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Chsr&Itristics and Significance of Uranium Bearing Fan African Younger Granite in the Eastern Desert

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Chsr&Itristics and Significance of Uranium Bearing Fan African Younger Granite in the Eastern Desert EG0000327 Tlu?'l--'ri'!i C'unfciTncc on the Peaceful Uses ofAtonm. t^nmsy, uurnascus y - u uec. IVVb AAEA Chsr&itristics and Significance of Uranium Bearing Fan African Younger Granite in the Eastern Desert, Egypt M. A, Hassan, G.A. Dabbour and T.F. Mohammden Nuclear .vlntonals Authority, P.O. Box 530, Maadi, ;\;)i!;innya. Cairo. Egypt. J.". ; . ; . -c> •-, --S, •'. ~ )__•; j • ~''i-J I t I • "<• • --*> I I i p •• v_a V I f j J-LJ *LJL_J I *\ l I 4_J_J y -^ I I tj a, , ^i I ( .-j—^UJi _wi ^' > ". > '•• i j. ^ H J " ^ 1 I 6JJ& o 'I ^." 4 • 11 -y II \ MjljjJI .JI.J (] l^| :.-• ;!—•—•-=-• ;.-{' d—~:L'_i La—i—G_2W L^_i I ,i_a. j Ji.)...L.-k <—LJI—i ft \ S j) \ -^ 1 I j < ' a J ^JJ "' * ; _ •—-o—j K~i j t J_J X-2i_j jk_j j_i j . 4—J j I -»j—I_J I jj-i • .' ' •''J _) yj .'J ' ^••* J- ~Q CJV I ft "i -^ I ..--.Vwj _ftJU ^..^J i j jj I ^J -^ A :_^_< L'.'i .vj I j..^..l ' ^-* fr J *^. i J **> ^'. M • . • •• I j j 1 I r- •_.• • _c—> . .i -1. yjj i 1__^ij ( • J a 4 i a I y^i. 6 •, " ' I I ^' ,,,.| I ) jJ I • f • -y ^ •. c JJ I — " ' ' *' * *' I i •? t I I • L -• ! _^ja_J ui yJt-IiJ 1 J i O_ul Jfcij I a JJ& CjjLJft J_JS a _ -::• t ''I v -^ J ( i T V -^ _i djj " Abstract Surficial uranium mineralization was discoverd in lour Pan African younger granite plutons in the Eastern Desert of Egypt. Tlu: prc^c.it.'t'; revealed great similarity between these plutons both in pcirography a>;.: geochimestry. They are two-feldspar, two-mica pcraluir.i.n.ous ;:r p.i_>.:. which have been formed by melting of crustal materials and cr^nkr•:••.'. .ivir ing the late stage of a late Proterozoic ocogcnic cycle. Radit>rr«•'.:••<..• •••A- chemical investigations indicate that these granites are fertile wv.)\ iv.cr to U and form a potential target for primary uranium deposites. Four x•>•;'. els are suggested to explaine the source and mechanism of the surficia' ;•;•:> nium mineralization in these granites. The most applicable mod'-M •> U:e oxi- dation of U+4 found in minute dissiminated uraninite grains and its subsequent mobilization. This is supported by petrographic and autoradio- graphic studies. The bearings of the present study on further exploration for uranium deposits in granites of the Arabian-Nubian shield in general are discussed. Introduction Surficial uranium mineralization were discovered in four younger Pan- African granite plutons in the Eastern Desert of Egypt (Fig. 1) namely Qat- tar, El Erediya, El Missikat and Um Ara. Secondary uranium minerals mainly uranophane (Fig. 2), occur as dissiminations and fracture filling mostly in association with sheer zones. These four granite plutons show many common features (Mohammaden, 1995)11 j which suggest a common mode of formation of the secondary uranium mineralization. This raised the possibility that these granites could be fertile granites and host primary ura- nium deposits. Accordingly, comparative petrographic, geochemical and radiometric studies were carried out on 45 representative fresh samples from these granites to identify their common features. The impact of these studies on the understanding of the mode of formation of the associated surficial ura- nium deposits and the possibilities of the occurrence of primary uranium deposits are discussed. YAT Fig.'(l): Sketch map showing the studied areas O . 300Km • G. Um-Ara *• G. EI-Erediya * G. El-Missikat 0 G. Qattar Precambrian Basement Common Features of the Uraniferous Granite Geologic Features Besides their belonging to the younger post orogenic phase of the Pan African cycle, these granites are characterized by wide spread post- intrusion tectonic activities in the form of faults, fractures and shear zones. Multiple post magnetic activity in the form of variable veins and dykes as vvo!l as alkaline plug*-, is also common. Although all studied plutons have no !ar-iprophyn> dykes, yet they have other basic magmatism such as basaltic unc! <j'-.:.eriii>. dykes as weil as basaltic sheets(Bakhit,1978[2], Abu Dief, 1985 [31, Ibrahim. 