Exploration History and Conceptual Model For The Dixie Meadows Geothermal Field, Nevada, Usa

Ormat has executed a comprehensive exploration program at Dixie Meadows, Nevada, leading to the discovery of a high permeability, 150°C geothermal resource. The reservoir is a low TDS (0.17 wt%) Na-Cl, low NCG fluid of meteoric origin, hosted within Triassic Metasediments and Cretaceous intrusive rock. Exploration drilling during the early 1980’s and by Ormat in 2012 identified outflow ranging in temperature from 70-140°C which is channeled in the upper 50 m of the subsurface near the trace of ENE-striking fault zones within permeable units in the alluvium and is also manifested as weak steam vents along the Dixie Valley range front fault scarp which ruptured in 1954 (M6.8). The thermal fluids discharge as hot springs in marshlands to the east.

The early exploration drilling during the 1980’s and in 2011 failed to identify the source of upflow. A revised conceptual model was developed based on detailed geologic mapping by Ormat and synthesis with the available drilling, geophysical, and geochemical datasets. A deep core hole tested two theories and proved the reservoir to be sourced from below the Dixie Valley Fault zone. Upflow for the resource is dominantly controlled by a series of ENE-striking faults which contain dilated fractures oriented ENE to ESE that occur at an extensional left step/bend of the Dixie Valley Range Front Fault.This paper serves as a case study to document the geoscientific data, conceptual model, and exploration strategy of an archetypal Basin and Range system in Nevada.