GEOCHEMISTRY AND CHEMICAL DATING OF URANINITE IN THE JADUGUDA URANIUM DEPOSIT, SINGHBHUM SHEAR ZONE, INDIA-IMPLICATIONS FOR URANIUM MINERALIZATION AND GEOCHEMICAL EVOLUTION OF URANINITE

摘要

The Jaduguda uranium deposit in the Singhbhum shear zone is the most important and best-known uranium deposit in India. Uranium mineralization is hosted in hydrothermally altered, metamorphosed, and deformed chlorite and biotite schists. Uraninite is the most abundant and ubiquitous U ore mineral in the shear zone, including the deposit at Jaduguda. The deposit is known to have undergone multiple events of hydrothermal fluid flux. Integrating chemical texture, geochemistry, and in situ electron microprobe U-Th-Pb chemical dating, we aim at deciphering the geochemical and temporal evolution of uranium mineralization in the Jaduguda deposit. Geochemistry of uraninite and X-ray mapping of selected elements demonstrate that, though compositions of small uraninite grains (～10 μm) were mostly or completely modified by subsequent hydrothermal alteration, the larger grains (～100 μm) locally retain the footprints of the earlier events and capture the imprints of subsequent events. In general, all analyzed uraninite grains are poor in Th (<2.5 wt % ThO_2) and most grains contain detectable rare earth elements (REEs; ΣREE_2_O3: ～1.0-～12.5 wt %). Y and heavy rare earth elements (HREEs) are ubiquitous and most important in terms of concentrations.