The mineralogical composition, textural characteristics, and uranium occurrence of sandstone-hosted uranium ores significantly influence the leaching performance during in situ recovery. This study investigates ore samples from the Zhenyuan uranium deposit, China, utilizing SEM, EPMA, XRD, and XRF to characterize their texture and mineralogy. Combined with thin-section leaching tests, batch stirring experiments, and pressurized column leaching experiments, the leaching behavior of pitchblende, associated gangue minerals, and the whole rocks were evaluated. The results indicate that: Uranium mainly occurs as nano-spherical and film-like pitchblende distributed along the edges of detrital grains and Ti-oxides. Minor uranium is incorporated into Ti-oxides and dolomite lattices via isomorphic substitution or adsorbed by chlorite. Under CO₂ + O₂ leaching conditions, pitchblende was almost completely dissolved, while U-bearing Ti-oxides experienced slight corrosion. Dolomite underwent partial dissolution, providing bicarbonate ions and improving rock permeability. Pyrite dissolution was limited during the early stage of leaching. The high dolomite content, low clay abundance, favorable pore structure, and easily leachable pitchblende suggest that the Zhenyuan deposit is well suited for CO₂ + O₂ in situ recovery. Increasing CO₂ pressure is recommended to enhance dolomite dissolution and improve uranium recovery efficiency.

Uranium occurrence and gangue mineralogy govern the choice of leaching process for sandstone-hosted uranium deposits. This study evaluates CO₂ + O₂ leaching of calcite-rich uranium ore from the Bayinqinggeli deposit in the northern Ordos Basin using mineralogical characterization, thin-section and agitated leaching experiments, and PHREEQC modeling. The dominant U–Si-bearing phase is interpreted as coffinite, although its mineralogical identification remains provisional in the absence of phase-specific structural and oxidation-state analyses. Thin-section observations revealed pronounced dissolution of exposed calcite and coffinite grains, but only minor surface corrosion of pyrite. Agitated leaching tests showed that increasing bicarbonate concentration improved uranium recovery, with diminishing gains above approximately 2 g/L. Calcite dissolution supplied bicarbonate, but equilibrium calculations indicated that the amount dissolved within a single pore-water volume was small relative to the calcite inventory. Thus, bicarbonate generation does not necessarily imply extensive liberation of encapsulated uranium minerals or a substantial increase in aquifer permeability. Pyrite oxidation may promote carbonate dissolution through acid generation, while also consuming oxygen and potentially producing pore-clogging precipitates. The results support further evaluation of CO₂ + O₂ recovery for this deposit. A modeled initial CO₂ dosage of 5 g/L produces approximately 2 g/L bicarbonate, and maintaining pressure in the surface processing circuit may limit CO₂ loss and calcite precipitation. These operating suggestions require validation under field flow and recirculation conditions.