Uranium Geochemistry in Peraluminous Leucogranites of Wadi El-Shallal Area, Sinai, Egypt

Uranium Geochemistry in Peraluminous Leucogranites of Wadi El-Shallal Area, Sinai, Egypt

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  Uranium Geochemistry inPeraluminous... 17JKAU: Earth Sci., vol. 12, pp. 17-37 (1421 A.H. / 2000 A.D.) 17 Uranium Geochemistry in Peraluminous Leucogranites of Wadi El-Shallal Area, Sinai, Egypt M.E. Ibrahim, A.H. Hussein, A.M. OSMAN* and I.H. IBRAHIM Nuclear Materials Authority, and *Ain Shams University, Cairo, Egypt Received: 20/2/99 Revised: 29/1/2000 Accepted: 15/10/2000 ABSTRACT. The two mica granites of El-Shallal area being emplaced into biotite schists, which underwent high temperature low pressure metamorphism. The two mica granite is peraluminous leucoadamellite to leucogranite in composition, Fe-rich sub-alkaline, with low contents of Ba, Ce and Sm and high contents of Rb, U and K. These facts sub- stantiate the geochemical characteristics of S-type granites. The field observations and petrochemical characteristics are consistent with the derivation of El-Shallal two mica granites from biotite schists. Many of geochemical and mineralogical characteristics of El-Shallal two mica granites are similar to those of fertile Granites Uranifere Français (G.U.F). The average uranium and thorium con- tents of the two mica granites are relatively high (17 and 32 ppm re- spectively) and increase during late magmatic stage (72 and 134 ppm respectively) close to basic dykes (chemical traps for U-bearing solu- tions) compared to the average granitic rocks and exceed the inter- national average content in the crustal rocks. El-Shallal leucogranites may represent the source for uranium occurrences at Um Bogma for- mation as a result of leaching and remobilization by circulated me- teoric water and precipitated simultaneous with and after sed- imentation. Introduction The granitoid rocks of Sinai and Eastern Desert massif are mainly of Pan Af- rican age emplaced at a time span between 417 and 780 Ma. They are classified into older (synorogenic) and younger (late to post-orogenic) granites (El Shazly, 1964; and El Ramly, 1972). The synorogenic older granitoids (OG) are of dio-
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  M.E. Ibrahim etal.18 ritic-tonalitic to granodioritic composition, calc-alkaline I-type and range in ages between 610 and 711 Ma (Dixon et al., 1979; Stern and Hedge, 1985). They get as old as 780 Ma in Sinai (Stern and Manton, 1987). The younger granitoids (YG) are considered as the final stage of the Pan African magmatism ceased at the end of the Precambrian at 550 Ma (El-Shazly et al., 1980). The YG plutons in age between 549-597 Ma, while some alkali plutons get as young as 417 Ma ( Stern and Hedge, 1985). The source and genetic relationship be- tween the OG and YG is still constrained. Most of the Post-tectonic YG are K- and LILE-enriched, calc-alkaline to mid- ly alkaline rocks with I-type affinity. A part of the YG has been recently clas- sified as A-type granitoids (Eby, 1992). Economic uranium deposits genetically related to granitoids are mostly locat- ed in anatectic melts or in strongly peraluminous two mica leucogranites (Cu- ney et al., 1984; and Poty et al., 1986). U deposits associated with peraluminous granites occur as veins or disseminations principally in the European Hercynian Belt (Moreau, 1977; Cuney, 1987; Leroy, 1978; Cathelineau, 1981; and Poty et al., 1986), in the north American Hercynian Belt (Chatterjee & Strong, 1984), in the Yanshan granitoids of southeastern China (Jiashu & Zehong, 1984) and in Argentina (Rodrigo & Belluco, 1981). Most of Egyptian uranium occurrences (Um Ara, Gattar, Missikat and Er- ediya) belong to slightly peraluminous granites (biotite only or biotite with sub- ordinate secondary muscovite, calc-alkaline in nature and equivalent to A-type (Ibrahim, 1996). Uranium deposits associated with A-type granites are less common (example in China) than those associated with S-type granites (ex- ample, Central Massif of France, Cuney, 1998) and the size of the U-deposits is generally smaller in the first type (some hundreds to some thousands of metric tons uranium metal). This work is a contribution to the understanding of U geochemistry in two mica granites. The data is provided by analyses of the two mica granites (14 samples), the hornblende-biotite granitoids (12 samples) and the biotite schists (3 samples). U and Th have been measured radiometrically by using multi- channel analyzer γ-ray detector (Gamma-spectrometer technique). Geologic Setting & Petrography The rocks in Wadi El-Shallal area can be chronologically arranged with the oldest as follows: Schists, gneisses and migmatites, hornblende-biotite gran- itoids, Dokhan volcanic rocks (porphyritic rhyolites), two mica granites and post granitic dykes.
