Geochemistry of Flooded Underground Mine Workings Influenced by Bacterial Sulfate Reduction

Abstract

Unlike the majority of the water in the flooded mine complex of Butte Montana, which includes the highly acidic Berkeley pit lake, groundwater in the flooded West Camp underground mine workings has a circum-neutral pH and contains at least 8 mM aqueous sulfide. This article examines the geochemistry and stable isotope composition of this unusual H 2 S-rich mine water, and also discusses problems related to the colorimetric analysis of sulfide in waters that contain FeS (aq) cluster compounds. The West Camp mine pool is maintained at a constant elevation by continuous pumping, with discharge water that contains elevated Mn (90 mM), Fe (16 mM), and As (1.3 mM) but otherwise low metal concentrations. Dissolved inorganic carbon in the mine water is in chemical and isotopic equilibrium with rhodochrosite in the mineralized veins. The mine water is under-saturated with mackinawite and amorphous FeS, but is supersaturated with Cu-and Zn-sulfides. However, voltammetry studies show that much of the dissolved sulfide and ferrous iron are present as FeS (aq) cluster molecules: as a result, the free H 2 S + HS À concentration of the West Camp water is poorly constrained. Concentrations of dissolved sulfide determined by colorimetry were lower than gravimetric assays obtained by AgNO 3 addition, implying that the FeS (aq) clusters are not completely extracted by the Methylene Blue reagent. In contrast, the clusters are quantitatively extracted as Ag 2 S after addition of AgNO 3 . Isotopic analysis of co-existing aqueous sulfide and sulfate confirms that the sulfide was produced by sulfate-reducing bacteria (SRB). The H 2 S-rich mine water is not confined to the immediate vicinity of the extraction well, but is also present in flooded mine shafts up to 3 km away, and in samples bailed from mine shafts at depths up to 300 m below static water level. This illustrates that SRB are well established throughout the southwestern portion of the extensive (>15 km 3 ) Butte flooded mine complex.

Evaluation of the Potential for Beneficial Use of Contaminated Water in a Flooded Mine Shaft in Butte, Montana

“…5 Table 2), some of which could be due to problems related to sample impurities (see ''Methods''). Nonetheless, the results are similar to the d 13 C-DIC data reported by Roesler et al (2007) from the West Camp Extraction Well at Butte. The latter authors concluded that the main source of DIC in the West Camp mine waters was dissolution of primary carbonate minerals (e.g., rhodochrosite) in the hydrothermal veins.…”

“…Overall, the chemistry of the purged Belmont mine waters is similar to that of other flooded mine shafts in the East Camp of Butte, such as the Anselmo, Steward, Pilot Butte, and Granite Mountain shafts (Pellicori et al 2005;Gammons et al 2006a), but is quite different from the flooded West Camp mine workings of Butte, which contain elevated concentrations of dissolved sulfide and low metal concentrations (Roesler et al 2007). Detectable quantities of H 2 S would not be expected in the Belmont waters, given their high concentrations of dissolved metals such as Fe and Zn that form insoluble sulfide minerals.…”

Low-oxygen and chemical kinetic constraints on the geochemical niche of neutrophilic iron(II) oxidizing microorganisms

“…some combination of different Fe x S y species). Iron sulfide clusters are known to exist in a number of marine and freshwater environments (Theberge and Luther, 1997;De Vitre et al, 1988;Davison et al, 1999;Luther et al, 2003;Druschel et al, 2004;Luther and Rickard, 2005;Roesler et al, 2007), and are thought to play a significant role in the precipitation of iron sulfide minerals (Rickard and Luther, 1997;Butler et al, 2004;Rickard, 2006;Roesler et al, 2007). Rickard (2006) recently showed that FeS (aq) establishes an equilibrium with the Fe-S mineral mackinawite which is the first Fe-S mineral formed in low temperature reducing environments (Rickard, 2006).…”

Sulfide-driven arsenic mobilization from arsenopyrite and black shale pyrite

“…Sulfide is produced by sulfate reducing anaerobes in groundwater only under anoxic conditions where sulfate is present at concentrations high enough to support its use as a terminal electron acceptor (Singleton, 1993;Saunders et al, 2005;Roesler et al, 2007). Under such conditions, dissolved arsenite and arsenate may react with sulfide to form solid phases (Das et al, 1996;O'Day et al, 2004) or aqueous complexes (Stauder et al, 2005).…”