Geochemistry of Surficial Uranium Deposits from Central Jordan

Inhomogeneous unusual surface uranium mineralization hosted by chalk marl/travertine and calcrete/top soil covers large areas in central Jordan. Quarries and trenches with bituminous marl, varicolored marble, travertine and caliche were sampled to understand the geochemistry of the uranium deposits. The samples were characterized mineralogically and chemically using XRD, XRF, SEM, EDX techniques. Relatively high uranium concentrations were found in the calcrete samples where it reaches up to 419 ppm. The secondary uranium mineralization is restricted to the permeable fractured and porous zones. The combustion of the bituminous marl led to the formation of the varicoloured marble in central Jordan. This was followed by the action of circulating highly alkaline water that accelerated the leaching of the redox sensitive trace elements as U and V. Such an alkaline oxidizing environment (pH~12.7) is currently active in Maqarin area, north Jordan. The paleo-circulating water in the combusted rocks of central Jordan oxidized the dissolved V4+ to V5+ and fixed the uranyl-ion as uranyl vanadate. Strelkinite and/or tyuyamunite precipitation and the solid solution, between the two end members, were dependent on the Ca/Na ratio in solution. Carnotite is restricted to the veins associated with the varicoloured marble. The uranyl-vanadate minerals were precipitated from highly alkaline solutions during the dry periods after the precipitation of the thick travertine deposits.