URANIUN{ AND THORIUM IN THE ACCESSORY ALLANITE

OF IGNEOUS ROCKS1

Wrrrreu Lre Slrttn,2 MoNa L. Fna'Ncr,3 ,q.Np Ar-BxeNnrn M.

Suonwooo, Ll . S. Geological Suraey, Washington 25, D'C '

ABsrRAcr

u'eight in the rocks studied. The mineral is confined largely to the more siiiceous phanerites.

The uranium content is highest in the ailanite from the granites sampled, ranging from

0.004 to 0.066 per cent, whereas the thorium content is high or low regionally, ranging from

0.35 to 2.33 per cent. Allanite was found to be otherwise of exceptionally uniform composi-

tion.

IwrnooucrroN

Allanite, (RE,*Ca)z(Fe,Al)sSirOrz(OH), may occur as an accessory

mineral in siliceous and intermediate igneous rocks, in limestone contact

skarns, pegmatites, crystalline metamorphic rocks, and as a component

of magmatic iron ores. The mineral is monoclinic and varies in color from

light brown to black. Its hardness ranges from 5 to 6 depending upon

its degree of alteration, and similarly its specific gravity varies from 3.4

to 4.2. Allanite is a member of the epidote group with rare earths sub-

stituting for calcium. Allanite is often found with epidote; some of it is

intergrown with epidote (Hobbs, 1889). The metamictization of allanite

produces an amorphous alteration product, and some allanite from

pegmatite is completely isotropic. The alteration is inferred to be the

result of the destruction of the crystalline structure of allanite by the

radioactive decay of its uranium and thorium.

N{rNBnarocv

Separat'ion method.s

In the granitic rocks that were studied, allanite was found to average

0.1 mm. in diameter. The rocks were pulverized on a roll-type crusher

which liberated the allanite cleanly. The allanite was generally found to

concentrate in the 100- to 200-mesh size fraction. Allanite concentrates

+ Rare earths.1 Publication authorized by the Director, U. S. Geological Survey.2 Present address: Minerals Benefication Div., Battelle Memorial Institute, columbus,

Ohio.3 Present address: Ferro Corp., Technical Service Lab., Cleveland, Ohio'

367

368 w. L. SMITH, M. L. FRANCR AND A. M. SIIERWOOD

with the other accessory minerals in the sink of a methylene iodide sep-aration (sp.g..3.33). It is easily separable from the other heavy mineralsin a Frantz rsodynamic magnetic separator, allanite becoming magneticbetween 0.4 and 0.6 amp. at cross and logitudinal settings of 10o. whenepidote occurs with allanite, the separation becomes more difficult. Theepidote floated and the allanite sank in methylene iodide saturated withiodoform (sp.gr.3.45). Thus a minimum of hand-picking was required. toobtain clean separates of the minerals.

Opti,cal properties

All of the ailanite studied was optically negative. The indices of re-fraction of the allanite were generally higher than those described inliterature. This may be because the minerals generally described are themore metamict varieties from pegmatites. rt is l ikely that the allanitedescribed here is more abundant and more typical of the fresh mineralthan the larger specimens obtained from pegmatites.

The optical data in Table 1 show that the a indices range from 1.690to 1.775, B f rom 1.70 to 7.789, and 7 f rom 1.706 to 1.291 wi th a possib leerror of +0.002. Allanite is reported to have indices as low as n 1.60

Teslr 1. Imrcrs or.RprrlcrroN ol All,qxrre lnou Icxuous Rocrs

q Rl_ o I Birefrin-

____l_-i:_Southern California batholith

Coarse phase

Granite from Rubidoux Mountain, RiversideFine Phase

Granite from Rubidoux Mountain, RiversideWoodson Mountain granodiorite, DescansoWoodson Mountain granodiorite, TemeculaWoodson Mountain granodiorite, RainbowWoodson Mountain granodiorite, ElsinoreGranodiorite, Stonewall formation, CuyamacaMount Hole granodiorite, Mount HoleTonalite, Aguanga