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  Uranium Geochemistry inPeraluminous... 19 The metamorphic assemblage minerals; garnet, cordierite, sillimanite and staurolite which present in both schists and biotite gneisses may suggest that, the schists have been exposed to different subsequent stages of regional meta- morphism (Ibrahim, 1997). The syntectonic semi-rounded porphyroblast garnet is mainly Mn-rich, while the cordierite, sillimanite and staurolite are formed in Al-rich pelites under high temperature, low to medium pressure of meta- morphism in amphibolite facies (Ibrahim, op. cit.). Hornblende-biotite granitoids (653 ± 26 Ma on the basis of K/Ar dating by Abdel Kariem & Arva-Sos, 1992) covering about 54 km2 and form moderate to high relief (699 m a.s.l.). The Paleozoic sediments unconformably overlie these rocks. They are usually medium- to coarse-grained, grey to darkish grey in col- our, highly fractured and sheared, sometimes filled by calcite veinlets, iron ox- ides and epidote. They also enclose xenoliths of variable dimensions and shapes ranging in composition from gneissic diorite to amphibolite through gneiss and migmatite. These sharp xenoliths are mostly ovoidal in shape, sometimes el- ongated or angular to sub-rounded, with massive and gneissose structures and sometimes without assimilation. Petrographyically, the hornblende-biotite granitoids are ranging in composi- tion from diorite, quartz diorite, trondhjemite, tonalite and granodiorite without contacts in between. They are consisting mainly of plagioclase (An16-32), horn- blende, biotite, quartz and potash feldspars (orthoclase, micro-perthite) in de- creasing order. Sphene, zircon, apatite, prehnite and magnetite are the main ac- cessory minerals (Table 1). TABLE 1. Modal composition of the examined granitoid rocks, Wadi El-Shallal area. Ser. Sam. Qz K- Plag. Bio. Hb Mus. Acces. Q A P no. no. Feld 1 143 31.19 55.66 11.18 0.39 – 0.96 0.62 31.8 56.8 11.4 2 200 35.04 60.76 2.99 0.05 – 0.91 0.25 35.5 61.5 3 3 29 40.27 48.58 10.13 0.58 – – 0.44 40.7 49.1 10.2 4 153 30.04 56.18 9.64 0.26 – 0.5 3.38 31.3 58.6 10.1 5 172 25.28 48.75 25.03 0.53 – 0.06 0.35 25.5 49.2 25.3 6 179 38.4 43.32 15.66 2.45 – 0.04 0.13 39.4 44.5 16.1 Average 33.37 52.21 12.44 0.71 – 0.41 0.86 34.0 53.3 12.7 7 9 33.17 40.16 25.78 0.68 – – 0.21 33.5 40.5 26 8 130 43.84 23.76 30.76 0.35 – 0.42 0.96 45 24 31 9 184 32.8 41.7 24.21 0.9 – 0.08 0.31 33.2 42.2 24.5 10 193 39.63 32.44 25.32 2.28 – 0.21 0.12 40.7 33.3 26
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  M.E. Ibrahim etal.20 TABLE 1. Contd. Ser. Sam. Qz K- Plag. Bio. Hb Mus. Acces. Q A P no. no. Feld Average 37.36 34.52 26.5 1.05 – 0.18 0.39 38 35.1 26.9 11 66 2.86 3.53 60.35 6.45 26.29 – 0.52 4.3 5.3 90.4 12 72 2.04 2.7 53.19 7.35 33.38 – 1.34 3.5 4.7 91.8 Average 2.45 3.2 56.77 6.9 29.83 – 0.99 3.9 5.1 91 13 30 13.79 4.19 71.75 8.42 1.51 – 0.34 15.4 4.7 89.7 14 76 10.94 3.54 63.93 11.16 9.57 – 0.86 14 4.5 81.5 15 84 12.55 2.88 64.9 10.55 8.73 – 0.39 15.6 3.6 80.5 16 104 5.23 4.66 69.29 10.37 10.11 – 0.34 6.6 5.9 87.5 Average 10.63 3.82 67.47 10.12 7.48 – 0.48 13 4.7 82.5 17 7 5.41 8.26 56.1 12.24 17.43 – 0.56 7.7 11.8 80.4 18 92 6.71 7.91 46.85 11.82 25.66 – 1.05 11 13 76 19 97 8.64 9.38 60.04 6.65 14.8 – 0.49 11.1 12 76.9 Average 6.92 8.52 54.33 10.23 19.3 – 0.7 9.9 12.2 77.9 20 211 16.34 3.39 56.66 16.59 6.6 – 0.43 21.4 4.4 74.2 21 12 19.83 2.67 59.76 12.59 4.58 – 0.57 24.1 3.3 72.6 22 108 14.95 3.63 51.85 17.64 11.65 – 0.28 21.2 5.2 73.6 Average 17.04 3.23 56.09 15.61 7.61 – 0.41 22.3 4.2 73.5 23 5 28.86 7.11 45.74 15.84 2.14 – 0.31 35.3 8.7 56 24 54 24.1 10.47 54.52 7.15 3.51 – 0.25 27.1 11.8 61.2 25 81 23.03 13.98 50.37 6.82 5.4 – 0.4 26 16 58 Average 25.33 10.52 50.21 9.94 3.68 – 0.32 29.4 12.2 58.4 Ser. No = Serial Number, Sam. No.= Sample Number, Qz = Quartz, K-feld. = Potash feldspar including per- thite, Plag. = Plagioclase, Bio. = Biotite, Hb. = Hornblende, Mus. = Muscovite, Acces. = Accessory including opaques, Q = quartz content, A = potash-feldspar content and P = plagioclase content. 1-10 = Two mica granites (1-6 = Syenogranites and 7-10 = Monzogranites) 11-25 = hornblnde-bitite granitoids (11-12 = Diorites, 13-16 = Quartz diorites, 17-19 = Trondhjamite, 20-22 = Tonalites and 23-25 = Granodiorites). Note: All values are in volume percent. The two mica granites are medium to coarse-grained, pink in colour, sheared, cavernous, highly weathered and exposed in the central to southeastern part of the mapped area (Fig. 1), covering about 70 km2 and occur as narrow elongated
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  Uranium Geochemistry inPeraluminous... 21 sheets. They form high relief (1039 m a.s.l.), intruded in older rocks with sharp intrusive contacts, sometimes occur as apophyses into the older rocks and en- closed schist enclaves. FIG. 1. Geological map of Wadi El-Shallal area. Petrographyically, the two mica granites are essentially composed of quartz, potash feldspars, plagioclase, biotite and muscovite. Fluorite, ilmenite, allanite, zircon, sphene and monazite are accessories. Quartz occurs as anhedral crystals. Some crystals show uniform extinction manifesting secondary phase filling the interstices between the feldspars crystals. Potach feldspars are mainly displayed by perthite and orthoclase prthite. They are mostly flamy, patchy and string types, with fractures filled by ilmenite and sericite. They are often stained with dusty brown kaolinite and iron oxides due to alteration. Plagiocalses are repre- sented by albite-oligoclase (An6-18) in composition, and often enclose mus-
