279

PETROGENESIS OF GRANITOID ROCKS AND ORIGIN

OF URANIUM MINERALIZATIONS OF UM SAFI AREA,

CENTRAL EASTERN DESERT, EGYPT.

M. E. Ibrahim*, A. M. Osman**, M. Y. Attawiya* and I. H. Ibrahim*

* Nuclear Materials Authority, Cairo, Egypt.

** Geology Department, Faculty of Science, Ain Shams University, Cairo, Egypt.

ABSTRACT:

The granitoid rocks of Um Safi area have been subdivided according to their field relationships, petrography as

well as geochemical characteristics into three categories termed magmatic cycles of emplacement during

successive tectonic events. Granites of the first magmatic cycle (diorites, quartz diorites, tonalites and gneissic

granodiorites) have calc-alkaline, metaluminous, I-type character and emplaced during pre-plate collision to post

collision uplift regime under a high water-vapour pressured (5-10 k-bar) and high temperature (800-840 oC). The

second magmatic cycle is represented by biotite granites and perthite sub-leucogranites and characterized by

calc-alkaline, metaluminous magma and emplaced during late-orogenic regime. Granites of the third magmatic

cycle are mainly peraluminous muscovite sub-leucogranites in composition and crosscut all other rock types in

the region and were emplaced during syn-collision regime. The latter two magmatic cycles were emplaced at

moderate water-vapour pressure (2-5 k-bar) and temperature (760-800 oC).

The average eU- and eTh-contents increase gradually from older granitoids (3 ppm eU & 7 ppm eTh) through

biotite granites (6 ppm eU & 13 ppm eTh), perthite sub-leucogranites (7 ppm eU & 15 ppm eTh) to muscovite

sub-leucogranites (9 ppm eU & 17 ppm eTh). The shear zone in muscovite sub-leucogranites is considered as a

good trap for uranium mineralizations (288 ppm eU and 28 ppm eTh).

The occurrence of secondary U-mineralizations (zippeite and beta-uranophane) along the shear zone indicates

that, these two minerals occurred as a result of leaching of pre-existing uranium minerals in peraluminous

muscovite sub-leucogranites by circulating water. Finally, Um Safi peraluminous muscovite sub-leucogranites

could represent a favorable source for U-deposits, but total uranium content does not automatically give a

measure of fertility.

Keywords: Um Safi – petrogenesis - uranium mineralizations.

1. INTRODUCTION

Generally, the older granitoids were previously

mapped as grey granites by Hume (1935), older grey

granites (formed at depth by the granitization of pre-

existing masses) by El Ramly and Akaad (1960),

syn- to late-orogenic plutonites by El Shazly (1964)

and synorogenic granitoids of El Gaby (1975). They

pertain to the earlier phases of calc-alkaline granite

series by El-Gaby and Habib (1982), and G1-granites

(subduction related I-type granite formed above old

Benioff zones) by Hussein et al., (1982). The

emplacement of the older granitoids occurred at

around 850-930Ma, possibly extend to 711Ma (El

Manharawy, 1977; Dixon, 1979; Hashad, 1980;

Rogers and Greenberg, 1983).

The younger granites have been referred in Egyptian

literature as Gattarian granites (Hume, 1935),

younger intrusive red and pink granites (El Ramly

and Akaad, 1960), late- to post-orogenic granites (El

Gaby, 1975) and G-II to G-III granites (Hussein et

al., 1982). They are emplaced around 430-622Ma,

which are contemporaneous with the Pan-African

tectonic thermal events (El Manharawy, 1977;

Dixon, 1979; Hashad, 1980; Rogers and Greenberg,

1983).

Most of the Egyptian uranium occurrences in

granites (G. Um Ara, G. Gattar, G. Missikat and El-

Erediya) belong to metaluminous to slightly

peraluminous granites (biotite only or biotite +

hornblende, with subordinate secondary muscovite).

Uranium deposits associated with this type of

granites are less common than those associated with

peraluminous granites (Cuney, 1998). This work is a

contribution to the understanding of geology,

geochemistry, petrogenesis and origin of uranium

mineralization along the shear zone in Um Safi

muscovite sub-leucogranites.

Egyptian Journal of Geology, v. 45/1, 2001, pp. 279-294

280

2. Methodology

Fourteen samples from older granitoids and twenty

samples from younger granites representing the

different granitoid rocks in Um Safi area were

subjected to modal analyses for computing the

volumetric percentages of their mineral assemblage

and also for the proper identification and

nomenclature. Data were given in Table (1). The

quartz, plagioclase and potash feldspar percentages

are recalculated to 100 % and represented in the Q-

A-P diagram after Streckeisen (1976). Figure (2)

shows that, the older granitoids lie in quartz diorites,

tonalites and granodiorites fields. The biotite granite

lie in monzogranite field, the perthite sub-

leucogranites lie in alkali feldspar granite except

one-sample lies in the syenogranite field, while the

muscovite sub-leucogranites plot mainly in

monzogranite and slightly syenogranite fields.

Chemical analyses of major oxides (by wet chemical

technique after Shapiro and Brannock, 1962) as well

as some trace elements (using the X-ray

fluorescence techniques) of different granitoid

samples were carried out and the results are given in

(Table 2). The equivalent uranium (eU) and thorium

(eTh) have been measured radiometrically by using

multichannel analyzer γ-ray detector (Gamma-

spectrometer-technique).

3. Geologic Setting

The basement rock units in Um Safi area can be

chronologically arranged with the oldest as follows;

ophiolitic assemblage (serpentinites and ortho-

amphibolites), melange, arc assemblage

(metavolcanics, volcaniclastic and volcano-

sedimentary association, older granitoids and

volcanic rocks), molasse sediments, younger

gabbros (normal gabbros, hornblende gabbros and

noritic troctolites), younger granites (biotite granites,

perthite sub-leucogranites and muscovite sub-

leucogranites), post granitic dykes, and trachyte plug

(Fig. 1).

