Altered granitic rocks, Nusab El Balgum Area, Southwestern Desert, Egypt: Mineralogical and geochemical aspects of REEs

Gabel Nusab El Balgum is located in the northern part of Bir Safsaf Area Southwestern Desert, Egypt (about 600 km southwest of Aswan City) and covers an area of about 40 km2. A few workers have investigated the Nusab El Balgum Area from the mineralogical and geochemical point of view. The area consists mainly of Devonian sandstone, Permo–Triassic volcanic rocks, altered granitic rocks and post-granitic dykes. The altered granitic rocks (silicified and kaolinized) have undergone several hydrothermal alteration processes and were subjected to different types of alteration (hematitization, carbonatization, kaolinization, sericitization and silicification) and are characterized by extreme enrichment in rare metals (such as Zr, Nb, Y and REEs).Bastnaesite, parisite, fergusonite, columbite, hydrothermal zircon, monazite and xenotime are common in the silicified and kaolinized granites. The silicified granite commonly contains more rare metals than the kaolinized granite. The REEs in Nusab El Balgum granites were introduced by hydrothermal fluids during alteration and occur in carbonate minerals such as bastnaesite (LREE) (CO3) F and parisite Ca (LREE) 2(CO3)3F2.The REE chondrite-normalized patterns of altered granites show an M-type tetrad effect and indicate higher LREEs, negative Ce anomaly (due to alteration by hydrothermal fluids) and negative Eu anomaly.