Enargite-luzonite hydrothermal vents in Manus Back-Arc Basin: submarine analogues of high-sulfidation epithermal mineralization

Type Article
Date 2016-11
Language English
Author(s) Dekov Vesselin M.1, 9, Rouxel OlivierORCID1, 2, 3, Kouzmanov Kalin4, Bindi Luca5, Asael Dan6, Fouquet Yves1, Etoubleau Joel1, Burgaud Gaetan7, Walle Markus8
Affiliation(s) 1 : IFREMER, Dept Marine Geosci, F-29280 Plouzane, France.
2 : Woods Hole Oceanog Inst, Marine Chem & Geochem Dept, Woods Hole, MA 02543 USA.
3 : Univ Hawaii Manoa, Sch Ocean & Earth Sci & Technol, Dept Oceanog, 1000 Pope Rd,MSB 510, Honolulu, HI 96822 USA.
4 : Univ Geneva, Dept Earth Sci, Rue Maraichers 13, CH-1205 Geneva, Switzerland.
5 : Univ Florence, Dipartimento Sci Terra, Via Giorgio La Pira 4, I-50121 Florence, Italy.
6 : Yale Univ, Dept Geol & Geophys, New Haven, CT 06520 USA.
7 : Univ Brest, ESIAB, Lab Univ Biodivers & Ecol Microbienne EA 3882, Univ Europeenne Bretagne,IFR 148, Technopole Brest Iroise, F-29280 Plouzane, France.
8 : ETH, Inst Geochem & Petr, Clausiusstr 25, CH-8092 Zurich, Switzerland.
9 : Tokyo Univ Marine Sci & Technol, Minato Ku, 4-5-7 Konan, Tokyo 1088477, Japan.
Source Chemical Geology (0009-2541) (Elsevier Science Bv), 2016-11 , Vol. 438 , P. 36-57
DOI 10.1016/j.chemgeo.2016.05.021
WOS© Times Cited 10
Keyword(s) Enargite, Epithermal, Hydrothermal vent, Luzonite, S-Cu isotopes, Seafloor
Abstract Active and inactive hydrothermal chimneys composed almost entirely of enargite and luzonite, rare minerals in seafloor hydrothermal deposits, were found at the summits of two submarine volcanoes, North Su and Kaia Natai, in the Manus Back-Arc Basin. Detailed mineralogical and geochemical studies revealed that most probably these deposits precipitated at T = 200°–330 °C and high fS2. The negative δ34S values (− 8.58 to − 3.70‰) of the enargite-luzonite are best explained by disproportionation reactions of magmatic SO2 and suggest that the high fS2 is likely provided by direct magmatic input of SO2 into the hydrothermal system. Fractionation of Cu stable isotopes during the precipitation of enargite-luzonite (δ65Cu ranges from − 0.20 to + 0.35‰) is inferred to be associated with either Rayleigh-type fractionation, or redox processes (Cu+ oxidation to Cu2 +) and the mass balance of dissolved Cu+ and Cu2 + species in the hydrothermal fluid. The trace element composition of enargite and luzonite indicates a temporal fluctuation of the chemistry of the ore-forming fluid with an increase of Fe, Ga, Tl, Au, Hg, Pb and Ag, and decrease of Sb, Sn, Te, Ge and V concentrations with time and points out that this type of deposits is the richest in Au (average 11.9 ppm) and Te (average 169 ppm) among all other types of seafloor metal deposits.

In addition to the widespread inorganic precipitation of enargite and luzonite in this setting, there is evidence that this mineralization may be biogenically mediated on the external surfaces of the active vents. Fungi-like filaments mineralized by luzonite imply that the fungi (Dikarya subkingdom) may be implicated in a mechanism of bio-sequestration of As, S and Cu, and provide the initial substrate for luzonite precipitation.

The studied enargite-luzonite deposits have characteristics similar to those of subaerial high-sulfidation epithermal mineralization: back-arc basin setting; acid-sulfate and boiling ore-forming fluids; altered (advanced argillic stage) dacitic host rocks; major enargite-luzonite and minor pyrite, barite and S0; δ34S < 0‰. Therefore, they may be considered as submarine analogues of subaerial high-sulfidation epithermal deposits with the potential for concealed porphyry Cu(single bondAu) mineralization at depth.
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Dekov Vesselin M., Rouxel Olivier, Kouzmanov Kalin, Bindi Luca, Asael Dan, Fouquet Yves, Etoubleau Joel, Burgaud Gaetan, Walle Markus (2016). Enargite-luzonite hydrothermal vents in Manus Back-Arc Basin: submarine analogues of high-sulfidation epithermal mineralization. Chemical Geology, 438, 36-57. Publisher's official version : https://doi.org/10.1016/j.chemgeo.2016.05.021 , Open Access version : https://archimer.ifremer.fr/doc/00337/44844/