Field Features, Mineral assemblages and Geochemistry of Radioactive Pegmatite in the Wadi Abu Zawal Area, North Eastern Desert, Egypt

Abstract

Many geologists are increasingly paying attention to granitic pegmatites since they are important sources of rare metals (London, 2008). Rare-element pegmatites are classified into LCT (rich in Li, Cs, and Ta), NYF (rich in Nb, Y and F), and mixed petrogenetic families (Ĉerny and Ecrit 2005). LCT family is suggested to be associated usually with Ior S-type granite derived from a sedimentary source in a lateor post-orogenic setting. The NYF family is suggested to be associated with A-type granite derived from a mixed source of lower crust. GRANITIC pegmatites of the Wadi Abu Zawal area, North Eastern Desert of Egypt, intruded the syn-tectonic granites, younger gabbros and post-orogenic granites. Two unzoned pegmatite masses are quarried for feldspars and quartz, which injected within the older granites. One of them shows high radioactivity related to formation of U-ThREEs mineralization. The mineralization occurs at the margins of this pegmatite body in close proximity to contacts with the host older granite. Hydrothermal hematite, kaolinite and epidote are dominant along the contact zone. Petrographic observations showed that the mineralized parts are mainly albite-rich with minor quartz and muscovite. The hydrothermal mineral assemblage contains secondary uranium minerals (uranophane and kasolite), uranothorite and monazite-Ce. The mineralization occurs as stains or crystallizes in the microsfractures of the pegmatite. Whole-rock analytical data of albite-rich samples display high contents of Na2O, CaO and Al2O3 with significant lower concentrations of SiO2 and K2O. The analyzed samples are enriched with U, Th, REEs, Zn, Pb, Sr and Ba. Detailed field, mineralogical and geochemical data have provided evidence that the investigated pegmatite has similar characters to other fractionated NYF-type pegmatites in the North Eastern Desert of Egypt.