Sulfur Isotope Fractionation During Sulfide Generation in the Hydrothermal Submarine Systems: The Case of Logatchev, Kra
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CATED TO THE 90TH ANNIVERSARY OF IGEM RAS
Sulfur Isotope Fractionation During Sulfide Generation in the Hydrothermal Submarine Systems: The Case of Logatchev, Krasnov, and Rainbow Hydrothermal Fields, Mid-Atlantic Ridge E. O. Dubininaa, *, N. S. Bortnikova, O. O. Stavrovaa, and S. A. Kossovaa a Institute
of Geology of Ore Deposits, Petrography, Mineralogy and Geochemistry, Russian Academy of Sciences, Moscow, 109017, Russia *e-mail: [email protected]
Received March 20, 2020; revised May 16, 2020; accepted May 17, 2020
Abstract—The sulfur isotope composition of single sulfide grains has been studied taking into account their paragenetic sequence in the samples collected from three hydrothermal fields (Logatchev, Krasnov, and Rainbow), located in the northern part of the Mid-Atlantic Ridge. The δ34S values of sulfides are +3.9 to +6, +7.1 to +9.8, and +2.1 to +8.4 ‰ in the Logatchev, Krasnov, and Rainbow fields, respectively. Late-generation sulfides within the studied domains (1–10 mm) of the samples are enriched in 34S isotope relative to early generations, and the sulfur isotope composition shows no relationship with the composition of sulfide minerals. In single grains of hydrothermal barite, the δ34S values exceed the generally accepted range for modern seawater sulfates. A model of the sulfur isotope fractionation in the hydrothermal system is proposed, based on the assumption of thermogenic sulfate reduction during fluid–rock interaction in the system, which is closed with respect to fluid. The model also takes into account simultaneous sulfur leaching from host rocks, the proportion of released sulfur from which depends on the progress of thermogenic sulfate reduction. Application of this model explains some well-known contradictions found in studying the sulfur isotope composition of sulfides from other hydrothermal fields in the World Ocean. Keywords: sulfur isotope composition, hydrothermal fields, MAR, thermogenic sulfate reduction, fluid-rock interaction DOI: 10.1134/S1075701520050025
INTRODUCTION The study of modern oceanic hydrothermal sulfide sediments in is crucial to understanding the formation of massive sulfide deposits, which distinguish geodynamic spreading and back-arc basin settings (Bortnikov and Vikentiev, 2005; Grichuk, 2000; Eremin et al., 2000; McDonald et al., 2018; Brueckner et al., 2015; Aggarwal and Nessbit, 1984; Hannington et al., 1998; Growe et al., 1992; Green and Vokes, 1990; Haymon et al., 1989; Neathery, Hollister, 1984). Massive sulfide deposits are major producers of copper, zinc, lead, gold, silver, and accompanying cadmium, gallium, indium, tellurium, and selenium, which are widely used in the high-tech industry (Bortnikov et al., 2016). These deposits are unique among other types. They formed during almost three-quarters of the Earth’s history: starting almost 3.55 Ga and continuing at present on the seafloor (Bortnikov and Vikentiev, 2005; Smirnov, 1968; Shanks, 2001; Hannington et al., 2005; Huston et al., 2010; Shanks and Thurston, 2012). Massive sulfide deposits
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