"FAVOURABLE GEOLOGIC ENVIRONMENTS FOR URANIUM CONCENTRATION IN SOME AREAS IN THE NORTH WESTERN DESERT, EGYPT"

Abstract

Uranium occunences m the noth Fayium depression arc hosted in Post­ Oligocene sediments that. occupied low lands and basins. Differential weathering and erosional processes fonn such basins. The thesis deals with the geologic environment of uranium occmTences in the area in tcnns of field discrimination (paleotopography and geology), geochemistty and petrography. The study is hence concemed with uranium fonnation in Fayium depression and constmction of a model for uranium development in the study area.• The geologic and geomorphologic studies revealed that urannnn occunences arc restt•icted to Post-Oligocene topographic basisns initiated on sub-plateau surface of Fayium depression. Uranium occurrences arc distributed in eight basins. Basins 1,2 and 3 are located in eastem part of the study area and scoured in sandstone bed oflower Oligocene age. These basins are fonncd in the sub-plateau of the fomih scarp bounding the depression. Uranium anomalies of these basins are hosted in channel-fill sandstone'occupied some features such as pockets, cavities, rills, tubes and coated sand grains. Basin 4 and 5 are located in the middle pmi of the study area and are scoured in clay belonging to upper member of the Upper Oligocene Qatrani Formation. These basins are formed in the sub-plateau of the third scarp. Uranium of these basins is hosted in Post-Oligocene black shale that was deposited on the iiTigular surface of the underlying clay bed. Basins 6,7 and 8 are fonncd on the upper eroded surface of cherty limestone bed belonging to the Qatrani Formation. The uraniferous sediments are generally composed of siliciclastic framework grains of quartz sand cemented by calcite, goethite, hematite anrl gypsum. Petrographic studies revealed that uranium is associated with calcrete, gypcrete, fenicrete and alcrete. These deposits represent four dmicmst types observed in the area. From the petwgraphic and geochemical investigation it is obse1vcd that U, Zr, Si, and Nb are concentrated in globular and framboidal bodies that present in the uraniferous sediments. These bodies can be held as a signature of microbial action, which played an impmtant role in uranium precipitation.