湘南地区东湘桥沉积型锰矿床地球化学特征及成矿机理OA北大核心CSTPCD

The Permian marine sedimentary manganese deposits are widely developed in the southern Hunan region.In order to reveal the ore-forming processes and mechanisms,this study focuses on the sedimentary profile of the Dongxiangqiao manganese deposit in Yongzhou,Hunan Province.Major and trace elements,as well as carbon-oxygen isotopes,were analyzed.The results indicate that the manganese-rich rock layers enrich in elements such as Cr,Ni,Co.The ratios of Co/Zn,Mn/Fe,and Y/Ho,along with interpretations from multiple discriminant dia-grams,collectively indicate that the ore deposit is a hydrothermal deposit,suggesting that the ore-forming materi-al,manganese(Mn),primarily derived from seafloor hydrothermal fluid.The analysis results of sedimentary re-dox indicators,such as the enrichment factor of Mo and U(MoEF and UEF),as well as U/Th and V/(V+Ni)ratios,indicate that the layers of high-grade manganese ores were formed in the context of the transition from oxic to an-oxic conditions.In contrast,low-grade manganese-bearing rock layers were mainly formed in oxic or strongly anoxic conditions.The δ 13 CPDB(-0.2‰～1.9‰)and δ18 OSOMW(18.1‰～23.1‰)values of the manganese-rich rock layers,similar to marine carbonate rocks,suggest that the sources of ore-forming materials C and O are pri-marily derived from seawater.Based on these results,this study proposes that the ore-forming process of the Dongxiangqiao manganese deposit is controlled by both seawater CO 2-3 concentration and sedimentary redox conditions.The ore-forming process can be summarized infollowing two stages:① Hydrothermal Mn in deep-water basins migrates towards nearshore CO 2-3 supersaturated shallow-water platforms under reducing condi-tions;②When the sedimentary environment transitions from oxic to anoxic conditions,manganese oxides at the sediment/water interface are reduced to release Mn2+,significantly increasing the dissolved Mn concentration in the water column,promoting the precipitation of manganese-rich carbonate minerals,and forming high-grade manganese ores.