Structural Controls of Black Warrior Geothermal System
Washoe-Churchill Counties, Truckee Range, Northwestern Nevada, USA
Masters Thesis Defense by Andrew J. Sadowski
Advisor: Jim Faulds, NBMG Director and State Geologist
Monday, May 2, 2016, 3:00 p.m., LME 417 at University of Nevada, Reno
The Black Warrior geothermal system lies 20 km east of the southern end of Pyramid Lake in the Truckee Range of northwestern Nevada on the Washoe-Churchill county line. It is an amagmatic blind geothermal system, as the region lacks recent (<5 Ma) volcanism and the system lacks hydrothermal surface manifestations (no fumaroles, hot springs, sinter deposits, or high temperature alteration). The system was discovered by shallow temperature gradient drilling (100-600 m, max temp: 128°C) by Phillips Petroleum Company in the 1980s and 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 igneous intrusive and metamorphic basement. 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: (1) a fault termination of the southeastern range-front fault with accompanying horse-tail splaying producing an area with abundant closely spaced faults and high fracture permeability; and/or (2) a fault step-over in a broad left-step of the major normal faults, whereby many closely-spaced minor faults provide hard linkage and a zone of high fracture permeability. In either case, the study area lies in a favorable structural setting for geothermal activity and may host a robust geothermal system at depth.