associated editorE Widom for their constructive reviews of this manuscriptand M Prieto for his editorial work
References
Alfonso P Melgarejo JC Yusta I Velasco F (2003)
Geochemistry of feldspars and muscovite in granitic pegmatite
from the Cap de Creus field Catalonia Spain Can Mineral 41
103ndash116
Antunes IMHR Neiva AMR Ramos JMF Silva PB
Silva MMVG Corfu F (2013) Petrogenetic links between
lepidolite-subtype aplite-pegmatite aplite veins and associated
granites at Segura (central Portugal) Chemie der Erde in press
httpdxdoiorg101016jchemer20121203
Batchelor RA amp Kinnaird JA (1984) Gahnite compositions
compared Mineral Mag 48 425ndash430
Beurlen H Da Silva MRR Thomas R Soares DR Olivier P
(2008) Nb-Ta-(Ti-Sn) oxide mineral chemistry as tracer of rare-
element granitic pegmatite fractionation in the Borborema pro-
vince Northeastern Brazil Miner Deposita 43 207ndash228
Cameron EN Jahns RH McNair AH Page LR (1949)
Internal structure of granitic pegmatites Econ Geol
Monograph 2 115 p
Cerny P (1991a) Fertile granites of Precambrian rare-element
pegmatite fields is geochemistry controlled by tectonic setting
or source lithologies Precambrian Res 51 429ndash468
mdash (1991b) Rare-element granite pegmatites I Anatomy and inter-
nal evolution of pegmatite deposits Geoscience Canada 18
49ndash67
mdash (1992) Geochemical and petrogenetic features of mineralization
in rare-element granitic pegmatites in the light of current
research Applied Geochemistry 7 393ndash416
mdash (1994) Evolution of feldspars in granitic pegmatites in
lsquolsquoFeldspars and their Reactionsrsquorsquo I Parsons ed NATO
Advanced Study Institute Series C421 501ndash539
mdash (2005) The Tanco rare-element pegmatite deposit Manitoba
regional context internal anatomy and global comparisons in
lsquolsquoRare-element Geochemistry and Mineral Depositsrsquorsquo RL
Linnen amp IM Samson eds Geochemical Association of
Canada Short Course Notes St Catherines 17 127ndash158
Silicate and oxide minerals from a zoned granitic pegmatite 983
eschweizerbart_xxx
Cerny P amp Ercit TS (2005) The classification of granitic pegma-
tites revisited Can Mineral 43 2005ndash2026
Cerny P Meintzer RE Andersen AJ (1985) Extreme fractiona-
tion in rare-element granitic pegmatites selected examples of
data and mechanisms Can Mineral 23 381ndash421
Cerny P Goad BE Hawthorne FC Chapmann R (1986)
Fractionation trends of the Nb- and Ta-bearing oxide minerals
in the Greer Lake pegmatite granite and its pegmatite aureole
southeastern Manitoba Am Mineral 71 501ndash517
Cerny P Stanek J Novak M Baadsgaard H Rieder M
Ottolini L Kavalova M Chapman R (1995) Geochemical
and structural evolution of micas in the Rozna amp Dobra Voda
pegmatites Czech Republic Mineral Petrol 55 177ndash201
Cerny P Ercit TS Vanstone PJ (1998) Mineralogy and petrol-
ogy of the Tanco rare-element pegmatite deposit southeastern
Manitoba International Mineralogical Association 17th General
Meeting Toronto Field Guidebook B6
Cerny P Chapman R Ferreira K Smeds SA (2004)
Geochemistry of oxide minerals of Nb Ta Sn and Sb in
the Varutrask granitic pegmatite Sweden The case of an
lsquolsquoanomalousrsquorsquo columbitendashtantalite trend Am Mineral 89
505ndash518
Cerny P Masau M Goad BE Ferreira K (2005) The Greer
Lake leucogranite Manitoba and the origin of lepidolite-sub-
type granitic pegmatites Lithos 80 305ndash321
Cerny P Teertstra DK Chapman R Selway JB Hawthorne
FC Ferreira K Chackowsky LE Wang X-J Meintzer
RE (2012a) Extreme fractionation and deformation of the
leucogranite-pegmatite suite at Red Cross Lake Manitoba
Canada IV Mineralogy Can Mineral 50 1839ndash1875
Cerny P Halden NM Ferreira K Meintzer RE Brisbin WC
Chackowsky LE (2012b) Extreme fractionation and deforma-
tion of the leucogranite-pegmatite suite at Red Cross Lake
Manitoba Canada II Petrology of the leucogranites and peg-
matites Can Mineral 50 1807ndash1822
Dahl PS When DC Feldmann SG (1993) The systematics of
trace-element partitioning between coexisting muscovite and
biotite in metamorphic rocks from the Black Hills South
Dakota USA Geochim Cosmochim Acta 57 2487ndash2505
Dias MB amp Wilson WE (2000) The Alto Ligonha Pegmatites
Mozambique Mineral Record 31 459ndash497
Fleet ME (2003) Rock-Forming Minerals vol 3A Sheet silicates
micas The Geological Society London second edition chap 6
Lithium micas 651ndash690
Foord EE Cerny P Jackson LL Sherman DM Eby RK
(1995) Mineralogical and geochemical evolutions of micas
from miarolitic pegmatites of the anorogenic pikes-Peak
Batholith Colorado Mineral Petrol 55 1ndash26
Foster MD (1960) Interpretation of the composition of lithium
micas US Geol Surv Prof Paper 354-E 115ndash147
Fuhrman ML amp Lindsley DK (1988) Ternary-feldspar modeling
and thermometry Am Mineral 73 201ndash215
Gomes CL Castro P Alves C (1995) Caracterizacao das espi-
nelas zincıferas e do par ganite-nigerite no campo aplito-
pegmatıtico da Serra de Arga-Minho N de Portugal IV
Congresso Nacional de Geologia Resumos Alargados
Universidade do Porto Mem 4 629ndash633
Gordiyenko VV Ilyina AN Timochina LA Badamina EB
Stanek J (1996) Geochemical model of evolution of a pegma-
tite-forming ore-magmatic system of western Moravia Proc
Russ Mineral Soc 125 38ndash48 (in Russian)
Icenhower JP amp London D (1995) An experimental study for
element partitioning between biotite muscovite and coexisting
peraluminous granitic melt at 200 MPa (H2O) Am Mineral 80
1229ndash1251
Jahns RH (1982) Internal evolution of pegmatite bodies in lsquolsquoGranitic
Pegmatites in science and industryrsquorsquo P Cerny ed Mineralogical
Association of Canada Short Course Handbook 8 293ndash327
Jahns RH amp Burnham CW (1969) Experimental studies of
pegmatite genesis I A model for the derivation and crystal-
lization of granitic pegmatites Econ Geol 64 843ndash864
Jolliff BL Papike JJ Shearer CK (1987) Fractionation trends
in mica and tourmaline as indicators of pegmatite internal evo-
lution Bob Ingersoll pegmatite Black Hills South Dakota
USA GeochimCosmochim Acta 51 519ndash534
Kile DE amp Foord EE (1998) Micas from the Pikes Peak bath-
olith and its cogenetic granitic pegmatites Colorado optical
properties composition and correlation with pegmatite evolu-
tion Can Mineral 36 463ndash482
Linnen RL (1998) The solubility of Nb-Ta-Zr-Hf-W in granitic
melts with Li and Li thorn F constraints for mineralization in rare
metal granites and pegmatites Econ Geol 93 1013ndash1025
Linnen RL amp Cuney M (2005) Granite-related rare-element
deposits and experimental constraints on Ta-Nb-W-Sn-Zr-Hf
mineralization in lsquolsquoRare-element geochemistry and mineral
depositsrsquorsquo RL Linnen amp IM Samson eds Geochemical
Association of Canada Short Course Notes 17 45ndash68
London D (1990) Internal differentiation of rare-element pegmatites
a synthesis of recent research in lsquolsquoOre Bearing Granite Systems
Petrogenesis and Mineralizing Processesrsquorsquo HJ Stein amp JL
Hannah eds Geol Soc America Special Paper 246 35ndash50
mdash (2008) Pegmatites The Canadian Mineralogist Special
Publication 10 347 p
mdash (2009) The origin of primary textures in granitic pegmatites
Can Mineral 47 697ndash724
London D amp Morgan GB VI (2012) The pegmatite puzzle
Elements 8 263ndash268
London D Morgan GB VI Hervig RL (1989) Vapor-under-
saturated experiments in the system macusanite-H2O at 200
MPa and the internal differentiation of granitic pegmatites
Contrib Mineral Petrol 102 1ndash17
London D Morgan GB VI Paul KA Guttery BM (2012)
Internal evolution of miarolitic granitic pegmatites at the Little
Three mine Ramona California USA Can Mineral 50
1025ndash1054
Martins T Lima A Simmons WB Folster AU Noronha F
(2011) Geochemical fractionation of Nb-Ta oxides in Li-bear-
ing pegmatites from the Barroso-Alvao pegmatite field northern
Portugal Can Mineral 49 777ndash791
Monier G Charoy B Cuney M Ohnenstetter D Robert JL
(1987) Evolution spatiale et temporelle de la composition des
micas du granite albitique a topaze-lepidolite de Beauvoir
Geologie De La France 2ndash3 179ndash188
Monier G amp Robert JL (1986) Evolution of the miscibility gap
between muscovite and biotite solid solutions with increasing
lithium content an experimental study in the systems
K2OndashLi2OndashMgOndashAl2O3ndashSiO2ndashH2OndashHF at 600 C 2 kbar
PH2O comparison with natural lithium micas Mineral Mag
50 641ndash651
Morgan GBVI amp London D (1999) Crystallization of the little
three layered pegmatite-aplite dike Ramona District California
Contrib Mineral Petrol 136 310ndash330
984 A M R Neiva
eschweizerbart_xxx
Nabelek PI amp Russ-Nabelek C (1992) The generation and crys-
tallization conditions of the Proterozoic Harney Peak
