Pb-Zn-Cu accumulation from seafloor sedimentation to metamorphism: Constraints from ore textures coupled with elemental and isotopic geochemistry of the Tiemurt in Chinese Altay Orogen,NW China |
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| Institution: | 1. GNS Science, PO Box 30-368, Lower Hutt, New Zealand;2. GEOMAR, Helmholtz Center for Ocean Research Kiel, Wischhofstrasse 1-3, 24148 Kiel, Germany;3. Institut für Geowissenschaften, Christian-Albrechts-Universität zu Kiel, Ludewig-Meyn-Strasse 10, 24118 Kiel, Germany;4. Department of Earth Sciences, Carleton University, 1125 Colonel By Drive, Ottawa, ON K1S5B6, Canada;5. National Institute of Water and Atmospheric Research, PO Box 14-901, Wellington, New Zealand;6. School of Geography, Environment and Earth Sciences, Victoria University of Wellington, PO Box 600, Wellington 6140, New Zealand;1. School of Earth Sciences and Geological Engineering, Key Lab of Geological Processes and Mineral Resource of Guangdong Province, Sun Yat-sen University, Guangzhou 510275, China;2. Key Laboratory of Crust and Orogen Evolution, Peking University, Beijing 100871, China;3. Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;4. Department of Earth Sciences, University of St. Andrews, North Street, St. Andrews KY16 9AL, UK;5. School of Earth and Environment, University of Western Australia, WA 6009, Australia |
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| Abstract: | The Tiemurt Pb-Zn-Cu deposit (metal reserve: 0.29 Mt (Pb + Zn) and 0.14 Mt Cu) is hosted in the Kangbutiebao Formation volcanic-sedimentary rocks in the Chinese Altay Orogen, NW China. Although some geological and geochemical characteristics of primary seafloor sedimentary mineralization are preserved, major fault-controlled Pb-Zn-Cu orebodies are adjacent to the Sarekbuobu orogenic gold deposit, and therefore it is also interpreted to be closely related to regional deformational-metamorphic processes. The seafloor sedimentary mineralization is evidenced by the occurrence of the banded ores and marine sulfate-originated sulfur isotopic compositions of the sulfides (bimodal δ34S values of 17.29–18.67‰ and ?25.03 to ?17.58‰). The lead isotope compositions accord with the evolution line of mantle, implying that the Pb were chiefly sourced from the mantle-reservoir. The later deformational and metamorphic overprinting are recorded by the fault-controlled lodes with ore textures of epigenetic infilling and replacement. Besides well-developed CO2-rich fluid inclusions, the D-O isotopic data of the overprinting fluids fall into the area between metamorphic fluids and meteoric water line, indicative of metamorphic fluids origin with meteoric water involvement. To further trace the Pb-Zn-Cu accumulation and remobilization processes, systematic in-situ trace elements in sulfides of different generations are analyzed using LA-ICP-MS. Ti-Mn-Cu-Pb-Zn-Bi concentrations in pyrite show a trend of progressive decrease from early to late generations. Similar decreasing trends of trace element concentrations are also present in sphalerite, galena, chalcopyrite and pyrrhotite, although the combinations of trace element are slightly different. This indicates that the ore-forming metals (esp. Cu, Pb and Zn) were initially locked up in the crystal lattice of the VMS sulfides (especially pyrite). Deformational and metamorphic processes of the primary ores during the Permian-Triassic collisional orogeny have likely led to trace element remobilization and sulfides purification, which redistributed the metals and upgraded the ores. Combined with previous studies, we proposed that the Pb-Zn-Cu of Tiemurt had been accumulated from seafloor sedimentation (ca. 400 Ma) to deformation-metamorphism processes (ca. 240 Ma). |
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