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  M.E. Ibrahim etal.22 covite, fluorite, quartz and secondary epidote. Biotite is pleochroic as X = yel- lowish brown, Y = brown and Z = dark brown and greenish brown. It is partly altered to pale green chlorite and replaced by iron oxides along its cleavage planes. Muscovite occurs in three forms; euhedral tabular crystals, usually as- sociated with biotite and ilmenite, or as interstitial filling space between other minerals or as fine inclusion in quartz and feldspar grains. Zircon occurs as eu- hedral prismatic crystals (0.1 × 0.2 mm) enclosed in quartz, feldspars and mica with pleochroic halos. Apatite is less abundant, sphene forms aggregates (0.1 × 0.3 mm) closely re- lated to goethite and mica. Fluorite varying from colourless to pale pink in col- our, present as lensoidal shape enclosed between mica cleavage, or as interstitial filling space between essential minerals enclosing zircon, allanite and quartz. All the granitoid rocks are invaded by dyke swarms of variable composition, including acidic, intermediate and basic types. Aplitic, quartz veins and peg- matite pockets (20 × 120 cm) are also recorded. They are dissected by several normal faults (N-S, NNW-SSE and NW-SE trends), and generally the granitic rocks capped by Paleozoic sedimentary sequences ranging from Cambro- Ordovician to Carboniferous and attain thickness of 200-375 m. (Kora, 1984). The lower Carboniferous Um Bogma Formation is subdivided into three mem- bers: Upper and Lower dolomite members separated by a middle member (4-10 m) composed of intercalations of siltstone, marl, sandy dolomite and shale (Kora, op. cit.). The middle carbonate rock units (Um Bogma formation) have visible uranium showing (El Assay et al., 1986). Analytical Methods The major oxides were measured using conventional techniques of Shapiro and Brannock (1962), with some modification given by El Reedy (1984). The SiO2, TiO2, Al2O3 and P2O5 were analyzed using Unicam UV2/100 Spectro- photometer while Na2O and K2O were analyzed using PFP-7 Flame Photometer and MnO analyzed by GBC 932/933 Atomic Absorption Spectrophotometer. The XRF technique, Philips X' Unique model II was used. The Zr, Y, Sr, Rb and Nb were measured by calibrating the system under the conditions of W- radiation, LIf-220 crystal, 70 kV and 1.5 mA. The Ba was measured under the same conditions except kV and mA are 100 and 10 respectively. The radio- metric measurements was carried out using a Bicron Scintillation detector NaI (TI) 76 × 76 mm. All the analyses were carried out in Nuclear Materials Au- thority (NMA). An X-ray diffraction unit (PW 3710/31), with generator (PW 1830), Scintillation counter (PW 3020), Cu target tube (PW 2233/20) and Ni fil- ter at 40 kV and 30 mA were used for identifying the separated heavy mineral fraction.
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  Uranium Geochemistry inPeraluminous... 23 Major Element Geochemistry Chemical analyses were carried out for 29 samples, collected from El-Shallal area. The analyzed samples include three samples from the biotite schists, twelve samples from hornblende biotite granitoids and fourteen samples from the two mica granites. The results are given in Tables 2 & 3. TABLE 2. Chemical analyses for the hornblende-biotite granitoids, Wadi El-Shallal area. Hornblende-biotite granitoids 12 72 66 104 54 108 30 211 76 81 84 97 SiO2 61.18 54.45 54.70 54.91 63.65 62.81 65.00 65.17 61.14 63.43 63.23 64.75 TiO2 0.19 0.28 0.31 0.21 0.16 0.20 0.18 0.19 0.21 0.22 0.13 0.11 Al3O3 15.61 16.18 15.81 16.31 15.13 16.01 13.99 14.65 16.1 15.66 15.61 14.98 Fe2O3 4.85 8.15 7.14 6.18 4.11 5.16 4.77 4.09 5.61 4.79 5.01 4.16 FeO 1.03 1.32 1.77 2.01 0.91 0.71 0.82 0.74 0.91 0.91 0.91 0.80 MnO 0.08 0.08 0.10 0.08 0.04 0.05 0.03 0.02 0.03 0.03 0.02 0.03 MgO 2.71 4.15 4.32 4.18 2.18 1.91 1.87 1.61 2.04 1.91 2.07 1.76 CaO 4.31 6.34 6.18 7.01 4.61 4.18 3.98 4.18 4.16 4.26 4.42 4.17 Na2O 4.89 4.91 5.16 4.89 4.61 4.80 4.73 4.51 5.01 4.61 4.26 4.36 K2O 3.63 2.78 3.16 3.16 3.21 3.08 3.37 3.71 3.61 3.25 3.19 3.71 P2O5 0.26 0.19 0.17 0.20 0.17 0.16 0.09 0.20 0.19 0.16 0.11 0.18 L.O.I 1.23 1.06 1.12 0.94 1.16 0.94 1.23 0.89 0.91 0.79 1.02 0.99 Total 99.97 99.89 99.94 100.08 99.94 100.01 100.06 99.96 99.92 99.94 99.92 99.98 Rb 63 40 33 60 52 58 80 74 42 58 52 46 Sr 420 460 490 459 432 387 462 328 511 508 475 474 Ba 921 1091 1039 460 533 879 726 460 961 753 1063 921 Zr 215 193 210 243 205 188 268 211 231 278 229 210 Y 28 25 21 25 26 26 31 31 24 26 26 26 Nb 22 20 17 20 21 20 23 24 20 21 21 22 Zn 70 65 68 72 37 63 70 41 71 69 68 59 Cu 16 26 23 21 21 12 15 14 15 12 14 13 Ce 109 90 106 119 93 107 142 107 96 141 113 78 Sm 5 15 15 10 4 8 4 4 10 5 11 11 Sample no.