Leucrogranite Black Hills South Dakota USA petrologic and
geochemical constraints Contrib Mineral Petrol 110
173ndash191
Nabelek PI Russ-Nabelek C Haeussler GT (1992) Stable
isotope evidence for the petrogenesis and fluid evolution in
the Proterozoic Harney Peak leucogranite Black Hills
South Dakota Geochim Cosmochim Acta 56 403ndash417
Neiva AMR amp Champness PE (1997) Nigerite and gahnite from
the granitic pegmatite veins of Cabanas Ponte de Lima northern
Portugal N Jb Mineral Mh 9 385ndash409
Neiva AMR Gomes MEP Ramos JMF Silva PB (2008)
Geochemistry of granitic aplite-pegmatite sills and their miner-
als from Arcozelo da Serra area (Gouveia central Portugal)
Eur J Mineral 20 465ndash485
Neiva AMR amp Neiva JMC (2005) Beryl from the granitic
pegmatite at Namivo Alto Ligonha Mozambique N Jb
Mineral Abh 181 173ndash182
Neiva AMR amp Ramos JMF (2010) Geochemistry of granitic
aplite-pegmatite sills and petrogenetic links with granites
Guarda-Belmonte area central Portugal Eur J Mineral 22
837ndash854
Neiva AMR Silva PB Ramos JMF (2012) Geochemistry of
granitic aplite-pegmatite veins and sills and their minerals from the
Sabugal area central Portugal N Jb Mineral Abh 189 49ndash74
Novak M amp Cerny P (1998) Niobium-tantalum oxide minerals
from complex granitic pegmatites in the Moldanubicum Czech
Republic primary versus secondary compositional trends Can
Mineral 36 659ndash672
Pesquera Perez A Torres-Ruiz J Gil PP Velilla N (1999)
Chemistry and genetic implications of tourmaline and Li-F-Cs
micas from the Valdeflores (Caceres Spain) Am Mineral 84
55ndash69
Rieder M Cavazzini G DrsquoYakonov YuS Frank-Kamenetskii
VA Gottardi G Guggenheim S Koval PV Muller G
Neiva AMR Radoslovich EW Robert J-L Sassi FP
Takeda H Weiss Z Wones DR (1999) Nomenclature of the
micas Mineral Mag 63 267ndash279
Roda Robles E Pesquera Perez A Velasco Roldan F Fontan F
(1999) The granitic pegmatites of the Fregeneda area
(Salamanca Spain) characteristics and petrogenesis Mineral
Mag 63 535ndash558
Roda Robles E Pesquera A Gil-Crespo PP Torres-Ruiz J
Fontan F (2005) Origin and internal evolution of the Li-F-
Be-P-bearing Pinilla de Fermoselle pegmatite (Central Iberian
Zone Zamora Spain) Am Mineral 90 1887ndash1899
Roda Robles E Pesquera Perez A Gil PP Torres-Ruiz J de
Parseval P (2006) Mineralogy and geochemistry of micas from
the Pinilla de Fermoselle pegmatite (Zamora Spain) Eur J
Mineral 18 369ndash377
Roda Robles E Keller P Pesquera Perez A Fontan F (2007)
Micas of the muscovite-lepidolite series from Karibib pegma-
tites Namibia Mineral Mag 71 41ndash62
Roda Robles E Pesquera A Gil-Crespo P Torres-Ruiz J
(2012) From granite to highly evolved pegmatite a case study
of the Pinilla de Fermoselle granite-pegmatite system (Zamora
Spain) Lithos 153 192ndash207
Selway JB Novak M Cerny P Hawthorne FC (1999)
Compositional evolution of tourmaline in lepidolite-subtype
pegmatites Eur J Mineral 11 569ndash584
Shearer CK Papike JJ Jolliff B (1992) Petrogenetic links
among granites and pegmatites in the Harney Peak rare-element
granite-pegmatite system Black Hills South Dakota Can
Mineral 30 785ndash809
Soares DR Hartmut B Ferreira ACM da Silva MRR
(2007) Chemical composition of gahnite and degree of peg-
matitic fractionation in the Borborema Pegmatitic Province
northeastern Brazil Anais Da Academ Bras Cien 79
395ndash404
Stewart DB (1978) Petrogenesis of lithium-rich pegmatites Am
Mineral 63 970ndash980
Tischendorff G Gattesmann B Forster H-J Trumbull RB
(1997) On Li-bearing micas estimating Li from electron
microprobe analyses and an improved diagram for graphical
representation Mineral Mag 61 809ndash834
Van Lichtervelde M Linnen RL Salvi S Beziat D (2006)
The role of metagabbro rafts on tantalum mineralization in the
Tanco granitic pegmatite Manitoba Can Mineral 44
625ndash644
Van Lichtervelde M Gregoire M Linnen RL Beziat D Salvi
S (2008) Trace element geochemistry by laser ablation ICP-
MS of micas associated with Ta mineralization in the Tanco
pegmatite Manitoba Canada Contrib Mineral Petrol 155
791ndash806
Vieira R Roda-Robles E Pesquera A Lima A (2011)
Chemical variation and significance of micas from the
Fregeneda-Almendra pegmatitic field (Central-Iberian Zone
Spain and Portugal) Am Mineral 96 637ndash645
Wen S amp Nekvasil H (1994) SOLVCALC an interactive gra-
phics program package for calculating ternary feldspar solvus
and two-feldspar geothermometry Comput Geosci 20
1025ndash1040
Wise MA (1995) Trace element chemistry of lithium-rich micas
from rare-element granitic pegmatites Mineral Petrol 55
203ndash215
Zasedatelev AM (1974) Possible accumulation of lithium in host
rocks of lithium pegmatite veins during old sedimentation pro-
cesses Doklady Acad Sci USSR Earth Sci Ser 218 196ndash198
(in Russian)
mdash (1977) Quantitative of metamorphic generation of rare-metal
pegmatites with lithium mineralization Doklady Acad Sci
USSR Earth Sci Ser 236 219ndash221 (in Russian)
Received 26 January 2013
Modified version received 21 May 2013
Accepted 23 July 2013
Silicate and oxide minerals from a zoned granitic pegmatite 985
eschweizerbart_xxx
2005) At the Tanco pegmatite Ta oxides are also asso-ciated with lepidolite enriched in Li and F from the wallzone (Van Lichtervelde et al 2008)
93 Origin and evolution of the zoned graniticlepidolite-subtype pegmatite at Namivo
In general granitic pegmatites particularly those belong-ing to the rare-element class are accepted as having beenformed by the fractional crystallization of a granite melt(eg Cerny 1991a b 1992 Neiva et al 2008 2012 Roda-Robles et al 2012) But it also has been proposed thatpegmatites may be formed by partial melting of appropri-ate rock compositions (eg Nabelek et al 1992 Nabelekamp Russ-Nabelek 1992 Shearer et al 1992 Roda Robleset al 1999) The lepidolite-subtype pegmatites belong tothe LCT (lithium-cesium-tantalum) family (Cerny amp Ercit2005) They are derived by fractional crystallization of agranite magma (eg Cerny et al 2005 Neiva amp Ramos2010 Cerny et al 2012b) Experimental work by Londonet al (1989) and London (1990) using Macusani glass as astarting material equivalent to the bulk composition ofhighly fractionated rare-alkali-rich pegmatites underhighly evolved and hydrous but H2O undersaturatedmelt obtained the latest primary assemblage consisting
of an Li-rich mica thorn albite thorn quartz deposited directlyfrom the primary melt phase Other authors egZasedatelev (1974 1977) and Stewart (1978) argue thatlepidolite-bearing pegmatites are derived from direct ana-texis and Gordiyenko et al (1996) consider that they arederived from an undefined medium and the rare-elementmineralization is superimposed on preexisting barrenpegmatites
Lepidolite-subtype pegmatites may migrate a long wayfrom their parent granites because their volatile-rich highlyfluid pegmatite melts are stable at relatively low tempera-tures (eg Cerny et al 2005 Antunes et al 2013)Therefore the Namivo pegmatite is probably derived byfractional crystallization of an S-type granite magmawhich resulted from partial melting of metamorphosed juve-nile sediments containing micas that carry most of the traceelements that define the signature of the LCT pegmatites(eg Dahl et al 1993)
The two main models for the internal evolution of peg-matites that dominated for more than a century are a) thefractional crystallization of a flux-bearing granitic melt fromthe margins to the center of the pegmatite (Cameron et al1949) b) the interactions of an aqueous fluid with graniticmelt (Jahns amp Burnham 1969 Jahns 1982) The recentmodel of constitutional zone refining combines aspects ofboth models and invokes the formation of a flux-enriched
Table 4 Electron microprobe analyses in wt of zoned gahnite from the outer intermediate zone (OIZ) of the Namivo granitic pegmatiteMozambique
Darker Zone Lighter Zone
Mean s Range Mean s Range
SnO2 036 050 0ndash097 658 281 151ndash998TiO2 008 008 0ndash021 065 034 008ndash105Nb2O5 001 002 0ndash006 018 007 007ndash029Ta2O5 001 004 0ndash010 015 013 0ndash033ZnO 3998 123 3810ndash4109 3339 318 3004ndash3848FeO 367 048 331ndash442 433 065 306ndash498MnO 032 004 028ndash040 039 006 032ndash048MgO 003 004 0ndash010 ndash ndash ndashAl2O3 5507 050 5436ndash5572 5337 070 5257ndash5443SiO2 003 003 0ndash007 008 010 0ndash025Total 9956 9912n 8 8Sn 0035 0048 0ndash0095 0648 0278 0149ndash0983Ti 0015 0015 0ndash0038 0120 0064 0015ndash0195Nb ndash 0003 0ndash0006 0021 0009 0009ndash0037Ta ndash 0002 0ndash0006 0009 0009 0ndash0021Zn 7226 0182 6890ndash7382 6086 0568 5482ndash6965Fe2thornt 0752 0103 0675ndash0913 0894 0135 0628ndash1029Mn 0066 0008 0057ndash0083 0082 0013 0066ndash0101Mg 0010 0015 0ndash0037 ndash ndash ndashAl 15887 0052 15805ndash15954 15526 0170 15375ndash15853Si 0007 0008 0ndash0018 0019 0025 0ndash0062P
