Petrology and Radioactivity of Gabal Al - Aglab Younger Granite, Central Eastern Desert, Egypt

Abstract

This study deals with petrology and radioactivity of Gabal Al-Aglab younger granite, central Eastern desert, Egypt. Geologically the area consists of ophiolotic Mélange and younger granite. The study reveals that the younger granite are post orogenic granites, characterized by high differential index, which in turn represents the latest stage of the successive younger granite intrusions. Microscopically, Gabal Al-Aglab younger granites is holocrystalline, medium to coarse grained, characterized by the predominance of perthite over plagioclase, quartz and biotite. Zircon, apatite, titanite, allanite, and opaque minerals are the accessory and secondary minerals. The pegmatites occur as lenticular and circular pockets at the periphery of the younger granites. Geochemically, the younger granites show mainly peraluminous to metaluminous character and originated from subalkaline magma in within plate tectonic setting (crustal thickness > 30 km) at water vapour pressure varying from 0.5 to 3 kb with crystallization temperature between 670º to 800º C. Field survey together with the complied total count aeroradiometric map reveal that the pegmatites of Gabal Al-Aglab younger granite is significantly highly radioactive compared to the surrounding rocks. The uranium content varies between 3 to 12 ppm with an average of 7.1 ppm and thorium from 11 to 35 ppm with an average of 20 ppm and an average ratio (Th/U) 2.8.The pegmatites show higher U contents relative to their hosted younger granites as identified by microscopic investigation, scanning electron microscopy and confirmed by XRD.