沉积学报2026，Vol.44Issue(4)：1353-1368,16.DOI:10.14027/j.issn.1000-0550.2025.006
湘西民乐地区大塘坡组锰矿沉积氧化还原条件
Redox Conditions of Manganese Deposits in the Datangpo Formation,Minle Area,Western Hunan Province:Mineralogical and geochemical constraints
摘要
Abstract
[Objective]The western Hunan region hosts extensive Neoproterozoic marine sedimentary manganese de-posits.Manganese(Mn)is a typical redox-sensitive metallic element whose enrichment in sediments is strongly corre-lated with the redox condition of the bottom water in the basin.A detailed study of the sedimentary redox conditions of such deposits helps to explain their metallogenic mechanisms and the constraints on their marine cycling during the mineralization period,and also provides theoretical support for the assessment of regional mineralization potential.[Methods]This study involved mineralogical,geochemical and inorganic carbon isotope analyses of 16 manganese ore samples of various grades from the Nanhua System Datangpo Formation in the Minle area,western Hunan.[Results]Mineralogical and carbon isotope analyses revealed that high-grade(MnO>20%)and medium-grade(10%<MnO<20%)manganese ores consist of predominantly subhedral granular microcrystalline rhodochrosite(grain size<5 μm)and are relatively enriched in light carbon isotope(δ13C=-10.4‰～-8.3‰;n=10).Conversely,low-grade(MnO<10%)manganese ores contain larger-grained(>20 μm)subhedral platy rhodochrosite enriched in heavier carbon isotope(δ13C=-7.4‰～-5.3‰;n=6).Pyrite morphology and element geochemical proxies(Mo,V,Ni concentrations and Ni/Co,V/Cr ratios)indicate that the high-grade manganese ores were deposited in oxic condi-tions,the medium-grade ore in suboxic conditions,and the low-grade ore in anoxic conditions.Additionally,high-grade ores exhibit geochemical characteristics indicating hydrothermal deposition(e.g.,high Eu* values and high Fe/Ti ratios).[Conclusions]These findings suggest that,in the Minle area of western Hunan,the rhodochrosite in the medium-to high-grade manganese ores was formed as a result of the reaction between Mn oxides with organic matter during diagenesis,whereas in the low-grade manganese ores the rhodochrosite was probably precipitated from Mn2+and CO2-3 in highly alkaline and anoxic conditions.Submarine gas-hydrothermal activity in the deep-water basin of northeastern Guizhou most likely supplied the Mn2+ions for these manganese deposits;oxidation of bottom water in the basin was the key factor determining manganese enrichment and mineralization in the region.关键词
新元古代/沉积型锰矿/氧化还原指标/碳同位素/热液活动Key words
Neoproterozoic/sedimentary manganese deposits/redox proxies/carbon isotope/hydrothermal activity分类
天文与地球科学引用本文复制引用
王勇,文春华,谭静强,曹创华,丁永刚,曾广乾,王灵珏,谢文泉,黄乐清..湘西民乐地区大塘坡组锰矿沉积氧化还原条件[J].沉积学报,2026,44(4):1353-1368,16.基金项目
国家重点研发计划(2017YFC0601506) （2017YFC0601506）
湖南省自然资源厅科技计划(HBZ20240128) National Key Research and Development Project,No.2017YFC0601506 （HBZ20240128）
Research Foundation of the Department of Natural Resources of Hunan Province,No.HBZ20240128 （）
