Stanford Geothermal WorkshopFebruary 10-12, 2025

The Mdeek Geothermal System is a low-temperature ( less than 180°C), fracture-controlled, transtensional system hosted in the Lakelse Graben 17 km south of Terrace, BC. The system is expressed at the surface by the Lakelse Hot Springs, which are sodium-chloride-sulphate-type waters and are one of the the hottest geothermal springs in British Columbia at 85°C. Kitselas Geothermal Inc. (KGI) has been exploring the Mdeek Geothermal System for almost a decade and is now in the process of planning and preparing for the drilling of the first deep geothermal exploration wells targeting the resource. Justification for these exploration wells is partly based on the interpretations made from the chemistry of the hot spring water, which has provided insight into the source and temperature of the geothermal reservoir. The high sulphate content of the Lakelse hot springs and proximal location to the Stikine Volcanic Zone suggests that the system could be related to a magmatic heat source. To evaluate the temperature and source of the Mdeek system, KGI conducted the most comprehensive investigation of the hot springs to date between 2021–2023. During this sampling campaign, water and gas samples were collected from the hot springs and other surficial water. These water samples were analyzed for cation and anion chemistry, gas chemistry, and O, H, He and Ne isotopes. Physical properties including pH, temperature, and conductivity, were also recorded. By examining new and historic chemical data from the hot springs, KGI was able to use the Na-K-Mg and silica geothermometers to estimate a reservoir temperature for the Mdeek system. This estimated temperature is further supported by the relative concentrations of silica and CaCO3[equiv], which indicate that the geothermal system does not boil in the subsurface. Additionally, slightly elevated 3He concentrations in the hot spring water suggests a deep connection to a primordial 3He source (i.e., a magmatic system); however, compared to other magmatic geothermal systems, 3He concentrations are still rather low. Instead, extensional structures such as the Kitsumkalum-Kitimat Fault and the active Amesbury Creek Fault are more likely to act as deep conduits for 3He transport from relatively shallow mantle material in the area. While a direct link to a magmatic source is unlikely, it does remain a possibility. Future drilling at the Mdeek system aims to target and sample the geothermal reservoir. Undiluted samples collected directly from the reservoir should conclusively determine the source of the geothermal system.

Topic: Geochemistry