Low grade metamorphosed sandstone-type uranium deposit, Wadi Sikait, South Eastern Desert, Egypt

Abstract

Wadi Sikait (WNW-ESE) is one of the most famous emerald sites in the world, since Pharonic times. The exposed rocks are ophiolitic melange (consists of mafic-ultramafic fragments set in metapelites matrix), metamorphosed sandstones, gabbros, granites and post-granite dykes (lamprophyres) and veins (quartz). The metamorphosed sandstone (MSS) rocks (vary from greywacke to arkosic in composition) outcrop at Wadi Sikait at two locations. The first MSS outcrop (Sikait-1) is located west the upstream of W. Sikait highly tectonized, elongated in NW-SE (1.8 km in length) and thinning in NE-SW (100-400 m in width) forming float-boat-like shape and intruded by fertile porphyritic granite (15 ppm eU) and lamprophyre dykes (vary in thickness from 0.5 to 2 m and up to 1.4 km in length). The second MSS outcrop (Sikait 2), is located at the bending of Wadi Sikait covering a small area (0.5 km) and intruded also by the fertile porphyritic granites. The MSS rocks cut by two generation of quartz veins; a) barren quartz veins (E-W, N-S and NNE-SSW) cross-cut the foliation planes of MSS and b) mineralized quartz veins (NE-SW)-bearing visible mineralization (wolframite, cassiterite and xenotime) and varies from 1-2 m in width and extends for 15 m in length parallel to the foliation planes. The MSS rocks show relics of primary bedding, banding and obvious foliation in NW-SE with angel of dip 35°/SW. The common alteration products are represented by kaolinitization, flouritization, hematitization, chloritization and manganese dendrites. The alterations are associated with visible greenish yellow U- minerals in Sikait-1. The results of the spectrometric survey were achieved in the form of 1:1,000 scale radiometric maps (K%, eU, eTh, U-mobility) for the first outcrop (Sikait 1). The chemical U content (60 to 480 ppm) is more than the equivalent U content (15 -100 ppm), this result support the youngest age (less than one million years) for U-mineralization. The emplacement of both of lamprophyre dykes and porphyritic granites may be played an important role as a heat source, which lead to U-mobilization from hot granites, transported (along deep faults, foliation planes and banding) and redeposit in MSS rocks under suitable conditions. Key words: Sandstone, lamprophyre, U-minerals, Sikait.