3.1. Older granitoids The older granitoids crop out in three localities

covering about 61.2 km2, representing 21.2 % of the

total basement rocks of the mapped area (Fig. 1).

The first exposure, occurrs in the northeastern part

of the mapped area, extending from Marwit El

Siwiqat in the east to westward until southern of G.

Atwani. The second exposure occurs as elongated

mass with NW-SE trend, located in the southeastern

sector with sharp contacts with gabbroic mass, while

the third exposure occupies the southwestern corner

of the mapped area, forming an extensive mass crops

out along south entrance of W. Siwiqat Um Lassaf.

These rocks are medium- to coarse-grained, grey to

dark grey in colour, exfoliated, fractured and

enclosed elongate amphibolite xenoliths. The older

granitoids intrude the older rocks with intrusive

sharp contacts. They are sheared especially in the

extreme southern pluton, forming an elongated belt

(20 km long in NW-SE trend) of cataclastic

gneissose granodiorites extending from G. El Hadid

to eastward out side the study area. They are

crosscut by numerous dykes of variable

compositions and trends, including felsic and mafic

ones (N-S, NE-SW and ENE-WSW trends) and

dissected by strike slip faults.

The older granitoids consist of different varieties

(diorites, quartz diorites, tonalites and granodiorites)

without contacts in between. Diorite is composed of

plagioclase (An16-38), hornblende, biotite, orthoclase

and quartz in decreasing order. Opaques, zircon,

apatite, sphene, epidote and prehnite are accessory

minerals. Quartz diorite is composed of plagioclase

(An 34-40), hornblende, quartz, biotite, and orthoclase.

Opaques, epidote, zircon, apatite and sphene are the

main accessory minerals. Tonalites are composed of

plagioclase (An 18-35), quartz, hornblende, biotite,

and potash feldspars (orthoclase and microperthite).

Opaques, epidote, zircon, sphene and apatite and

prehnite are accessories. Granodiorites are showing

gneissic texture and comprise two-varieties (i)

hornblende granodiorites which are composed of

plagioclase (An 23-36), quartz, orthoclase and

hornblende. Opaques, apatite, zircon and epidote are

accessories. (ii) biotite granodiorites which are

affected by muscovitization and composed of

plagioclase (An 21-35), quartz, orthoclase and biotite.

Opaques, apatite, sphene, zircon and epidote are

accessories. Muscovite, chlorite, epidote, zoisite,

and carbonate represent secondary minerals. The

older granites are extremely normal in eU (2-5 ppm)

and eTh (5-11 ppm) (Table 3).

3.2. Younger granites They cover about 50.2 km

2, representing 17.3 % of

the total basement rocks. The larger exposures of the

younger granites are exposed in the central and

southern parts, as well as, small masses scattered in

the northeast of the mapped area (Fig. 1). They

involve three types, biotite granites, perthite sub-

leucogranites and muscovite sub-leucogranites,

which are corresponding to phases II and III of the

Egyptian younger granites. They form a very high

relief and intruded serpentinites, melange, volcano-

sedimentary association, older granitoids and

younger gabbros with intrusive sharp contacts. The

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younger granites send offshoots in the older rocks,

also barren pegmatitic veins and pockets are

common especially near their contacts. The younger

granites are invaded by dykes of different

composition ranging from felsic (rhyolite, aplite and

felsite) to mafic (basalt) through alkaline ones

(bostonite) and dissected by several strike-slip faults

(N-S, NW-SE and NE-SW trends).

Biotite granites form low topography cropping at the

eastern bank of Khour Um Safi, covering about 8.6

km2, representing 2.9 % of the total basement rocks.

They intruded older rocks and are intruded by

perthite sub-leucogranites with sharp contacts. They

are medium-grained of pinkish grey colour, showing

massive, boulder appearance. They are also

characterized by exfoliation and presence of

cavernous as a result of intensive weathering. Biotite

granites are composed of plagioclase (An 8-28),

potash feldspars (microperthite and orthoclase

microperthite), quartz and biotite. Opaques, sphene,

fluorite, zircon and apatite are accessories. Chlorite,

epidote, muscovite and sericite are secondary

minerals. The biotite granites show a variation in eU

and eTh contents ranging from 4-10 ppm with an

average of 6 ppm and from 10-14 ppm with an

average of 13 ppm respectively (Table 3).

Perthite sub-leucogranites are medium- to coarse-

grained, covering about 28.3 km2, representing 9.8

% of the total basement rocks. They are represented

by G. Um Bakra and G. Um Samra and elongated in

a WNW-ESE direction parallel to the regional

structure. They are pink to reddish pink in colour

and characterized by boulder and blocky appearance,

exfoliation and highly fractured in different

directions. The perthite sub-leucogranite is non-

xenolithic, with the exception of a single occurrence

towards the southern foothills of G. Um Bakra,

where gabbroic rocks form xenolithic bodies either

as thin elongated or even dyke-like masses.

Silicification and hematitization along the fracture

planes represent the post-magmatic hydrothermal

alteration features. These rocks are dissected by

strike-slip fault filled by quartz, which sometimes

contains violet fluorite and sulphide mineralization.

Perthite sub-leucogranites are composed of potash

feldspars (microperthite, orthoclase microperthite

and microcline microperthite), quartz, plagioclase

(An 5-13), hornblende and biotite. Opaques, fluorite,

zircon, apatite and sphene are accessories. Kaolinite,

chlorite, epidote and muscovite mainly represent the

secondary minerals. The perthite sub-leucogranites

show a variation in eU and eTh contents from 4-12

ppm with an average of 7 ppm and from 11-18 ppm

with an average of 15 ppm respectively (Table 3).

Muscovite sub-leucogranites are medium- to coarse-

grained, whitish to reddish pink in colour, covering

about 13.3 km2, representing 4.6 % of the total

basement rocks. They crop out in the eastern bank of

G. Um Bakra and intruded in perthite sub-

leucogranites, as well as, carried them as roof

pendant. In the northeastern part of the study area,

they intruded the older granitoids and are extruded

by trachyte and quartz boss of Marwit El Siwiqat.

