Mineralogy and geochemistry of carbonate cement in sandstone and implications for mineralization of the Qianjiadian sandstone-hosted uranium deposit, southern Songliao Basin, China

摘要

Morphology, concentration, paragenetic sequence, fluid inclusion, and trace element concentrations of carbonate cements in sandstone from the Qianjiadian sandstone-hosted uranium deposit, southern Songliao Basin, are illustrated in order to reveal the properties of ore-forming fluids and the effects of hydrothermal fluids on uranium mineralization. The carbonate cements contain dolomite, siderite, ankerite and calcite. Dolomite with a crystalline granular texture has the greatest average concentration, forming up to 3.3% of the yellow sandstone, and this dolomite has orange red cathodoluminescence. Siderite forms up to 2.7% of the primary grey sandstone, and everywhere forms grains with an idiomorphic shape. Ankerite forms up to 6.6% of the mineralized grey sandstone and commonly have a mosaic granular structure. Calcite characterized by mosaic granular texture reaches the maximum level of average concentration of 10.2% in the non-mineralized grey sandstone, and its cathodoluminescence is orange. Studies of mineral paragenetic sequence indicate that the dolomite, siderite, ankerite and calcite are chronologically generated. Average homogenization temperatures of the fluid inclusions in the ankerite and calcite are 160 degrees C and 136 degrees C, respectively, and their average salinities are 9.9 wt% and 7.7 wt%, respectively. The uranium content of the ankerite is up to 11.8 ppm, which is greater than that of the other carbonate cement. This study indicates that the ankerite is associated with uranium mineralization, and the Qianjiadian sandstone-hosted uranium deposit could be mobilized by low-temperature, high-salinity hydrothermal fluids, which can lead to formation of brannerite and coffinite.