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

Abstract

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.