Sierra Nevada batholith

Quartz monzonite, Basin MountainIdaho batholith

Porphyritic granodiorlte, CascadeGranodiorite, StanleyGranodiorite, Atlanta

White Mountains, New HampshireFresh Conway granite, ConwayWeathered Conway granite, ConwayAlbany porphyritic quartz syenite, Passaconway

t . l t J

r . / .1. )1 . 7 4 51 , . 7351 740r .7401 . 7 0 51 .6951 . 7 4 3

1 .750

1 . 7 4 0r . 7 6 r1 .752

1 . 7 2 r1 . 7 2 01 .690

1 . 7 8 9

I . / . ) t ,

1 . 7 6 01 .7501 . 7 5 5I . / . ) . )

1 . 7 r 71 . 7 1 01 . 7 6 0

l . / o o

r . / . ) l

1 . 7 7 61 . 7 6 8

r . 7 3 8| . 7 3 71 . 7 0 0

1 . 7 9 1

l - l J z

1 .7631 . 7 5 3I . I J 9

1 .760| . 7 2 0t . t l +

1 . 7 6 3

1 . 7 7 0

I . / J J

1 7801 . 7 7 1

1 1 A 1

1 . 7 4 01 . 7 0 6

0 .016

0 .0170 .0180 .0180 .019o.o200 .0150 .0190.020

0.020

0 .0150 .0190 .019

0.021o.0200 .016

TJ AND TE IN ACCESSORY ALLANITE 369

among its isotropic varieties. The birefringence' 7-a, is shown to vary

from 0.015 to 0.021 in the specimens studied. The indices of refraction

of allanite from a single rock were found to be variable. The indices

listed are representative. fn the fresh Conway granite the allanite varies

in a index from 1.695 to I.739, and in the Cascade granodiorite the allan-

ite varies in a index from 1.740 to 1.760.There seems to be no clear relationship between the indices of refrac-

tion and the rock type. The Idaho minerals have consistently higher in-

dices, whereas those from New Hampshire have lower indices. AII of the

allanite studied is from rocks of Late Jurassic or Cretaceous age (Larsen,

1948; Chapman, 1955; Hinds, 1934) with the exception of the New

Hampshire samples which are of Mississippian age (Billings, 1945).

Cneursrnv

Chernical analysis

Chemical analyses (Table 2) of allanite from different areas and of

different optical properties were made by Glen Edgington of the Geolog-

ical Survey.

Tltntn2. Cgrurclr AxAtvsns, ru Pnn Cnwr, or Ar,laNrrn lnou ClscAor,Io.lno; Cotwev, Nnw Heursurnnl eNn Rrvrnspr, CeluonxtAl

ConstituentCascade

granodiorite

Granite from

Conway granite Rubidoux Mountain,(fine), Calif.

SiozAlzOsFe:OaCaOMgoMnOHrO (total)

CezOaRe2OB (other)(Total RE incl. ThO)

Total

30. 35/ . 5 0

1 8 . 1 412.907 . 4 30 . 3 82 . 0 0

1 1 . 0 615 .69

(26.7s)99.51

26.057 .54

t7 .o l10 .450 . 8 10. 585 . 6 0

12.451 8 . 6 9

( 3 1 . 1 4 )99. 18

29.758 . 4 2

20.688. S50 . 9 10 . 3 12 . 4 0

1 1 . 3 81 5 . 8 1

(27 .re)98.61

Determined on separate

samoles bv Sherwoodz

Th02U

1 . 20.0036

o .920.0540

0 . 7 60.0400

I Analyses made by methods outlined in Hillebrand and Lundell (1929)2 Uranium determined fluorimetricallv. Thoria determined colorimetrically by thoron

method.

370 w. L. SMITH, M. L. FRANCK AND A. .4[. SHERWOOD

S pectroscopy

Semiquantitative spectrographic analyses of nine allanites from igne-ous rocks are compared in Table 3. The minerals were separated fromrocks of the white Mountains batholith of New Hampshire, the southerncalifornia batholith, the Sierra Nevada batholith, and the rdaho batho-

Aside from the radioactive components, which are discussed separately,most of the variations in composition are within the l imits of precisionof the method. one immediately obvious fact is that each alianite con-tains the same 37 elements, with the exception of the absence of thuliumfrom the Basin I'rountain minerar and the absence of Iutetium from thecascade granodiorite mineral. The variations, which seem to be regional,are the higher content of Nb, Be, and sn in the New Hampshire minerals,and the higher content of the elements Mn, Ti, Ni, and cu in the SierraNevada specimen.

