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Creators/Authors contains: "Hummer, D_R"

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  1. Abstract 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 (wMEECV) values of U6+minerals increases through time, particularly during the Phanerozoic. Conversely, the range of wMEECVvalues 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. 
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