Pyrite brines

Vapor and brine from the Brandon vent of the East Pacific Rise have identical Fe isotope compositions, implying that phase separation does not produce an isotopic fractionation (Beard et al. 2003a). The role that sulfide precipitation plays in controlling the Fe isotope composition of the fluid remains unknown. The precision of the two sulfide analyses reported by Sharma et al. (2001) was not sufficient to resolve if sulfide precipitation would produce Fe isotope fractionation in the vent fluid. In a detailed study of sulfldes from the Lucky Strike hydrothermal field from the mid Atlantic Ridge, however, Rouxel et al. (2004) found that sulfldes span a range in 5 Fe values from -2.0 to +0.2%o, and that pyrite/marcasite has lower 5 Fe values ( l%o) as compared to chalcopyrite. The variations in mineralogy and isotope composition are inferred to represent open-system equilibrium fractionation of Fe whereby... 

In the bituminous coals of the US Illinois and Appalachian basins, arsenic primarily occurs in pyrite. The arsenian pyrite probably originated from subsurface fluids that existed about 270 million years ago during the formation of the Ouachita and Appalachian mountains (Goldhaber, Lee and Hatch, 2003). The arsenic-bearing fluids in the midcontinent Illinois Basin were primarily brines derived from surrounding sedimentary basins that were also responsible for the formation of the Mississippi Valley lead-zinc deposits. In contrast, the fluids that were responsible for the arsenian pyrites in the Appalachians (especially in the coals of the Warrior Basin of Alabama) were metamorphic and not as saline as those in the midcontinent (Goldhaber, Lee and Hatch, 2003). 

Basinal Brines as a Source of Sulfur in High-Sulfur Coals. Sulfide minerals, such as pyrite and sphalerite, in coal seams may be deposited from basinal hydrothermal fluids. The occurrence of epigenetic sphalerite in Illinois Basin coals has been described by Hatch et al. (119) and Cobb (120). Whelan et al. (121) studied the isotopic composition of pyrite and sphalerite in coal beds from the Illinois Basin and the Forest City Basin, and suggested that some of the coals were affected by Mississippi Valley-type hydrothermal solutions. 

The possibility of using brine to slurry the ore in the presence of an oxidizer such as chlorine in order to extract metals from the more common sulfide minerals has been studied by Strickland and co-workers (Jl, S12, S13). The reactions of acid chlorine solutions with galena (PbS), pyrite (FeSj), sphalerite (ZnS), chalcocite (CujS), covellite (CuS), chalcopyrite (CuFeSs), bornite (CusFeSi), pyrrhotite (FeS), and arsenopyrite (FeAsS) were examined with respect to their reaction rates and mechanisms. 

For example, and 5 0 of SO was used to assess mixing between a vertically stacked aquifer system in contact with a salt dome located in northern Germany (Berner era/., 2002). Two major sulfate pools were identified based upon their isotopic compositions (i) SO from the dissolution of evaporite minerals, and (ii) SO derived from atmospheric deposition and from the oxidation of pyrite. Using both the and of the sol , zones of variable groundwater mixing and significant amounts of bacterial sulfate reduction were identified. The SOl derived from the dissolution of the rock salt in the highly saline deep brine showed nearly constant values between +9.6%c and 11.9%o and between +9.5%c and 12.1%o, consistent with the Permian evaporite deposits. Sulfate in near-surface... 

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