Geology, Petrography, and Geochemistry of Younger Granites and Related Radioactive Pegmatite from Gabal El Urf Area, North Eastern Desert, Egypt: Implications for the Evolution of the NYF-Type Rare-Elements Granitic Pegmatite

Abstract

Gabal El Urf region is located in the northern Egyptian Eastern Desert and overlain essentially by older and younger granitoids of Late Proterozoic age. These granitoids contain numerous outcrops of pegmatites, mostly occurring as dikes and veins or huge separated masses. In the contrary, pegmatites form lens-like bodies enclosed within the younger granites along their margins. Previous radiometric surveys showed anomalous concentrations of radioactivity on pegmatite body, located to the south of the study region. The younger granites and the associated radioactive pegmatite are studied in details with the aim to describe this pegmatite, petrogenesis and its relation with the encolsing granite. The younger granites are monzogranite and syenogranite according to mineralogical and chemical classification. Petrographically, the two younger granitic phases are strikingly similar. Both consist of potash feldspar, plagioclase and biotite with some hornblende in the earlier phase. Gabal El Urf younger granites are categorized as highly fractionated I-type granites with metaluminous to mildly peraluminous characters, which emplaced at 600 ± 11 Ma in post-collisional environment. The radioactive pegmatite is located within the syenogranite and enriched with Zr, Nb, Ta, Y, Th, U and REEs; accordingly it was classified as NYF-type rare-elements pegmatite. Metal-bearing generations of minerals within the rare-elements pegmatite include zircon, uranothorite, betafite, aeschynite, fluorite, pyrite and ilmenite.