Among the rare earths, in all samples the order of abundance isCe,(La,Nd,Pr), (Sm,Gd), variable traces of Lu, Ho, and Eu. Tm is theleast abundant. Of the cerium earths the order is Ce,(La,Nd,pr), Sm,and Eu. Of the yttrium earths the order is (Gd,Dy), (Er,yb,Lu),(Ho,Tm.)

Rad i oo cl iae com ponen ! s

371U AND TH IN ACCESSORY ALLANITE

+ @F . _ , , x - 3

0 a - r n > r : l u- q d ' " r i I d , - - !

, q < ! a i N l E F z e' 6 6 2 > E a > E z o 6 t 4 r c

d s

a 2- ! 3 v

- ' r F l i i o

. X ^ i ;

4 6

' 1 F P '

, 9 < Z >i t s g i i

- 4 3z c - E zA a - , ; t , \ 6

, e e S i i y r \ S ; ; f 3E o I g F EE , i ; f i i 6 f i

8"1 .=E.q d E ; ? Tc X S

.', i s ; s i !-: E z7, ,v 2 a tr i ia d ,:,8 &

E - 3 . r 88d nE I ;3 i

n 1 f g s* t d ' i 4 z-a 3 2 > i r 8 A ; f i d d F d

O

( J i

Q Z

* a

. 9 oi E

O

> H '

O

F . 8 . :{ : €;g f ,

u q

N . :

d N

. Y B !! 9 F: x

Fr

z|l

z< , y

E I :

6 F.l

& - ;

p . a.h ::F X

H 1

tsz

Ea

|ltr

F

3 XF

d s , ct FZ - F L r o t . = r J > 3 iJ F I _ > r , 1 ;

f , o T" E a ; - i az 2 ,F 'a 3 ? # i r B s # E - 3 a A A

E i . qa r

. 2 2 )< d g E F Z n t -

d r i 7 , > F 14 > r , ? , zFa s s F sE A aE i l o ; a

z z a ? _ o, i F c A o g . ga a i > > E #

, y 8d s i : f i d j i . tE a af i i ia A aA H c, i

- S a 3 . - EA q

2 g d f i df i q 6s c I S ; 1 a 2a ; f i _i l c < e gE A a i I o€

i 5

F

' 5 =

0 .,i4.

E

z

F

F . ,

U E

q . 1 E{ : €;s g

9 r c ;

c * a 6 IE C = G

: o! ? Q 9 9 9

Y Y ; Y Y YP : A = P : e x x =

E t 5o o o do o

E -. 9 0 0 'v : = b H o

; A ; ] ; J\ d c ;

W. L. SMITH, M. L. FRANCR AND A M. SHERII/OOD372

O H O \ 4 O \ N b € ( ) o ON N i : i i i i i N

O \ \ c ) \ O @ S N : \ c ) N \ O. + 4 o | . \ O o O O \ r + O O \€ N N N N N i H H O

- i - l : - i ; , i - i - i - : . {

d ( q o ^

d ; - f id ' d ; J O

a ) a o

O N \ O < r O \ N O d N c Oo O O o O \ O < t \ O a O < t O \ c O4 N N N N : i i O O- i . i ^ , { - i : - : ^ - : . {

O N < i n O \ N N \ O @ DO O \ d O O \ \ O N A O O

\ O Q Q \ O 1 4 O H h N c Oh + = f l o : t r O - ! Q q \\ 9 v ) O O c ) . + 1 - v - e

d o c ; d c j d o i c j o

o

r ! ?

a

a

@

o

o

O c ] O h i N O o o O$ $ o o b N Q N 4 \ O N\ \ \ \ \ \ \ \ : \- H H H i i i H H d

N € \ O i @ O N O O \ Os o N b \ o r o i 4 \ o \ o

\ \ \ \ \ \ \ \ \ " :H i H H H i i i i i

o i i o N b h 4 4 0N N \ O < t 4 O O O < r r -\ \ \ \ \ \ \ \ \ \

i _ H i H

r a d N @ N \ o

; ; d * ' < i ' c ; < , J * < .O i o O O \ N i \ O c ) O < r

N N N i

d o

- o

h

tr

U AND TH IN ACCESSORY ALLANITE

Partly because of their similarity to the rare earths in ionic radius,

uranium and thorium may be incorporated in the structure of allanite.

