Pyrite-H2S/SO4 S isotope exchange at hydrothermal conditions: An experimental study at 300°C and 500 bars
Abstract
The rate of exchange and multiple S isotope fractionation between pyrite and dissolved H2S and SO4 was determined at 300°C and 500 bars at physiochemical conditions indicative of natural MOR hydrothermal systems by using the flexible gold cell reactor system [1]. A 34S enriched solution was designed to track reaction progress and to not significantly perturb mass dependent relationships between 33S and 36S, allowing for observations of natural mass dependent fractionation between pyrite and dissolved species during dissolution and recrystallization. The experimental data are compared with previously determined experimental constraints of S isotope exchange between fluid species [2] and with Fe and S isotope experiments conducted at higher temperature and where pyrite was precipitated rapidly from solution at 300 and 350°C and 500 bars [3, 4]. Briefly, the 34S isotope data indicate that the rate of exchange between pyrite and dissolved aqueous species is sluggish, where insignificant exchange occurred after the course of 4000 hours at 300°C, approximately 4%. Furthermore, the 33,36S mineral-fluid data indicate that upon pyrite dissolution, the light isotopes are preferentially removed into solution and incorporated as H2S and SO4-. These data are consistent with natural observations of pyrite-dissolved S disequilibrium and provide important insight towards mineral reactivity and retentiveness of recording mineral formation conditions. [1] Seyfried Jr., W.E., Janecky, D.R. & Berndt, M.E. 1987 Rocking autoclaves for hydrothermal experiments: II. The flexible reaction-cell system. Hydrothermal Experimental Techniques 216-239. [2] Ohmoto, H. & Lasaga, A.C. 1982 Kinetics of reactions between aqueous sulfates and sulfides in hydrothermal systems. Geochimica et Cosmochimica Acta 46, 1727-1745. [3] Syverson, D.D., Borrok, D.M. & Seyfried Jr., W.E. 2013 Experimental determination of equilibrium Fe isotopic fractionation between pyrite and dissolved Fe under hydrothermal conditions. Geochimica et Cosmochimica Acta 122, 170-183. [4] Syverson, D.D., Ono, S., Shanks, W.C. & Seyfried Jr., W.E. 2015 Multiple sulfur isotope fractionation and mass transfer processes during pyrite precipitation and recrystallization: An experimental study at 300 and 350°C. Geochimica et Cosmochimica Acta 165, 418-434.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2017
- Bibcode:
- 2017AGUFM.V33D0550S
- Keywords:
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- 3640 Igneous petrology;
- MINERALOGY AND PETROLOGY;
- 3660 Metamorphic petrology;
- MINERALOGY AND PETROLOGY;
- 5225 Early environment of Earth;
- PLANETARY SCIENCES: ASTROBIOLOGY;
- 8439 Physics and chemistry of magma bodies;
- VOLCANOLOGY