23998 23405Fe3thorn 0064 0230Fe2thorn 0686 0658SnZn 0005 0007 0ndash0014 0106 0052 0021ndash0179ZnFe2thornt 961 143 768ndash1093 681 190 536ndash1109
n number of analysis Cation formula based on 32 atoms of oxygen Fe2thornt total Fe2thorn estimated
982 A M R Neiva
eschweizerbart_xxx
boundary layer of silicate liquid in advance of a crystal-lization front (London 2008 London amp Morgan 2012)
Lepidolite-subtype pegmatites are generally scarce(Cerny et al 2005) particularly the zoned ones In thesymmetrically zoned lepidolite-subtype pegmatites ofRozna and Dobra Voda Czech Republic micas (Cernyet al 1995) tourmaline (Selway et al 1999) and colum-bite-group minerals (Novak amp Cerny 1998) evolve fromthe outermost zone to the innermost zone following thecrystallization sequence The same was found in tourma-line from the zoned Lastovicky Dolnı Bory and Raddovicelepidolite-subtype pegmatite dikes in the Czeck Republic(Selway et al 1999)
In general beryl (Neiva amp Neiva 2005) feldsparsmicas and columbite-(Mn) (in this paper) from theNamivo lepidolite-subtype pegmatite record the progres-sive chemical evolution of the pegmatite from the wallzone to the core These minerals were produced by crystal-lization from a silicate melt rather than an aqueous fluidphase The slow cooling of melt shown by the magmaticcrystallization temperatures of feldspars cannot explain theincrease in grain-size of minerals from the wall zone to thecore but fluxes will be necessary to promote the change oftexture particularly a flux-rich hydrosilicate liquidaccording to the experimental evidence (London 2009)The constitutional zone refining model will be the best forthis zoned pegmatite and probably for all lepidolite-sub-type pegmatites because this model also produces a higherfinal concentration of incompatible components in a smal-ler volume of rock than fractional crystallization does(Morgan amp London 1999)
The core margin at the Rozna pegmatite contains K-feld-spar and quartz and the core consists mainly of quartz but it issurrounded and penetrated by a quartz-bearing albitethorn lepi-dolite complex which contains several minerals At theDobra Voda pegmatite the center of the dike is occupiedby the lepidolite unit containing albite and other minerals(Cerny et al 1995) At the Namivo pegmatite the coremargin consists of quartz and beryl and the core containsmainly quartz and spodumene but also albite lepidolite andother minerals The last-unit assemblages of primary miner-als in most of the highly fractionated LCT pegmatites are richin albite and commonly contain lepidolite or spodumene andmost of the other rare phases These units represent the lastmost fractionated liquid that can be derived by fractionalcrystallization of a crustal melt (London 2008)
The Namivo granitic pegmatite shows a significant dis-tinction from the other zoned lepidolite-subtype pegmatitesand LCT pegmatites except the Tanco petalite-subtypepegmatite in Canada because the lepidolite richest in SiLi and F FeMg-containing polylithionite and associatedcolumbite-(Mn) with the highest Ta(Ta thorn Nb) ratio tanta-lite-(Fe) and tantalite-(Mn) only occur in the outer inter-mediate zone These minerals usually form late in theconsolidation of pegmatites The lepidolite and polylithio-nite are probably derived from the disequilibrium crystal-lization of an undercooled melt Tantalite may reflect a localdecrease in Li and F that caused Ta precipitation
This paper contributes to a better understanding of theorigin and evolution of the rare zoned lepidolite-subtypepegmatites and shows that although the pegmatite evolvedfrom the wall zone to the core it presents an unusualassociation of lepidolite polylithionite and tantalite in theouter intermediate zone
Acknowledgments Thanks are due to JM Cotelo Neivaand MB Dias for the samples and information providedand to MR Machado Leite and MF Guimaraes for theuse of the electron microprobe facilities at the LaboratorioNacional de Energia e Geologia (LNEG) PortugalFinancial support was provided by the PortugueseGovernment for the project Pest-OECTEUI00732011of the Geosciences Centre through the PortugueseFoundation for Science and Technology I would like tothank D London WB Simmons and the associated editorE Widom for their constructive reviews of this manuscriptand M Prieto for his editorial work
References
Alfonso P Melgarejo JC Yusta I Velasco F (2003)
Geochemistry of feldspars and muscovite in granitic pegmatite
from the Cap de Creus field Catalonia Spain Can Mineral 41
103ndash116
Antunes IMHR Neiva AMR Ramos JMF Silva PB
Silva MMVG Corfu F (2013) Petrogenetic links between
lepidolite-subtype aplite-pegmatite aplite veins and associated
granites at Segura (central Portugal) Chemie der Erde in press
httpdxdoiorg101016jchemer20121203
Batchelor RA amp Kinnaird JA (1984) Gahnite compositions
compared Mineral Mag 48 425ndash430
Beurlen H Da Silva MRR Thomas R Soares DR Olivier P
(2008) Nb-Ta-(Ti-Sn) oxide mineral chemistry as tracer of rare-
element granitic pegmatite fractionation in the Borborema pro-
vince Northeastern Brazil Miner Deposita 43 207ndash228
Cameron EN Jahns RH McNair AH Page LR (1949)
Internal structure of granitic pegmatites Econ Geol
Monograph 2 115 p
Cerny P (1991a) Fertile granites of Precambrian rare-element
pegmatite fields is geochemistry controlled by tectonic setting
or source lithologies Precambrian Res 51 429ndash468
mdash (1991b) Rare-element granite pegmatites I Anatomy and inter-
nal evolution of pegmatite deposits Geoscience Canada 18
49ndash67
mdash (1992) Geochemical and petrogenetic features of mineralization
in rare-element granitic pegmatites in the light of current
research Applied Geochemistry 7 393ndash416
mdash (1994) Evolution of feldspars in granitic pegmatites in
lsquolsquoFeldspars and their Reactionsrsquorsquo I Parsons ed NATO
Advanced Study Institute Series C421 501ndash539
mdash (2005) The Tanco rare-element pegmatite deposit Manitoba
regional context internal anatomy and global comparisons in
lsquolsquoRare-element Geochemistry and Mineral Depositsrsquorsquo RL
Linnen amp IM Samson eds Geochemical Association of
Canada Short Course Notes St Catherines 17 127ndash158
Silicate and oxide minerals from a zoned granitic pegmatite 983
eschweizerbart_xxx
Cerny P amp Ercit TS (2005) The classification of granitic pegma-
tites revisited Can Mineral 43 2005ndash2026
Cerny P Meintzer RE Andersen AJ (1985) Extreme fractiona-
tion in rare-element granitic pegmatites selected examples of
data and mechanisms Can Mineral 23 381ndash421
Cerny P Goad BE Hawthorne FC Chapmann R (1986)
Fractionation trends of the Nb- and Ta-bearing oxide minerals
in the Greer Lake pegmatite granite and its pegmatite aureole
southeastern Manitoba Am Mineral 71 501ndash517
Cerny P Stanek J Novak M Baadsgaard H Rieder M
Ottolini L Kavalova M Chapman R (1995) Geochemical
and structural evolution of micas in the Rozna amp Dobra Voda
pegmatites Czech Republic Mineral Petrol 55 177ndash201
Cerny P Ercit TS Vanstone PJ (1998) Mineralogy and petrol-
ogy of the Tanco rare-element pegmatite deposit southeastern
Manitoba International Mineralogical Association 17th General
Meeting Toronto Field Guidebook B6
Cerny P Chapman R Ferreira K Smeds SA (2004)
Geochemistry of oxide minerals of Nb Ta Sn and Sb in
the Varutrask granitic pegmatite Sweden The case of an
lsquolsquoanomalousrsquorsquo columbitendashtantalite trend Am Mineral 89
505ndash518
Cerny P Masau M Goad BE Ferreira K (2005) The Greer
Lake leucogranite Manitoba and the origin of lepidolite-sub-
type granitic pegmatites Lithos 80 305ndash321
Cerny P Teertstra DK Chapman R Selway JB Hawthorne
FC Ferreira K Chackowsky LE Wang X-J Meintzer
RE (2012a) Extreme fractionation and deformation of the
leucogranite-pegmatite suite at Red Cross Lake Manitoba
Canada IV Mineralogy Can Mineral 50 1839ndash1875
Cerny P Halden NM Ferreira K Meintzer RE Brisbin WC
Chackowsky LE (2012b) Extreme fractionation and deforma-
tion of the leucogranite-pegmatite suite at Red Cross Lake
Manitoba Canada II Petrology of the leucogranites and peg-
matites Can Mineral 50 1807ndash1822
Dahl PS When DC Feldmann SG (1993) The systematics of
trace-element partitioning between coexisting muscovite and
biotite in metamorphic rocks from the Black Hills South
Dakota USA Geochim Cosmochim Acta 57 2487ndash2505
Dias MB amp Wilson WE (2000) The Alto Ligonha Pegmatites
Mozambique Mineral Record 31 459ndash497
Fleet ME (2003) Rock-Forming Minerals vol 3A Sheet silicates
micas The Geological Society London second edition chap 6
