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Au and Te Minerals in Seafloor Massive Sulphides from Semyenov-2 Hydrothermal Field, Mid-Atlantic Ridge

1
Institute for Geology and Mineral Resources of the Ocean (FSBI “VNIIOkeangeologia”), 1 Angliisky Ave., 190121 St. Petersburg, Russia
2
Institute of Earth Sciences, St. Petersburg State University, 7/9 Universitetskaya Emb., 199034 St. Petersburg, Russia
*
Authors to whom correspondence should be addressed.
Minerals 2019, 9(5), 294; https://doi.org/10.3390/min9050294
Received: 4 March 2019 / Revised: 5 May 2019 / Accepted: 10 May 2019 / Published: 15 May 2019
(This article belongs to the Special Issue Deep-Sea Minerals and Gas Hydrates)
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Abstract

The Semyenov-2 hydrothermal field located at 13°31′N of the Mid-Atlantic Ridge (MAR) is associated with an oceanic core complex (OCC) and hosted by peridotites and basalts with minor amounts of gabbro and plagiogranites. Seafloor massive sulphides (SMS) are represented by chimneys with zonality, massive sulphides without zonality and sulphide breccia cemented by opal and aragonite. The mean value of Au (20.6 ppm) and Te (40 ppm) is much higher than average for the MAR SMS deposits (3.2 ppm and 8.0 ppm, respectively). Generally, these high concentrations reflect the presence of a wide diversity of Au and Te minerals associated with major mineral paragenesis: primary native gold, melonite (NiTe2) and tellurobismuthite (Bi2Te3) are related to high-temperature chalcopyrite (~350 °C); electrum (AuAg)1, hessite (Ag2Te) and altaite (PbTe) are related to medium- and low-temperature Zn-sulphide and opal assemblages (260–230 °C). Calaverite (AuTe2) and Te-rich “fahlore” Cu12(Sb,As,Te)4S13 are texturally related to the chalcopyrite-bornite-covellite. Enrichment of Au in sulphide breccia with opal and aragonite cement is driven by the re-deposition and the process of hydrothermal reworking of sulphide. The low-temperature fluid mobilizes gold from primary sulphide, along with Au and Te minerals. As a result, the secondary gold re-precipitate in cement of sulphide breccia. An additional contribution of Au enrichment is the presence of aragonite in the Cu-Zn breccia where the maximal Au content (188 ppm) is reached. View Full-Text
Keywords: seafloor massive sulphides; Mid-Atlantic Ridge; hydrothermal processes; gold; tellurides; aragonite; mechanism of precipitation; oceanic core complex seafloor massive sulphides; Mid-Atlantic Ridge; hydrothermal processes; gold; tellurides; aragonite; mechanism of precipitation; oceanic core complex
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Firstova, A.; Stepanova, T.; Sukhanova, A.; Cherkashov, G.; Poroshina, I. Au and Te Minerals in Seafloor Massive Sulphides from Semyenov-2 Hydrothermal Field, Mid-Atlantic Ridge. Minerals 2019, 9, 294.

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