BIBLIOS

Document type
Conference papers

Document subtype
Abstract

Title
Ore-Forming Process of the Menez Gwen Hydrothermal Field: In situ S Isotopes and Trace Metals Constraints

Participants in the publication
Wenhong Qiu (Author)
Ágata Alveirinho Dias (Author)
Dep. Geologia
IDL
Isabel Maria Amaral Costa (Author)
Fernando J A S Barriga (Author)
IDL

Summary
The Menez Gwen hydrothermal field (37º50’N), is\\\\nlocated near the top of a young volcano at the Mid\\\\nAtlantic Ridge. It is characterized by small chimneys,\\\\ndiffuse venting associated with breccia cemented by\\\\nhydrothermal amorphous silica-barite. This work\\\\npresents in situ trace elemental and S isotopic\\\\ncompositions of pyrite and chalcopyrite in three types\\\\nof hydrothermal samples from this field: hightemperature chalcopyrite-pyrite chimney (HT-ch); midtemperature sphalerite-pyrite-barite chimney (MT-ch)\\\\nand low-temperature amorphous silica-barite breccia\\\\n(LT-br). The results show a systematic distribution of\\\\ntrace metals from LT-br to HT-ch. Trace metals of\\\\npyrite analysed on HT-ch samples contain higher\\\\nconcentrations of elements derived from high-T fluids\\\\n(e.g. Se, Co, Ni and Cu), indicating preferential\\\\nincorporation of these elements in the lattice of pyrite at\\\\nhigher-Ts. However, some pyrite-chalcopyrite\\\\naggregate identified within the base of LT-br also show\\\\nhigh-T derived elements, suggesting higher temperature\\\\nconditions below the sub-surface, probably as a result\\\\nof a decrease in permeability during slab formation.\\\\nFramboidal and colloform pyrite observed in most of\\\\nthe LT-br clearly display an enrichment of elements\\\\nderived from lower-T and oxidative conditions (e.g. Mn,\\\\nTl, Mo, Cr and V). Sulphide phases have δ34S values\\\\nranging from -2.5 to 7.8‰ with an average of 1.5‰,\\\\nindicating a mantle S source. Analyses of framboidal\\\\npyrite from LT-br show the lowest δ34S values, ranging\\\\nfrom -5.6‰ to -12.2‰, inferring the contribution of\\\\nbiogenic S. The chalcopyrite-pyrite pairs in HT-ch\\\\nshow an equilibrium fractionation of S isotope (Δ34SPyCpy: 0.2‰ to 1.4‰, average of 1.0‰), indicating a\\\\ntemperature ca. 390°C. Our study highlights that S and\\\\nmetals of sulphides in Mendez Gwen were derived\\\\nfrom the basement mafic crust leached by high-T\\\\nhydrothermal fluids, where the impermeable breccia\\\\nseems to work as a barrier for oxidative and biogenic\\\\ninvolvement beneath the sub-surface.


Event
Goldschmidt Abstracts

Publication Identifiers

Publisher
Geochemical Society

Document Identifiers
DOI - https://doi.org/10.46427/gold2020.2143
URL - http://dx.doi.org/10.46427/gold2020.2143

Keywords
Menez Gwen hydrothermal processes sulfur isotopes geochemistry MAR

Tags
Marine Geology Deep-sea processes

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