Occurrence of Ishikawaite (Uranium-Rich Samarskite) in the Mineralized Abu Rushied Gneiss, Southeastern Desert, Egypt

摘要

Ishikawaite, with an average assay of about 50 percent Nb_2O_5 and 26 percent UO_2 has been identified for the first time in Egypt in the mineralized Abu Rushied gneissose granite. The mineral is associated with columbite, Hf-rich zircon, and dark Li-mica mineral (zinnwaldite). The mineralogy and geochemistry of the studied ishikawaite were determined using microscopic investigation as well as quantitative analysis by both field emission scanning electron microscope and electron microprobe analyses. Analytical results indicate a structural formula of (U, Fe, Y, Ca) (Nb, Ta)O_4 for the ishikawaite, with U ranging from 0.12 to 0.61 per formula unit.