Sulfur and lead isotopic compositions of massive sulfides from deep-sea hydrothermal systems: Implications for ore genesis and fluid circulation |
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| Institution: | 1. Seafloor Hydrothermal Activity Laboratory of the Key Laboratory of Marine Geology and Environment, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China;2. Laboratory for Marine Mineral Resources, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266071, China;3. University of Chinese Academy of Sciences, Beijing 100049, China;4. Qingdao Collaborative Innovation Center of Marine Science and Technology, Qingdao 266071, China;5. Department of Earth Sciences, University of Durham, Durham DH1 3LE, UK;1. Institute for Geology and Mineral Resources of the Ocean (VNIIOkeangeologia), Angliysky Avenue 1, 190121 St. Petersburg, Russia;2. St. Petersburg State University, 7/9 Universitetskaya nab., 199034 St. Petersburg, Russia;3. Polar Marine Geosurvey Expedition, Pobedy Str. 24, Lomonosov, 198412 St. Petersburg, Russia;1. Key Laboratory of Submarine Geosciences, Second Institute of Oceanography, State Oceanic Administration, Hangzhou 310012, China;2. China Ocean Exploration Technology and Geosciences R&D Base, State Oceanic Administration, Hangzhou 310012, China;3. GEOMAR, Helmholtz Centre for Ocean Research Kiel, 24148 Kiel, Germany;1. School of Marine Science and Policy, College of Earth Ocean and Environment, University of Delaware 700 Pilottown Road, Lewes, DE 19958, United States;2. Department of Chemistry and Biochemistry, University of South Carolina, 631 Sumter Street Columbia, SC 29208, United States |
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| Abstract: | Studies of sulfur and lead isotopic compositions in hydrothermal deposits are an important tool to determine the source and processes of both sulfur and lead, and to understand the origin of hydrothermal ore deposits. Here, the sulfur and lead isotopic compositions of sulfide minerals have been studied for different hydrothermal fields in the East Pacific Rise (EPR), Mid-Atlantic Ridge (MAR), Central Indian Ridge (CIR), Southwest Indian Ridge (SWIR), and North Fiji Basin (NFB). The sulfur isotopic compositions of the studied sulfide samples are variable (δ34S 0.0 to 9.6‰, avg. δ34S 4.7‰; n = 60), being close to the associated igneous rocks (~ 0‰ for, e.g., basalt, serpentinized peridotite), which may reflect the S in the sulfide samples is derived mainly from the associated igneous rocks, and a relatively small proportion (< 36%) of seawater sulfur incorporated into these sulfides during mixing between seawater (δ34S 21‰) and hydrothermal fluid. In contrast for a mixed origin for the source of S, the majority of the lead isotopic compositions (206Pb/204Pb 17.541 ± 0.004 to 19.268 ± 0.001, 207Pb/204Pb 15.451 ± 0.001 to 15.684 ± 0.001, 208Pb/204Pb 37.557 ± 0.008 to 38.988 ± 0.002, n = 21) of the sulfides possess a basaltic Pb isotopic composition, suggesting that the lead in the massive sulfide is mainly leached from local basaltic rocks that host the sub-seafloor hydrothermal systems in sediment-free mid-ocean ridges and mature back-arc basins. Furthermore, sulfide minerals in the super-fast and fast spreading mid-ocean ridges (MORs) exhibit less spread in their the δ34S values compared to sulfides from super-slow, and slow spreading MORs, which is most easily explained as a lesser degree of fluid-rock interaction and hydrothermal fluid-seawater mixing during hydrothermal ore-forming process. Additionally, the S and Pb isotope compositions of sulfides are controlled by the fluid processes for forming seafloor massive sulfide deposits. We demonstrate that the variable sulfur and lead isotopic compositions exhibit a relationship with the sulfur and lead sources, fluid–rock interaction, and fluid–seawater mixing. |
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