| Abstract
| - The stable isotope composition of waters (δ2H, δ18O) canbe used as a natural tracer of hydrologic processes insystems affected by acid mine drainage. We investigatedthe δ2H and δ18O values of pore waters from four oxidizingsulfidic mine tailings impoundments in different climaticregions of Chile (Piuquenes at La Andina with Alpine climate,Cauquenes and Carén at El Teniente with Mediterraneanclimate, and Talabre at the Chuquicamata deposit withhyperarid climate). No clear relationship was found betweenaltitude and isotopic composition. The observed displacementof the tailings pore waters from the local meteoricwater line toward higher δ18O values (by ∼ +2‰ δ18Orelative to δ2H) is partly due to water−rock interactionprocesses, including hydration and O-isotope exchange withsulfates and Fe(III) oxyhydroxides produced by pyriteoxidation. In most tailings, from the saturated zone towardthe surface, isotopically different zones can be distinguished.Zone I is characterized by an upward depletion of 2Hand 18O in the pore waters from the saturated zone andthe lowermost vadose zone, due to ascending diffusedisotopically light water triggered by the constant loss ofwater vapor by evaporation at the surface. In zone II, thecapillary flow of a mix of vapor and liquid water causesan evaporative isotopic enrichment in 2H and 18O. At the topof the tailings in dry climate a zone III between thecapillary zone and the surface contains isotopically lightdiffused and atmospheric water vapor. In temperate climates,the upper part of the profile is affected by recent rainfalland zone III may not differ isotopically from zone II.
|