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  M.E. Ibrahim etal.24 TABLE 3. Chemical analyses for two mica granites and biotite schist, Wadi El-Shallal area. Tow mica granites 193 184 172 138 127R 143 29 140 168G 200 153 130 179 181 SiO2 72.05 72.43 72.01 74.13 74.18 73.67 73.85 73.34 74.28 73.22 72.71 75.00 74.02 74.16 TiO2 0.11 0.13 0.09 0.12 0.10 0.08 0.09 0.10 0.16 0.09 0.13 0.17 0.2 0.09 Al3O3 13.65 13.74 14.22 14.1 13.7 13.65 13.94 14.91 13.62 14.11 14.61 13.91 13.75 13.91 Fe2O3 1.75 2.01 1.27 0.81 0.75 1.01 0.81 0.41 0.57 0.92 1.07 0.85 0.71 1.08 FeO 0.46 0.39 0.50 0.46 0.51 0.61 0.72 0.63 0.71 0.61 0.51 0.49 0.52 0.49 MnO 0.03 0.03 0.02 0.02 0.02 0.02 0.03 0.02 0.01 0.04 0.02 0.03 0.02 0.01 MgO 0.81 0.80 0.73 0.42 0.36 0.33 0.49 0.61 0.45 0.31 0.57 0.41 0.60 0.41 CaO 1.85 1.62 1.74 0.89 1.02 0.91 0.75 1.31 0.82 1.01 0.94 0.72 0.93 0.82 Na2O 3.70 3.36 3.81 4.00 3.89 4.03 3.75 3.77 3.91 4.01 3.71 3.27 3.87 3.91 K2O 4.89 4.78 5.01 4.98 4.81 5.13 4.79 4.09 4.82 4.89 5.07 4.51 4.62 4.39 P2O5 0.16 0.20 0.18 0.20 0.09 0.15 0.16 0.09 0.20 0.13 0.12 0.11 0.17 0.15 L.O.I 0.51 0.48 0.46 0.38 0.52 0.41 0.50 0.61 0.43 0.52 0.49 0.47 0.51 0.48 Total 99.97 99.97 100.04 100.51 99.95 100.00 99.88 99.89 99.98 99.96 99.95 100.02 99.98 99.90 Rb 204 214 211 261 216 219 146 249 243 119 199 230 134 207 Sr 113 94 114 109 88 125 92 99 112 107 94 100 104 104 Ba 379 494 376 356 420 362 380 304 467 418 383 311 382 363 Zr 177 180 177 179 146 185 180 168 188 181 161 165 160 176 Y 44 44 45 48 40 49 38 47 54 38 45 46 36 44 Nb 27 26 27 29 24 30 26 26 30 27 26 26 24 27 Zn 42 35 51 30 77 16 31 41 118 22 53 18 33 32 Cu 23 14 19 17 21 36 19 17 25 20 14 17 18 17 Ce 16 11 10 3 14 22 5 8 20 5 3 23 2 2 Sm 1 2 2 1 1 1 1 1 2 2 1 1 1 1 a – Granitic Typology The R1-R2 diagram (Fig. 2) of De La Roche et al. (1980) shows clearly that all the samples of El-Shallal granitoids lie between the alkaline and calc- alkaline suites. This situation is typical of evolved, Fe-rich sub-alkaline suite, as defined by Pagel and Leterrier (1980). Average schist ( n = 3) Sample no. 70.49 0.50 13.30 4.10 – 0.10 2.20 3.15 3.30 2.0 – 0.70 99.84 40 250 510 220 60
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  Uranium Geochemistry inPeraluminous... 25 On the A-B and Q-P multicationic variation diagrams (Fig. 3&4) after Debon and Le Fort (1983), all the hornblende-biotite granitoid samples are mon- zodioritic in composition, metaluminous in characters (I-type), whereas, most of the two mica granitic samples correspond to peraluminous (S-type) leu- coadamillites and leucogranites (Fig. 3&4) with biotite ≥ muscovite. Argillic al- teration (H + metasomatism) is not indicated in the A-B diagram (Fig. 3) where it characterized by high values of the A parameter (decrease of alkali content in relation to alumina; A = Al – (K + Na + 2Ca) and most of the investigated sam- ples show low values of A parameter. In contrast, three samples (Nos. 172, 143 & 193) of the two mica granites show increase in alkali content in relation to alumina and situated in metaluminous domains. FIG. 2. R1-R2 chemical and mineralogical classification diagram (De la Roche et al., 1980). o = two- mica granites and v = hornblende-biotite granitoids. Symbols are fixed in all diagrams. FIG. 3. A-B diagram for El-Shallal granitoid rocks, after Debon and la Fort (1983).
