A Comparative Study of the Geochemical Characteristics and Genetic Mechanisms of Sedimentary Manganese Deposits from the Permian and Nanhua Periods in Hunan Province

Abstract

This study presents a comparative geochemical and mineralogical investigation of two representative sedimentary manganese deposits in Hunan Province, China: the Datangpo Formation deposit in Xiangtan and the Gufeng Formation deposit in southern Hunan. The Shuibutou deposit (Gufeng Formation) is hosted in carbonate rocks and is dominated by Mn-bearing calcite, exhibiting near-zero δ13Ccarb values (−0.13‰ to 0.95‰), positive Y anomalies, high Y/Ho ratios (average 36.19), and enrichment in redox-sensitive elements (average MoEF = 88.5; average UEF = 19.7), together with abundant framboidal pyrite (<8 μm), and these features are consistent with formation under an anoxic environment via direct precipitation of manganese carbonates. In contrast, the Xiangtan Datangpo deposit is hosted in black shales and characterized by rhodochrosite, negative δ13Ccarb values (−7.43‰ to −5.79‰), pronounced positive Ce anomalies, and low concentrations of redox-sensitive elements (e.g., low Mo/Al, U/Al ratios), suggesting initial Mn oxide precipitation under oxic conditions followed by diagenetic transformation. Based on these differences, two distinct metallogenic models are proposed: (1) a two-stage process involving Mn oxide precipitation and subsequent diagenetic reduction for the Datangpo deposit, and (2) direct precipitation of manganese carbonates in an anoxic water column for the Shuibutou deposit. Although both formed in fault-controlled rift basins under extensional settings, their contrasting redox conditions led to fundamentally different mineralization pathways. These findings provide new insights into the genetic diversity of sedimentary manganese deposits and have important implications for mineral exploration.