The stable isotope composition of waters (delta H-2, delta O-18) can be
used as a natural tracer of hydrologic processes in systems affected by
acid mine drainage. We investigated the delta H-2 and delta O-18 values
of pore waters from four oxidizing sulfidic mine tailings impoundments
in different climatic regions of Chile (Piuquenes at La Andina with
Alpine climate, Cauquenes and Caren at El Teniente with Mediterranean
climate, and Talabre at the Chuquicamata deposit with hyperarid
climate). No clear relationship was found between altitude and isotopic
composition. The observed displacement of the tailings pore waters from
the local meteoric water line toward higher delta O-18 values (by
similar to +2% delta O-18 relative to delta H-2) is partly due to
water-rock interaction processes, including hydration and O-isotope
exchange with sulfates and Fe(III) oxyhydroxides produced by pyrite
oxidation. In most tailings, from the saturated zone toward the surface,
isotopically different zones can be distinguished. Zone I is
characterized by an upward depletion of H-2 and O-18 in the pore waters
from the saturated zone and the lowermost vadose zone, due to ascending
diffused isotopically light water triggered by the constant loss of
water vapor by evaporation at the surface. In zone II, the capillary
flow of a mix of vapor and liquid water causes an evaporative isotopic
enrichment in H-2 and O-18. At the top of the tailings in dry climate a
zone III between the capillary zone and the surface contains
isotopically light diffused and atmospheric water vapor. In temperate
climates, the upper part of the profile is affected by recent rainfall
and zone III may not differ isotopically from zone II.