| Abstract |
The M’deek Geothermal System is a low-temperature (<180°C), fracture-controlled, geothermal system hosted in the transtensional Lakelse Graben 17 km south of Terrace, British Columbia. The system is expressed at the surface by the Lakelse Hot Springs, which are sodium-chloride-sulphate-type waters that reach temperatures up to 86°C. The temperature and chemistry of the Lakelse Hot Springs, and their proximal location to the Northern Cordilleran Volcanic Province, suggests that the system could be related to a magmatic heat source. To evaluate the temperature and source of the M’deek system, Kitselas Geothermal Inc. (KGI) conducted the most comprehensive investigation of the hot springs to date between 2021–2023. Water and gas samples were collected from the hot springs and regional water sources. These samples were analyzed for chemical composition and O, H, He and Ne isotopes. Physical properties including pH, temperature, and conductivity were also recorded. Na-K-Mg and silica geothermometers estimate a fluid temperature of 130–140°C for the M’deek system. This temperature is further supported by the hot springs’ chemical and isotopic compositions that indicate that subsurface boiling does not occur. Additionally, 3He/4He concentrations up to 1.55 R/Ra in the hot spring waters confirm the presence of mantle volatiles; however, these concentrations are still low compared to many other magmatically heated systems. Instead, extensional structures such as the Kitsumkalum-Kitimat Fault and the active Amesbury Creek Fault may facilitate deep crustal circulation, and possibly the upwelling of mantle related fluids to the surface from the relatively shallow mantle material underlying the area. |