الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
 |  | from | 95 |  |  |
| | | from | 95 | | |
Abstract
The present study deals with the geochemistry and uranium potentiality of Wadi Nugrus - Wadi El Nom area, which is located between latitudes 24° 40’ and 24° 50’ and longitudes 34° 32’ and 34° 40’ in the south Eastern Desert of Egypt covering an area about 405 km2. Detailed field studies revealed that the area comprises the main lithologic rock types beginning from the oldest: 1- serpentinite rocks, 2- ophiolitic metagabbros, 3- ophiolitic mélange, 4- metasediments, 5- gneisses rocks, 6- granodiorites 7- monzogranites, 8-syenogranites and 9- post granitic dykes and veins. The serpentinites occur either as huge masses or as small scattered masses extending from NNE-SSW trend, occupying the northeast and central parts of the mapped area. The serpentinite rocks of Wadi Nugrus - Wadi El Nom area are variable in composition from talc carbonate serpentinite which are highly tectonized and foliated to sheared antigorite - chrysotile serpentinite. Microscopically, they consist mainly from antigorite, chrysotile, actinolite and tremolite associated with few amounts of carbonates. The ophiolitic metagabbros are showing variety of colours due to the relative proportions of felsic and mafic phases. These rocks are intruded by large number of pegmatite veins having about 20 m in length which are either paralleled to the layering planes or crossing them. They are composed of plagioclase, actinolite and tremolite with very little relics of pyroxenes, associated with few amounts of accessory minerals as apatite, titanite. Chlorite and carbonates are secondary minerals. Ophiolitic mélange covers an area about 50 km2 and composed of meta-ultramafics and layered metagabbros mounted in schist. They form irregular relief with scattered higher hills due to weather resistant huge blocks of hard rocks. Ophiolitic mélange are represented by wide varities of talc schist, beryliferous tremolite/actinolite schist, silimanite graphite schist, granetiferous hornblende biotite schist, phlogopite schist and granetiferous staurolite schist (Saleh, 1997 and El Bahariya, 2012). The metasediments have wide distribution in the area, covering about 45 km2. These rocks are represented by foliated biotite and hornblende schists extend NNW-SSE near the most upper stream of Wadi Nugrus - Wadi El Nom area. Field relations clear that the contacts between the metasedinemts and the monzogranites are intrusive contacts. Microscopically, they are composed mainly of biotite and quartz associated with few flakes of muscovite and plagioclase found in fine grained matrix with subordinate amounts of sericite, chlorite and carbonates as secondary minerals and minor amounts of iron oxides and zircon as accessory minerals. The gneisses rocks are generally to medium grained and display black to light grey colours. Gneisses rocks in the study area correspond to the huge masses of G. Hafafit, which represent the highest peaks in the area. They are overthrusted by thrust fault trending WNW-ESE dipping 25º/SSW by ultramafic rocks. Pegmatite veins (0.5 × 10 m) trend N35ºE with steeply angle of dip, 50º / NW are cutting the gneisses rocks. Microscopically, gneisses rocks consist of plagioclases and quartz as felsic minerals; biotite, chlorite and muscovite as mafic minerals; zircon, apatite and titanite as accessory minerals. Granodiorites are whitish grey in colour, medium to coarse grained and having obvious biotite flakes. These rocks are cut and crossed by number of pegmatite and quartz veins as well as basic dykes, strike 135º with dip N 30º E/50º. Microscopically, they consist of plagioclase, quartz, k-feldspar with minor amounts and biotite, hornblende, iron oxides as mafics and titanite, zircon as accessory minerals. The monzogranites are emplaced along NNW-SSE trend, reached from 0.5 - 4.5 Km. in length and 150 - 300 m. in width. The monzogranites appear as small off-shoots of boss-like bodies, as dike-like bodies, and a huge semi-circular mass forms domal shape around Wadi Nugrus - Wadi El Nom area, located close to the major Nugrus thrust. The major sets of joints are N-S, NNE-SSW and NW-SE trends with steep angle of dip. Monzogranites are essentially composed of quartz, potash-feldspars, plagioclases, biotite and muscovite. Zircon and opaques are accessories. Garnet and allanite are secondary minerals. The syenogranites are characterized by massive, fine to medium-grained, buff to greyish buff in colour showing boulder appearance, exfoliated and cavernous due to highly weathering. These rocks are cut and crossed by number of pegmatite veins and basic dykes, strike 120º with dip N 35º E/40º. They are highly sheared and dissected by numerous faults.The rocks are mainly composed of potash-feldspars quartz plagioclases, biotite and subordinate muscovite. Opaques, fluorite, zircon, apatite and titanite are accessories. The basement rocks of Wadi Nugrus - Wadi El Nom area are cutted and crossed by various basic dykes, quartz and pegmatites veins. The studied monzo - syenogranites originated from calc-alkaline magma with peraluminous affinities. They were formed in a within plate tectonic regime. They have A-type granites geochemical characteristics and can be assigned to A2-type granites. They were derived from crustal materials at relatively 2-3 K-bar and temperature ranging from760-800oC indicating that they were probably formed at low levels in the crust. The analyzed monzogranites have relative enrichment in the ΣLREEs contents varying between 58.33 and 84.91 with an average as 68.67, while the syenogranites have ΣLREEs contents varying between 16.08 and 33.96 with 24.01. The ΣHREEs ranges from 16.16 to 17.90 in the monzogranites with 16.77 as an average, while they are ranged from 5.59 to 12.47 with 10.27 as an average in the syenogranites. The monzogranitic rocks of wadi Nugrus - Wadi El Nom have Eu/Eu* values ranged from 0.24 to 0.43 with an average as 0.39, while the syenogranites have Eu/Eu* values ranged from 0.14 to 0.51 with an average as 0.31. The negative Eu-anomalies are related to Eu2+ and are attributed to the crystal fractionation of plagioclase from the felsic granitic melt at low pressures or partitioning into feldspar during fractionation. The ground gamma - ray measurements reveals that the studied monzo - syenogranites are uraniferous granites where the average uranium contents are 7.31 to 6.88 ppm, thorium contents 18.29 ppm to 15.44 and the potassium contents are 4.26 to 3.77 respectively. The dose rate (D.R.) ranges from 550 to 1100 (mSvy-1) with an average of 650 (mSvy-1) along trenches (T1-T14) in mineralized monzogranites. from the D - factor (U/eU) of the Wadi Nugrus - Wadi El Nom samples, the studied mineralized trenches (T1 - T14) clear that chemical uranium is less than the radiometric uranium in all samples, which reflects disequilibrium due to the removal of uranium. The mineralogical studies of Wadi Nugrus - Wadi El Nom mineralized monzogranites, reveal that the common heavy minerals can be classified into radioactive secondary minerals including uranophane and meta- autunite, and uranium bearing minerals as uranothorite, zircon, ferrocolumbite as well as non radioactive minerals as pyrite, galena, molybdenite, sphalerite, franklinite, garnet, apatite, zincite and fluorite.