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Sulfur and lead isotopic compositions of massive sulfides from deep-sea hydrothermal systems : implications for ore genesis and fluid circulation.

Zeng, Z. and Ma, Y. and Chen, S. and Selby, D. and Wang, X. and Yin, X. (2017) 'Sulfur and lead isotopic compositions of massive sulfides from deep-sea hydrothermal systems : implications for ore genesis and fluid circulation.', Ore geology reviews., 87 . pp. 155-171.

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.

Item Type:Article
Full text:(AM) Accepted Manuscript
Available under License - Creative Commons Attribution Non-commercial No Derivatives.
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Status:Peer-reviewed
Publisher Web site:https://doi.org/10.1016/j.oregeorev.2016.10.014
Publisher statement:© 2016 This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/
Date accepted:14 October 2016
Date deposited:17 January 2017
Date of first online publication:20 October 2016
Date first made open access:20 October 2017

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