They are also present either as a minor intrusion at

the footwall of G. Atwani or elongated sheet-like

masses trending NW to WNW accompanied with the

regional structures. Silicification, hematitization,

kaolinitization and spotty or dendrite manganese

oxides along the fracture planes mainly represent the

post-magmatic hydrothermal alteration features.

They are crosscut by strike slip fault (N20oW-

S20oE) filled by jasperoid veins, along shear zone

(6m thick.) characterized by highly silicification,

kaolinitization and higher intensity of radioactivity.

Muscovite sub-leucogranites are composed of potash

feldspars (microcline, orthoclase microperthite and

microcline microperthite), quartz, plagioclase (An 6-

18), muscovite and subordinate biotite. Opaques,

fluorite, garnet, zircon, monazite and apatite are

mainly accessories. They show a wide variation in

eU and eTh contents from 5-16 ppm with an average

of 9 ppm and from 13-25 ppm with an average of 17

ppm respectively (Table 3). Along the shear zone the

eU-content ranges from 268-304 ppm with an

average of 288 ppm and the eTh-content ranges from

24-33 ppm with an average of 28 ppm. The eU/eTh

ratio ranges from 8.9 to 12.6 with an average of 10.3

(Table 4).

The occurrence of secondary uranium

mineralizations zippeite [K4 (UO2)6 (SO4)3

(OH)10.4H2O] and beta-uranophane [Ca (UO2)2

(SiO3)2 (OH).5H2O] confirmed by the present

authors (Table 5) indicate that these minerals

occurred as a result of leaching of pre-existing

uranium minerals in peraluminous muscovite sub-

leucogranites by circulating water.

4. GEOCHEMISTRY

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4.1. Classification The granitoid rocks under consideration can be

classified by applying the relation between Q= 1/3

Si- (K+Na+2/3 Ca) and P= K-(Na+Ca) after Debon

and LeFort (1983). The diagram given in (Fig. 3)

shows that, the data points of the older granitoids

fall within granodiorite, monzonite-quartz diorite,

quartz diorite and tonalite fields. The data plots of

the younger granites show that the biotite granites

and perthite sub-leucogranites fall within adamellite

field, while the muscovite sub-leucogranites fall at

the boundary between granite and adamellite fields.

Genetically, the I-type granites have been generated

from igneous source materials and the S-type

granites from sedimentary materials and both types

originated in the continental crust (White and

Chappell, 1977). The subgroups of the I-type

granites include those derived from recycled or

dehydrated continental crust (A-type) and those

derived directly from melting of subducted oceanic

crust or mantle (M-type). The K2O-Na2O diagram

(Fig. 4) after White and Chappell (1983) and Liew et

al., (1989) is used to distinguish between I-type, S-

type and T-type (transition) granites. The transition

(T-type) field represents a primitive magma

signature produced by more or less deep crustal

magmas mixing and assimilation. The plot (Fig. 4)

shows that, most of granitoid samples are plotted in

I-type field, except muscovite sub-leucogranites

which are falling in the transition (T-type) field.

4.2. Magma type and tectonic setting All the older granitoid samples have normative

(Di+Hy), indicating silica saturation and

metaluminous nature. The younger granitoid

samples (Table 3) divided between those with

normative Cor (all muscovite sub-leucogranite

samples and two from perthite sub-leucogranites),

indicating peraluminous nature and those without

normative Cor but have normative Di+Hy (all biotite

granites and remainder perthite sub-leucogranites),

indicating silica saturation and metaluminous nature

On the A–B binary diagram (Fig. 5), where A= Al-

(K+Na+2Ca) and B= (Fe+Mg+Ti) of Debon and

LeFort, (1983), the older granitoid and biotite

granitoid samples are calc-alkaline and

metaluminous in characters. The muscovite sub-

leucogranite samples (granite to rarely adamellite in

composition) lie in peraluminous domain. The

perthitic leucogranite samples lie between

metaluminous and peraluminous domains. In the A-

B diagram, the degree of differentiation is indicated

by the decrease in the B-parameter which mainly

represents the amount of biotite + magnetite in the

rock. Generally, the previous diagram indicates calc-

alkaline magma origin, not originated from

peralkaline magma type. However, instead the

majority of the analyzed samples indicate

metaluminous to peraluminous magma regime.

Rittmann (1973) used Log σ = Log

(Na2O+K2O)2/(SiO2-43) versus Log µ=Log (Al2O3-

Na2O)/(P2O5+TiO2) diagram (Fig. 6), to discriminate

magmatic igneous rocks in the orogenic belts and

mature island arcs environment from the non-

orogenic ones. All the plots of older and younger

granites lie within the field of magmatic rocks

situated in orogenic belt and island arcs.

Batchelor and Bowden (1985) used R1 - R2

multications relation of De La Roche et al., (1980) to

discriminate between the different tectonic setting of

the granitoid rocks (Fig. 7). The plot shows that the

older granitoids are emplaced during the pre-plate

collision to post-collision uplift stage. The younger

granites (biotite granites and perthite sub-

leucogranites) are intruded at late orogenic stage,

whereas the muscovite sub-leucogranites are

intruded during syn-collision stage.

4.3. Temperatures and pressures estimation

Plotting normative Ab-Q-Or values on the ternary

diagram (Figs. 8&9) where the first figure shows the

water-vapour pressures up to 3 K- bar after Tuttle

and Bowen (1958) and 5 to 10 K-bars after Luth et

al., (1964). The second diagram shows the

temperature isotherms for crystallization of the

rocks. The older granitoids fall in a high water-

vapour pressure, varying between 5-10 K-bar and

high temperature ranging about (800-840 oC),

indicating that, they were possibly formed at

relatively deep levels in the crust. The younger

granites fall in a region of low to moderate water-

vapour pressure ranging from 2 to 5 K-bars and

temperature about (760-800 oC), suggesting that,

they were possibly formed at moderate levels in the

crust.

