二叠纪茅口晚期锰矿成矿作用的地球化学约束--以遵义市南茶锰矿为例

遵义锰矿是我国二叠纪时期一种重要的锰矿类型。南茶锰矿床是近年来在遵义锰矿区发现的又一中型隐伏锰矿床，是遵义锰矿的典型代表。南茶锰矿含锰岩系的微量元素、稀土元素、碳同位素研究结果表明:南茶锰矿成锰期前样品V/（V+Ni）值在0.6与0.65之间或与0.60接近，V/Cr值在0.71~2.05之间，均值为1.34，Ce呈中等程度的负异常，说明该期沉积环境属贫氧环境；成锰期样品V/（V+Ni）值接近0.45，V/Cr值为0.28、1.30，Ce呈轻微的负异常，反映此时属氧化-贫氧的沉积环境；成锰期后样品中，V/（V+Ni）值则介于0.65~0.88，均值为0.76，大部分样品V/Cr值>4.18，Ce呈轻微的正异常，说明成锰期后可能处于缺氧环境；含锰岩系δEu值均显示为弱的正Eu异常（成锰期前、成锰期以及成锰期后Eu/Eu*均值分别为0.88、1、0.85），反应含锰岩系沉积时期受到热水作用的影响较弱；锰碳酸盐岩地层的碳同位素具有一次明显的负偏，至锰矿层达最低（-12.5‰ V-PDB），显示与有机质的降解有关。综上所述，南茶锰矿的形成经历了前期氧化锰沉淀和之后氧化锰沉淀被还原形成碳酸锰的过程。

Geochemical Constraints on the Manganese Mineralization during the Latest Maokou Epoch of Permian——Example from the Nancha manganese ore deposit in Zunyi city,northern Guizhou

The manganese ore deposit in Zunyi is one of the important types of manganese ore deposits in the Permian in China. The Nancha manganese ore deposit is a medium-scale subtle one found in the manganese ore zone of Zunyi area in recent years, and is the representative of the Zunyi-type manganese ore deposits. Trace element, rare earth element, and carbon isotope geochemical studies on manganese-bearing rock in Nancha manganese ore deposit show that samples predating Mn-ore deposition have V/(V+Ni) ratios between 0.6 and 0.65 (close to 0.60),and V/Cr ratios from 0.71 to 2.05 (avg. 1.34), as well as moderate Ce negative anomalies, indicating a dysoxic water condition under which they were deposited. The samples of Mn-ore deposits yield V/(V+Ni) ratios close to 0.45, and V/Cr ratios between 0.71 and 2.05, as well as weak Ce negative anomalies, pointing to an oxic to dysoxic condition. Those samples postdating the Mn-ore deposition have V/(V+Ni) ratios between 0.65 and 0.85 (avg. 0.76), and V/Cr ratios of > 4.18 mostly, as well as slightly Ce positive anomalies, suggesting an anoxic to dysoxic condition. The δEu values range mostly between 0.50 and 1.00, indicative of a weak influence of hydrothermal activity. Carbon isotope data reveal an obvious negative excursion across the Mn-bearing succession, reaching the nadir in the manganese ore horizon (-12.5‰ V-PDB), indicative of organic involvement likely associated with organic decaying. Therefore, the Nancha manganese ore deposit was initially precipitated as manganese (hydro-)oxides in the oxic water condition, which were reduced to Mn2+ and subsequently combined with CO₃2- to form the carbonate manganese ore deposit (MnCO₃) below the sediment-water interface while the redox interface was gotten rising due to the sea-level rise (or transgression).