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  M.E. Ibrahim etal.26 b – Magmatic Evolution On Q-B-F or “quartz – dark minerals – feldspars + muscovite” diagram (Fig. 5) show two domains for hornblende-biotite granitoids and two mica granites with fractionation of biotite, Fe-Ti oxides and plagioclase (decrease of B factor Fig. 5). During this evolution, the anorthite content of the plagioclase decreases, whereas the quartz and potash feldspar increases (increases of Q and F factors, Fig. 5). The composition of the studied two mica granites is relatively similar to those of the two mica granites of the Granites Uranifere Français (G.U.F) as in- dicated from Fig. 5. On the ACF diagram (Fig. 6) where A= Al2O3-Na2O-K2O, C = CaO and F = FeO + MgO (in molar values), after White and Chappell (1977). The studied hornblende-biotite granitoids fall in I-type field, while the two mica granites fall in S-type granitic field. White and Chappell (1983) concluded that the S-type granites probably were formed near continental margin environment from an- atexis of sediments at the base of a thickened crust during continental collision, whereas the I-type granites probably assumed as products of Cordilleran sub- duction post orogenic uplift regimes (Pitcher, 1983). S-type granites are commonly associated with regionally metamorphosed ter- ranes (Debon et al., 1986; and Inger & Harris, 1993). Numerous mechanisms have been proposed to explain the derivation from the metamorphosed host- FIG. 4. Q-P diagram for El-Shallal granitoid rocks. G = granite, AD = adamellite, GD = gra- nodiorite and MdQ = quartz monzodiorite.
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  Uranium Geochemistry inPeraluminous... 27 FIG. 5. Q-B-F diagram for El-Shallal granitoid rocks. The dotted field responds to 80% of G.U.F. (granites uraniferous français). FIG. 6. ACF discrimination diagram between I- and S- type granitic field, after White and Chap- pell (1977).
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  M.E. Ibrahim etal.28 rocks, but partial melting of metapelites (Holtz & Barbey, 1991; and Inger & Harris, 1993) is still the most widely accepted model for the generation of these peraluminous leucogranites. Most of the water required for this partial melting process may be derived from the breakdown of hydrous silicates in these meta- pelites (e.g., biotite and muscovite), (Fyfe, 1969). According to field observations, the presence of numerous schist enclaves within El-Shallal two mica granites, suggest that the biotite schists are assumed to be the potential source lithologies for the two mica leucogranite. The average composition of the biotite schist is used as the normalizing factor to construct the trace element normalized spider diagram (Fig. 7). It is clearly noticed that the leucogranite is markedly depleted in Ba, Ce, Sm, Ti and Y with some en- richment in Rb, Th, U and K. The particular depletion in Ce in the two mica leucogranite is due to fractionation of LREE-rich phases such as monazite, al- lanite, zircon and apatite and uranium will be liberated. FIG. 7. Incompatible elements spider diagrams for El-Shallal two mica granites normalized to the average composition of biotite schist. Uranium and Thorium Geochemistry In Wadi El-Shallal area (Table 4) the U content of the granites increases with magmatic evolution. Uranium content and Th/U ratio increases with Th from hornblende-biotite granitoids to two mica granites (Fig. 8a&b). This type of be- haviour indicates that U in the two mica peraluminous leucogranites is mostly located in Th- rich accessory minerals such as monazite. It is well known that Rb, Y, U, Th and Nb have a large radii or higher electric charges. These ions do not easily to substitute for major ions in common silicate minerals (Krauskopf, 1979), so they are segregated and concentrated in late stage of the granitic melt. If magmatic processes controlled U and Th contents,
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  Uranium Geochemistry inPeraluminous... 29 these elements would be expected to increase. The relations between Rb-U and Y-U (Fig. 9a&b) show that, the U contents increase with the increase of Rb and Y contents, a fact which is related to incompatible behavior during magmatic processes. The positive correlation between U and Y as well as Th and Nb (Fig. 9c) indicate that, the magma from which the two granitic mass developed was emplaced at shallow depths (Briqueu et al., 1984). TABLE 4. U- and Th- contents in ppm and K content in % in the granitoid rocks and high radio- active anomalies within two mica granites, Wadi El-Shallal area. Radiometric measurements Rock types U ppm Th ppm K % Th / U Max. 6 7 2.11 6.93 Min. 1 2 0.12 0.44 Average 4 5 1.56 1.89 Max. 40 43 4.08 6.15 Min. 5 13 2.98 0.33 Average 17 32 3.52 2.21 Radiometric measurements U ppm Th ppm K % Th / U 80 13 140 1.49 10.77 80 G 10 126 0.45 12.6 80 R 16 136 1.24 8.5 Average 13 134 1.06 10.62 177 R 23 57 3.34 2.49 177 G 59 58 3.69 0.98 172 R 37 52 4.65 1.41 140 G 56 40 0.99 0.72 Average 44 52 3.17 1.4 195 38 14 0.79 0.37 195 R 48 14 1.01 0.29 195 G 72 9 1.11 0.13 Average 53 12 0.97 0.26 Hornblende-biotite granitoids (12 Samples) Two mica granites (25 Samples) (2) Along fractured granites (3) Along fault zone Anomaly no. Sample no. (1) Pegmatitic pockets
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  M.E. Ibrahim etal.30 The hornblende-biotite granitoids show normal U (1-6 ppm) contents and poor Th (2-7 ppm) ones compared with the average concentrations in the crustal rocks reported by IAEA (1979) and Clark value (U = 3-4 ppm, Th = 12-14 ppm). The two mica granites show wide variation in U and Th contents (Table 4) from 5-40 ppm with an average of 17 ppm and from 13 - 43 ppm with an av- erage of 32 ppm respectively. They have highly variable Th/U ratios (< 1 to > 4) and could be considered as fertile or uraniferous granites. When Th/U ratio of the magma is low, excess uranium is incorporated in low-thorium uraninite (Pagel, 1981), whereas if the magma has high Th/U ratios, any exess uranium, not substituted in the main minerales or common accessories, is incorporated in uranothorite. Radiometric Lab. measurements provide evidence of large increase in U con- tent (23-72 ppm, Table 4) and Th content (9-58 ppm) close to basic dykes FIG. 8. U-Th (a) and Th/U-U (b) variation diagrams for the studied granitoid rocks, Wadi El- Shallal area.