The radioactive elements accompany the rare earths in many minerals,

for example, in monazite, xenotime, bastnaesite, chevkinite, doverite, and

keilhauite. In the rocks studied allanite has a lesser amount of radioac-

Tnsrn 5. Unexruu Coxrrltr ol Accassonv Arr,ANrto er'ro ol Its Hosr Rocr<sAnalysts: A. M. Sherwood, M. Molloy, and M. Schnepfe

Rock, locationU in allanite U in rocks

(pp-) (PP-)

J / J

GranitesBiotite granite, weathered, Conway, N. H.

Biotite granite, fresh, Conway, N. H.

Leucogranite, fine, Riverside, Calif .

Leucogranite, coarse, Riverside, Calif .

GranodioritesCalifornia

Mount HoleCuyamacaDescansoTemecula

IdahoAtlantaStanleyCascade

Quartz monzonitesCalifornia

Mt. Tom quadrangle

Mt. Goddard quadrangle

Mt. Goddard quadrangle

Big Pine quadrangle

Quartz syenitePassaconway, N. If.

656 12 .0540 13 .0400 3 .7241 4 .1

208 5.91 1 r 1 . 5102 3.7. ) J r . z

45 2 .340 0 .83 6 I . T

9I

7850

7 . 75 . 83 . 82 . O

4 . 6

tive elements captured in its structure than ziron, xenotime' or monazite,

and it generally approximates the radioactivity of sphene, apatite' and

the rare-earth carbonates.Table 4 shows thorium to be high in the New Hampshire and Idaho

minerals and low in the California minerals, regardless of rock type'

Uranium is seen to be high in the allanites from granites from both lo-

calities listed in Table 5.Figures I and 2 show the relation of the calculated total per cent eU

to the birefringence and to the beta index of allanite samples.

A black high-index allanite occurring in late calcite-celestite veins

s74 W. L. SMITH, M. L. FRANCK AND A. M. SHERWOOD

0 . I . 2 . j . 4 . , . 6 . 7Percent eU

Frc. 1. Per cent eU as related to birefringence in allanite from New Hampshire O,Idaho A, and California f.

cutting rare-earth-bearing carbonate rock from Mountain Pass, Cali-fornia (personal communication, H. W. Jafie, 1955) has indices of re-fraction of a 1.79O, P I.8I2, and 7 1.818; a U content of 0.0018 per centand Th in the range of 0.01-0.1 per cent. J. P. Marble (1940) describedisotropic allanite from the Baringer Hil l, Texas, pegmatite withn:1.716,as containing 0.715 per cent Th and 0.033 per cent U. Wells (1934) pre-

0 .1 .2 .1 . l+ .5 .6 ,7Percent eU

Frc. 2. Per cent eU as related to beta index in allanite from New Hamphsire Q,Idaho A, and Califomia O.

q)q .

q)brg..{- k .o)frrl€

x -E

..{

0tq

T] AND TE IN ACCESSORY ALLANITE

sented the analysis of allanite from a Wyoming pegmatite with 1.12

per cent Th and0.017 per cent U. Hutton (1951) describes allanite from

a pegmatite in Yosemite National Park, Calif., as containing 0'95 per

. "nt ThOr,0.015 per cent UOz, and opt ics a 1.769, P l '782,and7l '791'

In a microscopic study of five specimens of black, vitreous allanite from

pegmatites by E. S. Larsen, Jr., of the Geological Survey (Watson, 1917)

u ,ung. from the isotropic to the birefracting forms of the mineral is

resrt 6' unaNruu t;ffiil,xlff:rr"il:T c'rr'rrot*re Rocrs

J / J

RockUranium in epidote

(pp-)

Mount Hole granodiorite

Quartz monzonite, Mt. Goddard quadrangle

Quartz monzonite, Big Pine quadrangle

1310220180

described. The isotropic forms show indices of refraction from ra:1'60

to 1.72. fn a study of the radioactivity of allanite from igneous rocks

Hayase (1954) concluded that thorium was the major radioactive com-

ponent, ranging from 0.5 to 1.6 per cent.The uranium content of rocks varies regionally, and generally in each

region the more siliceous rocks have the higher uranium content. The

relationship of high uranium allanite to high uranium rocks is apparent

from observation (Table 5), but it should be pointed out that only a per

cent or two of the total uranium in the rocks is traceable to allanite.