4.4. Petrogenesis The origin of the study granitic rocks can be

deduced through a group of relationships. Generally,

the older and younger granites of the studied area are

impoverished in Rb, Ba and Sr except the average

Ba value of the older granitoids (534 ppm) which is

higher than corresponding value of high-Ca-granites

(420 ppm) when compared with the average world

values of Turekian and Wedepohl, (1961) (Table 6).

The K-Rb diagram (Fig. 10) shows that the

magmatic trend (1000-200 MT) is given by Shaw,

(1968), while the average crustal K/Rb ratio is 250

(Taylor, 1965) or 217 ± 69 (Harris et al., 1983). The

older granitoid samples plot around the mantle line

283

(K/Rb= 1000), while the younger granites scatter

within a large field extending from below the mantle

line to below the crustal line (K/Rb ~175). This

indicates that the studied older granitoid rocks were

generated from source regions depleted in Rb or

generated by partial melting of the lower or upper

mantle, (Gast, 1965 & Hart and Aldrich, 1969). The

lower K/Rb ratios in the younger granites indicate

more differentiated and more evolved granitic

liquids.

Mason (1966) used K-Ba variation diagram in which

the crustal average ratio (K/Ba= 65). Applying this

diagram as shown in figure (11) it can be seen that

the older granitoid samples plot below the average

crustal ratio of Mason, exhibiting lower K2O

contents and hence they have K/Ba ratios (<65). The

younger granites plot above the average crustal ratio

with K/Ba ratio (>65), showing Ba depletion with

K2O enrichment which indicates the involvement of

a second process acting with the crystal fractionation

and leading to depletion of Ba with differentiation.

The Ba-Rb diagram shows that Ba is depleted

relative to Rb (Fig. 12). The older granitoid samples

plot above average crustal (Ba/Rb= 4.4) of Mason,

whereas the younger granitic samples plot around

the average crustal values and range between (4.4

and 4.4 × 10-1). This is also consistent with the high

degree of evolution of the younger granitic magmas

and confirms the previous statement of the

involvement of an additional process during the

differentiation of these younger granitic rocks.

The Rb/Sr ratio is used as a measure of magmatic

differentiation increasing with higher degree of

differentiation. The older granitoids and biotite

younger granite samples show Rb/Sr= 0.1 (Fig. 13),

while the perthitic and muscovite leucogranite

samples that show the Rb/Sr ratios (1-10), are more

fractionated during the crystallization of these rocks.

Depletion of Sr with differentiation from the older

granitoids towards the younger granite samples is

shown on the Sr-CaO diagram (Fig. 14). The K/Rb

ratio against Rb is useful parameters for comparing

of different sources (Fig. 15). As this plot shows the

same trend for all members of petrogenitic

sequences of granitoid rocks, a single process could

produce them. The curved relationships on the Ba-

Rb, Rb-Sr, Sr-CaO and K/Rb-Rb diagrams could

suggest that crystal fractionation was the dominating

process during magmatic differentiation.

4.5. Interelement Relationship The eU-content increases with eTh (Fig. 16) and

decreases with eTh/eU ratios (Fig. 17) from older

granitoids to younger granites. This type of behavior

indicates that U in the peraluminous muscovite sub-

leucogranites is mostly located in Th-rich accessory

minerals such as monazite. Such a trend results in

the preferential leaching of the U fraction located in

uraninite-easily leachable in oxidizing supergene

conditions whereas the U fraction located in

monazite remains essentially undisturbed (Cuney

and Friedrrich, 1987).

It is well know that Rb, Y, U, Th and Nb have a

large radii or higher electric charges. These ions are

less extensive to substituting for major ions in

common silicate minerals (Krauskopf, 1979), so

they segregated and concentrated at late stage in

granitic melt. If magmatic processes controlled U-

and Th- contents, these elements would be expected

to increase. The relation between Rb-eU (Fig. 18),

Y-eU (Fig. 19) and Zr-eU (Fig. 20) shows that, the

eU-contents increase with the increase of Rb, Y and

Zr contents, a fact which is related to magmatic

processes. The positive correlation between eU and

Y as well as eTh and Nb (Fig. 21) indicates that, the

magma from which the two granitic mass had been

developed was emplaced at shallow depths (Briqueu

et al., 1984).

4.6. Origin of Uranium Mineralizations In general, the uranium and thorium increase from

basaltic rocks to low Ca-granite during magmatic

differentiation. From the distribution of eU- and

eTh-contents in the different rock types of Um Safi

area, it is clear that, the average eU- and eTh-

contents increase gradually from older granitoids (3

ppm eU & 7 ppm eTh) through biotite granites (6

ppm eU & 13 ppm eTh) to perthite sub-

leucogranites (7 ppm eU & 15 ppm eTh) and

muscovite sub-leucogranites (9 ppm eU & 17 ppm

eTh). This can be attributed to the tendency of the

radioactive elements to concentrate in the residual

magma indicating that, the enrichment is due to

magmatic processes. These coincide with the

presence of zircon, sphene, rutile, monazite and

epidote as accessory minerals associated with violet

fluorite, pyrite and goethite.

The source of uranium especially in the shear zone

may come from leaching of the mobile element from

the surrounding rocks especially muscovite sub-

leucogranites and later accumulated in open shear

zone.

Thus the shear zone can be considered as a good trap

for uranium mineralizations for the following

factors; a) the high U-contents of muscovite sub-

leucogranites could represent a good source, b) a

barrier of silica or jaspar veins (5 - 50 cm) along the

shear zone and c) tectonically, the N-S and NNW-

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SSE fault trends played at least a role in the

remobilization of uranium along the shear zone.

5. DISCUSSION AND CONCLUSION

Um Safi granitoids are composed of a succession of

metaluminous calc-alkaline and metaluminous to

peraluminous sub-alkaline sub-leucogranites

emplaced during successive tectonic events. The

first tectonic is represented by older granitoids

characterized by calc- alkaline, metaluminous and

were emplaced under a high water- vapour pressure

(5-10 k-bar) and compressional stresses. They were

emplaced during island arc regimes and formed by

fractional crystallization with crustal contamination.

