Potential application of oxygen-18 and deuterium in mining effluent and acid rock drainage studies

Oxygen-18 (O-18) and deuterium (D, or H-2) are routinely used in hydrologic , climatologic and geothermal studies. In hydrology, stable isotopes provid e information on the type and topology (altitude and latitude) of the recha rge waters and the historical effects on water, related to such physical pr ocesses as evaporation (in ponds), melting (of snow or ice), condensation, evapotranspiration and mixing. In geothermal studies, stable isotopes provi de key information related to recharge and the various temperature-dependen t water/rock isotope exchange reactions. The latter is assessed through the oxygen shift in the O-18/D correlation. At acid rock drainage (ARD) sites, water/rock interactions are primarily controlled by pH and oxidation poten tial. Using the isotopic characteristics of the rocks and the recharge wate rs as a basis, the relative oxygen shift of the ARD effluent can provide in formation on: (1) the residence time, (2) the rate of water/rock reactions, and (3) the actual pH at the rock/water interface. This paper offers a met hodology for conducting oxygen and hydrogen isotope studies related to ARD and other mineral effluent problems. The methodology is based on: (1) compr ehensive sampling of regional waters, ARD effluent and major contributing m inerals and rocks, (2) isotopic and elemental analysis, and (3) data interp retation on the basis of a zero-dimensional (mass balance), multi-component mixing model.