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Trace metal and sulfur cycling in a hydrothermally active arc volcano: deep-sea drilling of the Brothers volcano, Kermadec arc, New Zealand

Martin, Andrew J., Jamieson, John W., de Ronde, Cornel E. J., Humphris, Susan E., McDonald, Iain ORCID:, Layne, Graham D., Piercey, Glenn and MacLeod, Christopher J. ORCID: 2023. Trace metal and sulfur cycling in a hydrothermally active arc volcano: deep-sea drilling of the Brothers volcano, Kermadec arc, New Zealand. Mineralium Deposita 58 (2) , pp. 402-425. 10.1007/s00126-022-01135-x

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Brothers volcano, located on the Kermadec arc north of New Zealand, hosts two geochemically distinct hydrothermal systems. The NW Caldera and Upper Cone hydrothermal fields exhibit distinct fluid compositions that are significantly influenced by seawater and magmatic volatiles, respectively. In this study, we present trace metal chemistry and sulfur isotope compositions of pyrite within hydrothermally altered volcanic rocks recovered from drill cores at depths of up to 429 m below the seafloor collected during the International Ocean Discovery Program’s Expedition 376. Magmatic volatile-influenced alteration resulting in pyrophyllite ± natroalunite assemblages occurs at the Upper Cone and at the NW Caldera below 189 m. At the NW Caldera, a later seawater-derived hydrothermal fluid overprints magmatic volatile alteration forming chlorite-rich alteration. Pyrite at the Upper Cone is fine-grained, euhedral and enriched in Cu, As, Sb, Pb and Pt and has an average δ34S composition of − 5.5 ± 2.9‰ (1σ, n = 32). In contrast, pyrite associated with pyrophyllite-rich alteration at the older NW Caldera site is coarse-grained, subhedral and has higher Co, Se, Te, and Bi contents but a comparable average δ34S value of -4.8 ± 5.5‰ (1σ, n = 26). The difference in trace metal content between pyrite from pyrophyllite ± natroalunite assemblages at the NW Caldera and Upper Cone site indicates a change in the trace metal enrichment signature of pyrite with the age of the hydrothermal system. Pyrite from chlorite-rich alteration (NW Caldera) is depleted in Cu, Te and Bi relative to all magmatic volatile-influenced pyrite but has a similar average δ34S composition of − 4.6 ± 3.5‰ (1σ, n = 20). The similarity in trace metal enrichment signature and average δ34S composition of pyrite, regardless of associated alteration mineral assemblage shows that the initial magmatic volatile trace metal signature and sulfur isotope composition of pyrite is preserved during fluid overprinting. The lower content of Cu, Te, and Bi in pyrite from chlorite-rich alteration confirms the importance of seawater-derived hydrothermal fluids in metal mobilization and consequent formation of hydrothermal precipitates at the seafloor.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Earth and Environmental Sciences
Publisher: Springer
ISSN: 0026-4598
Date of First Compliant Deposit: 24 May 2023
Date of Acceptance: 22 August 2022
Last Modified: 07 Nov 2023 18:13

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