The O and H isotopic composition of minerals can provide valuable information on the source of the fluids and temperature of mineral precipitation. To obtain accurate isotopic measurements using SIMS, it is important to select chemically similar standards and samples to correct for both matrix effects and instrumental mass fractionation (IMF), collectively termed instrumental mass bias (IMB). For certain mineral groups (e.g. tourmalines), there are large variations in major element composition between species. This study uses three of these tourmaline species (schorl, dravite, and elbaite) to construct calibration curves to correct for IMB during SIMS analysis of O and H isotopes. I have applied my technique to analyses of tourmalines from the Wollaston Group, Athabasca region, Saskatchewan to test my method, and I have calculated the O and H isotopic composition of the fluids that formed these tourmalines.