Abstract

Acidic (pH 3 to 4) and neutral (pH 6.1 to 7.5) mine drainage has been identified and sampled in the mining districts in the central Wasatch Range of Utah. Solute data suggest neutral mine discharges are either low iron calcium bicarbonate waters or high iron-sulphur waters. Mean delta 34-sulphur (δ³⁴S) of −0.5‰ (permil) and −0.2‰ vs Canyon Diablo δ³⁴S, for neutral and acid waters, respectively, suggest that the oxidation of pyrite and other sulfide minerals is the principal factor controlling the iron and sulfate concentrations in mine environments. Geologic and stable carbon isotopic data suggest acid mine waters (mean delta 13-carbon (δ¹³C) = −15.0‰ vs Peedee Formation Belemite) discharge from ground-water flow systems generally devoid of carbonate rocks, whereas neutral mine waters (mean δ¹³C = −9.7‰ vs Peedee Formation Belemite) discharge from aquifers containing abundant carbonate rocks.

Stable isotopic values of delta deuterium (δ²H) and delta 18-oxygen (δ¹⁸O) plot parallel to the meteoric water line, suggesting a meteoric origin for mine waters. Tritium concentrations (20.9 to 40.8 tritium units) and 14-carbon activities (46.2 to 96.2 percent modern carbon) indicate mine waters have a major component of modern recharge water. Shallow circulation of most mine discharges is suggested by low total dissolved solids, non-thermal discharge temperatures, the absence of ¹⁸O isotope shift, and the proximity of most mine workings to the surface. Factors causing iron-sulphur-rich vs iron-poor neutral mine water are unknown and need to be the subject of additional study.