GEOCHEMISTRY AND RADIOELEMENTS DISTRIBUTION IN THE FRESH AND ALTERED HAMMAMAT SEDIMENTARY ROCKS ALONG WADI BELIH, SOUTHERN GABAL UM TAWAT, NORTH EASTERN DESERT, EGYPT. MAHMOUD H. SHALABY and ASHRAF F. MOHAREM Nuclear Materials Authority, Cairo, Egypt. A few of the Precambrian sedimentary rocks show high radioactivity as the Hammamat sedimentary rocks along Wadi Belih, Eastern Desert, Egypt, which host secondary uranium mineralization (uranophane). The average U content in fresh Hammamat is 8.4 ppm (more than five times of the normal content) but the average Th content is 5 ppm (normal value). On the other hand, the average U and Th content in the hematitized Hammamat rocks is 2091 and 10.3 ppm respectively. The microprobe analysis for the accessory minerals revealed that the secondary minerals (fluorite and hematite) concentrate much more U than Th, indicating that U enrichment is mainly controlled by secondary processes. The genesis of U deposits in the studied area in relation to geochemical behavior could have proceeded through the following successive stages: (1) Uranium was first mainly trapped in the crystal lattice of accessory minerals of the granites, (2) The area was affected by tectonic events producing faults and shear zones which acted as good channels for the hydrothermal asccending fluids and the percolating meteoric water generating a low temperature hydrothermal system. This system released U from the essential and accessory minerals of the hosting granites and redeposited it as uranium minerals in the shear zones, and (3) The supergene meteoric water and hydrothermal solutions could pass through the structural network. They leached some of the magmatic U from the younger granites and reprecipitated their loads in the shear and weak zones of the Hammamat sediments, by the effect of evaporation and adsorption on the surface of Fe oxides and clay minerals.