TOPIC: Structural Controls of Black Warrior Blind Geothermal System, Washoe-Churchill Counties, Truckee Range, Northwestern Nevada, USA
SPEAKER: Andrew Sadowski, Geologist, Reno, NV
ABSTRACT: The Black Warrior geothermal system lies 20 km east of the southern end of Pyramid Lake in the Truckee Range of northwestern Nevada. It is an amagmatic blind geothermal system, lacking hydrothermal surface manifestations (no fumaroles, hot springs, sinter deposits, or high temperature alteration) and also lacks recent (<5 Ma) volcanism. The system was discovered by shallow temperature gradient drilling (100-600 m, max temp: 128°C) by Phillips Petroleum Company in the 1980s and also observed with a 2-m shallow temperature survey circa 2011.
The thermal anomaly resides in a structurally complex zone that has not been previously characterized. Detailed geologic mapping in the area has identified faults and stratigraphic relationships between successive and interfingering Tertiary volcanic sequences that nonconformably overlie Mesozoic plutonic and metamorphic basement. Inversion of kinematic fault data and regional relations indicate a NW-trending extension direction (300-310°). The structural framework is characterized by north-northeast-striking, moderately to steeply west-dipping normal faults that terminate and step in the vicinity of the thermal anomaly. This suggests two possible favorable structural settings for this geothermal system: (1) a fault termination of the southeastern range-front fault with accompanying ~2 km wide horse-tail splaying producing an area with abundant closely spaced faults and high fracture permeability; and/or (2) a fault step-over ~3-5 km wide between two major west-dipping normal faults, whereby many closely-spaced minor faults produce a zone of high fracture permeability. Thus, the Black Warrior thermal anomaly appears to reside in a hybrid structural setting in which the faults are favorably oriented for dilation in the local stress field. These structural characteristics are advantageous for geothermal activity and suggest that Black Warrior may host a viable geothermal system with suitable permeability at depth. However, additional exploration is recommended to better define the system and select drilling sites. Ultimately, the structural relationships at Black Warrior may help to guide exploration efforts for other blind geothermal systems in the Great Basin region and other extensional settings.
BIO: Andrew Sadowski
Born and raised on the east coast in south Florida, Andrew began pursuing geology during his undergraduate career at Cornell University in upstate New York. After graduation, he worked in the water resources and environmental sector in New Hampshire, before returning to graduate school to study the structural geology of geothermal systems. He attended field camp across the western US as well as western Argentina, and TA’d UNR’s field camp. He has toured Iceland with fellow NBMG/UNR folks to further his understanding of geothermal systems, and has had geothermal industry internships at Ormat Nevada and Calpine’s The Geysers. At the 2016 Geological Society of America annual meeting in Denver, he took second place in the student mapping competition for his geologic map of Black Warrior. In May 2016 he earned a masters in geology from the University of Nevada, Reno, and is now working on the Nevada play fairway project with Dr. Jim Faulds.
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