After a period of time, where thickened crust is

affected by shearing and thrust the second tectonic

event occurs, characterized by biotite granites and

perthite sub-leucogranites, which have calc-alkaline

affinity and metaluminous in nature. Granites of the

third tectonic event are represented by peraluminous

muscovite sub-leucogranites and were emplaced

during syn-collision regime. The granites of the

second and third tectonic events are produced

through closed-system of fractional crystallization of

metaluminous magmas at shallow to moderate levels

in the crust under low to moderate water-vapour

pressures (2-5 k-bar) and converted finally to

peraluminous magma.

Uranium distribution actually observed in

peraluminous granitoids results from five

main phenomena: partial melting, magmatic

differentiation, late-magmatic processes,

hydrothermal and meteoric alterations (Friedrich et

al., 1987).

The present studies provide an evidence of a strong

increase in eU-content in the shear zone. Such an

increase in the uranium quantity available for

subsolidus reworkings obviously favours the

mineralizing efficiency of the hydrothermal

circulations.

Mineral fractionations, defined by chemical-

mineralogical diagrams indicate the simultaneous

fractionation of Fe-Mg minerals and monazite. This

type of relation, together with the low solubility of

monazite in peraluminous melt and the absence of

cordierite and / or garnet, suggests that muscovite

and monazite were essentially resistitic minerals,

scavenged by the magmas from the anatectic zone

(White and Chappell, 1977). However, this type of

fractionation is very different from S-type granites

of Australia (White and Chappell, op. cit), which

show a much higher content of mafic minerals (B

parameter) and a simultaneous decrease of the

peraluminous character (A parameter) and the mafic

mineral content.

Um Safi sub-leucogranites might have undergone

subsolidus alteration (either hydrothermal or

meteoric), which may strongly disturb the primary U

content especially in supergene conditions. It is

noticeable that the U content increases (268-304

ppm) during late magmatic stage (shear zones) and

associated with pyrite, fluorite, goethite, muscovite,

monazite, zircon, rutile, zippeite and beta-

uranophane. Also muscovite occurs in three forms;

euhedral early magmatic crystals, or as interstitial

late magmatic filling between the essential minerals

or as fine inclusion in quartz and feldspar crystals.

Finally, Um Safi peraluminous muscovite sub-

leucogranites could represent a favorable source for

U-deposits, but total uranium content does not

automatically give a measure of fertility. An

accurate specification of the percentage of U host

minerals is required in the different stages of magma

evolution as well as a drilling program can be

proposed.

REFERENCES

Batchelor, R. A. and Bowden, P. (1985): Petrogenetic interpretation of granitoid rock

series using multicationic parameters. Chem.

Geol., 48, 43-55.

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286

Table (1): Modal composition of granitoid rocks, Um Safi area.

Sr.

No.

Sm.

No.

Qz K-

Feld.

