Geology, mineralogy and mineral chemistry of the NYF-type pegmatites at the Gabal El Faliq area, South Eastern Desert, Egypt

Abstract

The Gabal El Faliq area is located in the Eastern Desert of Egypt and belongs to the Wadi Hafafit–Wadi Ghadir fold belt. Lenses and dykes of rare metal-bearing pegmatites occur along major weak zones in the area (Wadi El Gemal strike-slip and its Riedel shears), by which they are structurally controlled. These pegmatites are mineralogically complex. Moreover, they are zoned, and the intermediate zones of the pegmatite varieties contain high amounts of zircon, fergusonite-(Y), columbite-(Fe), allanite-(Ce), xenotime-(Y), monazite-(Ce and Nd), thorite and gummite. These minerals carry Zr, rare earth element (REE), Nb, Ta, Th, U >Ta, F, and they are classified into rare-metal pegmatites, specifically, the niobium, yttrium and fluorine (NYF) enrichment family. The geochemistry aspects of these pegmatites indicate Zr up to 28,984 ppm, Hf up to 1171 ppm, REE up to 19,206 ppm, Nb up to 9962 ppm, Ta up to 152 ppm, U up to 565.5 ppm, Th up to 850 ppm and Ga up to 90 ppm. They were formed under an intracontinental tectonic setting from a basaltic magma similar to the oceanic island basalts (OIBs) contaminated with the crust. Consequently, this study could be used as a guide for the exploration of rare metals in similar regions of the world.