Occurrence of Ishikawaite (Uranium-Rich Samarskite) in the Mineralized Abu Rushied Gneiss, Southeastern Desert, Egypt (original) (raw)
Based on petrographic investigation applied to the picked core samples through pre-pilot drillhole north of Wadi Abu Rusheid, SED, Egypt with depth of 47m which have been studied perfectly, the subsurface metamorphic sequence are (from top to bottom): mica schist, buffish gray mylonitic gneiss, quartz feldspar whitish mylonitic gneiss, caverneous mica schist, quartz-hornblend-biotite schist and finally whitish gray mylonite gneiss interrupted by thin layer of quartz-carbonate-hornblend-biotite schist. Mineral association found for the first time in the area under investigation, the yttriumuraninite (gummite), uranophane, are found together with botryoidal sphalerite (with colloform texture), Przibramite ((Zn,Cd)S), Clausthalite (PbSe) and Berzelianite (Cu 2 Se) as well as well-developed pyrite that confirmed by Scanning Electron Microscope (SEM). Thorite and uranothorite are also predominant primary radioactive minerals in the studied borehole. Uranophane and Kasolite are the uranium secondary mineral more abundant. Other radioelements-bearing minerals were recorded such as Betafite [(Fe,Ca,Th,U)(Ti,Nb,Ta)O 6-•nH 2 O], samarskite (YFe 3+ Fe 2+ U,Th,Ca) 2 (Nb,Ta) 2 O 8 , fergusonite (Nb, Y, Ta, U, Al, Mg, Fe, REE) and zircon. The dominantly associated of their minerals are xenotime, monazite, fluorite, and opaques, this mineralization with epigenetic contribution by circulating hydrothermal solutions illustrates by the presence of colloform textures. The radiometric analysis revealed that, the whitish gray mylonitic gneiss samples represent the highest radioactive zone, where the eU ranges from 68 to 179 ppm with an average 147 ppm and the eTh content varies from 155 to 467 ppm with an average 253ppm. The (eTh/eU) ratio ranged from 0.9 to 2.8 with an average 1.8 as well as thorium content at this zone represents the highest thorium content along the borehole while the schistose rock types represent the lowest values along the studied borehole in addition to there is a general trend for increasing of uranium and decreasing thorium with depth for the studied borehole.