Plag. Bio. Hb. Ms. Op. Acc. Q A P

1 39 32.9 9.4 45.8 - 10.0 - 0.3 1.5 37.3 10.7 52.0

2 40 30.6 10.5 47.8 - 9.8 - 0.4 0.9 34.4 11.8 53.8

Average 31.7 10.0 46.8 - 9.9 - 0.3 1.2 35.9 11.2 52.9

3 74 26.3 11.2 51.4 10.6 - - 0.1 0.4 29.6 12.6 57.8

4 75 25.5 12.4 50.0 11.3 - - 0.2 0.6 29.0 14.1 56.9

Average 25.9 11.8 50.7 11.0 - - 0.1 0.5 29.3 13.4 57.3

5 43 32.1 4.2 47.7 11.0 1.2 - 0.4 0.7 38.2 5.0 56.8

6 59 23.2 5.6 64.2 5.3 0.2 - 0.7 0.5 24.9 6.2 68.9

7 105 18.3 2.5 62.2 5.2 10.9 - 0.6 0.3 22.1 3.0 74.9

8 107 20.2 2.8 62.6 6.0 7.5 - 0.5 0.4 23.6 3.3 73.1

9 155 20.4 1.9 54.8 1.7 19.9 - 0.9 0.4 26.4 2.5 71.1

Average 22.8 3.4 58.3 5.9 8.0 - 0.6 0.5 27.1 4.0 68.9

10 104 12.0 1.4 61.7 5.2 19.0 - 0.4 0.3 16.0 1.9 82.1

11 147 7.8 3.2 61.9 4.8 20.6 - 1.2 0.5 10.7 4.4 84.9

12 154 10.9 1.6 57.1 11.8 17.9 - 0.4 0.3 15.7 2.3 82.0

Average 10.2 2.1 60.2 7.3 19.2 - 0.6 0.4 14.1 2.9 83.0

13 171 2.9 3.5 60.4 6.5 25.9 - 0.5 0.3 4.3 5.3 90.4

14 117 2.1 2.6 56.3 12.1 26.2 - 0.4 0.3 3.5 4.3 92.2

Average 2.5 3.1 58.3 9.3 26.1 - 0.4 0.3 3.9 4.8 91.3

15 5 23.7 29.9 39.3 4.9 - - 1.4 0.8 25.5 32.2 42.3

16 122 22.7 28.7 39.2 5.1 - - 1.7 2.6 25.1 31.7 43.2

17 169 22.8 31.9 35.3 7.3 - - 1.4 1.3 25.3 35.4 39.2

18 170 23.6 32.2 35.2 6.2 - - 1.6 1.2 25.9 35.4 38.7

Average 23.2 30.7 37.2 5.9 - - 1.5 1.5 25.4 33.7 40.9

19 26 34.2 56.6 5.5 0.3 1.8 - 0.7 0.9 35.5 58.8 5.7

20 113 28.9 60.5 0.8 2.7 3.5 - 1.0 2.6 32.0 67.1 0.9

21 131 31.5 58.2 2.6 1.6 - 0.3 2.3 3.5 34.1 63.1 2.8

22 133 34.8 50.2 9.5 1.8 1.7 - 0.4 1.6 36.8 53.1 10.1

23 134 22.5 68.1 5.4 0.5 - 0.2 1.7 1.6 23.4 70.9 5.6

24 143 23.6 66.0 4.8 1.1 1.6 - 1.1 1.8 25.0 69.9 5.1

25 160 28.2 68.2 0.5 0.3 1.5 - 0.5 0.8 29.1 70.4 0.5

26 161 31.6 63.7 0.8 0.1 2.1 - 0.6 1.1 32.9 66.3 0.8

27 164 24.8 72.2 0.7 0.2 0.9 - 0.7 0.5 25.4 73.9 0.7

Average 28.9 62.6 3.4 0.9 1.5 0.1 1.0 1.6 30.4 66.0 4.6

28 1 33.2 39.5 20.9 0.2 - 5.8 0.1 0.3 35.5 42.2 22.3

29 2 32.8 41.0 21.2 0.3 - 4.1 0.1 0.5 34.5 43.2 22.3

30 3 32.6 40.2 21.4 0.2 - 5.1 0.1 0.4 34.6 42.7 22.7

31 9 29.1 37.4 28.9 0.1 - 3.7 0.4 0.4 30.5 39.2 30.3

32 41 31.5 32.1 26.8 0.2 - 6.9 0.1 2.4 33.3 36.8 29.9

33 42 32.0 34.3 26.9 0.3 - 4.4 0.5 1.6 34.3 36.8 28.9

34 44 31.9 36.3 25.7 0.2 - 4.9 0.3 0.7 34.0 38.7 27.3

Average 31.9 37.3 24.5 0.2 - 5.0 0.2 0.9 34.0 39.8 26.2

Sr. No.= serial number, Sm. No.= sample number, Qz= quartz, K-feld.= potash feldspar

including perthite, Plag.= plagioclase, Bio.= biotite, Hb.= hornblende, Ms.= muscovite,

Acc. = accessory, Op= opaques, Q= quartz content, A= potash feldspar content and P=

plagioclase content.

1-2= hornblende granodiorites, 3-4= biotite granodiorites, 5-9= tonalites, 10-12 = quartz

diorites, 13-14= diorites, 15-18= biotite granites, 19-27= perthite sub-leucogranites and 28-

34 = muscovite sub-leucogranites.

Note: All values are in volume percent.

287

Table ( 2 ): Chemical analyses and CIPW normative minerals for granitoid rocks,

Um Safi area.

Younger granites Older granitoids

(n=13)

Biotite granites

(n=4)

Perthite sub-

leucogranites (n=9)

Muscovite sub-

leucogranites (n=7) Major

Oxides Range Average Range Average Range Average Range Average

SiO2 60.40-65.40 63.19 67.57-69.5 68.39 70.9-74.18 72.79 72.96-75.1 73.19

TiO2 0.30-0.62 0.49 0.39-0.53 0.46 0.12-0.28 0.2 0.11-0.15 0.12

Al3O3 13.70-17.40 15.73 12.59-14.13 13.52 11.44-13.72 12.42 13.01-14.54 13.46

Fe2O3 2.20-5.20 3.6 3.10-3.40 3.27 1.92-3.79 2.56 1.18-1.56 1.48

FeO 0.20-2.0 1.31 0.7-1.34 1.14 0.8-1.32 1.12 0.2-0.84 0.49

MnO 0.08-0.17 0.1 0.05-0.08 0.06 0.03-0.07 0.06 0.02-0.07 0.04

MgO 1.61-2.80 2.21 1.10-1.80 1.53 0.4-1.2 0.7 0.4-0.8 0.6

CaO 4.00-5.40 4.65 1.85-2.36 2.10 0.84-1.12 0.99 0.56-1.14 0.79

Na2O 3.47-4.73 4.2 3.89-4.19 4.09 3.85-4.05 3.95 3.47-3.69 3.58

K2O 2.12-3.24 2.76 4.22-4.46 4.34 3.99-4.69 4.35 4.62-4.9 4.7

P2O5 0.01-0.24 0.12 0.07-0.24 0.17 0.11-0.13 0.12 0.11-0.12 0.11

L.O.I 0.64-1.91 1.37 0.63-0.91 0.78 0.31-0.95 0.64 0.19-0.81 0.46

Trace elements (in ppm)

