Geochemistry of Uranium and Thorium Isotopes in their Ores and associated Groundwater, El Atshan, El Erediya and El Missikat areas,central Eastern Desert, Egypt

Abstract

Fourteen secondary uranium ore samples, forty rock samples and twelve groundwater samples were collected from El Atshan, El Erediya and El Missikat mining areas in the central Eastern Desert, Egypt. The mineralogy, geochemistry and U-Th isotopic.composition were studied using different collaborative techniques. Petrographical and mineralogical studies have been performed using optical microscope, X-ray diffraction technique and Scanning Electron Microscope equipped with Energy Dispersive X-ray analyzer. Uraninite is identified i:, the radioactive silica veins of El Missikat mining area. Sulfide minerals: galena, pyrite, chalcopyrite, and sphalerite are found associated with uraninite. The most common secondary uranium minerals identified are soddyite, kasolite, and uranophane at El Atshan mine and uranophane and kasolite at El Erediya and El Missikat mining areas. These 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 bostonite sill cutting siltstones, and at El Erediya and El Missikat the host rocks are silica veins cutting granitic pluton in several shear zones. The occurrence of these secondary uranium minerals as idiomorphic crystals indicates episodic rather than continuous growth. Radiochemical method was used to separate uranium and thorium isotopes from other elements. These isotopes were measured by Alpha Spectrometry. At El Atshan and El Erediya, whereas the primary mineralization is pre-Tertiary, the secondary mineralization at both sites is dated using U-series methods at 80,000 to 140,000 years. At both sites adsorbed uranium in the host rock immediately below the secondary ores is shown to have been emplaced at I 0,000 to 60,000 years. These episodes of uranium mobilization seem to have resulted from groundwater saturation during humid oxygen isotope climatic