Seawater sulfate reduction and sulfur isotope fractionation in basaltic systems: Interaction of seawater with fayalite and magnetite at 200–350°C

Mineralogical and Geochemical Characteristics of Hydrothermal Minerals Collected from Hydrothermal Vent Fields in the Southern Mariana Spreading Center

“…Thus, this process cannot explain the range in the δ 34 S values of the Snail and Yamanaka sites. Around seafloor hydrothermal sites, heating (150-200 C) of seawater during downflow in upper oceanic crust commonly results in the formation of anhydrite (Shanks et al 1981;Janecky and Shanks 1988). At high-temperature conditions of above 200 C, the anhydrite (SO 4 2À ) is subsequently dissolved, and partially reduced to sulfide (H 2 S) without isotope fractionation (Shanks et al 1981;Shanks and Seyfried 1987).…”

“…Around seafloor hydrothermal sites, heating (150-200 C) of seawater during downflow in upper oceanic crust commonly results in the formation of anhydrite (Shanks et al 1981;Janecky and Shanks 1988). At high-temperature conditions of above 200 C, the anhydrite (SO 4 2À ) is subsequently dissolved, and partially reduced to sulfide (H 2 S) without isotope fractionation (Shanks et al 1981;Shanks and Seyfried 1987). Therefore, the degree of mixing of this isotopically heavy sulfur with magmatic sulfur can account for the variation of δ 34 S values of sulfide minerals in the four hydrothermal sites.…”

Sulfur and lead isotopic compositions of massive sulfides from deep-sea hydrothermal systems: Implications for ore genesis and fluid circulation

“…In addition, on the EPR near 21°N, the δ 34 S values of the late-stage pyrite samples, which appear to infill fluid conduits, are among the lowest observed, suggesting precipitation in the fluid conduits of sulfide deposits isolated from seawater influx or perhaps at temperatures below 200-250°C, above which sulfate reduction becomes rapid (Shanks et al, 1981;Ohmoto and Lasaga, 1982;Woodruff and Shanks, 1988).…”

“…Sulfur isotopic values of seafloor hydrothermal sulfides indicate that the sulfur is most likely derived from multiple sources: (1) seawater sulfate (δ 34 S ~ 21‰); (2) igneousrock-derived sulfur (δ 34 S ~ 0‰), including mid-ocean ridge basalt, mantle peridotites, and calc-alkaline volcanic rocks (e.g., andesites, rhyolites); (3) magmatic sulfur derived from magmatic degassing (e.g., δ 34 S -5‰ of sulfides from the Hine Hina field in the Lau basin; Herzig et al, 1998a); and (4) bacteriogenic sulfide from sediments (e.g., Ohmoto and Rye, 1979;Shanks et al, 1981Shanks et al, , 1995Shanks and Niemitz, 1982;Solomon et al, 1988;Peter and Shanks, 1992;Herzig et al, 1998a). For sedimentstarved MORs, the variation in the sulfur isotopic composition of the sulfides is explained by varying proportions of reduced seawater sulfate and mantle-derived sulfur leached from the underlying igneous rocks (e.g., Arnold and Sheppard, 1981;Herzig et al, 1998a).…”

Mineralogy, geochemistry and sulfur isotope characterization of Cerro de Maimón (Dominican Republic), San Fernando and Antonio (Cuba) lower Cretaceous VMS deposits: Formation during subduction initiation of the proto-Caribbean lithosphere within a fore-arc

“…This range is, in contrast, in good agreement with sulfide derived from the inorganic reduction of seawater and/or a magmatic source. Inorganic thermochemical reduction of seawater sulfate favored by high temperature formation of the deposits and the Fe-rich nature of the host basaltic rocks (Shanks III et al, 1981) was surely dominant, leaving a string of δ 34 S values as…”