Lithium micas 651ndash690
Foord EE Cerny P Jackson LL Sherman DM Eby RK
(1995) Mineralogical and geochemical evolutions of micas
from miarolitic pegmatites of the anorogenic pikes-Peak
Batholith Colorado Mineral Petrol 55 1ndash26
Foster MD (1960) Interpretation of the composition of lithium
micas US Geol Surv Prof Paper 354-E 115ndash147
Fuhrman ML amp Lindsley DK (1988) Ternary-feldspar modeling
and thermometry Am Mineral 73 201ndash215
Gomes CL Castro P Alves C (1995) Caracterizacao das espi-
nelas zincıferas e do par ganite-nigerite no campo aplito-
pegmatıtico da Serra de Arga-Minho N de Portugal IV
Congresso Nacional de Geologia Resumos Alargados
Universidade do Porto Mem 4 629ndash633
Gordiyenko VV Ilyina AN Timochina LA Badamina EB
Stanek J (1996) Geochemical model of evolution of a pegma-
tite-forming ore-magmatic system of western Moravia Proc
Russ Mineral Soc 125 38ndash48 (in Russian)
Icenhower JP amp London D (1995) An experimental study for
element partitioning between biotite muscovite and coexisting
peraluminous granitic melt at 200 MPa (H2O) Am Mineral 80
1229ndash1251
Jahns RH (1982) Internal evolution of pegmatite bodies in lsquolsquoGranitic
Pegmatites in science and industryrsquorsquo P Cerny ed Mineralogical
Association of Canada Short Course Handbook 8 293ndash327
Jahns RH amp Burnham CW (1969) Experimental studies of
pegmatite genesis I A model for the derivation and crystal-
lization of granitic pegmatites Econ Geol 64 843ndash864
Jolliff BL Papike JJ Shearer CK (1987) Fractionation trends
in mica and tourmaline as indicators of pegmatite internal evo-
lution Bob Ingersoll pegmatite Black Hills South Dakota
USA GeochimCosmochim Acta 51 519ndash534
Kile DE amp Foord EE (1998) Micas from the Pikes Peak bath-
olith and its cogenetic granitic pegmatites Colorado optical
properties composition and correlation with pegmatite evolu-
tion Can Mineral 36 463ndash482
Linnen RL (1998) The solubility of Nb-Ta-Zr-Hf-W in granitic
melts with Li and Li thorn F constraints for mineralization in rare
metal granites and pegmatites Econ Geol 93 1013ndash1025
Linnen RL amp Cuney M (2005) Granite-related rare-element
deposits and experimental constraints on Ta-Nb-W-Sn-Zr-Hf
mineralization in lsquolsquoRare-element geochemistry and mineral
depositsrsquorsquo RL Linnen amp IM Samson eds Geochemical
Association of Canada Short Course Notes 17 45ndash68
London D (1990) Internal differentiation of rare-element pegmatites
a synthesis of recent research in lsquolsquoOre Bearing Granite Systems
Petrogenesis and Mineralizing Processesrsquorsquo HJ Stein amp JL
Hannah eds Geol Soc America Special Paper 246 35ndash50
mdash (2008) Pegmatites The Canadian Mineralogist Special
Publication 10 347 p
mdash (2009) The origin of primary textures in granitic pegmatites
Can Mineral 47 697ndash724
London D amp Morgan GB VI (2012) The pegmatite puzzle
Elements 8 263ndash268
London D Morgan GB VI Hervig RL (1989) Vapor-under-
saturated experiments in the system macusanite-H2O at 200
MPa and the internal differentiation of granitic pegmatites
Contrib Mineral Petrol 102 1ndash17
London D Morgan GB VI Paul KA Guttery BM (2012)
Internal evolution of miarolitic granitic pegmatites at the Little
Three mine Ramona California USA Can Mineral 50
1025ndash1054
Martins T Lima A Simmons WB Folster AU Noronha F
(2011) Geochemical fractionation of Nb-Ta oxides in Li-bear-
ing pegmatites from the Barroso-Alvao pegmatite field northern
Portugal Can Mineral 49 777ndash791
Monier G Charoy B Cuney M Ohnenstetter D Robert JL
(1987) Evolution spatiale et temporelle de la composition des
micas du granite albitique a topaze-lepidolite de Beauvoir
Geologie De La France 2ndash3 179ndash188
Monier G amp Robert JL (1986) Evolution of the miscibility gap
between muscovite and biotite solid solutions with increasing
lithium content an experimental study in the systems
K2OndashLi2OndashMgOndashAl2O3ndashSiO2ndashH2OndashHF at 600 C 2 kbar
PH2O comparison with natural lithium micas Mineral Mag
50 641ndash651
Morgan GBVI amp London D (1999) Crystallization of the little
three layered pegmatite-aplite dike Ramona District California
Contrib Mineral Petrol 136 310ndash330
984 A M R Neiva
eschweizerbart_xxx
Nabelek PI amp Russ-Nabelek C (1992) The generation and crys-
tallization conditions of the Proterozoic Harney Peak
Leucrogranite Black Hills South Dakota USA petrologic and
geochemical constraints Contrib Mineral Petrol 110
173ndash191
Nabelek PI Russ-Nabelek C Haeussler GT (1992) Stable
isotope evidence for the petrogenesis and fluid evolution in
the Proterozoic Harney Peak leucogranite Black Hills
South Dakota Geochim Cosmochim Acta 56 403ndash417
Neiva AMR amp Champness PE (1997) Nigerite and gahnite from
the granitic pegmatite veins of Cabanas Ponte de Lima northern
Portugal N Jb Mineral Mh 9 385ndash409
Neiva AMR Gomes MEP Ramos JMF Silva PB (2008)
Geochemistry of granitic aplite-pegmatite sills and their miner-
als from Arcozelo da Serra area (Gouveia central Portugal)
Eur J Mineral 20 465ndash485
Neiva AMR amp Neiva JMC (2005) Beryl from the granitic
pegmatite at Namivo Alto Ligonha Mozambique N Jb
Mineral Abh 181 173ndash182
Neiva AMR amp Ramos JMF (2010) Geochemistry of granitic
aplite-pegmatite sills and petrogenetic links with granites
Guarda-Belmonte area central Portugal Eur J Mineral 22
837ndash854
Neiva AMR Silva PB Ramos JMF (2012) Geochemistry of
granitic aplite-pegmatite veins and sills and their minerals from the
Sabugal area central Portugal N Jb Mineral Abh 189 49ndash74
Novak M amp Cerny P (1998) Niobium-tantalum oxide minerals
from complex granitic pegmatites in the Moldanubicum Czech
Republic primary versus secondary compositional trends Can
Mineral 36 659ndash672
Pesquera Perez A Torres-Ruiz J Gil PP Velilla N (1999)
Chemistry and genetic implications of tourmaline and Li-F-Cs
micas from the Valdeflores (Caceres Spain) Am Mineral 84
55ndash69
Rieder M Cavazzini G DrsquoYakonov YuS Frank-Kamenetskii
VA Gottardi G Guggenheim S Koval PV Muller G
Neiva AMR Radoslovich EW Robert J-L Sassi FP
Takeda H Weiss Z Wones DR (1999) Nomenclature of the
micas Mineral Mag 63 267ndash279
Roda Robles E Pesquera Perez A Velasco Roldan F Fontan F
(1999) The granitic pegmatites of the Fregeneda area
(Salamanca Spain) characteristics and petrogenesis Mineral
Mag 63 535ndash558
Roda Robles E Pesquera A Gil-Crespo PP Torres-Ruiz J
Fontan F (2005) Origin and internal evolution of the Li-F-
Be-P-bearing Pinilla de Fermoselle pegmatite (Central Iberian
Zone Zamora Spain) Am Mineral 90 1887ndash1899
Roda Robles E Pesquera Perez A Gil PP Torres-Ruiz J de
Parseval P (2006) Mineralogy and geochemistry of micas from
the Pinilla de Fermoselle pegmatite (Zamora Spain) Eur J
Mineral 18 369ndash377
Roda Robles E Keller P Pesquera Perez A Fontan F (2007)
Micas of the muscovite-lepidolite series from Karibib pegma-
tites Namibia Mineral Mag 71 41ndash62
Roda Robles E Pesquera A Gil-Crespo P Torres-Ruiz J
(2012) From granite to highly evolved pegmatite a case study
of the Pinilla de Fermoselle granite-pegmatite system (Zamora
Spain) Lithos 153 192ndash207
Selway JB Novak M Cerny P Hawthorne FC (1999)
Compositional evolution of tourmaline in lepidolite-subtype
pegmatites Eur J Mineral 11 569ndash584
Shearer CK Papike JJ Jolliff B (1992) Petrogenetic links
among granites and pegmatites in the Harney Peak rare-element
granite-pegmatite system Black Hills South Dakota Can
Mineral 30 785ndash809
Soares DR Hartmut B Ferreira ACM da Silva MRR
(2007) Chemical composition of gahnite and degree of peg-
matitic fractionation in the Borborema Pegmatitic Province
northeastern Brazil Anais Da Academ Bras Cien 79
395ndash404
Stewart DB (1978) Petrogenesis of lithium-rich pegmatites Am
Mineral 63 970ndash980
Tischendorff G Gattesmann B Forster H-J Trumbull RB
(1997) On Li-bearing micas estimating Li from electron
microprobe analyses and an improved diagram for graphical
representation Mineral Mag 61 809ndash834
Van Lichtervelde M Linnen RL Salvi S Beziat D (2006)
The role of metagabbro rafts on tantalum mineralization in the
Tanco granitic pegmatite Manitoba Can Mineral 44
625ndash644
Van Lichtervelde M Gregoire M Linnen RL Beziat D Salvi
S (2008) Trace element geochemistry by laser ablation ICP-
MS of micas associated with Ta mineralization in the Tanco
pegmatite Manitoba Canada Contrib Mineral Petrol 155
791ndash806
Vieira R Roda-Robles E Pesquera A Lima A (2011)
Chemical variation and significance of micas from the
Fregeneda-Almendra pegmatitic field (Central-Iberian Zone
Spain and Portugal) Am Mineral 96 637ndash645
Wen S amp Nekvasil H (1994) SOLVCALC an interactive gra-
