Pan-African rare metals bearing pegmatites in Wadi Ghadir, South Eastern desert, Egypt: the geochemical evolution and implications for mineralization

Abstract

Quartz-diorites, monzogranites and pegmatites are the main rock units in the studied area. The pegmatites occur as zoned pockets within monzogranites with zonal arrangement: border, wall, intermediate, and core zones. The wall zone have enrichment of radioactive and RREs-bearing minerals. K-feldspar, plagioclase and quartz are essential minerals, whereas uranothorite, columbite, zircon, xenotime, monazite, sphalerite and pyrite are accessories. Geochemically, the pegmatites of W. Ghadir have peraluminous character, ferroan with alkalic–calcic affinity and emplaced in within plate setting. These pegmatites revealed Li-bearing variety and high level of rare earth elements mineralization. The studied pegmatites exhibit high contents of Li, Nb, Cu, Ta, U, Th, Pb, Zr, Zn and Ga, can be from the previous data, the studied pegmatites can be classified as a Niobium–Yttrium–Fluorine (NYF) pegmatite or rare metal pegmatite. The trace elements ratio supports a low degree of fractionation and metasomatism in the evolutionary history of the pegmatites, and the very low Cs values (2.2–4.3 ppm) indicate paucity of alkali metal fractionation. Spectrometric investigation revealed that monzogranites are not uraniferous, while the radioactive anomaly is confined to the pegmatites. Applying the U mobilization equation proved that pegmatite samples have been originated from a late magmatic phase of magma very rich in radioelements, and the pegmatites affected with hydrothermal solutions rich in uranium than thorium which indicates uranium addition. Radioactive and important heavy minerals are represented by uranothorite, columbite, zircon, monazite, xenotime, sphalerite and pyrite.