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Geology, Radioactivity and Mineralogy of Granitic Rocks and Silica Veins of El-Erediya area, Central Eastern Desert, Egypt |
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PP: 57-79 |
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doi:10.18576/jrna/070208
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Author(s) |
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Nasser M. Moghazy,
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Abstract |
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| This work discusses the geology, geochemistry, distribution of the natural radionuclides and the mineralogical studies of the radioactive minerals in El Erediya granites, Central Eastern Desert, Egypt. EI-Erediya syenogranite mass showing characteristic higher topography than the surrounding rocks. It is oval shaped, elongated in NW-SE direction and dissected with numerous sub-parallel shear zones trending NE-SW in the southwestern part of the G. El Erediya. The pluton is characterized by different degrees of alterations comprises silicification, hematitization, sericitization (± minor greisenization), kaolinization as well as jasper and quartz veins. The uranium mineralization is closely associated with Jasper veins, varying in thickness of 20 cm in average and length from few meters to more than 100 meters within the granites and with no extensions to the surrounding country rocks. U-mineralization encountered in jasper veins and veinlets are believed to be of magmatic and hydrothermal origin after the emplacement, contraction and fracturing of the crystallized magma.
Geochemically, the studied granites are true granites in composition and characteristics and most probably originated from high K calc-alkaline magma. The studied granites predominantly show metaluminous to slightly peraluminous nature and syenogranites are A-type granites and belonging to A2 group which represents magmas derived from continental crust or under-plated crust that has been subjected to a cycle of continent- continent collision or island-arc magmatism. The El Erediya granites were developed in within plate tectonic setting and derived from tonalite magmas or crustal sources under pressure varying between (2->5kb) and temperatures of crystallization ranging from 820o to 840o c, emplaced at moderate depths >30 km and the crystal fractionation was the predominant process during magmatic differentiation. Hydrothermal alterations are common in the form of silicification, hematitization, sericitization , greisenization and kaolinitization.
Radiometricaly, we may concluded that the syenogranites are considered as anomalous granites and the silica veins as fertile rocks. Also, a magmatic and strong post-magmatic condition play an important role in the distribution of uranium in the studied rocks. The uranium and thorium contents are encountered in uranium and thorium minerals as well as radioactive bearing minerals as uranophane, autonite, uranothorite, thorite, columbite, xenotime, zircon, monazite, sphene, fluorite, allanite and apatite.
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