Implication of the Precipitation Mode of Manganese and Ultra-High δ34S Values of Pyrite in Mn-Carbonate of Xixibao Mn Ore Deposit in Northeastern Guizhou Province
详细信息
- 责任者：Zhang Feifei (Laboratory of Isotope Geology ; MLR ; Institute of Geology ; CAGS ; Beijing 100037 ; China) ; Zhu Xiangkun
- 刊名：Geological Review
- 出版年：2013
- 卷期：59(2)
- 关键词：锰矿 ; manganese ores ; 硫同位素 ; sulfur isotopes ; 贵州 ; Guizhou Province
- 页码：p.274-286
- 图表：illus., 3 tables, 79 refs.
- 分类号：1001
- issnNo：ISSN0371-5736
- isbnNo：CN11-1952/P
摘要
Here, in an effort to explore the precipication mode of manganese and the possible cause for ultrahigh δ34S values for pyrite in the manganese carbonate series deposited during Nanhuan (Cryogenian) period , we present results for elements analyses of Mn ores, coupled with trace elements and sulfur isotope of pyrite, in the basal of the Neoproterozoic Cryogenian (Nanhuan) Datangpo Formation, deposited between the two major Neoproterozoic glacial episodes (Sturtian and Marinoan), in South China. REE and trace elements characteristics indicate Mn was precipitated as Mn oxides or hydroxide, following transformation of manganese-oxide or manganese-hydroxide into rhodochrosite during diagenesis is responsible for the formation of Datangpo-type manganese carbonate ore deposit. The morphology, trace elements and REE characteristics of pyrite suggeset pyrite formed during early diagenesis in an anoxic and sub-alkalinity diagenetic environment as suggested by trace elements and REE characteristics of pyrite. Ultra-high δ34S values of pyrite suggest low sulfate concentration and high BSR rates in the deep Cryogenian ocean, which means Cryogenian deep ocean was not "oxidized" in the early stage of the Datangpo interglacial interval. Two possible mechanism would contribute ultra-high δ34S values for pyrite in the basal of the Datangpo Formation: very low sulfate concentrations in deep water with δ34S values for sulfate as high as 58.7‰ is the most likely reason to cause untra-high δ34S values for pyrite , low sulfate concentrations and high δ34S values, but not as high as 58.7‰, of sulfate in the deep ocean, coupled with the isotopic fractionation during disproportionation reaction between FeS(the precursor for pyrite formation)and MnO2 is another possible reason.
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