| Abstract |
Understanding regional controls on the location and viability of geothermal resources is a key part of the geothermal exploration process and can increase the success-rate and cost-effectiveness of subsequent targeted reservoir-scale studies. The magnetotelluric (MT) method has been widely used in this exploration task as it can determine fluid distribution within the crust on both regional and local scales. In the region 48-54°N and 112-122°W, we have assembled data from more than 300 broadband and long-period MT stations, including data from the LITHOPROBE transects, our own deployments, and those of other research groups. In this paper we apply this extensive MT dataset to geothermal exploration in the Southern Rocky Mountain Trench (SRMT), a major fault-controlled valley in southeastern British Columbia. The SRMT is a promising geothermal target as it is characterized by relatively high heat flow (~75 mW/m2) and a number of surface geothermal features such as the Radium and Fairmont hot springs. It is thought that geothermal fluid circulation in the SRMT is controlled by fault structures, although the depth of the underlying heat source is uncertain. MT data can potentially detect the presence of fluids in fault zones in the upper crust, as well as the deeper sources of heat. The MT data were converted into a resistivity model using a 3-D inversion algorithm, and the upper 80 km is presented and discussed in terms of the potential for future geothermal exploration. In our preliminary model, low resistivity zones are observed in the crust of southeastern British Columbia and likely indicate the presence of saline fluids, and perhaps partial melt in the lowermost crust. Crustal conductors beneath the SRMT are commonly, but not always, associated with hot springs, and may be representative of fluids in faults and reservoirs. An especially notable conductive feature occurs under the Canoe River hot spring and we have named it the Valemount Conductor. This feature is 10-20 km thick, extends horizontally for more than 100 km, and may represent a combination of saline fluids, partial melt, and conductive minerals. Future geophysical investigations, such as higher density MT deployments, are recommended for two regions in order to define the fine-scale crustal resistivity structure associated with these regional features: (1) the Redwall and Lussier River faults and (2) the SRMT northwest of Golden, BC. |