Abstract

Geochemical characterization of metal-bearing sulphate salts from underground mine complexes in Nevada, USA, illustrates a variety of compositional and paragenetic trends. The most common metal species observed were Fe, Al, and Mg; and Al-bearing salts were the most commonly observed minerals. Mineralogical investigation shows that salts have variable grain sizes, are inter-grown, and display relationships that differ from those observed at many sites with similar minerals. Determinations for samples collected from one area show the presence of both paragenetically-early and -late minerals. These complex relationships may be the result of multiple generations of mineral growth. Simple dissolution testing indicates the propensity for each of the six distinct mineral phases observed to rapidly produce acidic solutions. Speciation and mineral equilibrium calculations using two different thermodynamic databases (Pitzer and Minteq.v4) show that different solution properties and mineral solubilities would be predicted depending on the database used. Additionally, some speciation results display unreasonable charge imbalances that would need to be rectified for the results to be utilized in predictive modeling. These results highlight the importance of considering various modeling codes and databases when simulating the environmental impact of concentrated solutions resulting from the oxidation of sulphides and formation of secondary minerals.

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