For comparison three samples of epidote wete analyzed and show com-

paratively higher uranium contents for their rock type and area (table 6).

bpidote is less abundant than allanite in the rocks studied. In all the

rocks epidote was green and allanite was brown or black'

PBrnocnapnv

Allanite was found to be present in the rocks studied in amounts rang-

ing from 0.25 per cent in the granodiorite from Cascade to 0'005 per cent

in the granodiorite from the Stonewall formation. The abundance of

allanite in a rock has no apparent direct relation to the uranium or

thorium content of the rock or mineral and is not related to rock type or

area. Of 81 rocks studied, 31 were found to contain allanite. No allanite

was found in any of 10 siliceous lavas from the San Juan region of Colo-

rado. None was found in five alkalic rocks from sussex county, New

Jersey. No allanite was found in any basalts, norites, gabbros, diorites,

lr nepheline rocks, although geologic literature describes occasional

376 w. L. SMITH, M.L.FRANCK AND A. M. SEERWOOD

occurrences of allanite within such rock types (Iddings and Cross, 1885).Table 7 lists the incidence and abundances of allanite in five suites of

allanite-bearing rocks.

MBr.q.lrrcrrzarroN

Brdgger (1893) in proposing the term metamict for certain rare-earthminerals suggested, " . . . The reason for the amorphous rearrangementof the molecules might perhaps be sought in the lesser stabii ity which so

Tanln 7. INcrloNcn eNn AsuNoeNce or Accrssony Ar-r,alstrE

LocationNumber of Number

of rocks rocks withstudied allanite

Percentage of allanite and rock type

0 0X 0.00X or less

Idaho batholith

Sierra Nevada batholith, Calif.

Southern California batholith 34

Sterling batholith, R I.

White Mountain batholith,N. H.

1,1 6

o 4

4 3

8 5 I granite

2 granodiorites

3 qaartz monzo-nites

2 granodiorites1 granite

1 granodiorite

2 granites1 quartz syeDite

3 granodiorites

7 granodiorites1 quartz syenite1 qtartz mo\zo-

nite

2 granites

complicated a crystal molecule as that of these minerals must have in thepresence of outside influences."* He implied that the rare-earth mineralswere so complex as to prevent them from being permanently combined inthe crystalline state-a definition no longer accepted.

Des Cloizeaux and Damour (1860) noted that isotropic allanite be-came birefringent on heating and showed that both the isotropic andbirefringent allanite existed both anhydrous and hydrated.

Goldschmidt and Thomassen (1924) described the alteration of rare-earth minerals from the crystalline to the glassy state. They concludedthat the important factor is the weak chemical bonding between rareearths and weak acids (sil icic, tantalic). Goldschmidt proposed that formetamictization to take place the crystal lattice must have a weakenough ionic structure to permit decomposition and hydrolysis. Also,he proposed that it is necessary that radiation provide the energy todischarge the ions of the rare-earth eiements. This radioactivity couldbe either from within or from without the crystal. Metamictization would

* Translated by A. Pabst (1952, p. 138).

U AND TE IN ACCESSORV ALLANITE

thus occur as the ionic bond breaks by hydrolysis, and the lattice be-comes isotropic.

Ellsworth (1925) stated that " . . . all minerals containing UOs auto-matically oxidize themselves at a rate depending on the rate of uraniumand thorium decomposition."

Hata (1939) in describing the weathering of allanite reports the alteredportions as being conspicuously high in thoria and conspicuously lowin the rare earths, as compared with the fresh part of the same mineral.As the result of leaching studies, Hata concluded that the alteration isIikely to take place when the ratio of FezOs to AlzOa is less than 1.3 andthe content of thoria is more than 1.5 per cent. The other variables andthe relative proportions of the rare earths were found to have no influenceon the alteration.

Ueda and Korekawa (1954) suggest that the metamictization ofallanite is due to the repeated expansion and quenching of the lattice,resulting in the formation of an aggregate of several phases in both thecrystalline and amorphous state.

