Geochemical and Mineralogical Studies of the Mylonite Xenoliths and Monzogranite Rocks at Wadi Abu Rusheid,South Eastern Desert,Egypt:Insights on the Genesis of Mineralization

Abu Rusheid area lie in the south of the Eastern Desert of Egypt and comprises(1)ophiolitic mélange,consisting of ultramafic rocks and layered metagabbros in metasedimentary matrix(2)cataclastic group,consisting of protomylonites,mylonites,ultramylonites and silicified ultramylonites(3)monzogranites(4)pegmatite pockets,quartz veins and postgranite dykes.Focus on the monzogranites and the xenoliths of mylonite rocks from the geochemical and mineralogical points of view introduces a new view about the genesis of the related mineralization.Geochemically,the monzogranites have a metaluminous character and were crystallized under moderate water-vapor pressure around 3 kb and temperatures of 750–800°C.The monzogranites are altered along strike-slip faults exhibiting propylitic,with slightly sodic metasomatism and record high radioactive measurements.The average uranium and thorium(U and Th)contents in fresh monzogranites,mylonite xenolith and altered monzogranites are(7.3,21.20),(40.36,94.82),(60.34 and 347.88 ppm),respectively.These high radioactivities are attributed to the presence of kasolite,uranothorite,cerite,fluorite,zircon,apatite and columbite.The mylonite xenolith is higher in radioactivity than the surrounding fresh monzogranites,reflecting U and Th enrichment before emplacement of the monzogranites,then the latter were subjected to right lateral strike-slip faulting with producing hydrothermal solution rich in Th and U.

New Occurrence of Gold Mineralization at the Eastern Part of Wadi El Gemal, South Eastern Desert, Egypt

The basement rock units of the study area are represented by metasediments-metavolcanics association, diorite rocks, granodiorites and syenogranites. The whole sequence is cut by basic dykes, pegmatites and different quartz (jasper) veins. Metasediments-metavolcanics association is represented by hornblende schist and metadacite respectively. There is visible sulfides mineralization in hornblende schist, metadacite and diorite rocks at their contacts at the wadi level. So, polished sections were prepared to study opaque minerals under the ore microscope, which reveals the presence of gold, pyrite and goethite. The radioactivity of this area is weak, where the average eU contents in metasediments-metavolcanics association, diorites, granodiorites, syenogranites, pegmatites and jasper veins are 2.8 ppm, 1.9 ppm, 3.26 ppm, 4.91 ppm, 4.32 ppm and 6.7 ppm respectively. The intrusion of granodiorite rocks may act as a source for hydrothermal solutions ascending along fractures of all older rocks. During this stage, a chemical reaction of hydrothermal fluids with metasediments-metavolcanics association and diorite rocks lead to forming sericite and enrichment of silica content. The enrichment of silica content led to the formation of quartz-diorite. Also, iron derived from the host rocks and sulfur from the hydrothermal fluids could have formed pyrite while the gold was precipitated at the contact between metasediments-metavolcanics association and diorite rocks.