湘西民乐地区大塘坡组锰矿沉积氧化还原条件——来自矿物学和地球化学特征的约束
- 收稿日期:
2024-09-10
- 网络出版日期:
2025-03-13
摘要: 【目的】湘西地区广泛发育新元古代海相沉积型锰矿床，深入研究这些锰矿的沉积氧化还原条件有助于揭示其成矿机理，约束成矿期海洋锰循环过程，为区域成矿潜力评估提供理论支撑。【方法】本文对湘西民乐地区南华系大塘坡组的16件不同品位锰矿样品开展了矿物学、元素地球化学和无机碳同位素分析。【结果】矿物学和碳同位素分析显示：高品位（MnO>20%）和中等品位（1020μm）半自形板片状菱锰矿为主，相对富集重的碳同位素（δ13C=-7.4‰~-5.3‰）。黄铁矿形貌和元素地球化学指标分析显示：高品位锰矿沉积于氧化环境，中等品位锰矿沉积于贫氧环境，而低品位锰矿沉积于缺氧环境。此外，高品位锰矿具有高Eu*值和高Fe/Ti比值等热液沉积地球化学特征。【结论】中-高品位锰矿中菱锰矿由初始沉淀的锰氧化物在成岩过程中与有机质反应形成；低品位锰矿中的菱锰矿则可能是在高碱度条件下，水体中Mn2+与CO32-直接结合形成。黔东北深水盆地的气-热液喷溢活动可能为湘西地区锰矿床形成提供了Mn2+来源，而盆地底水氧化则是该地区锰富集成矿的关键控制因素。
Redox conditions of manganese deposits in Datangpo Formation, Minle Area, western Hunan Province: constraints from mineralogy and geochemistry
- Received Date:
2024-09-10
- Available Online:
2025-03-13
Abstract: [Objective] Manganese (Mn), as a typical redox-sensitive metal element, shows a strong correlation between its enrichment in sediments and the redox conditions of the bottom water in basin. The western Hunan region hosts extensive Neoproterozoic marine sedimentary manganese deposits. A detailed study of the sedimentary redox conditions of these manganese deposits aids in elucidating their metallogenic mechanisms, constraining the marine manganese cycling during the mineralization period, and providing theoretical support for regional mineralization potential assessments. [Methods] This study involved mineralogical, geochemical, and inorganic carbon isotope analyses of 16 manganese ore samples of varying grades from the Datangpo Formation of the the Nanhua System from the Minle area in western Hunan. [Results] Mineralogical and carbon isotope analyses reveal that high-grade (MnO>20%) and medium-grade (1020 μm) subhedral platy rhodochrosite, with relative enrichment 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 high-grade manganese ore layers were deposited in an oxic condition, medium-grade manganese ore layers in a suboxic condition, and low-grade manganese ore layers in an anoxic condition. Additionally, high-grade manganese ores exhibit geochemical characteristics indicative of hydrothermal deposition, such as high Eu* values and high Fe/Ti ratios. [Conclusions] These findings suggest that rhodochrosite in medium- to high-grade manganese ores formed through the reaction of manganese oxides with organic matter during diagenesis, while the rhodochrosite in low-grade manganese ores likely precipitated from Mn2+ and CO32- under high alkalinity and anoxic conditions in the Minle area of western Hunan. The submarine gas-hydrothermal activity in the deep-water basin of northeastern Guizhou likely supplied Mn2? for manganese deposit in western Hunan, while the oxidation of bottom water in the basin was the key controlling factor for manganese enrichment and mineralization in the region.
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——来自矿物学和地球化学特征的约束[J]. 沉积学报. doi: 10.14027/j.issn.1000-0550.2025.006
Redox conditions of manganese deposits in Datangpo Formation, Minle Area, western Hunan Province: constraints from mineralogy and geochemistry[J]. Acta Sedimentologica Sinica. doi: 10.14027/j.issn.1000-0550.2025.006
| Citation: |
Redox conditions of manganese deposits in Datangpo Formation, Minle Area, western Hunan Province: constraints from mineralogy and geochemistry[J]. Acta Sedimentologica Sinica. doi: 10.14027/j.issn.1000-0550.2025.006
|
点击查看大图
下载:
