Relations of Uranium Enrichment and Metal Sulfides within the Shuanglong Uranium Deposit, Southern Ordos Basin

Large quantities of metal sulfides are widely distributed in uranium ores from the Middle Jurassic Zhiluo Formation of the Shuanglong uranium deposit, southern Ordos Basin, providing a convenient condition to study the relationship between metal sulfides and uranium minerals. The morphology and composition of uranium minerals and metal sulfides are illustrated to study uranium mineralization and mechanisms of metallogenesis. Uranium minerals can be broadly categorized as pitchblende, coffinite and brannerite. Metal sulfides associated with uranium minerals are pyrite, sphalerite, chalcopyrite and galena. Some assemblages of various metal sulfides and uranium minerals indicate that they are coeval, but the order of formation is different. Based on mineralogical observations, paragenetic sequences for mineral assemblages are discussed. Alteration of Fe-Ti oxides forms Ti oxides, brannerite and pyrite. The formation of chalcopyrite was later than that of pyrite. Clausthalite (PbSe) replaces sphalerite or shows isomorphism with galena. There are three genetic types of galena, of which type I is related to tectonic thermal events and can interact with uranyl ions to form uranium oxides and Pb2+. When sulfur activity is relatively high, Pb2+ can form new anhedral galena, that is, type II. Type III of galena is related to the decay of uranium minerals. The genetic order of the main minerals was determined as follows: Fe-Ti oxides>Ti oxides/sphalerite/pyrite>clausthalite/galena I/chalcopyrite>galena I /uranium minerals>galena m during the diagenetic stage. Hydrogen sulfide (H2S) is a decisive factor in the interaction between metal sulfides and uranium. Metal ions can react with H2S, accompanied by precipitation and enrichment of uranium minerals.