Geochemical alteration and spectrometric analyses in Abu Rusheid altered uraniferous gneissose granites, South Eastern Desert, Egypt

Altered uraniferous gneissose granites at Abu Rusheid were affected by meta somatic events. This is seen in geochemical, chemical, mineralogical and te xtural changes of the rocks. Altered surface samples were mainly peralkaline to slightly peraluminous wi th mainly biotite +/- muscovite and affected mainly by Na- and K-metasomati sm. Drill core samples (about 176 m below wadi level) are mainly prealumino us to slightly peralkaline with increasing muscovite on the expense of biot ite and were affected by two alteration processes; albitization either prec eding or contemporaneous with loss of SiO2. The leached quartz was followed by vugs filled by secondary quartz. Fluids of similar composition having a meteoric origin produce these processes. The estimate thickness (20 m) of the SiO2 poor zone at depth 35-55 m below wadi Abu Rusheid level. The altered surface and the upper most part of drill core samples are chara cterized by high U, Nb, Ta, Pb, W, Zr and Sn which lead to the formation of uranophane, beta -uranophane, columbite, becquerelite and fergusonite. The progressive decrease of Nb, Ta, Zr, Si, Ti and Fe2O3 between 35-55 m below wadi level (desilification zone) will expect to progressive increase of ur anium content at the expense of columbite and zircon.