3D STRUCTURAL ANALYSIS OF THE NORRIS HOT SPRINGS AND LINKED GEOTHERMAL SYSTEM

Recent work demonstrates that many geothermal systems are structurally controlled, suggesting geothermal exploration requires a comprehensive understanding of local and regional faulting. The Norris Hot Springs, located in the foothills of the Tobacco Root Mountains, Southwestern Montana, presents a novel study area to test structural control on geothermal system development. Further, extensive mining adjacent to the Norris Hot Springs suggests a correlation between local lode deposits and geothermal activity. We combine traditional geologic mapping, UAV-based photogrammetry, zircon U-Pb geochronology, seismic data, and 3D structural modeling using Petex Move to date and interpret the multistage development of local structures and their influence on the geothermal system beneath the Norris Hot Springs.

Thermal mapping and constraints provided by earthquake epicenters reveal that the geothermal activity and associated fluid pathways are hosted by Precambrian gneiss basement, but also outflows through the volcaniclastic Red Bluff unit. A nearby fault system is primarily comprised of high angle NNW-SSE trending normal faults, which often display pervasive alteration and polymetallic vein mineralization. Detrital zircon U-Pb dates from the Red Bluff unit suggest major faulting and associated hydrothermal alteration was complete by 71 Ma. Results from this study demonstrate the utility of combining surface mapping, 3D modeling, structural analysis, geochronology, and seismic data toward geothermal exploration and constrain the timing and influence of local faulting on geothermal activity at the Norris Hot Springs.