Late Cretaceous granitoids are developed in the eastern and western districts of the Gejiu ore district, but tin deposits mainly occur in the eastern district, and the reasons for the difference in mineralization between the eastern and western districts are still controversial. Considering the main factors controlling granite Sn fertility, the whole-rock geochemical characteristics of granites on both sides are compared. LA-ICP-MS zircon U-Pb analyses of the Gejiu granites yielded two age periods: the early phase from 79.2 to 83.3 Ma and the later phase from 73.8 to 75.6 Ma. The western district granites have higher zircon ε_Hf(t), CaO/Na₂O, Ba, and Sr concentrations and lower Rb/Sr ratios than the eastern district granites, indicating that the western district granites have more mantle-derived materials in the source than the eastern district granites. Results of oxygen fugacity show that the western granites have a higher oxygen fugacity condition. More depleted Ba, Sr, P, Eu and Ti characteristics with obviously negative Eu anomalies in the eastern granites also have high Rb/Sr ratios and low Nb/Ta and Zr/Hf ratios, indicating that the eastern granites experienced highly magmatic differentiation, attributed to high volatile F contents that can reduce the viscosity and solidus of magma. Combined with the differences in field observations and structural styles, on the whole, the western district granites have higher oxygen fugacities and lower F contents and magmatic differentiation than those in the eastern district granites, indicating that the western district granites are not conducive to mineralization.

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.