Research article Environmental Geology 39 (7) May 2000 7 Q Springer-Verlag 767 Potential application of oxygen-18 and deuterium in mining effluent and acid rock drainage studies M. M. Ghomshei 7 D. M. Allen Abstract Oxygen-18 ( 18 O) and deuterium (D, or 2 H) are routinely used in hydrologic, climatologic and geothermal studies. In hydrology, stable iso- topes provide information on the type and topolo- gy (altitude and latitude) of the recharge waters and the historical effects on water, related to such physical processes as evaporation (in ponds), melt- ing (of snow or ice), condensation, evapotranspira- tion and mixing. In geothermal studies, stable iso- topes provide key information related to recharge and the various temperature-dependent water/rock isotope exchange reactions. The latter is assessed through the oxygen shift in the 18 O/D correlation. At acid rock drainage (ARD) sites, water/rock in- teractions are primarily controlled by pH and oxi- dation potential. Using the isotopic characteristics of the rocks and the recharge waters as a basis, the relative oxygen shift of the ARD effluent can pro- vide information 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 methodology for conducting oxygen and hydrogen isotope studies related to ARD and other mineral effluent problems. The methodology is based on: (1) comprehensive sampling of regional waters, ARD effluent and major contributing minerals and rocks, (2) isotopic and elemental analysis, and (3) data interpretation on the basis of a zero-dimen- sional (mass balance), multi-component mixing model. Key words Stable isotopes 7 Acid rock drainage 7 Mining effluent 7 Geochemical mixing Received: 15 January 1999 7 Accepted: 3 May 1999 M. M. Ghomshei Dept. of Mining and Min. Process Eng., 6350 Stores Rd., University of British Columbia, Vancouver, B.C. V6 T 1Z4, Canada D. M. Allen (Y) Dept. of Earth Sciences, Simon Fraser University, Burnaby, B.C. V5 A 1S6, Canada email: dallen6sfu.ca, Fax: c604–291–4198) Background Different isotopes of the same element differ slightly in chemical, and more significantly, in physical properties because of their mass differences. These mass differences are more pronounced in light elements, therefore, iso- topes of light elements are commonly used to character- ize the origin and cycle of different materials in environ- mental systems. The nuclear stability and the relative abundance of isotopes of oxygen and hydrogen have been widely documented (Table 1). Among these isotopes, 18 O, 16 O, 1 H, 2 H (D) and 3 H are routinely used in hydrologi- cal, climatological and geological studies. Oxygen and hydrogen isotopes are important in envi- ronmental studies because they are constituents of water and because they are conservative at near-surface tem- peratures. Oxygen and hydrogen isotopes are often used together in order to characterize the present and past processes in which water is a dynamic component. An important attribute of these isotopes, which makes them relatively unique in isotopic studies, is that their relative abundance in nature is highly variable. Isotopes of light elements (i.e. with low atomic numbers) undergo signifi- cant partitioning (enrichment or depletion) during the course of many mass-dependent chemical and physical processes. For example, the relative mass difference be- tween hydrogen isotopes ( 1 H and D) is two orders of magnitude greater than that of uranium isotopes. There- fore, natural isotopic partitioning (or fractionation) is de- tectable only in light elements up to potassium and cal- cium in the periodic table of elements. The most impor- tant elements, in which natural variations of the isotopic composition have been observed, include hydrogen, oxy- gen, carbon, nitrogen and sulfur (Jager and Hunziker 1979). Stable isotopes are analyzed using a mass spectrometer. 18 O and D (Deuterium) are determined by equilibration with carbon dioxide and uranium reduction, respectively. Analytical results are expressed as “permil” differences (denoted by d 18 O‰ and dD‰ from VSMOW (Vienna Standard Mean Ocean Water) with analytical precision of B0.15 and B1 permil, respectively. Measurements on VSMOW show that: D/H (VSMOW)p(155.76B0.05)!10 P6 (1) 18 O/ 16 O (VSMOW)p(2005.2B0.45)!10 P6 (2)