Assessment of thermo-hydraulic properties of rock samples near Takhini Hot Springs, Yukon

The Takhini Hot Springs area north of Whitehorse, Yukon overlies a geothermal heat source that manifests as a 46°C water seep at surface. Despite its long-term use as a tourist swimming facility, the origins and geological setting of the hot spring remains poorly understood. The objective of this study is to assess the thermo-hydraulic properties of rock samples from drill core and outcrops near Takhini Hot Springs to better explain the presence of this hydrothermal system. A moderate rock thermal conductivity (average of ~3 W m-1 K-1) and a low matrix hydraulic conductivity for consolidated rocks (on the order of 10-9 m s-1) corresponding to a linear geothermal gradient of 16°C km-1 in the upper part of the Takhini well indicate conductive heat transfer between 50 and 450 m depth. Hydraulic conductivity of fractured and brecciated rocks on the order of 10-5  m s-1, and topographic contrasts affecting the hydrostatic pressure driving groundwater flow in the area suggest that forced convective heat transfer in the bottom of the Takhini well is responsible for the strong geothermal gradient of 250°C km-1 observed between 450 and 500 m depth. Steep faults appear to be a key pathway for deep groundwater to seep to surface and can explain the geothermal context in the vicinity of the Takhini well. Such a framework is a typical geothermal play type in orogenic belts. This research, therefore, helps to characterize the subsurface and provides critical information needed for a successful exploration of geothermal energy resources.