Allanite shows various degrees of metamictization and, in the extremecases of some pegmatite specimens, approaches isotropism. The altera-tion of the allanite is suggested to be due to radiation from the uraniumand thorium components which breaks the ionic bonds and permits theentry of water into the lattice of the mineral.

Acrr.towr-BncMENTS

We wish to thank Professor Esper S. Larsen, Jr., of the Geological

Survey who suggested this study and who checked the optical properties

of many of the allanite samples. Thanks are also due to George H. Hay-

field for assistance in mineral separations, and to Glen Edgington,

Marjorie Molloy, and Marian Schnepfe, also of the Geological Survey,for chemical analyses. This work is part of a program conducted by the

U. S. Geological Survey on behalf of the Division of Research of the

u' S' Atomic Energy t"--tttt;:"ERENcES

Brr-r.tucs, M. P. (1945), Mechanics of igneous intrusion in New Hampshite: Arn. Jou,r. Sci'.,243-4, Daly Volume, 43.

Bttiocnn, W. C. (1393), Amofi: Salmonsens store i,ll,ustrereile Konaersationslerikon: l,742-743.

Craru.tN, R. W., Gor:rlnron, Devp, .nxo WAnrNG, C. L., (1955), Age determinations on

some rocks from the Boulder batholith and other batholiths of western Montana:

Geol. S oc. America Bull., 66, 607-609.Drs Cr,orzneux, A., exo Dauoun, A. (1860), Examen des propri6t6s optiques et pyro-

g6n6tiques des mindraux connus sous les noms de gadolinites, allanites, orthites,

euxenite, yrite, yttrotantalite et fergusonite: Ann. chim. phys. (3), 59' 357-379.

377

378 W. L. SMITH. M. L. FRANCK AND A. M. SHERWOOD

Er,r-swonrn, H. V. (1925), Radioactive minerais as geological age indicators: Am. Jow.

Sci., 5th ser., 9, 127-lM.Gornscnurnr, V. M., exo TnouessrN, L. (1924), Geochemische Verteilungsgesetze der

Elemente III: Norshe aidensk.-akad'. Osl'o Arbok 5' 51-109.

Here, S. (1939), The alteration of allanite: Tokyo Inst. Phys. Chem. Res., Sci. Papers,r'o.

923 ,36 ,301 -311 .Hev,tsr, I. (1954), The radioactivity of rocks and minerals studied with nuclear emulsion.

Pt. 2. Thorium content of granitic allanites: Kyoto Imp. Unizt., CoIl. Sci., Mem. ser.

8,21,no.2, t7 l - t83.Hrr.r.ennAro, W. F., nnn Lunonlr., G. E. F. (1929), Applied inorganic analysis: New York,

John Wiley & Sons.Hinds, N. E. A. (1934), The Jurassic age of the last granitoid intrusives in the Klamath

Mountains and Sierra Nevada, California: Am. Jou,r. Sci., 5th ser.,27, 182-192.

I{onns, W. H. (1889), On the paragenesis of allanite and epidote as rock forming minerals:

Am. Jonr. Sci . , 38, 223-228.HurroN, C. O. (1951), Allanite from Yosemite National Park, Tuolumne Co., Calif.:

A m. M i,ner aI., 36, 233148.Inorwcs, J. P., axn Cnoss, W. (1885), On the widespread occurrence of allanite as an ac-

cessory constituent of many rocks: Am. Jour. Sci.,3d ser.,30, 108-111.

MARBTE, J. P. (1940), Allanite from Barringer Hill, Texas: Am. Mi.neral'.,25, p. 168-173.

Pensr, A. (1952), The metamict state: Am. Mineral'.,37r 137-157.

Rawxeue, K., axr Senaue, Tn. G. (19.50), Geochemistry, Univ. Chicago Press.

Uroe, T., AND KoREKAwA, M. (1954), On the metamictization: Kyoto Imp. Unit:., Coll.

Sci., Mem., ser. B, 21, no. 2, !51-162,

WArsoN, T.L. (1917), Weathering of allanite: Geol. Soe. Ameriea Bull'.,28,463-500.

Wnrrs, R. C. (1934), Allanite from Wyoming : Am. Mineral'.,19' 81-82.

Maqwscribt receitd, NotLember 11, 1956