Redox and hydrodynamic controls on roll-front sandstone-type uranium mineralization: Insights from reactive transport modeling

Roll-front sandstone-type uranium deposits are important uranium resources worldwide, but their orebodies vary significantly in location, geometry and grade despite broadly similar redox-controlled mineralization processes. This variability is attributed to differences in redox conditions, uranium source availability and groundwater flow, yet how these geological factors control orebody variability under hydrodynamic regimes remains poorly constrained. This study is the first to use reactive transport modeling to reproduce the dynamic process of roll-front uranium mineralization and to evaluate the effects of different geological factors on uranium orebody formation. The modeling results demonstrate that the dynamic balance between the reducing capacity of host sandstones and the oxidizing capacity of fluids exerts primary control on the localization, geometry and lateral extent of roll-front orebodies. Both strongly reducing host sandstones and weakly oxidizing fluids can limit interlayer oxidation, favoring narrow, relatively high-grade roll-front orebodies near the recharge area. In contrast, weakly reducing host sandstones and more oxidizing fluids allow significant interlayer oxidation, producing larger but relatively lower-grade mineralized zones farther from the recharge area. The uranium concentration in the fluids and the pre-enriched uranium content of the host sandstones are positively correlated with ore grade and together exert a primary control on the formation of high-grade roll-front uranium orebodies. Groundwater flow rate also exerts a non-linear influence on uranium mineralization, with moderate flow rates most favorable for uranium dissolving in the oxidization zone and reprecipitation at the redox front. Extremely low flow rates limit oxidation-front advance, whereas high flow rates promote extensive oxidation. These findings help explain the geological controls on orebody localization, geometry, and grade variability in roll-front uranium systems and provide a quantitative framework to guide future exploration.