phics program package for calculating ternary feldspar solvus
and two-feldspar geothermometry Comput Geosci 20
1025ndash1040
Wise MA (1995) Trace element chemistry of lithium-rich micas
from rare-element granitic pegmatites Mineral Petrol 55
203ndash215
Zasedatelev AM (1974) Possible accumulation of lithium in host
rocks of lithium pegmatite veins during old sedimentation pro-
cesses Doklady Acad Sci USSR Earth Sci Ser 218 196ndash198
(in Russian)
mdash (1977) Quantitative of metamorphic generation of rare-metal
pegmatites with lithium mineralization Doklady Acad Sci
USSR Earth Sci Ser 236 219ndash221 (in Russian)
Received 26 January 2013
Modified version received 21 May 2013
Accepted 23 July 2013
Silicate and oxide minerals from a zoned granitic pegmatite 985
eschweizerbart_xxx
boundary layer of silicate liquid in advance of a crystal-lization front (London 2008 London amp Morgan 2012)
Lepidolite-subtype pegmatites are generally scarce(Cerny et al 2005) particularly the zoned ones In thesymmetrically zoned lepidolite-subtype pegmatites ofRozna and Dobra Voda Czech Republic micas (Cernyet al 1995) tourmaline (Selway et al 1999) and colum-bite-group minerals (Novak amp Cerny 1998) evolve fromthe outermost zone to the innermost zone following thecrystallization sequence The same was found in tourma-line from the zoned Lastovicky Dolnı Bory and Raddovicelepidolite-subtype pegmatite dikes in the Czeck Republic(Selway et al 1999)
In general beryl (Neiva amp Neiva 2005) feldsparsmicas and columbite-(Mn) (in this paper) from theNamivo lepidolite-subtype pegmatite record the progres-sive chemical evolution of the pegmatite from the wallzone to the core These minerals were produced by crystal-lization from a silicate melt rather than an aqueous fluidphase The slow cooling of melt shown by the magmaticcrystallization temperatures of feldspars cannot explain theincrease in grain-size of minerals from the wall zone to thecore but fluxes will be necessary to promote the change oftexture particularly a flux-rich hydrosilicate liquidaccording to the experimental evidence (London 2009)The constitutional zone refining model will be the best forthis zoned pegmatite and probably for all lepidolite-sub-type pegmatites because this model also produces a higherfinal concentration of incompatible components in a smal-ler volume of rock than fractional crystallization does(Morgan amp London 1999)
The core margin at the Rozna pegmatite contains K-feld-spar and quartz and the core consists mainly of quartz but it issurrounded and penetrated by a quartz-bearing albitethorn lepi-dolite complex which contains several minerals At theDobra Voda pegmatite the center of the dike is occupiedby the lepidolite unit containing albite and other minerals(Cerny et al 1995) At the Namivo pegmatite the coremargin consists of quartz and beryl and the core containsmainly quartz and spodumene but also albite lepidolite andother minerals The last-unit assemblages of primary miner-als in most of the highly fractionated LCT pegmatites are richin albite and commonly contain lepidolite or spodumene andmost of the other rare phases These units represent the lastmost fractionated liquid that can be derived by fractionalcrystallization of a crustal melt (London 2008)
The Namivo granitic pegmatite shows a significant dis-tinction from the other zoned lepidolite-subtype pegmatitesand LCT pegmatites except the Tanco petalite-subtypepegmatite in Canada because the lepidolite richest in SiLi and F FeMg-containing polylithionite and associatedcolumbite-(Mn) with the highest Ta(Ta thorn Nb) ratio tanta-lite-(Fe) and tantalite-(Mn) only occur in the outer inter-mediate zone These minerals usually form late in theconsolidation of pegmatites The lepidolite and polylithio-nite are probably derived from the disequilibrium crystal-lization of an undercooled melt Tantalite may reflect a localdecrease in Li and F that caused Ta precipitation
This paper contributes to a better understanding of theorigin and evolution of the rare zoned lepidolite-subtypepegmatites and shows that although the pegmatite evolvedfrom the wall zone to the core it presents an unusualassociation of lepidolite polylithionite and tantalite in theouter intermediate zone
Acknowledgments Thanks are due to JM Cotelo Neivaand MB Dias for the samples and information providedand to MR Machado Leite and MF Guimaraes for theuse of the electron microprobe facilities at the LaboratorioNacional de Energia e Geologia (LNEG) PortugalFinancial support was provided by the PortugueseGovernment for the project Pest-OECTEUI00732011of the Geosciences Centre through the PortugueseFoundation for Science and Technology I would like tothank D London WB Simmons and the associated editorE Widom for their constructive reviews of this manuscriptand M Prieto for his editorial work
References
Alfonso P Melgarejo JC Yusta I Velasco F (2003)
Geochemistry of feldspars and muscovite in granitic pegmatite
from the Cap de Creus field Catalonia Spain Can Mineral 41
103ndash116
Antunes IMHR Neiva AMR Ramos JMF Silva PB
Silva MMVG Corfu F (2013) Petrogenetic links between
lepidolite-subtype aplite-pegmatite aplite veins and associated
granites at Segura (central Portugal) Chemie der Erde in press
httpdxdoiorg101016jchemer20121203
Batchelor RA amp Kinnaird JA (1984) Gahnite compositions
compared Mineral Mag 48 425ndash430
Beurlen H Da Silva MRR Thomas R Soares DR Olivier P
(2008) Nb-Ta-(Ti-Sn) oxide mineral chemistry as tracer of rare-
element granitic pegmatite fractionation in the Borborema pro-
vince Northeastern Brazil Miner Deposita 43 207ndash228
Cameron EN Jahns RH McNair AH Page LR (1949)
Internal structure of granitic pegmatites Econ Geol
Monograph 2 115 p
Cerny P (1991a) Fertile granites of Precambrian rare-element
pegmatite fields is geochemistry controlled by tectonic setting
or source lithologies Precambrian Res 51 429ndash468
mdash (1991b) Rare-element granite pegmatites I Anatomy and inter-
nal evolution of pegmatite deposits Geoscience Canada 18
49ndash67
mdash (1992) Geochemical and petrogenetic features of mineralization
in rare-element granitic pegmatites in the light of current
research Applied Geochemistry 7 393ndash416
mdash (1994) Evolution of feldspars in granitic pegmatites in
lsquolsquoFeldspars and their Reactionsrsquorsquo I Parsons ed NATO
Advanced Study Institute Series C421 501ndash539
mdash (2005) The Tanco rare-element pegmatite deposit Manitoba
regional context internal anatomy and global comparisons in
lsquolsquoRare-element Geochemistry and Mineral Depositsrsquorsquo RL
Linnen amp IM Samson eds Geochemical Association of
Canada Short Course Notes St Catherines 17 127ndash158
Silicate and oxide minerals from a zoned granitic pegmatite 983
eschweizerbart_xxx
Cerny P amp Ercit TS (2005) The classification of granitic pegma-
tites revisited Can Mineral 43 2005ndash2026
Cerny P Meintzer RE Andersen AJ (1985) Extreme fractiona-
tion in rare-element granitic pegmatites selected examples of
data and mechanisms Can Mineral 23 381ndash421
Cerny P Goad BE Hawthorne FC Chapmann R (1986)
Fractionation trends of the Nb- and Ta-bearing oxide minerals
in the Greer Lake pegmatite granite and its pegmatite aureole
southeastern Manitoba Am Mineral 71 501ndash517
Cerny P Stanek J Novak M Baadsgaard H Rieder M
Ottolini L Kavalova M Chapman R (1995) Geochemical
and structural evolution of micas in the Rozna amp Dobra Voda
pegmatites Czech Republic Mineral Petrol 55 177ndash201
Cerny P Ercit TS Vanstone PJ (1998) Mineralogy and petrol-
ogy of the Tanco rare-element pegmatite deposit southeastern
Manitoba International Mineralogical Association 17th General
Meeting Toronto Field Guidebook B6
Cerny P Chapman R Ferreira K Smeds SA (2004)
Geochemistry of oxide minerals of Nb Ta Sn and Sb in
the Varutrask granitic pegmatite Sweden The case of an
lsquolsquoanomalousrsquorsquo columbitendashtantalite trend Am Mineral 89
505ndash518
Cerny P Masau M Goad BE Ferreira K (2005) The Greer
Lake leucogranite Manitoba and the origin of lepidolite-sub-
type granitic pegmatites Lithos 80 305ndash321
Cerny P Teertstra DK Chapman R Selway JB Hawthorne
FC Ferreira K Chackowsky LE Wang X-J Meintzer
RE (2012a) Extreme fractionation and deformation of the
leucogranite-pegmatite suite at Red Cross Lake Manitoba
Canada IV Mineralogy Can Mineral 50 1839ndash1875
Cerny P Halden NM Ferreira K Meintzer RE Brisbin WC
Chackowsky LE (2012b) Extreme fractionation and deforma-
tion of the leucogranite-pegmatite suite at Red Cross Lake
Manitoba Canada II Petrology of the leucogranites and peg-
matites Can Mineral 50 1807ndash1822
Dahl PS When DC Feldmann SG (1993) The systematics of