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  Uranium Geochemistry inPeraluminous... 31 FIG. 9. U versus Rb & Y (a&b) and Th versus Nb (c) variation diagrams for the studied granitoid rocks, Wadi El-Shallal area.
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  M.E. Ibrahim etal.32 (chemical traps for U-bearing solutions). The increase of U-content in the two mica granites is commonly associated with pyrite, goethite, fluorite, tapiolite, zircon and monazite as indicated from X-ray diffraction analysis. The latter par- agenesis leading to a hypothesis assigning a magmatic origin to uranium. Discussion and Conclusion El-Shallal igneous rocks include metaluminous sub-alkaline granitoids and peraluminous fertile leucogranites, probably non-cogenetic. Each granite group may represent individual magma batches. The hornblende-biotite granitoids fall in I-type field, while the two mica granites fall in S-type granitic field. Uranium distribution actually observed in peraluminous granitoids results from five main processes: partial melting, magmatic differentiation, late-magmatic, hydro- thermal and meteoric alterations processes (Friedrich et al., 1987). Ranchin (1971) and Pagel (1982) concluded that the peraluminous leu- cogranites with U content close to 20 ppm; 25-35% of the uranium is in- corporated mainly in zircon, monazite and apatite, and 5-6% is in disseminated and adsorbed form. Uraninite may account for an average of 60% of the whole rock uranium. If the U content is below the Clark value (3-4 ppm) most of it is located in accessory minerals such as zircon, apatite and monazite. The U contained in these minerals is difficult to remove in some Na-metasomatic processes. In con- trast, when the uranium content exceeds the Clark value, (the present study) in- itial magmatic uranium strongly fractionates into the melt during partial melting and may crystallize as uraninite (Cuney, 1987). for example, in U-rich per- aluminous leucogranitets (about 20 ppm U) 70-90% of the uranium is located in uraninite, which is easily leachable by hydrothermal solutions. The transportion of U depends on the geochemical characteristics of the fluids (temperature, pressure, oxygen fugacity fo2, concentration of complexing anions, and pH) and on the amount of fluids (water/rock ratio), which in turn is partly related to the number and size of channel ways which are controlled by the tectonic activity (Cuney, op. cit.). The present study provide also evidence of a strong increase in U content during late magmatic stage (swarms of acidic, intermediate and basic dykes). Mineral fractionation, defined by chemical-mineralogical diagrams, indicates the simultaneous fractionation of Fe-Mg minerals ( Fig. 5) and monazite (Fig. 7). This type of relation, together with the low solubility of monazite in per- aluminous melt (Cuney and Friedrich, 1987) and the absence of cordierite and/ or garnet, suggests that biotite and monazite were essentially restitic minerals, scavenged by the magmas from the anatectic zone (White and Chappel, 1977).
• 17.
  Uranium Geochemistry inPeraluminous... 33 However, this type of fractionation is very different from S-type granites of Australia (White and Chappel, op. cit), which show a much higher content of mafic minerals (B parameter, Fig. 3) and a simultaneous decrease of the per- aluminous character ( A parameter, Fig. 3) and the mafic mineral content. The low solubility of monazite, zircon and apatite in highly peraluminous melt leads to a rapid depletion of the magma in P, Zr and LREE (Ce & Sm). The abundances of these minerals decreases with differentiation (Cuney and Friedrich, 1987) El-Shallal leucogranites may have undergone subsolids alteration (either hy- drothermal or meteoric), these alterations may strongly disturb the primary U content especially in supergene conditions. It is noticeable that the U content in- creases (23-72 ppm) during late magmatic stage close to basic dykes and as- sociated with pyrite, fluorite, tapiolite, and goethite. The Paleozoic rocks unconformably overlie the peraluminous granites, con- sist of three units; Lower Sandstone, Middle Carbonate and Upper Sandstone Units (Barron, 1907). The middle member of Um Bogma Formation (inter- calated siltstone, marl, sandy dolomite and shale, Kora, 1984) is the most im- portant unit from the radioactive point of view. The occurrence of secondary U mineralizations restricted to both Quaternary rocks and the middle dolomitic unit in the Carboniferous Um Bogma formation, and the absence of any sig- nificant mineralizations along fractures or fault lines within the sedimentary rocks itself (Hussein et al., 1992, Abdel Monem et al., 1997), indicate that U mineralizations occurred as a result of leaching of pre-existing uranium rich- ac- cessory minerals in peraluminous leucogranites by circulating meteoric water and precipitated simultaneous with and after sedimentation. Finally, El-Shallel peraluminous two mica granites could represent a favor- able 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. References Abdel Kariem, A.M. and Arva-Sos, E. (1992) Geology and K-Ar ages of some older and young- er granites in Southwestern Sinai, Egypt, Proc. 3rd Conf. Geol. Sinai Develop., Ismailia, pp. 261-266. Abdel Monem, A.A., El Assay, I., Hegab, O.A., El Fayoumy, I.A. and El Agami, N. (1997) Gibbsite, uranium and copper mineralizations, Um Bogma area, southwestern Sinai, Egypt, J. Sed. Egypt, 5: 117-132. Barron, T. (1907) The Topography and Geology of the Peninsula of Sinai (Western portion), Egypt. Surv. Dep., Cairo, 241 p.
