Geochemical Characteristics of Sandstone-Type Uranium Deposits and Their Significance for Uranium Mineralization in Daqing Placanticline, Northern Songliao Basin

To reveal the uranium enrichment mechanism in the Daqing Placanticline area, northern Songliao Basin, this study collected a total of 41 samples of three geological types, namely uranium ore, uranium-mineralized sandstone and host rock from the Upper Cretaceous Sifangtai Formation. Combined with 109 geochemical datasets from exploration, systematic analyses were performed on major elements, trace elements, rare earth elements (REE), total organic carbon (TOC), total sulfur and other key geochemical parameters. The results indicate that uranium ore and mineralized sandstone are generally characterized by high TOC, high total sulfur, low Th/U and low Fe2O3/FeO ratios, while host rocks show the opposite geochemical assemblage, suggesting uranium enrichment took place in a strongly reducing sedimentary environment. The ore-forming system is significantly enriched in trace elements including U, Pb, Mo, Ba, Zn and Y, and depleted in Cu, Co, Ni, Cr, Sr, Nb, Ta, Zr and Hf. Among these elements, Mo and Pb have an extremely close relationship with uranium mineralization and can be used as effective ore-forming indicator elements. Uranium ore, mineralized sandstone and host rock exhibit consistent REE distribution patterns, implying that the strata in the study area share uniform provenance, sedimentary environment and tectonic setting. Some high-grade uranium ores are obviously enriched in heavy rare earth elements (HREE), demonstrating fluid modification during the late mineralization stage. Combined with regional tectonic evolution and hydrocarbon migration features, this study concludes that sandstone-type uranium deposits in the Daqing Placanticline mainly underwent two stages of mineralization: supergene fluid mineralization and superimposed reworking by deep hydrocarbon-bearing reducing fluids.