CALL FOR PROPOSALS:

ORGANIZERS

  • Harvey Thorleifson, Chair
    Minnesota Geological Survey
  • Carrie Jennings, Vice Chair
    Minnesota Geological Survey
  • David Bush, Technical Program Chair
    University of West Georgia
  • Jim Miller, Field Trip Chair
    University of Minnesota Duluth
  • Curtis M. Hudak, Sponsorship Chair
    Foth Infrastructure & Environment, LLC

 

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Paper No. 9
Presentation Time: 10:15 AM

FeS2-FeCl2(AQ) ISOTOPE EXCHANGE KINETICS AT HYDROTHERMAL CONDITIONS


SYVERSON, Drew D., Earth Sciences, University of Minnesota, 310 Pillsbury Drive SE, Minneapolis, MN 55414, SHANKS III, Wayne C., U.S. Geol Survey, PO Box 25046, Denver, CO 80225 and SEYFRIED Jr., William E., Department of Earth Sciences, University of Minnesota, 310 Pillsbury Drive SE, Minneapolis, MN 55455-0219, syve0063@umn.edu

The dearth of rate data for Fe mass transfer between hydrothermal fluids and Fe-bearing minerals presents a challenge to the interpretation of subseafloor alteration processes at mid-ocean ridges (MORs). Observations made from experiments performed at ambient conditions and equilibrium theoretical models are extrapolated to understand the processes and mechanisms of sulfide precipitation/recrystallization [1-3]. Quantification of rates will add constraints to the chemical and isotopic evolution of hydrothermal vent fluids and minerals.

An isotopically enriched 57Fe tracer was used to examine the exchange between pyrite and hydrothermal fluid (FeCl2(aq)) at 350C, 500 bars. The experimental design took advantage of liquid sulfur hydrolysis to buffer redox and pH, ensuring that pyrite is the only Fe-bearing mineral in the system exchanging with the hydrothermal fluid. The degree of Fe-isotopic exchange between pyrite-FeCl2(aq) rapidly approached ~85% within days (2.14*10-6 mmol/s), although exchange dramatically slowed subsequently apparently due to sulfur envelopment of pyrite crystals. Additional experiments where the pyrite/sulfur ratio was less than unity were also characterized by relatively slow exchange rates of Fe and S isotopes. When Fe isotope exchange occurred between pyrite and fluid, so too did pyrite-fluid sulfur isotope exchange (δ34St=0=0.16 to δ34St=final=6.73‰).

The rapid rate of isotopic exchange between pyrite and fluid for acidic, high temperature systems implies that sulfide minerals may record the effects of short-term isotopic/chemical perturbations with important implications for resolving the temporal evolution of seafloor sulfide deposits.

[1] Rickard, D. (1997) Geochim. Cosmochim. Ac. 61, 115-134. [2] Rouxel et al. (2008) Chem. Geol. 252, 214-227. [3] Polyakov & Soultanov (2011) Geochim. Cosmochim. Ac. 75, 1957-1974. [4] Ohmoto & Lasaga (1982) Geochim. Cosmochim. Ac. 46, 1727-1745. (1982) Geochim. Cosmochim. Ac. 46, 1727-1745.

Session No. 220

Geochemistry: Recent Advances in Geochemistry
Wednesday, 12 October 2011: 8:00 AM-12:00 PM
Room 102BC (Minneapolis Convention Center)
Geological Society of America Abstracts with Programs. Vol. 43, No. 5, p.532
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