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  M.E. Ibrahim etal.34 Briqueu, L., Bougault, H. and Joron, J. L. (1984) Quantification of Nb, Ta, Ti and V anomalies in magmas associated with subduction zones; petrogenetic implications, Earth Planet. Sci. Lett., 65: 297-308. Cathelineau, M. (1981) Les gisements d' uranium lies spatialement aux leucogranites Sud Ar- moricains et a leur encaissant metamorphique, Sci. Terra, Mem., Nancy, No. 42: 475 p. Cathelineau, M. (1987) U-Th-REE mobility during albitization and quartz dissolution in gran- itoids: Evidence from Southeast French Massif Central, Bull. Min., 110: 249-259. Chatterjee, A.K. and Strong, D.F. (1984) Discriminante and factor analysis of geochemical data from granitoid rocks hosting the Millet Brook uranium mineralization, South Mountain Batholith, Nova Scotia, Uranium, 1: 289-305. Cuney, M. (1987) Formation of Uranium Deposits, Reprinted from metallogenesis of uranium deposits, Vienna, pp. 469-473. Cuney, M. (1998) Metallogenic Studies and Uranium Exploration in Eastern Desert Granites, Egypt, Unpublished internal report, Nuclear Materials Authority, Cairo, Egypt. Cuney, M. and Friedrich, M. (1987) Physicochemical and crystal chemical controls on ac- cessory mineral paragenesis in granitiods, Implications on uranium metallogenesis, Bull. Mineral., 110: 235-247. Cuney, M., Le Fort, P. and Wang, Z.X. (1984) Uranium and thorium geochemistry and min- eralogy in the Manaslu leucogranites (Nepal, Himalaya), In: Geology of Granites and their Metalogenic Relations, Symp. Nanjing, 1982, University Press, Beijing, pp. 853-873. Debon, F. and Le Fort, P. (1983) Chemical-mineralogical classification of common plutonic rocks and associations. Examples from southern Asia belts, In: Geology of Granites and their Metallogentic Relations, Beijing, pp. 293-311. Debon, F., Le Fort, P., Sheppard, S.M.F. and Sonet, J. (1986) The four plutonic belts of the Transhimalaya-Himalaya: A chemical mineralogical isotopic and chronological synthesis along a TNepal Section, J. Petrol., 27: 219-250. De la Roche, H. , Leterrier, J. , Grandclaude, P. and Marchal, M. ( 1980) A classification of volcanic and plutonic rocks using R1-R2 diagram and major element analysis, Its re- lationships with current nomenclature, Chem. Geol., 29: 183-210. Dixon, T.H., Abdel Meguid, A.A. and Gillespie, J.G. (1979) Age, chemical and isotopic char- acteristics of some pre-Pan African rocks in the Egyptian Shield, Geol. Surv. Egypt, 9: 591- 610. Eby, G.N. (1992) Chemical subdivision of the A-type granitoids: Petrogenesis and tectonic im- plications, Geology, 20: 641-644. El Assay, I., El Rakaiby, M.L. and Botros, N.H. (1986) Geology and Radioactivity of East Abu Zeneima Area, Sinai, Egypt, Internal Report, Nueclear Materials Authority (NMA). El Ramly, M.F. (1972) A new geological map for the basement rocks in the Eastern and South Western Desert of Egypt, Geol. Survey Egypt Paper, 8: 35 p. El Reedy, M.W. (1984) The General Physical and Chemical Features and the Pollution Level of El Sabahia-Sabhan-El Reqa Soil Localities, State of Kuwait, Report represented to En- vironmental Protection Dept. Ministry of Public Health, El Kuwait (Part I: Chemical Methods). El-Shazly, E.M. ( 1964 ) On the classification of the Pre-Cambrian and other rocks of magmatic affiliation in Egypt, Inter. Geol. Congress, India, Sect. 10: 88 - 101. El-Shazly, E.M., Dixon, T.H., Engle, A.E.J., Abdel Meguide, A.A. and Stern, R.J. (1980) Late Precambrian crustal evolution of Afro-Arabia from ocean-arc to craton, Egypt. J. Geol., 24: 101-121. Friedrich, M., Cuney, M. and Poty, M. (1987) Uranium geochemistry in peraluminous leu- cogranites, Uranium, 3: 353-385.
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  Uranium Geochemistry inPeraluminous... 35 Fyfe, W.S. (1969) Some thoughts on granitic magmas, In: G. Newall and N. Rast (eds.), Mech- anism of Igneous Intrusions. Geol. J. Spec. Issue 2: 201- 216. Holtz, F. and Barbey, P. (1991) Genesis of peraluminous granites II, Mineralogy and chemistry of the Tourem Complex 9 North Portugal), Sequential melting vs. restite unmixing, J. Pet- rol, 32: 959-978. Hussein, A.H., Abdel Monem, A., Mahdy, M.A., El Assay, I. and Dabbour, G.A. (1992) On the genesis of surficial uranium occurrences in West Central Sinai, Egypt. Ore Geology Reviews, 7: 125-134. International Atomic Energy Agency (IAEA) (1979) Gamma-Ray Surveys in Uranium Ex- ploration, Technical Report Series, No. 186 Vienna, 89 p. Ibrahim, I.H. (1997) Geology and Radioactivity