Experimental determination of equilibrium Fe isotopic fractionation between pyrite and dissolved Fe under hydrothermal conditions

Multiple sulfur isotope fractionation and mass transfer processes during pyrite precipitation and recrystallization: An experimental study at 300 and 350 °C

“…The value is different from the previously recommended value of +1‰ [Ohmoto and 578 Rye, 1979] and from combination of recent spectroscopic and theoretical predictions [Blanchard 579 et al, 2009;Ono et al, 2007;Otake et al, 2008;Polyakov and Soultanov, 2011;Polyakov et al, 580 2013]. The revised 34 S/ 32 S pyrite-H 2 S equilibrium fractionation at 350°C compared with MOR 581 hydrothermal sulfide data suggests that the S isotope system is closer to equilibrium than isotope studies [Rouxel et al, 2008;Syverson et al, 2013], lends strength to this interpretation. length of the symbols, whereas the error (1σ) for observed Δ 33 S is 0.006‰.…”

“…Time series fractionation data for pyrite precipitation experiments at 300-350°C (Δ 33 S = Δ 33 S x - FeS as a likely precursor upon pyrite formation [Syverson et al, 2013]. (2σ) for the concentration of the individual dissolved components by ICP-OES and ion chromatography is ±2% for Na + and SO 4 , ±1% for Fe 2+ , and ±1% for Cl -.…”

“…Similarly, complimentary Fe isotope data from the pyrite precipitation experiments presented by 494Syverson et al [2013] indicate that the pyrite-aqueous Fe-reservoirs have also undergone a 495 considerable degree of iron isotopic exchange, approximately 76%, towards equilibrium during 496 the same extent of reaction progress. The variation in the degree of exchange between the S and 497 Fe isotope systems may reflect differences in 1) the analytical uncertainty of S and Fe isotope 498 measurements, 2) the uncertainty in the initial and final S and Fe fractionations between pyrite 499 and aqueous species, 3) uncertainty in the experimentally determined equilibrium fractionations, 500 and 4) dissimilar total concentrations of S and Fe in solution (…”

“…Thus, hydrothermal experiments at 77 300 and 350°C, 500 bars were carried out to assess the fractionation of multiple S isotopes 78 between dominant S-bearing aqueous species in the H 2 S-SO 4 -NaCl-FeCl 2 -HCl-H 2 O system 79 coexisting with pyrite. In the present experimental study, we apply the three isotope approach 80 initially developed by Matsuhisa et al [1978] for oxygen isotope fractionation ( 16 O, 17 Pyrite is ubiquitous in both marine and terrestrial hydrothermal systems and its 88 precipitation mechanisms have been studied and debated extensively [Berner, 1970;Butler et al, 89 2004; Guilbaud et al, 2011a;Guilbaud et al, 2010;Guilbaud et al, 2011b;Luther, 1991;90 Murowchick and Barnes, 1987;Rickard and Luther, 1997;Schoonen and Barnes, 1991; 91 Syverson et al, 2013;Yücel et al, 2011]. However, the potential role of pyrite in catalyzing or 92 inhibiting isotope exchange amongst aqueous S-species during precipitation and recrystallization 93 X-ray diffraction (XRD).…”

“…In 138 addition, the experimental solution is only exposed to inert chemical components during the 139 course of each experiment, maintaining the integrity of the chemical and isotopic composition of 140 sampled solutions. Further details of the flexible gold cell reactor system and of modifications 141 are provided by Syverson et al [2013].…”