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The Use of Solute and Isotopic Chemistry to Identify Flow Patterns and Factors Which Limit Acid Mine Drainage in the Wasatch Range, Utah
Author(s) -
Mayo Alan L.,
Nielsen Peter J.,
Loucks Mark,
Brimhall Willis H.
Publication year - 1992
Publication title -
groundwater
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.84
H-Index - 94
eISSN - 1745-6584
pISSN - 0017-467X
DOI - 10.1111/j.1745-6584.1992.tb01796.x
Subject(s) - acid mine drainage , meteoric water , sulfate , bicarbonate , groundwater recharge , environmental chemistry , geology , silicate , range (aeronautics) , hydrology (agriculture) , chemistry , geochemistry , mineralogy , groundwater , aquifer , materials science , geotechnical engineering , organic chemistry , composite material
In this case study, we have demonstrated how a minimal amount of relatively inexpensive isotopic data can be used to help solve a complex Hydrogeologie problem. Acidic (pH 3 to 4) and neutral (pH 6.0 to 7.7) mine drain waters have been identified and sampled in the mining districts in the central Wasatch Range of Utah. The chemical evolution of acid and neutral mine waters follow fundamentally different chemical and isotopic evolutionary pathways which reflect fundamentally different flow histories. Most neutral mine discharges are either low iron calcium‐bicarbonate waters or iron and sulfate rich waters. Stable isotopic values of δ 2 H and δ 18 O plot near and parallel to the meteoric water line (MWL), suggesting a meteoric origin for all mine waters. 3 H concentrations (20.9 to 40.8 TU) and 14 C activities (46.2 to 96.3 pmc) indicate mine waters have a major component of modern recharge water. Shallow circulation of most mine discharges is suggested by low TDS, nonthermal discharge temperatures and the proximity of most mine workings to the surface. The δ 34 S values of mine discharge waters tend to cluster about two nodes. Neutral mine drainages with low SO 4 2‐ contents cluster about δ 34 S = 0/o, whereas neutral mine drainages with high Sü42 contents cluster about δ 34 S =+5.5%o. An acid mine drainage also has a 534 S value of about 0 %o. δ 34 S values of ∼ 0 %o are attributed to the oxidation ofpyrite and other sulfide minerals, whereas more positive isotopic values are attributed to isotopic fractionation accompanying the dissolution of gypsum and anhydrite. Only mine discharges with a δ 34 S δ 0%o have the potential to produce acid drainage. Geologic and δ 13 C data suggest acid mine waters (mean δ 13 C =−15.0%o) discharge from ground‐water flow systems generally devoid of carbonate rocks. Neutral mine waters (mean δ 13 C =− 9.7%o) discharge from aquifers containing abundant carbonate rocks which neutralize excess H + ions released by the oxidization of sulfide minerals.