Inorganic and biogenic As-sulfide precipitation at seafloor hydrothermal fields

Dekov, Vesselin M., Bindi, Luca, Burgaud, Gaëtan, Petersen, Sven, Asael, Dan, Rédou, Vanessa, Fouquet, Yves and Pracejus, Bernhard (2013) Inorganic and biogenic As-sulfide precipitation at seafloor hydrothermal fields Marine Geology, 342 . pp. 28-38. DOI 10.1016/j.margeo.2013.06.006.

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Abstract

Highlights:
• As-sulfides are minor minerals at volcanic arc and back-arc hydrothermal settings.
• There are two modes of As-sulfide precipitation: inorganic and biogenic.
• The most stable As-sulfide at low-T seafloor hydrothermal conditions is orpiment.
• Biogenic type of orpiment represents completely mineralized fungal hyphae.
• Fungal orpiment precipitation is a mechanism of bio-sequestration of hydrothermal As.
We investigated As-sulfides (orpiment, As2S3 and realgar, As4S4) from four seafloor hydrothermal fields: three from back-arc and one from mid-ocean ridge settings. Our studies suggest two different modes of As-sulfide precipitation at the seafloor hydrothermal sites: inorganic and biogenic. The Eh–pH modeling shows that the most stable As-sulfide at low-temperature (T < 100 °C) seafloor hydrothermal conditions is orpiment, whereas realgar appears as a stable As-sulfide phase at T = 25 °C and under a narrow range of Eh–pH values. Inorganically precipitated realgar forms euhedral crystals whereas the orpiment is mostly colloform. The biogenic type of orpiment (no realgar of this type was found) represents completely mineralized fungal hyphae. The proposed scenario of biogenic orpiment formation assumes that crack-dwelling fungal filaments in the sub-seafloor were killed by an As-rich hydrothermal fluid moving along the same crack network. The fungal organic matter served as a geochemical trap for hydrothermal As which reacted with S (leached from the basement or reduced from seawater sulfate) and mineralized the fungal hyphae as As2S3. This process of fungal orpiment precipitation is a mechanism of bio-sequestration of hydrothermal As and another mode of soft-tissue fossilization not described so far.

Document Type: Article
Additional Information: WOS:000323690000003
Keywords: fungi; modeling; orpiment; realgar; submarine hydrothermal
Research affiliation: OceanRep > GEOMAR > FB4 Dynamics of the Ocean Floor > FB4-MUHS Magmatic and Hydrothermal Systems
Refereed: Yes
DOI etc.: 10.1016/j.margeo.2013.06.006
ISSN: 0025-3227
Projects: IsoBAB, SPIRIT
Date Deposited: 24 Jul 2013 08:11
Last Modified: 23 Jun 2017 09:43
URI: http://eprints.uni-kiel.de/id/eprint/21847

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