Geochemical Characteristics of the Shuibutou Sedimentary Manganese Deposit in Southern Hunan Province, South China

Permian marine sedimentary manganese deposits occur extensively across southern Hunan Province, South China, yet their ore-forming material sources and metallogenic mechanisms remain poorly constrained. This study focuses on the Permian marine sedimentary large-scale Shuibutou manganese deposit in Yongzhou, and presents an integrated investigation incorporating mineralogical observations, whole-rock major and trace element geochemistry, and carbonate carbon–oxygen isotope analyses on representative manganese ore samples. Mineralogical results show that the manganese ores are dominated by Mn-rich calcite. Systematic geochemical proxies, including Co/Zn, Mn/Fe and Y/Ho ratios, combined with classic ternary discrimination diagrams (Co–Ni–Zn) and [Mn–Fe–(Co+Ni+Cu)×10], consistently indicate a hydrothermal origin, implying that dissolved Mn²⁺ was mainly sourced from submarine hydrothermal fluids. Redox-sensitive element (Mo, U) enrichments, Ce anomalies, and widespread framboidal pyrite collectively demonstrate that the manganese ores were deposited under anoxic bottom-water conditions. In addition, the carbon and oxygen isotopic compositions of the manganese ores match well with those of typical marine carbonates, indicating a seawater source for carbon and oxygen. Integrating these lines of evidence, we propose a metallogenic mechanism whereby hydrothermally derived Mn²⁺ was transported from a deep-water basin via anoxic plumes to a shallow intra-platform depression. In this high-alkalinity water mass, dissolved Mn²⁺ reacted with dissolved HCO₃⁻ to precipitate Mn-rich calcite directly. This metallogenic mechanism is likely common to Middle Permian marine manganese deposits across South China.