Modeling a fractured geothermal reservoir using 3-D AMT data inversion: Insights from Garibaldi Volcanic Belt, British Columbia, Canada

Abstract

An audio-magnetotelluric (AMT) survey was conducted to explore for shallow geothermal resources in the Garibaldi Volcanic Belt, the location of which has the highest geothermal potential in Canada. The data cover the south Meager geothermal system, including Pylon Peak and Meager Creek which have proven borehole temperatures exceeding 250 °C. A dimensionality analysis of the AMT data suggests complex 3-D subsurface structure. The 3-D resistivity model of the area shows two high conductivity features near surface in the areas south of Pylon Peak and north of Meager Creek, both of which are related to hydrothermal alteration. These layers act as the caprock and connect close to the surface. The conductive zones reach surface near the locations of warm springs along Meager Creek. Clay cap layers are interpreted to consist mainly of smectite, illite and rare kaolinite with the resistivities below 15 Ωm in our model. The caprock overlays fractured quartz diorite permeated by hot water. This hot fluid reservoir is related to a higher resistivity feature coinciding with high temperature zones at a depth of approximately 1 km below sea level. This model illustrates possible conduits through which the hydrothermal fluids were transported to thermal springs at the surface. This research shows that integrating the AMT model, geology, and temperature data is crucial to build a conceptual model of the Mount Meager geothermal system to support targeted drilling by industry.