Rb 6.-33 19.1 58-67 62.3 59-169 98 58-210 116.7

Sr 204-689 418.5 336-374 352 12-14 13 20-37 25.9

Ba 464-612 534.6 26-29 27.3 253-475 332.7 170-453 300.3

Zr 37-169 102.9 187-218 197 214-423 285.9 125-170 144.9

Y 11-30 23.6 61-72 64.5 52-138 90.4 32-49 38

Nb 14-18 15.9 28-31 29.8 28-33 30.8 27-34 31.1

Zn 17-35 28.5 49-53 51 56-88 74 34-51 46.4

Pb 32-40 35 25-28 26.8 24-29 26.9 23-29 25.9

V 20-105 48.4 26-28 27 5-10 8.8 2-5 3

Cr 48-83 64 74-89 83 72-111 91.2 71-104 90.9

Ni 0-5 2.2 2-3 2.8 2-3 2.6 2-3 2.7

Co 5-9 6.8 3-4 3.8 3-4 3.2 2-3 2.7

Ga 12-21 17.7 21-24 22.5 23-32 26.7 16-42 29.4

U* 2-4 2.9 4-8 5.3 4-12 7.2 6-16 8.9

Th* 5-11 6.8 10-19 13 12-17 15 13-20 16

CIPW normative values

Q 12.14-21.28 16.87 21.03-23.46 22.45 26.17-33.69 30.63 31.29-34.56 32.8

Or 12.73-19.39 16.6 24.94-26.36 25.65 23.58-28.31 25.75 27.42-28.96 27.78

Ab 29.56-40.45 36.07 32.91-35.45 34.65 32.57-34.27 33.42 29.36-39.36 31.74

An 8.36-21.83 16.11 2.69-7.59 5.71 1.13-3.68 2.79 1.93-4.94 3.14

Di 1.22-10.99 5.05 1.05-6.66 2.80 0.0-2.84 1.05 0.0 0.0

Hy 0.0-5.64 3.34 0.9-3.72 2.51 0.41-2.57 1.26 1.0-2.14 1.55

C 0.0 0.0 0.0 0.0 0.0-1.09 0.19 0.61-2.17 1.33

Mt 0.0-4.09 1.61 1.32-3.71 2.65 2.34-3.7 3.15 0.46-1.71 1.25

Hm 0.35-2.28 0.98 0.91-2.29 1.54 0.0-1.37 0.38 0.0-1.06 0.62

Il 0.0-0.6 0.06 0.74-1.01 0.89 0.21-0.65 0.39 0.21-0.28 0.23

Ap 0.02-0.53 0.27 0.17-0.57 0.41 0.26-0.31 0.28 0.26-0.31 0.27

*= radiometric analyses

n= number of measured samples.

288

A p

Q

1 2a 2b 3 4

5

6

Older granitoids

Perthite sub-leucogranites

Muscovite sub-leucogranites

Biotite granites

): Modal analyses of granitoid rocks, Um Safi area, after Streckeisen (1976). 1= alkali

feldspar granites, 2a= syenogranites, 2b= monzogranites, 3= granodiorites, 4=

tonalites, 5= quartz diorites and 6= diortites

Table (3): eU, eTh, and Ra contents in ppm and K content in % in the granitoid rock

types, Um Safi area.

Radiometric measurements Rock types

eU (ppm) eTh (pmm) Ra (ppm) K %

Max. 5 11 4 2.16

Min. 2 5 2 0.36

Older granitoids

(n=13) Average 3 7 3 1.1

Max. 10 14 5 2.6

Min. 4 10 4 1.9

Biotite granites

(n=8) Average 6 13 4 2.4

Max. 12 18 10 3.91

Min. 4 11 3 2.81

Perthite sub-

leucogranites

(n=9) Average 7 15 15 3.53

Max. 16 25 15 3.23

Min. 5 13 3 2.41 Yo

un

ger

gra

nit

es

Muscovite sub-

leucogranites

(n=10) Average 9 17 8 2.84

n= number of measured samples

Table (4): eU, eTh and Ra contents in ppm and K (%) along shear zone, Um Safi area.

Ser. No. Sam. No. eU(ppm) eTh(ppm) Ra(ppm) K(%) eU/Ra eU/eTh eTh/eU

1 A1 302 24 159 1.63 1.89 12.6 0.08

2 A2 304 32 162 1.14 1.87 9.5 0.11

3 A3 273 24 150 1.15 1.82 11.4 0.08

4 A4 268 29 156 1.53 1.72 9.3 0.11

5 A5 294 33 160 1.34 1.84 8.9 0.11

Average 288 28 157 1.36 1.83 10.3 0.09

Minimum 268 24 150 1.14 1.72 8.9 0.08

Maximum 304 33 162 1.63 1.89 12.6 0.11

Median 294 29 159 1.34 1.84 9.5 0.11

St. Dev. 16.7 4.27 4.67 0.22 0.07 1.59 0.01

289

Table (5): XRD pattern of zippeite and beta-uranophane in shear zone of muscovite

sub-leucogranites.

Sample 1 Sample 2 Zippeite

(8-402)

Zippeite

(8-401)

Beta-uranophane

(8-301)

d/Ao I/IO d/Ao I/IO d/Ao I/IO d/Ao I/IO d/Ao I/IO

8.61 8 8.61 6 8.65 40

7.73 100 7.72 81 7.31 100 7.06 100 7.83 100

6.38 2 6.45 20 6.66 40

5.76 17 5.76 11 5.57 10 5.44 40

4.78 5 4.79 4 4.77 10 4.85 40

4.43 7 4.47 7 4.55 40

4.26 7 4.25 22 4.27 10 4.27 50

4.17 9 4.10 40

3.87 54 3.87 38 3.86 40 3.9 90

3.77 9 3.75 10

3.53 7 3.53 8 3.51 50 3.51 80 3.51 60

3.42 16 3.42 12 3.41 10

3.31 9 3.34 100 3.35 20

3.13 26 3.13 18 3.15 80 3.12 90 3.12 90

3.01 9 3.01 7 3.04 40

2.88 19 2.86 12 2.86 40 2.86 60 2.91 20

284 11 2.83 40

2.7 3 2.69 5 2.66 30 2.72 30

2.58 8 2.53 3 2.53 40 2.59 50

2.46 3 2.46 10 2.45 10

2.39 4 2.39 3 2.41 40

2.22 4 2.28 6 2.25 20 2.21 40 2.21 20

2.18 3 2.18 3 2.14 30

2.16 8 2.16 5 2.17 10

2.08 9 2.08 5 2.08 20 2.09 20

2.06 6 2.06 4 2.002 40 2.05 50 2.04 10

1.98 5 1.99 7 1.96 20 2.01 10

1.88 5 1.88 3 1.88 20 1.877 30

1.82 2 1.82 9 1.821 20 1.841 30

1.77 3 1.77 2 1.749 40 1.74.5 60 1.778 20

1.69 4 1.701 40 1.701 20

1.67 4 1.67 7 1.621 20 1.658 10

1.58 2 1.56 3 1.583 30 1.598 50 1.541 15

1.5 4 1.494 10

-250 -200 -150 -100 -50 0 50

50

100

150

200

250

P= K-(Na+Ca)

Q =

Si/3

-(K+

Na

+2/3

Ca)

TH

OL

ALKO

S

CALK

ALKSSALKD

SA

LK

LP

ota

ssic

Q~20%

Q~5%

Q~45%

K-feldsparPlagioclase

granodio

rite

adamel

lite

gran

ite

tonalit

e

quartz syenite

quartz

monzo

nitemonzonite

quartz diorite

quartzdiorite

Fig. (3): Q versus P diagram for granitoid rocks, Um Safi area, after Debon and

LeFort, (1983). (Symbols as in Fig. 2)

