HR: 1340h
AN: H23F-1504    [Abstracts]
TI: Iron Isotope Investigation of Sedimentary Pyrite Associated With Coal Mine Discharges (AMD)
AU: * Wolfe, A L
EM: alw11@pitt.edy
AF: Department of Geology & Planetary Science, University of Pittsburgh, 4107 O'Hara Street, SRCC 200, Pittsburgh, PA 15260 United States
AU: Stewart, B
EM: bstewart+@pitt.edu
AF: Department of Geology & Planetary Science, University of Pittsburgh, 4107 O'Hara Street, SRCC 200, Pittsburgh, PA 15260 United States
AU: Capo, R
EM: rcapo+@pitt.edu
AF: Department of Geology & Planetary Science, University of Pittsburgh, 4107 O'Hara Street, SRCC 200, Pittsburgh, PA 15260 United States
AB: Water-rock interactions in abandoned coal mines results in the dissolution of pyrite and associated generation of acidic water with relatively high concentrations of iron and other metals. Analysis of changes that occur during dissolution of pyrite could improve our understanding of the movement of iron species within contaminated mine outflows, elucidate reaction mechanisms and processes that occur in solid-liquid systems and provide insight into the biogeochemistry of iron. We have begun an iron isotope investigation of pyrite extracted from coal seams and adjacent stratigraphic units, along with associated mine discharges, located in western Pennsylvania. We expect to find variations in iron isotope compositions of pyrite collected from different coal beds and adjacent stratigraphic units due to the variety of conditions under which pyrite can form (e.g, freshwater, brackish or marine; biotic or abiotic),. Pyrite deposited under marine conditions is mediated by sulfate-reducing bacteria and formation proceeds through the dissolution and reduction of lithogenic Fe oxides and Fe silicates to Fe (II). Most of the reactive iron is scavenged to form pyrite, minimizing Fe isotope fractionation; such processes are unlikely to produce pyrite with δ⁵⁶Fe < -0.5 ‰ (Rouxel et al., 2005, Science 307: 1088). In contrast, in areas where high concentrations of Fe(II) accumulate under anoxic conditions and low sulfide concentrations (e.g., lacustrine or brackish water), large δ⁵⁶Fe values may occur because of partial Fe(II) oxidation, Fe(II) reduction, and distillation processes during mineral precipitation (Rouxel et al., 2005). Preliminary iron isotope measurements of sedimentary pyrite in this study yield a range in δ⁵⁶Fe of ~3.5‰. Additional analyses will be used to quantify and source-track the dissolution of pyrite within abandoned mine drainage systems. The iron in the outflows could potentially be used as a "fingerprint" to identify the most abundant and/or reactive pyrite within such systems. In addition, comparison of iron isotope signatures between pyrite and abandoned mine discharges, together with ongoing experimental investigations of pyrite dissolution, will help determine whether or not iron isotope fractionation takes place during generation of acidic mine drainage.
DE: 1000 GEOCHEMISTRY
DE: 1041 Stable isotope geochemistry (0454, 4870)
DE: 1800 HYDROLOGY
SC: Hydrology [H]
MN: Fall Meeting 2005