of the Basement Rocks of Wadi El Shallal Area, Southwestern Sinai, Egypt, M.Sc. Thesis Ain Shams Univ., 156 p. Ibrahim, M. E. (1996) Petrochemical investigations on Magal Gebriel uraniferous granites, South Eastern Desert, Egypt, Egypt. Acad. Sc., 46: 587-601. Inger, S. and Harris, N. (1993) Geochemical constraints on leucogranite magmatism in the Langtang Valley Nepal Himalaya, J. Petrol, 34: 345-368. Jiashu, R. and Zehong, H. (1984) Form of uranium occurrence and its distribution in uraniferous granites, In: Geology of Granites and their Metallogenetic Relations, Proc. Symp. Nonjing, University Press, Beijing, pp. 621-635. Kora, M. (1984) The Paleozoic Outcrops of Um Bogma Area, Ph.D. Thesis, Mansoura Univ., Egypt. Krauskopf, K.B. (1979) Introduction to Geochemistry, 2nd edition McGraw-Hill Book Co., New York, 617 pÆ Leory, J. (1978) The magmatic and Fanay uranium deposits of the La Crouzille district (Western Massif Central, France): Geologic and fluid inclusion studies, Econ. Geol., 73: 1611-1634. Moreau, M. (1977) L' uranium et less granitoides: Essai d' interpretation. In: Geology, Mining and Extractive Processing of Uranium, Symp. I.M.M. (Inst. Min. Metall.), London, pp. 83- 102. Pagel, M. (1981) Facteurs de Distribution et de Croisic (Loire-Alt-antique), Caracteristion Geo- chimique et Mineralogique de la Evolution Magmatique, Unpub. Thesis, INPL, Nancy, 309 p. Pagel, M. (1982) The mineralogy and geochemistry of uranium, thorium and rare-earth elements in two radioactive granites of Vosges France, Min. Mag., 46(339): 152-163. Pagel, M. and Leterrier, J. (1980) The subalkaline potassic magmatism of the Ballons massif (Southern Vosges, France): Shoshonitic affinity, Lithos, 13: 1-10. Picher, W.S. (1983) Granite type and tectonic environment. In: K. J. Hus (Ed.), Mountain Build- ing Processes, Academic Press, London, pp. 19-27. Poty, B., Leroy, J., Cathelineau, M., Cuney, M., Friedrich, M., Lespinassa, M. and Turpin, L. (1986) Uranium deposits spatially related to granites in the French part of the Her- cynian orogen, In: Vein Type Uranium Deposits, I.A.E.A., Vienna, TECDOC, 361: 215- 246. Ranchin, G. (1971) La Geochimie de la Uranium et la Differenciation Granitique dans la Prov- ince Uranifere du Nord Limousin, C.E.A., Paris, Rep. R. 4034, p. 467. Rodrigo, F. and Belluco, A.E. (1981) Programa nacional de desarello de los recursos uraniferos de la Argentina, In: Uranium Deposits in Latin America: Geology and Exploration, I.A.E.A., Vienna, pp. 395- 414. Shapiro, L. and Brannock, W.W. (1962) Rapid analysis of silicate, carbonate and phosphate rocks, U. S. Geol. Surv. Bull, 1144A: 56.
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  M.E. Ibrahim etal.36 Stern, R.J. and Hedge, C.E. (1985) Geochronologic and isotopic constrains on Late Precambrian crustal evolution in the Eastern Desert of Egypt, Ann. J. Sci., 285: 97-127. Stern, R.J. and Manton, W.I. ( 1987) Age of Feiran basement rocks, Sinai: Implications for Late pre-cambrian crustal evolution in the northern Arabian-Nubian Shield, J. Geol. Soc. Lon- don, 144: 569 - 575. White, A.J.R. and Chappell, B.W. (1977) Ultrametamorphism and granitoid genesis, Tec- tonophysics, 43: 7-22. White, A. J. R. and Chappell, B. W. (1983) Granitoid types and their distribution in the Lachlan Fold Belt, Southeastern Australia, In: J.A. Roddick (Ed.), Circum-Pacific Plutonic Ter- ranes, Geological Society American Memoir, pp. 21-34.
• 21.
  Uranium Geochemistry inPeraluminous... 37 ©wMOu_« ‚u® fM*«dO« XO«duJOK« w ÂuO«—uO« WOzUOLOuO dB − ¡UMO − ‰öA« Èœ«Ë WIDM0 ,* ÊUL bL rFM*« bË , 5 s;« b 5Ë , rO«d« ÈbL_« bL rO«d« s rO«d≈Ë fL 5 WFU , ÂuKF« WOK , UOuuO'« r * Ë , WËuM« œ«u*« WO dB − …d‡‡‡UI« l W??OzUM?« UJO*« Ë– ‰ö??A« W??IDM? XO«d?? q«b?? ÆhK????*« jG?{Ë WOU? …—«d W?—b W{d?F*« Wu?*« X? XOuO?« —u?8 v≈ XO«d?'« 5? VO?d?« w W?OzU?M« UJO*« Ë– XO«d?'« ÕË«d?? Æ qOK s qOK Èu??? Í–Ë bb?(U wMG« Wb?U?I« ju?? #U? XOKO?«œ√ Âub??OËd« s? wU?? Èu?????Ë , .d??U??«Ë Âu??OMO?KO??«Ë Âu—U??« XO«d?'« ÊQ UÎU?D« wDF hzU?B?)« ÁcË , ÂuO?Uu?«Ë ÂuO«—u?O«Ë Æ(S-type) Ÿu s WOzUM« UJO*« Í– XO«d?K WOzUOL?uO'«Ë WOb?FL« ’«u)« s d?O «c?N Âu—u«Ë Âu?O«—uO?« ju? Èu? Æ VB?)« XO«d?K tUA? w beË , ©w«u?« vK ÊuO?K*« w ¡e ≥≤−±∑® U?O? ̉U XO«d?'« ©w«u??« vK Êu??OK*« w ¡e?? ±≥¥ Ë ∑≤® …d??Q?*« d??O?N??B« q«d?? WKU??(« qOU??L?K W?OzU?O??L?O? bzU??B?® Wb?U??I« l«u?I« s »d??IU ju*« Èu? ÈbFË , XO«d'« —u8 ju0 W?—UI*U ©ÂuO«—uOK —u??B œuu*« Âu?O«—u?O« Ê√ qL??;« sË Æ …d?AI« —u??B w*U?F« W«–ù« W?O? WL? Â√ ÊuJ WI?DM0 ÂuO«—u?O« œuË —b?B u ‰ö?A« Æ WOud« —uB« VOd bFË ¡UM√ VOd« …œU≈Ë