1. Source Characteristics of the Carboniferous Ortokarnash Manganese Deposit in the Western Kunlun Mountains.
- Author
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Zhang, Bang-Lu, Lv, Zhi-Cheng, Dong, Zhi-Guo, Zhang, Xin, Yu, Xiao-Fei, Li, Yong-Sheng, Zhen, Shi-Min, and Wang, Chang-Le
- Subjects
CARBONATE rocks ,STRONTIUM isotopes ,CHEMICAL weathering ,TRACE elements ,MANGANESE ,CONTINENTAL crust ,NEODYMIUM isotopes - Abstract
The specific source of ancient sedimentary manganese (Mn) deposits is commonly complex. Here we use systematic major and trace element data with strontium (Sr) and neodymium (Nd) isotopic analyses of the Ortokarnash Mn(II) carbonate ores and associated carbonate rocks from the Upper Carboniferous Kalaatehe Formation (ca. 320 Ma) in order to constrain the Mn source. This formation consists of three members: the first member is a volcanic breccia limestone, the second member is a sandy limestone, and the third member is a black marlstone with the Mn(II) carbonate interlayers. Petrographic observations in combination with low Al
2 O3 (<3.0 wt%) and Hf (<0.40 ppm) contents and the lack of correlations between the Al2 O3 and87 Sr/86 Sr ratios as well as εNd(t) values demonstrate a negligible influence of terrigenous detrital contamination on both Sr and Nd isotopic compositions of the Mn(II) carbonate ores. The Sr isotopes of Mn(II) carbonate ores are most likely affected by post-depositional alteration, while Nd isotopes remain unaltered. The initial87 Sr/86 Sr ratios in the associated carbonate rocks are likely the result of a mixture of the chemical components (i.e., seawater) and the Al-rich components (e.g., volcanoclastic material), while the detrital effects on Nd isotopes are negligible. In addition, both Sr and Nd isotopes in these non-mineralized wall rocks remained unchanged during post-depositional processes. The relatively low Th/Sc ratios and positive εNd(t) values suggest that the aluminosilicate fraction in the calcarenite and sandy limestone was mainly derived from the weathering of a depleted mafic source, representing the riverine input into the seawater. Given that the Mn(II) carbonate ores are characterized by negative εNd(t) values, these suggest that seafloor-vented hydrothermal fluids derived from interaction with the underlying old continental crust mainly contribute to the source of the Mn(II) carbonates. [ABSTRACT FROM AUTHOR]- Published
- 2022
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