Kinetics of reactions between aqueous sulfates and sulfides in hydrothermal systems

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).…”

“…Therefore, the variation in sulfur isotopic compositions of hydrothermal sulfides might be due to changes in the end-member fluid composition, in-situ sulfate reduction, or local disequilibrium sulfur isotopic fractionation during sulfide deposition (Fouquet et al, 1996). In addition, the δ 34 S values of sulfides essentially reflect the isotope fractionation factor between sulfate (SO 4 ) and sulfide (H 2 S) (Ohmoto et al, 1983;Ohmoto and Goldhaber, 1997), and the isotope fractionation factors between SO 4 and H 2 S are 21‰ and 15‰ at 300 and 400 °C, respectively (Ohmoto and Lasaga, 1982).…”

Sulfur isotope ratios of the Akatani, Iide and Waga-Sennin skarn deposits, and their bearing on mineralizations in the "Green Tuff" region, Japan.

“…The difficulty of obtaining this exchange equilib rium in natural ore-forming processes is pointed out in some previous works (e.g. SAKAI, 1968). According to OHMOTO and LASAGA (1982), almost half a year would be required for the attainment of isotopic exchange equilibrium under the condition of T = 250°C, pH = 4 and total sulfur of 0.1 mole/kg H2O. In the solution under consideration, as estimated above, sulfate sulfur predominated over sulfide sulfur.…”

“…7). The rate of non bacterial reduction of sulfates depends also on the types of reducing compounds as pointed out by OHMOTO and LASAGA (1982). The kinetic isotopic effect increases with a decrease in the rate of reduction (OHMOTO and RYE, 1979).…”

“…This fact strongly suggests that the above estima tion on the S34S value of total sulfur on the as sumption of complete isotopic equilibrium, is not applicable in the present study. In recent works (e.g., OHMOTO and LASAGA, 1982;SHELTON and RYE, 1982), it is. confirmed that isotopic equi librium between aqueous H2S and sulfide minerals is attained faster than isotopic equilib rium between aqueous sulfate and aqueous sul fide.…”