trace-element partitioning between coexisting muscovite and
biotite in metamorphic rocks from the Black Hills South
Dakota USA Geochim Cosmochim Acta 57 2487ndash2505
Dias MB amp Wilson WE (2000) The Alto Ligonha Pegmatites
Mozambique Mineral Record 31 459ndash497
Fleet ME (2003) Rock-Forming Minerals vol 3A Sheet silicates
micas The Geological Society London second edition chap 6
Lithium micas 651ndash690
Foord EE Cerny P Jackson LL Sherman DM Eby RK
(1995) Mineralogical and geochemical evolutions of micas
from miarolitic pegmatites of the anorogenic pikes-Peak
Batholith Colorado Mineral Petrol 55 1ndash26
Foster MD (1960) Interpretation of the composition of lithium
micas US Geol Surv Prof Paper 354-E 115ndash147
Fuhrman ML amp Lindsley DK (1988) Ternary-feldspar modeling
and thermometry Am Mineral 73 201ndash215
Gomes CL Castro P Alves C (1995) Caracterizacao das espi-
nelas zincıferas e do par ganite-nigerite no campo aplito-
pegmatıtico da Serra de Arga-Minho N de Portugal IV
Congresso Nacional de Geologia Resumos Alargados
Universidade do Porto Mem 4 629ndash633
Gordiyenko VV Ilyina AN Timochina LA Badamina EB
Stanek J (1996) Geochemical model of evolution of a pegma-
tite-forming ore-magmatic system of western Moravia Proc
Russ Mineral Soc 125 38ndash48 (in Russian)
Icenhower JP amp London D (1995) An experimental study for
element partitioning between biotite muscovite and coexisting
peraluminous granitic melt at 200 MPa (H2O) Am Mineral 80
1229ndash1251
Jahns RH (1982) Internal evolution of pegmatite bodies in lsquolsquoGranitic
Pegmatites in science and industryrsquorsquo P Cerny ed Mineralogical
Association of Canada Short Course Handbook 8 293ndash327
Jahns RH amp Burnham CW (1969) Experimental studies of
pegmatite genesis I A model for the derivation and crystal-
lization of granitic pegmatites Econ Geol 64 843ndash864
Jolliff BL Papike JJ Shearer CK (1987) Fractionation trends
in mica and tourmaline as indicators of pegmatite internal evo-
lution Bob Ingersoll pegmatite Black Hills South Dakota
USA GeochimCosmochim Acta 51 519ndash534
Kile DE amp Foord EE (1998) Micas from the Pikes Peak bath-
olith and its cogenetic granitic pegmatites Colorado optical
properties composition and correlation with pegmatite evolu-
tion Can Mineral 36 463ndash482
Linnen RL (1998) The solubility of Nb-Ta-Zr-Hf-W in granitic
melts with Li and Li thorn F constraints for mineralization in rare
metal granites and pegmatites Econ Geol 93 1013ndash1025
Linnen RL amp Cuney M (2005) Granite-related rare-element
deposits and experimental constraints on Ta-Nb-W-Sn-Zr-Hf
mineralization in lsquolsquoRare-element geochemistry and mineral
depositsrsquorsquo RL Linnen amp IM Samson eds Geochemical
Association of Canada Short Course Notes 17 45ndash68
London D (1990) Internal differentiation of rare-element pegmatites
a synthesis of recent research in lsquolsquoOre Bearing Granite Systems
Petrogenesis and Mineralizing Processesrsquorsquo HJ Stein amp JL
Hannah eds Geol Soc America Special Paper 246 35ndash50
mdash (2008) Pegmatites The Canadian Mineralogist Special
Publication 10 347 p
mdash (2009) The origin of primary textures in granitic pegmatites
Can Mineral 47 697ndash724
London D amp Morgan GB VI (2012) The pegmatite puzzle
Elements 8 263ndash268
London D Morgan GB VI Hervig RL (1989) Vapor-under-
saturated experiments in the system macusanite-H2O at 200
MPa and the internal differentiation of granitic pegmatites
Contrib Mineral Petrol 102 1ndash17
London D Morgan GB VI Paul KA Guttery BM (2012)
Internal evolution of miarolitic granitic pegmatites at the Little
Three mine Ramona California USA Can Mineral 50
1025ndash1054
Martins T Lima A Simmons WB Folster AU Noronha F
(2011) Geochemical fractionation of Nb-Ta oxides in Li-bear-
ing pegmatites from the Barroso-Alvao pegmatite field northern
Portugal Can Mineral 49 777ndash791
Monier G Charoy B Cuney M Ohnenstetter D Robert JL
(1987) Evolution spatiale et temporelle de la composition des
micas du granite albitique a topaze-lepidolite de Beauvoir
Geologie De La France 2ndash3 179ndash188
Monier G amp Robert JL (1986) Evolution of the miscibility gap
between muscovite and biotite solid solutions with increasing
lithium content an experimental study in the systems
K2OndashLi2OndashMgOndashAl2O3ndashSiO2ndashH2OndashHF at 600 C 2 kbar
PH2O comparison with natural lithium micas Mineral Mag
50 641ndash651
Morgan GBVI amp London D (1999) Crystallization of the little
three layered pegmatite-aplite dike Ramona District California
Contrib Mineral Petrol 136 310ndash330
984 A M R Neiva
eschweizerbart_xxx
Nabelek PI amp Russ-Nabelek C (1992) The generation and crys-
tallization conditions of the Proterozoic Harney Peak
Leucrogranite Black Hills South Dakota USA petrologic and
geochemical constraints Contrib Mineral Petrol 110
173ndash191
Nabelek PI Russ-Nabelek C Haeussler GT (1992) Stable
isotope evidence for the petrogenesis and fluid evolution in
the Proterozoic Harney Peak leucogranite Black Hills
South Dakota Geochim Cosmochim Acta 56 403ndash417
Neiva AMR amp Champness PE (1997) Nigerite and gahnite from
the granitic pegmatite veins of Cabanas Ponte de Lima northern
Portugal N Jb Mineral Mh 9 385ndash409
Neiva AMR Gomes MEP Ramos JMF Silva PB (2008)
Geochemistry of granitic aplite-pegmatite sills and their miner-
als from Arcozelo da Serra area (Gouveia central Portugal)
Eur J Mineral 20 465ndash485
Neiva AMR amp Neiva JMC (2005) Beryl from the granitic
pegmatite at Namivo Alto Ligonha Mozambique N Jb
Mineral Abh 181 173ndash182
Neiva AMR amp Ramos JMF (2010) Geochemistry of granitic
aplite-pegmatite sills and petrogenetic links with granites
Guarda-Belmonte area central Portugal Eur J Mineral 22
837ndash854
Neiva AMR Silva PB Ramos JMF (2012) Geochemistry of
granitic aplite-pegmatite veins and sills and their minerals from the
Sabugal area central Portugal N Jb Mineral Abh 189 49ndash74
Novak M amp Cerny P (1998) Niobium-tantalum oxide minerals
from complex granitic pegmatites in the Moldanubicum Czech
Republic primary versus secondary compositional trends Can
Mineral 36 659ndash672
Pesquera Perez A Torres-Ruiz J Gil PP Velilla N (1999)
Chemistry and genetic implications of tourmaline and Li-F-Cs
micas from the Valdeflores (Caceres Spain) Am Mineral 84
55ndash69
Rieder M Cavazzini G DrsquoYakonov YuS Frank-Kamenetskii
VA Gottardi G Guggenheim S Koval PV Muller G
Neiva AMR Radoslovich EW Robert J-L Sassi FP
Takeda H Weiss Z Wones DR (1999) Nomenclature of the
micas Mineral Mag 63 267ndash279
Roda Robles E Pesquera Perez A Velasco Roldan F Fontan F
(1999) The granitic pegmatites of the Fregeneda area
(Salamanca Spain) characteristics and petrogenesis Mineral
Mag 63 535ndash558
Roda Robles E Pesquera A Gil-Crespo PP Torres-Ruiz J
Fontan F (2005) Origin and internal evolution of the Li-F-
Be-P-bearing Pinilla de Fermoselle pegmatite (Central Iberian
Zone Zamora Spain) Am Mineral 90 1887ndash1899
Roda Robles E Pesquera Perez A Gil PP Torres-Ruiz J de
Parseval P (2006) Mineralogy and geochemistry of micas from
the Pinilla de Fermoselle pegmatite (Zamora Spain) Eur J
Mineral 18 369ndash377
Roda Robles E Keller P Pesquera Perez A Fontan F (2007)
Micas of the muscovite-lepidolite series from Karibib pegma-
tites Namibia Mineral Mag 71 41ndash62
Roda Robles E Pesquera A Gil-Crespo P Torres-Ruiz J
(2012) From granite to highly evolved pegmatite a case study
of the Pinilla de Fermoselle granite-pegmatite system (Zamora
Spain) Lithos 153 192ndash207
Selway JB Novak M Cerny P Hawthorne FC (1999)
Compositional evolution of tourmaline in lepidolite-subtype
pegmatites Eur J Mineral 11 569ndash584
Shearer CK Papike JJ Jolliff B (1992) Petrogenetic links
among granites and pegmatites in the Harney Peak rare-element
granite-pegmatite system Black Hills South Dakota Can
Mineral 30 785ndash809
Soares DR Hartmut B Ferreira ACM da Silva MRR
(2007) Chemical composition of gahnite and degree of peg-
matitic fractionation in the Borborema Pegmatitic Province
northeastern Brazil Anais Da Academ Bras Cien 79
395ndash404
Stewart DB (1978) Petrogenesis of lithium-rich pegmatites Am
Mineral 63 970ndash980
Tischendorff G Gattesmann B Forster H-J Trumbull RB
(1997) On Li-bearing micas estimating Li from electron
microprobe analyses and an improved diagram for graphical
representation Mineral Mag 61 809ndash834
Van Lichtervelde M Linnen RL Salvi S Beziat D (2006)
The role of metagabbro rafts on tantalum mineralization in the
Tanco granitic pegmatite Manitoba Can Mineral 44
625ndash644
Van Lichtervelde M Gregoire M Linnen RL Beziat D Salvi
S (2008) Trace element geochemistry by laser ablation ICP-
MS of micas associated with Ta mineralization in the Tanco