290

0 1 2 3 4 5 62

3

4

5

6

I-type T-type

S-type

Na 2

O (

%)

K2O (%)

40 80 120

-100

-50

0

50

100

B= Fe+Mg+Ti

A=

Al-

(K+

Na

+2

Ca

)

Pera

lum

inou

s Dom

ain

Meta

lum

ino

us D

om

ain

*gd

*to

*mzq

*gr

*S

VVI

I II

III

IV

Bi >Ms

Bi < Ms

Bi = Ms

Leu

cogra

nit

es

CALK

*ad

Fig. (4): Na2O versusK2O diagram for granitoid rocks, Um Safi

area, after White and Chappell, (1983) and Liew et al.,

(1989). (Symbols as in Fig. 2)

Fig. (5): Characterisitic mineral diagram for granitoid rocks of

Um Safi area, after Debon and LeFort, 1983). (Symbols as

in Fig. 2)

-0.5 0.0 0.5 1.0 1.50.0

0.4

0.8

1.2

1.6

2.0

Log o

Lo

g u

B

C

A

0 500 1000 1500 2000 2500 30000

500

1000

1500

2000

2500

5

4

3

2

1

6

7

1 - Mantle Fractionates2 - Pre-Plate Collision

3 - Post-Collision Uplift

4 - Late-Orogenic5 - Anorogenic

6 - Syn-Collision

7 - Post-Orogenic

R1= 4Si-11(Na+K)-2(Fe+Ti)

R2=

6C

a+

2M

g+

Al

Fig. (6): Log u-Logo diagram for granitoid rocks, Um Safi

area, after Rittmann, (1973). A= Magmatic rocks

situated in non-orogenic regions, B= magmatic

rocks situated in orogenic belts and island arcs and

C= alkali derivatives of magmatic rocks linked to

either A or B. (Symbols as in Fig. 2)

Fig. (7): R1-R1 binary diagram for granitoid rocks, Um Safi

area, after Batchelor and Bowden, (1985). (Symbols as in

Fig. 2)

Ab Or

Q

1 kb2 kb

3 kb5 kb

10 kb

Ab Or

Q

840

760

800

800

840

Fig. (8): Ab-Q-Or ternary diagram for granitoid rocks, Um Safi

area. The dashed line represents the variation in position of

the minimum melting points in the granite system at

different water-vapour pressures. 1,2,3 k-bar after Tuttle

and Bowen, (1958). 5,10 k-bar after Luth et al., (1964).

(Symbols as in Fig. 2)

Fig. (9): Ab-Q-Or ternary diagram for granitoid rocks, Um Safi

area, after Tuttle and Bowen, (1958). (Symbols as in Fig. 2 )

2

Table (6): Average Rb, Ba and Sr of the studied granitoids in comparison with World values.

Um Safi Area Turekian and Wedepohl (1961)

Older granitoids Younger granites High Ca-granites Low Ca-granites

Rb 19 97 116 170

Ba 534 318 420 840

Sr 418 90 440 100

10 100 1000

1

10

Rb (ppm)

K (

%) K/R

b= 1

000

K/R

b= 2

50K

/Rb= 1

00

5 10 100 10001

10

Ba (ppm)K

(%

)

K/B

a= 6

5

Fig. (10): K-Rb variation diagram for granitoid rocks, Um Safi

area, after Shaw, (1968), crustal K/Rb ratio after Taylor,

(1965). (Symbols as in Fig. 2)

Fig. (11): K-Ba variation diagram for granitoid rocks, Um Safi

area, average crustal ratio after Mason, (1966). (Symbols as

in Fig. 2)

5 10 100 10005

10

100

1000

Rb (ppm)

Ba (

pp

m)

Ba/Rb= 4

.4

Ba/Rb= 4

.4x10 -1

Ba/Rb= 4.4x10 -2

10 100 10001

10

100

1000

Sr (ppm)

Rb

(p

pm

)

Rb/Sr= 10

Rb/Sr= 1

Rb/Sr= 0.1

Fig. (12): Ba-Rb diagram for granitoid rocks, Um Safi area,

after Mason, (1966). (Symbols as in Fig. 2)

Fig. (13): Rb-Sr diagram for granitoid rocks, Um Safi area.

(Symbols as In Fig. 2)

0 1 2 3 4 5 65

10

100

1000

CaO (%)

Sr

(pp

m)

- ve

0 100 2000

1000

2000

3000

Rb (ppm)

K/R

b

Excepected differentiation trend

Fig. (14): Sr-Ca variation diagram for granitoid rocks, Um Safi

area. (Symbols as in Fig. 2)

Fig. (15): K/Rb-Rb variation diagram for granitoid rocks, Um

Safi area. (Symbols as in Fig. 2)

3

4 10 302

10

30

eTh (ppm)

eU (

pp

m)

2 10 201

6

eU (ppm)

eTh

/eU

Fig. (16): eU-eTh variation diagram for granitoid rocks, Um

Safi area. (Symbols as in Fig. ).

Fig. (17): eU-Th/U relationship for granitoid rocks, Um Safi

area. (Symbols as in Fig. ).

2 10 205

10

100

400

eU (ppm)

Rb

(p

pm

)

1 10

10

100

Y (

pp

m)

eU (ppm)

200

20

Fig. (18): Rb-eU variation diagram for granitoid rocks,

Um Safi area. (Symbols as in Fig. )

Fig. (19): Y-eU variation diagram for granitoid rocks, Um

Safi area. (Symbols as in Fig. )

1 2030

100

700

Zr

(pp

m)

10

eU (ppm)

10 405

10

20

Nb (ppm)

eT

h (

pp

m)

Fig. (20): eU-Zr variation diagram for granitoid rocks,

Um Safi area. (Symbols as in Fig. )

Fig. (21): eTh-Nb variation diagram for granitoid rocks, Um

Safi area. (Symbols as in Fig. )

4

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