SULFUR AND URANIUM MINERAL CHEMISTRY NETWORKS REVEAL DIVERGENT REDOX EVOLUTION

The redox sensitive elements sulfur (S) and uranium (U) reflect changing environmental conditions as well as having numerous mineral species in which the oxidation state is unknown. Uranium is an important energy resource while S is important in energy resource formation. Here, we use mineral chemistry network analysis and the weighted Mineral Element Electronegativity Coefficient of Variation (wMEE_CV) metric to investigate the interactions of mineral constituent elements within each mineral species and localities of S-containing minerals and U-containing minerals from the Mineral Evolution Database (MED). This analysis allows further understanding of mineral formation by inferring the redox state of S and U in minerals where it was previously unknown (S^U, U^U). Louvain community detection of the separate S and U mineral chemistry networks show that network communities are strongly influenced by redox state for both elements. The distribution of wMEE_CV values indicate that S^U minerals typically contain reduced S (S^2- or S₂^2-), while U^U minerals contain U⁶⁺. The predicted redox states of S^U and U^U indicate that the number of localities of reduced S minerals are underestimated, and the number of localities of oxidized U minerals are also underestimated. The wMEE_CV values of S⁶⁺ minerals and U⁶⁺ minerals expand through time, coinciding with atmospheric and lithospheric oxidation from the late Proterozoic to Phanerozoic. The relative abundance of oxidized U⁶⁺ mineral localities increased much later during the Phanerozoic than oxidized S⁶⁺ mineral localities, indicating that S⁶⁺ was generated from oxidative weathering prior to U⁶⁺ partly because of the higher redox potential of the U⁶⁺/U⁴⁺ pair versus the S⁶⁺/S^2- pair. The late oxidation and formation of U⁶⁺ minerals illustrates the importance of land plant evolution and redox-controlled U deposition from ground water in continental sediments. While U deposition was impacted by organic matter, the prevalence S^2- deposition played an important role in organic matter diagenesis during the Phanerozoic.