Geochemistry and isotope hydrogeology of the Mount Edziza – Mess Creek geothermal area

Abstract

The Mount Edziza volcanic complex, a Recent volcano within British Columbia's northern Intermontane Belt, and the adjacent Mess Creek valley are investigated to evaluate the origin, geothermal history, and age of associated thermal waters. Samples of thermal and cold groundwaters, runoff, and glacier ice were collected for chemical and environmental isotope (18O/2H, 3H, [Formula: see text], [Formula: see text]) analysis.Mount Edziza thermal waters, discharging at 36 and 46 °C from extensive travertine formations at the base of the volcanic pile, originate as glacier meltwater on the summit of the complex. Their Na(Ca,Mg)–HCO3 chemistry is a product of alteration reactions with alkali basalts under a high CO2 partial pressure. Chemical and isotopic geothermometers suggest that subsurface temperatures are less than about 100 °C. Carbon-13 data show that the high carbon dioxide contents (close to 1 bar (100 kPa) pressure) likely originate through high-temperature decarbonation of marine carbonates at depth, and manifest a deep geothermal component in an essentially high-level geothermal flow system.Mess Creek thermal waters discharge at 43 °C from a fault-controlled flow system unrelated to the Mount Edziza complex, showing evidence of equilibrium with local basement rocks at temperatures less than about 100 °C. Deep circulation within a region of slightly higher than normal geothermal gradients is given as the mechanism for heating.The low 3H contents suggest that the thermal waters are tritium free (> 30 years old) and are mixing with between 10 and 40% nonthermal groundwater in the discharge areas.