干旱区生态环境知识资源中心

Altered uraniferous gneissose granites at Abu Rusheid were affected by metasomatic events. This is seen in geochemical, chemical, mineralogical and textural changes of the rocks.

Altered surface samples were mainly peralkaline to slightly peraluminous with mainly biotite +/- muscovite and affected mainly by Na- and K-metasomatism. Drill core samples (about 176 m below wadi level) are mainly prealuminous to slightly peralkaline with increasing muscovite on the expense of biotite and were affected by two alteration processes; albitization either preceding 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 characterized 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 uranium content at the expense of columbite and zircon.