The MH-2 core from project hotspot: Description, geologic interpretation, and significance to geothermal exploration in the Western Snake River Plain, Idaho

The MH-2 science drill hole, on Mountain Home Air Force Base, Idaho, was drilled in 2012 to a total depth 1821 m as part of Project Hotspot. It encountered flowing artesian thermal water at 1,745 m below ground surface. This signature of a potential blind high temperature geothermal resource indicates that further analyses are needed to characterize the resource. Whole rock core was recovered to a total depth of 1821 m below ground surface and a suite of wireline logs collected. In this thesis I describe the lithologies represented in the core, correlate these lithologies to outcrop analogs, and identify and characterize petrophysical properties observable within the wireline logs, which represent fine-scale variations in stratigraphy, composition and/or alteration.;The lithologies in the core are a series of basalts, brecciated and altered basalt, basaltic sands, carbonate-rich muds, and siliciclastic sediments. Basalt flows with evidence of increasing influence of an aqueous environment with time typify the lower half of core, whereas the upper half represents a period of diminished volcanism, lacustrine depositional environment, and a catastrophic water overflow event. The top of the core represents a resurgence of basaltic volcanism in the area. An overprint of brecciation at depth, fracturing, and secondary mineralization records the history of the geothermal system.;All the elements of a relatively shallow and potentially energy generating geothermal resource are present at the MH-2 well location. These new data from the MH-2 borehole contributes to evaluating a parallel geothermal risk assessment of the Snake River Plain. Play fairway analysis was implemented for perhaps the first time in a geothermal regime. The Snake River Plain was divided up into three distinct play types; the area surrounding the Mountain Home Air Force Base was systematically identified as prospective. A region where sedimentary and altered rocks may create a seal, and blind faults create porosity in deep basalts.