As a strategic mineral and energy resource, the enrichment and metallogenic mechanism of sandstone-hosted uranium deposits are highly dependent on hydrogeological conditions. However, the relationship between sandstone uranium mineralization and hydrogeological conditions has not received sufficient attention yet. The pumping test, hydrogeological parameters and hydrochemical characteristics were employed to analyze the change characteristics of hydrogeological conditions and evaluate the suitability of in situ leaching (ISL). The results showed that the study area in the Inner Mongolia Autonomous Region could be divided into two groundwater subsystems, namely Quanzha-Engeriyin and Luhai-Zhendai. The latter with relatively high water richness is confined and a main ore-bearing aquifer, which consists of four orebodies. The well discharge (Q) and hydraulic conductivity (K) of Orebody II ranged from 98.40 to 867.36 m³/d and 0.25 to 5.64 m/d, respectively, indicating the aquifer is suitable for the migration, enrichment and mineralization of uranium due to relatively high permeability and fast flow rate. The water storage of Orebodies III-IV gradually deteriorated from east to west in a stepped pattern. And the highest values of Q and K in Orebodies III-IV decreased from 1200 m³/d to 120 m³/d and 1.75 m/d to 0.035 m/d, respectively, suggesting these were conducive to a reduction in and accumulation of uranium under poor hydrodynamic conditions. Additionally, the study area would be defined as three grades, including favorable, relatively favorable and unfavorable areas of ISL according to a comprehensive evaluation. This study provided a scientific basis for evaluating the possibility of in situ leaching for sandstone-hosted uranium deposit.

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.