Oxygen and hydrogen isotopes in deep thermal waters from the south meager creek geothermal area, british columbia, canada

Abstract

Deuterium and oxygen-18 ( 18O) have been measured in deep thermal, shallow thermal and non-thermal water samples collected at various times between 1982 and 1989 from the Meager Creek area, with the aim of assessing the origin of the thermal waters. The isotopic composition of the reservoir waters ( δ 18 O = −13‰ and δ D = −114.8‰ ) was calculated from data on post-flash deep thermal waters, using a two-stage steam loss model. The reservoir composition shows an oxygen shift of 2.4‰ relative to the local meteoric water line. The composition of the recharge, obtained by removing the oxygen shift, is isotopically heavier than the average local meteoric waters, suggesting that the recharge may be from an area to the west of Mt Meager where isotopically heavier ground-waters are likely to be found. The small δ 18O shift of the deep high-temperature waters is indicative of dominance of fracture-related permeability in the reservoir. Analysis of the chemistry and the temperature of the waters from hot springs and shallow thermal wells suggests that these waters have evolved from the deep geothermal waters through dilution by meteoric waters and about 40°C adiabatic cooling (steam loss).