pegmatite Manitoba Canada Contrib Mineral Petrol 155
791ndash806
Vieira R Roda-Robles E Pesquera A Lima A (2011)
Chemical variation and significance of micas from the
Fregeneda-Almendra pegmatitic field (Central-Iberian Zone
Spain and Portugal) Am Mineral 96 637ndash645
Wen S amp Nekvasil H (1994) SOLVCALC an interactive gra-
phics program package for calculating ternary feldspar solvus
and two-feldspar geothermometry Comput Geosci 20
1025ndash1040
Wise MA (1995) Trace element chemistry of lithium-rich micas
from rare-element granitic pegmatites Mineral Petrol 55
203ndash215
Zasedatelev AM (1974) Possible accumulation of lithium in host
rocks of lithium pegmatite veins during old sedimentation pro-
cesses Doklady Acad Sci USSR Earth Sci Ser 218 196ndash198
(in Russian)
mdash (1977) Quantitative of metamorphic generation of rare-metal
pegmatites with lithium mineralization Doklady Acad Sci
USSR Earth Sci Ser 236 219ndash221 (in Russian)
Received 26 January 2013
Modified version received 21 May 2013
Accepted 23 July 2013
Silicate and oxide minerals from a zoned granitic pegmatite 985
eschweizerbart_xxx
Cerny P amp Ercit TS (2005) The classification of granitic pegma-
tites revisited Can Mineral 43 2005ndash2026
Cerny P Meintzer RE Andersen AJ (1985) Extreme fractiona-
tion in rare-element granitic pegmatites selected examples of
data and mechanisms Can Mineral 23 381ndash421
Cerny P Goad BE Hawthorne FC Chapmann R (1986)
Fractionation trends of the Nb- and Ta-bearing oxide minerals
in the Greer Lake pegmatite granite and its pegmatite aureole
southeastern Manitoba Am Mineral 71 501ndash517
Cerny P Stanek J Novak M Baadsgaard H Rieder M
Ottolini L Kavalova M Chapman R (1995) Geochemical
and structural evolution of micas in the Rozna amp Dobra Voda
pegmatites Czech Republic Mineral Petrol 55 177ndash201
Cerny P Ercit TS Vanstone PJ (1998) Mineralogy and petrol-
ogy of the Tanco rare-element pegmatite deposit southeastern
Manitoba International Mineralogical Association 17th General
Meeting Toronto Field Guidebook B6
Cerny P Chapman R Ferreira K Smeds SA (2004)
Geochemistry of oxide minerals of Nb Ta Sn and Sb in
the Varutrask granitic pegmatite Sweden The case of an
lsquolsquoanomalousrsquorsquo columbitendashtantalite trend Am Mineral 89
505ndash518
Cerny P Masau M Goad BE Ferreira K (2005) The Greer
Lake leucogranite Manitoba and the origin of lepidolite-sub-
type granitic pegmatites Lithos 80 305ndash321
Cerny P Teertstra DK Chapman R Selway JB Hawthorne
FC Ferreira K Chackowsky LE Wang X-J Meintzer
RE (2012a) Extreme fractionation and deformation of the
leucogranite-pegmatite suite at Red Cross Lake Manitoba
Canada IV Mineralogy Can Mineral 50 1839ndash1875
Cerny P Halden NM Ferreira K Meintzer RE Brisbin WC
Chackowsky LE (2012b) Extreme fractionation and deforma-
tion of the leucogranite-pegmatite suite at Red Cross Lake
Manitoba Canada II Petrology of the leucogranites and peg-
matites Can Mineral 50 1807ndash1822
Dahl PS When DC Feldmann SG (1993) The systematics of
trace-element partitioning between coexisting muscovite and
biotite in metamorphic rocks from the Black Hills South
Dakota USA Geochim Cosmochim Acta 57 2487ndash2505
Dias MB amp Wilson WE (2000) The Alto Ligonha Pegmatites
Mozambique Mineral Record 31 459ndash497
Fleet ME (2003) Rock-Forming Minerals vol 3A Sheet silicates
micas The Geological Society London second edition chap 6
Lithium micas 651ndash690
Foord EE Cerny P Jackson LL Sherman DM Eby RK
(1995) Mineralogical and geochemical evolutions of micas
from miarolitic pegmatites of the anorogenic pikes-Peak
Batholith Colorado Mineral Petrol 55 1ndash26
Foster MD (1960) Interpretation of the composition of lithium
micas US Geol Surv Prof Paper 354-E 115ndash147
Fuhrman ML amp Lindsley DK (1988) Ternary-feldspar modeling
and thermometry Am Mineral 73 201ndash215
Gomes CL Castro P Alves C (1995) Caracterizacao das espi-
nelas zincıferas e do par ganite-nigerite no campo aplito-
pegmatıtico da Serra de Arga-Minho N de Portugal IV
Congresso Nacional de Geologia Resumos Alargados
Universidade do Porto Mem 4 629ndash633
Gordiyenko VV Ilyina AN Timochina LA Badamina EB
Stanek J (1996) Geochemical model of evolution of a pegma-
tite-forming ore-magmatic system of western Moravia Proc
Russ Mineral Soc 125 38ndash48 (in Russian)
Icenhower JP amp London D (1995) An experimental study for
element partitioning between biotite muscovite and coexisting
peraluminous granitic melt at 200 MPa (H2O) Am Mineral 80
1229ndash1251
Jahns RH (1982) Internal evolution of pegmatite bodies in lsquolsquoGranitic
Pegmatites in science and industryrsquorsquo P Cerny ed Mineralogical
Association of Canada Short Course Handbook 8 293ndash327
Jahns RH amp Burnham CW (1969) Experimental studies of
pegmatite genesis I A model for the derivation and crystal-
lization of granitic pegmatites Econ Geol 64 843ndash864
Jolliff BL Papike JJ Shearer CK (1987) Fractionation trends
in mica and tourmaline as indicators of pegmatite internal evo-
lution Bob Ingersoll pegmatite Black Hills South Dakota
USA GeochimCosmochim Acta 51 519ndash534
Kile DE amp Foord EE (1998) Micas from the Pikes Peak bath-
olith and its cogenetic granitic pegmatites Colorado optical
properties composition and correlation with pegmatite evolu-
tion Can Mineral 36 463ndash482
Linnen RL (1998) The solubility of Nb-Ta-Zr-Hf-W in granitic
melts with Li and Li thorn F constraints for mineralization in rare
metal granites and pegmatites Econ Geol 93 1013ndash1025
Linnen RL amp Cuney M (2005) Granite-related rare-element
deposits and experimental constraints on Ta-Nb-W-Sn-Zr-Hf
mineralization in lsquolsquoRare-element geochemistry and mineral
depositsrsquorsquo RL Linnen amp IM Samson eds Geochemical
Association of Canada Short Course Notes 17 45ndash68
London D (1990) Internal differentiation of rare-element pegmatites
a synthesis of recent research in lsquolsquoOre Bearing Granite Systems
Petrogenesis and Mineralizing Processesrsquorsquo HJ Stein amp JL
Hannah eds Geol Soc America Special Paper 246 35ndash50
mdash (2008) Pegmatites The Canadian Mineralogist Special
Publication 10 347 p
mdash (2009) The origin of primary textures in granitic pegmatites
Can Mineral 47 697ndash724
London D amp Morgan GB VI (2012) The pegmatite puzzle
Elements 8 263ndash268
London D Morgan GB VI Hervig RL (1989) Vapor-under-
saturated experiments in the system macusanite-H2O at 200
MPa and the internal differentiation of granitic pegmatites
Contrib Mineral Petrol 102 1ndash17
London D Morgan GB VI Paul KA Guttery BM (2012)
Internal evolution of miarolitic granitic pegmatites at the Little
Three mine Ramona California USA Can Mineral 50
1025ndash1054
Martins T Lima A Simmons WB Folster AU Noronha F
(2011) Geochemical fractionation of Nb-Ta oxides in Li-bear-
ing pegmatites from the Barroso-Alvao pegmatite field northern
Portugal Can Mineral 49 777ndash791
Monier G Charoy B Cuney M Ohnenstetter D Robert JL
(1987) Evolution spatiale et temporelle de la composition des
micas du granite albitique a topaze-lepidolite de Beauvoir
Geologie De La France 2ndash3 179ndash188
Monier G amp Robert JL (1986) Evolution of the miscibility gap
between muscovite and biotite solid solutions with increasing
lithium content an experimental study in the systems
K2OndashLi2OndashMgOndashAl2O3ndashSiO2ndashH2OndashHF at 600 C 2 kbar
PH2O comparison with natural lithium micas Mineral Mag
50 641ndash651
Morgan GBVI amp London D (1999) Crystallization of the little
three layered pegmatite-aplite dike Ramona District California
Contrib Mineral Petrol 136 310ndash330
984 A M R Neiva
eschweizerbart_xxx
Nabelek PI amp Russ-Nabelek C (1992) The generation and crys-
tallization conditions of the Proterozoic Harney Peak
Leucrogranite Black Hills South Dakota USA petrologic and
geochemical constraints Contrib Mineral Petrol 110
173ndash191
Nabelek PI Russ-Nabelek C Haeussler GT (1992) Stable
isotope evidence for the petrogenesis and fluid evolution in
the Proterozoic Harney Peak leucogranite Black Hills
South Dakota Geochim Cosmochim Acta 56 403ndash417
Neiva AMR amp Champness PE (1997) Nigerite and gahnite from
the granitic pegmatite veins of Cabanas Ponte de Lima northern
Portugal N Jb Mineral Mh 9 385ndash409
Neiva AMR Gomes MEP Ramos JMF Silva PB (2008)
Geochemistry of granitic aplite-pegmatite sills and their miner-
als from Arcozelo da Serra area (Gouveia central Portugal)
Eur J Mineral 20 465ndash485
Neiva AMR amp Neiva JMC (2005) Beryl from the granitic
pegmatite at Namivo Alto Ligonha Mozambique N Jb
Mineral Abh 181 173ndash182
Neiva AMR amp Ramos JMF (2010) Geochemistry of granitic
aplite-pegmatite sills and petrogenetic links with granites