1986 j.4] & Roz, 1994 [5]) YAf I I- I II ill v. \ „•' "••* Qattar Figure (2) : Grains of uranophane collected from El-Hrediya ami Q.1 tur granites. TAt Petrographic Features The petrographic study of 32 representative thin sections from the con- cerned granites shows that these granites have similar petrograpmc charac- teristics. Felsic minerals (quartz, perthite and sodic plagioclase) have more than one mode of formation with intricate and complicated textural rela- tions between them, which indicate a complex history of crystallization (Mohammaden, 1995) [1] the presence of primary muscovite in the four granites reflects their peraluminous nature which was confirmed by the presence of garnet mineral (Fig. 3) in some of the studied samples. The presence of both muscovite and biotite classifies these granites as two-mica granites. Although the hypidiomorphic granular texture is prevailing, yet mylo- nitic texture (Fig.4) due to post crystallization shearing is not uncommon. The autoradiographic study of some thin sections indicated the presence of some accessory minerals such as zircon (Fig. 5) which seem to have cap- tured their uranium during crystallization. Alpha tracks associated with concentrations of iron oxides and micas (Fig. 6a&b) are mainly due to ad- sorption of uranium on their surfaces. A fine primary opaque mineral oc- curs ether in the form of dissiminated grains or clusters of grains (Fig. 6a-b & 7a-i) which contribute distinct and high concentrated alpha tracks. It is thus clear that the radioactivity of these granites is contributed both by pri- mary and secondry sources. The principles and procedures of the applied autoradiographic technique are described by Thiel et al. (1979)[6], Figure (3) : Grains of garnet coliected from Urn-Ara. I'.!... X ! 2. Figure (4) : Mylonitization and annealing ofquarty in qatiar ;uir.niK' L'.P... X 10. TA1 Figure (5) : Zircon, violet fluorite and iron oxide crystals, Um-Aragranite. b ive (5) : The same previous photomicrograph showing mica flake en- gulfing zircon crystal gire faint pleochroic halo, Um-Ara gran- ge, r p..;x Figure (5) : Distribution of cc-trckc •esulteJ nun. t!,^, radioactive zircon crystals of the above photomicrograph, Um-Ara granite. P.L., X 35.. Figure (6) : Altered biotite, iron oxide and black iadioacti\e •-< s t low corner, El-Erediya granite. P.L. X 35 Figure (6) : Distribution ot a-trakes or trie ano\e pnotomuio^iuph ml- their scattering in case of altered biotite and iron oxide and their high concentration in case of black radioactive spot . t\L. X35 •V niV Figure (7) : Black radioactive mineral of El-Missikat granite, note the red- dish brown alteration around the mineral. P.L. X 35 Figure (7) : Distribution of the a-trakes of the above photomicrograph, P.L. X 35 •» # Figure (7): Black radioactive spots of Qattar granite.. P.L. X 35 • r Figure (7) : Distribution of the a-trakes ot the above photomicrograph, P.L. X 35 Geochemical Features The geochemical investigation was carried out on 45 samples from the most fresh parts of the granites. Both major oxides and some trace elements were measured (Table 1). The relatively low loss on ignition values (generally < 1.5) indicates that the sampled units were not subjected to deep meteoric alteration. The obtained data were statistically treated and plotted on standard petrological diagrams (Fig. 8-11). These indicate that these granites are calc-alkaline, peraluminous, S-type granites and that they pos- sibly originated from the partial melting of crustal materials during an oro- genic collision stage. These characteristicistics agree with conclusions ob- tained from the petrographic study. Radioactivity Uranium and thorium contents of 33 non-mineralized samples, out of the 45 samples which were analyzed chemically, were measured radiomet- rically by g-spectrometric technique. Also, uranium was determined by LA- SER technique. The obtained data are presented in Table 2. All studied granites have high U and Th contents relative to the world averages, but they are low in K content which seems to be a regional characteristic for the Egyptian granites compared to the world granites. This feature is perhaps the only difference from the ideal parameters of fertile granites as suggest- ed by Cambon (1994) [7]. All the measured samples have eU/eTh > 0.4 ex- cept one sample in Urn Ara (Table 2). It is clear that there is a difference between both chemical and radimetric measured uranium, this is attributed to the disequilibrium state in the U-decay series. The same conculsion is obtained from the ratio of eU/Ra which differ than unity. Also, we note that Th/U ratio lower than the world average ratio of granitic rocks ,which equals to 4.5, this reflects a case of uranium addation. Table (1): Data of complete chemical analysis of Urn-Ara granite S.NU 1 J .1 1 5 ft 7 K 9 10 11 12 . 13 11 SICJ2 7U.& 12.* 1.1.9 71.01 . 71.1 71.5 72.1 7.1.71 72.8 7.1.SI 74.01 73.31 73.05 74.1 "1102 ans 0.1.1 0.09 0.1 ru 0.07 0.07 0.07 am o.ns 0.04 0.1 II 1)13 0.09 A1.7O.1 1.1.7 14.7 11.7 II) 14. 1 M.I 13.9 3.SJ N.f, n.» IX1I 13.4 14 46 13.5 TclOJ O.lW l.t 1! 1.01 I.I IUC 3.11 o.™ .1 0.9 Wl-I 0.JI 1.1)1 FBI aJS o.s nit 0.71 as 0.5 0.79 0.C] o.» 0.5 0.41 0.1 O.H ns Mirf) (1.02 i 003 0.02 0.(12 n.oi 0.01 0 01 0.02 0.01 0.01 O.tll 0.02 0.02 no] ass i o.j o.x or,} 0.1} 0.33 0.73 0.M 0.33 0.72 0.11 0.57 0JS7 ToT C-»O nm i.r 1.01 u 1.0 0L»! 1.1 O.»» 1.1 an, O.HJ 0.91 0.93 0.9 K2O 1.61 4.1 1.3 1.3 T5— TiT- -1.C7 4.2 1.7 4.72 -4lT~ -1.S6 4.7 0.12 0.15 0.11 O.t* 0.12 0.11 0.1 S O.H 0.A9 0.01 0.04 0.11 on 1-0.1.
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