Uranium mineralization in the Zhiluo Formation of the Saitai area preferentially occurs in carbonaceous debris- and pyrite-rich sandstones. This study characterizes ore fluid and reducing medium controls on uranium enrichment and uranium mineral genesis using core observations, SEM, EPMA, and geochemical tests. Uranium minerals mainly form zoned aggregates around carbonaceous debris, occur with colloform pyrite within feldspar and carbonate dissolution pores, and appear within zones of biotite breakdown. Whole-rock geochemical data from ore-bearing sandstone show variations: U(IV)/U(VI) (0.625–34.78; corresponding to U(IV)/total U of 0.38–0.97), Ce/Ce* (0.72–1.01), Fe²⁺/Fe³⁺ (0.70–92.35; Fe²⁺/total Fe of 0.41–0.99), TOC (0.026–3.35%), total sulfur (0.1–0.3%), and S²⁻ (3.4 × 10⁻⁶–83.3 × 10⁻⁶). Fluid inclusions in calcite cements show homogenization temperatures of 130–183 °C, and those hosted in intergranular calcite cluster at 130–138 °C, with salinities of 0.9–9.5 wt.% NaCl equivalent and CO₂-bearing characteristics. Mineralization of the Zhiluo Formation developed in a medium–low temperature, reducing alkaline environment. Carbonaceous debris shows close spatial and genetic links with uranium minerals. Authigenic pyrite correlates with uranium through paragenetic association with carbonaceous fragments. Alkaline fluid dissolution provides pore space for uranium and secondary pyrite precipitation.