投稿时间：2023-12-17
修订日期：2024-03-15
网络发布日期：2024-04-25
中文摘要:湘南地区广泛发育二叠纪海相沉积型锰矿，为揭示其成矿过程及机理，文章以湖南永州东湘桥锰矿床沉积剖面为研究对象，对其开展主、微量元素和碳-氧同位素分析。结果表明，富锰岩层富Cr、Ni、Co等元素的地球化学特征，其Co/Zn、Mn/Fe、Y/Ho比值和多判别图解共同指示该矿床为热液沉积，表明成矿物质Mn主要来源于海底热液。Mo和U元素富集因子（MoEF和UEF）、U/Th和V/（V+Ni）比值等沉积氧化还原指标分析结果表明，高品位锰矿石层产于氧化向缺氧转变的背景下，而低品位含锰岩层则主要产于氧化或强烈缺氧环境下。富锰岩层的δ13CPDB（-0.2‰~1.9‰）和δ18OSOMW（18.1‰~23.1‰）与海相碳酸盐岩相似，表明成矿物质的C和O主要来源于海水。基于上述结果，笔者认为东湘桥锰矿床成矿过程受海水CO23-浓度和沉积氧化还原条件的双重控制，其成矿过程可以概况为2个阶段：①深水盆地的热液Mn在还原条件下以可溶Mn2+向近岸CO23-过饱和的浅水台地迁移；②当沉积环境由氧化向缺氧转变时，锰氧化物在沉积/水界面还原释放Mn2+，显著提高水柱中溶解Mn浓度，促进富锰碳酸盐矿物析出，形成高品位锰矿石。
Abstract: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 diagrams, collectively indicate that the ore deposit is a hydrothermal deposit, suggesting that the ore-forming material, manganese (Mn), primarily derived from seafloor hydrothermal fluid. The analysis results of sedimentary redox 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 anoxic conditions. In contrast, low-grade manganese-bearing rock layers were mainly formed in oxic or strongly anoxic conditions. The δ13CPDB (-0.2‰~1.9‰) and δ18OSOMW (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 primarily 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 CO23- 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 CO23- supersaturated shallow-water platforms under reducing conditions; ② When 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.
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基金项目:本文得到湖南省地质院科研项目（编号：HNGSTP202402）和国家自然科学基金项目（编号：42073001、42372105）联合资助
引用文本：
廖凤初,刘湘华,徐军伟,熊伊曲,李斌,赖健清,骆检兰,陈雨林,罗益周,王勇.2024.湘南地区东湘桥沉积型锰矿床地球化学特征及成矿机理[J].矿床地质,43(2):289~303LIAO FengChu,LIU XiangHua,XU JunWei,XIONG YiQu,LI Bin,LAI JianQing,LUO JianLan,CHEN YuLin,LUO YiZhou,WANG Yong.2024.Geochemical characteristics and metallogenic mechanism of Dongxiangqiao sedimentary manganese deposit in southern Hunan Province[J].Mineral Deposits43(2):289~303
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