Uranium redox and deposition transitions embedded in deep-time geochemical models and mineral chemistry networks

Uranium (U) is an important global energy resource and a redox sensitive trace element that reflects changing environmental conditions and geochemical cycling. The redox evolution of U mineral chemistry can be interrogated to understand the formation and distribution of U deposits and the redox processes involved in U geochemistry throughout Earth history. In this study, geochemical modeling using thermodynamic data, and mineral chemistry network analysis are used to investigate U geochemistry and deposition through time. The number of U⁶⁺ mineral localities surpasses the number of U⁴⁺ mineral localities in the Paleoproterozoic. Moreover, the number of sedimentary U⁶⁺ mineral localities increases earlier in the Phanerozoic than the number of U⁴⁺ sedimentary mineral localities, likely due to the necessity of sufficient sedimentary organic matter to reduce U⁶⁺–U⁴⁺. Indeed, modeling calculations indicate that increased oxidative weathering due to surface oxygenation limited U⁴⁺ uraninite (UO₂) formation from weathered granite and basalt. Louvain network community detection shows that U⁶⁺ forms minerals with many more shared elements and redox states than U⁴⁺. The range of weighted Mineral Element Electronegativity Coefficient of Variation (wMEE_CV) values of U⁶⁺ minerals increases through time, particularly during the Phanerozoic. Conversely, the range of wMEE_CV values of U⁴⁺ minerals is consistent through time due to the relative abundance of uraninite, coffinite, and brannerite. The late oxidation and formation of U⁶⁺ minerals compared to S⁶⁺ minerals illustrates the importance of the development of land plants, organic matter deposition, and redox-controlled U deposition from ground water in continental sediments during this time-period.