U series age and origin of two secondary uranium deposits, central Eastern Desert, Egypt

Abstract

At two sites in the central Eastern Desert of Egypt secondary uranium minerals are found at the surfaces of tabular fractured rock bodies which host primary uranium mineralization at depth. At El Atshan the host rock is a 28-m-thick bostonite sill cutting siltstones, and at El Erediya the host rock is a 20-cm jasperoid vein cutting granite. Whereas the primary mineralization at depth is pre-Tertiary, we obtain U series ages for the secondary mineralization at both sites of 80,000 to 140,000 yr. We interpret this episode of uranium mobilization to have resulted from ground-water saturation during humid oxygen isotope climatic stage 5. At both sites adsorbed uranium in the host rock immediately below the secondary ores is shown to have been the result of subsequent mobilization during the last 60,000 yr.