Guarda-Belmonte area central Portugal Eur J Mineral 22
837ndash854
Neiva AMR Silva PB Ramos JMF (2012) Geochemistry of
granitic aplite-pegmatite veins and sills and their minerals from the
Sabugal area central Portugal N Jb Mineral Abh 189 49ndash74
Novak M amp Cerny P (1998) Niobium-tantalum oxide minerals
from complex granitic pegmatites in the Moldanubicum Czech
Republic primary versus secondary compositional trends Can
Mineral 36 659ndash672
Pesquera Perez A Torres-Ruiz J Gil PP Velilla N (1999)
Chemistry and genetic implications of tourmaline and Li-F-Cs
micas from the Valdeflores (Caceres Spain) Am Mineral 84
55ndash69
Rieder M Cavazzini G DrsquoYakonov YuS Frank-Kamenetskii
VA Gottardi G Guggenheim S Koval PV Muller G
Neiva AMR Radoslovich EW Robert J-L Sassi FP
Takeda H Weiss Z Wones DR (1999) Nomenclature of the
micas Mineral Mag 63 267ndash279
Roda Robles E Pesquera Perez A Velasco Roldan F Fontan F
(1999) The granitic pegmatites of the Fregeneda area
(Salamanca Spain) characteristics and petrogenesis Mineral
Mag 63 535ndash558
Roda Robles E Pesquera A Gil-Crespo PP Torres-Ruiz J
Fontan F (2005) Origin and internal evolution of the Li-F-
Be-P-bearing Pinilla de Fermoselle pegmatite (Central Iberian
Zone Zamora Spain) Am Mineral 90 1887ndash1899
Roda Robles E Pesquera Perez A Gil PP Torres-Ruiz J de
Parseval P (2006) Mineralogy and geochemistry of micas from
the Pinilla de Fermoselle pegmatite (Zamora Spain) Eur J
Mineral 18 369ndash377
Roda Robles E Keller P Pesquera Perez A Fontan F (2007)
Micas of the muscovite-lepidolite series from Karibib pegma-
tites Namibia Mineral Mag 71 41ndash62
Roda Robles E Pesquera A Gil-Crespo P Torres-Ruiz J
(2012) From granite to highly evolved pegmatite a case study
of the Pinilla de Fermoselle granite-pegmatite system (Zamora
Spain) Lithos 153 192ndash207
Selway JB Novak M Cerny P Hawthorne FC (1999)
Compositional evolution of tourmaline in lepidolite-subtype
pegmatites Eur J Mineral 11 569ndash584
Shearer CK Papike JJ Jolliff B (1992) Petrogenetic links
among granites and pegmatites in the Harney Peak rare-element
granite-pegmatite system Black Hills South Dakota Can
Mineral 30 785ndash809
Soares DR Hartmut B Ferreira ACM da Silva MRR
(2007) Chemical composition of gahnite and degree of peg-
matitic fractionation in the Borborema Pegmatitic Province
northeastern Brazil Anais Da Academ Bras Cien 79
395ndash404
Stewart DB (1978) Petrogenesis of lithium-rich pegmatites Am
Mineral 63 970ndash980
Tischendorff G Gattesmann B Forster H-J Trumbull RB
(1997) On Li-bearing micas estimating Li from electron
microprobe analyses and an improved diagram for graphical
representation Mineral Mag 61 809ndash834
Van Lichtervelde M Linnen RL Salvi S Beziat D (2006)
The role of metagabbro rafts on tantalum mineralization in the
Tanco granitic pegmatite Manitoba Can Mineral 44
625ndash644
Van Lichtervelde M Gregoire M Linnen RL Beziat D Salvi
S (2008) Trace element geochemistry by laser ablation ICP-
MS of micas associated with Ta mineralization in the Tanco
pegmatite Manitoba Canada Contrib Mineral Petrol 155
791ndash806
Vieira R Roda-Robles E Pesquera A Lima A (2011)
Chemical variation and significance of micas from the
Fregeneda-Almendra pegmatitic field (Central-Iberian Zone
Spain and Portugal) Am Mineral 96 637ndash645
Wen S amp Nekvasil H (1994) SOLVCALC an interactive gra-
phics program package for calculating ternary feldspar solvus
and two-feldspar geothermometry Comput Geosci 20
1025ndash1040
Wise MA (1995) Trace element chemistry of lithium-rich micas
from rare-element granitic pegmatites Mineral Petrol 55
203ndash215
Zasedatelev AM (1974) Possible accumulation of lithium in host
rocks of lithium pegmatite veins during old sedimentation pro-
cesses Doklady Acad Sci USSR Earth Sci Ser 218 196ndash198
(in Russian)
mdash (1977) Quantitative of metamorphic generation of rare-metal
pegmatites with lithium mineralization Doklady Acad Sci
USSR Earth Sci Ser 236 219ndash221 (in Russian)
Received 26 January 2013
Modified version received 21 May 2013
Accepted 23 July 2013
Silicate and oxide minerals from a zoned granitic pegmatite 985
eschweizerbart_xxx
Nabelek PI amp Russ-Nabelek C (1992) The generation and crys-
tallization conditions of the Proterozoic Harney Peak
Leucrogranite Black Hills South Dakota USA petrologic and
geochemical constraints Contrib Mineral Petrol 110
173ndash191
Nabelek PI Russ-Nabelek C Haeussler GT (1992) Stable
isotope evidence for the petrogenesis and fluid evolution in
the Proterozoic Harney Peak leucogranite Black Hills
South Dakota Geochim Cosmochim Acta 56 403ndash417
Neiva AMR amp Champness PE (1997) Nigerite and gahnite from
the granitic pegmatite veins of Cabanas Ponte de Lima northern
Portugal N Jb Mineral Mh 9 385ndash409
Neiva AMR Gomes MEP Ramos JMF Silva PB (2008)
Geochemistry of granitic aplite-pegmatite sills and their miner-
als from Arcozelo da Serra area (Gouveia central Portugal)
Eur J Mineral 20 465ndash485
Neiva AMR amp Neiva JMC (2005) Beryl from the granitic
pegmatite at Namivo Alto Ligonha Mozambique N Jb
Mineral Abh 181 173ndash182
Neiva AMR amp Ramos JMF (2010) Geochemistry of granitic
aplite-pegmatite sills and petrogenetic links with granites
Guarda-Belmonte area central Portugal Eur J Mineral 22
837ndash854
Neiva AMR Silva PB Ramos JMF (2012) Geochemistry of
granitic aplite-pegmatite veins and sills and their minerals from the
Sabugal area central Portugal N Jb Mineral Abh 189 49ndash74
Novak M amp Cerny P (1998) Niobium-tantalum oxide minerals
from complex granitic pegmatites in the Moldanubicum Czech
Republic primary versus secondary compositional trends Can
Mineral 36 659ndash672
Pesquera Perez A Torres-Ruiz J Gil PP Velilla N (1999)
Chemistry and genetic implications of tourmaline and Li-F-Cs
micas from the Valdeflores (Caceres Spain) Am Mineral 84
55ndash69
Rieder M Cavazzini G DrsquoYakonov YuS Frank-Kamenetskii
VA Gottardi G Guggenheim S Koval PV Muller G
Neiva AMR Radoslovich EW Robert J-L Sassi FP
Takeda H Weiss Z Wones DR (1999) Nomenclature of the
micas Mineral Mag 63 267ndash279
Roda Robles E Pesquera Perez A Velasco Roldan F Fontan F
(1999) The granitic pegmatites of the Fregeneda area
(Salamanca Spain) characteristics and petrogenesis Mineral
Mag 63 535ndash558
Roda Robles E Pesquera A Gil-Crespo PP Torres-Ruiz J
Fontan F (2005) Origin and internal evolution of the Li-F-
Be-P-bearing Pinilla de Fermoselle pegmatite (Central Iberian
Zone Zamora Spain) Am Mineral 90 1887ndash1899
Roda Robles E Pesquera Perez A Gil PP Torres-Ruiz J de
Parseval P (2006) Mineralogy and geochemistry of micas from
the Pinilla de Fermoselle pegmatite (Zamora Spain) Eur J
Mineral 18 369ndash377
Roda Robles E Keller P Pesquera Perez A Fontan F (2007)
Micas of the muscovite-lepidolite series from Karibib pegma-
tites Namibia Mineral Mag 71 41ndash62
Roda Robles E Pesquera A Gil-Crespo P Torres-Ruiz J
(2012) From granite to highly evolved pegmatite a case study
of the Pinilla de Fermoselle granite-pegmatite system (Zamora
Spain) Lithos 153 192ndash207
Selway JB Novak M Cerny P Hawthorne FC (1999)
Compositional evolution of tourmaline in lepidolite-subtype
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Shearer CK Papike JJ Jolliff B (1992) Petrogenetic links
among granites and pegmatites in the Harney Peak rare-element
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Soares DR Hartmut B Ferreira ACM da Silva MRR
(2007) Chemical composition of gahnite and degree of peg-
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395ndash404
Stewart DB (1978) Petrogenesis of lithium-rich pegmatites Am
Mineral 63 970ndash980
Tischendorff G Gattesmann B Forster H-J Trumbull RB
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Van Lichtervelde M Linnen RL Salvi S Beziat D (2006)
The role of metagabbro rafts on tantalum mineralization in the
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Van Lichtervelde M Gregoire M Linnen RL Beziat D Salvi
S (2008) Trace element geochemistry by laser ablation ICP-
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Vieira R Roda-Robles E Pesquera A Lima A (2011)
Chemical variation and significance of micas from the
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Wise MA (1995) Trace element chemistry of lithium-rich micas
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Zasedatelev AM (1974) Possible accumulation of lithium in host
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Received 26 January 2013
Modified version received 21 May 2013
Accepted 23 July 2013
Silicate and oxide minerals from a zoned granitic pegmatite 985
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