The Dixie Comstock Mine is situated on the eastern margin of the Stillwater Range, about 110 miles east of Reno. The range margin, which separates the Stillwater Range to the west from Dixie Valley to the east, is sharply curvilinear, locally very steep, and the site of several thermal springs. The mine was discovered in 1934 by panning drainages along the Stillwater Range margin, and yielded nearly five thousand ounces of gold during intermittent operations between 1938 to 1970 (Vikre, 1994, p. 707). The geology of the Dixie Comstock Mine is extensively discussed by Vikre (1994).
Vanderburg (1940, p. 48) reported that mining in the Dixie Comstock Mine was hindered by the intense heat and a large volume of hot water in the mine workings less than 23 m from the surface. These workings referred to by Vanderburg are in NW¼ Sec. 14, T23N, R35E near the major range-front fault which had movement in the 1954 Dixie Valley earthquake (Willden and Speed, 1974). This fault and related parallel faults continue south 8.8 km to the Dixie Hot Springs area, and north to Senator Fumaroles. Waring (1965) reported a small spring in T23N, R35E, which may possibly be near the Dixie Comstock Mine. In 1979, Thermal Power Co. drilled a 2,750-m well (Dixie Federal 45-14; NE¼ SW¼ Sec. 14, T23N, R35E) 762 m southeast of the mine. The well recorded a 176°C fluid entry zone at 1774-1789 m and 197°C at total depth (Edmiston and Benoit, 1984).
Located approximately 1 km southeast of the abandoned mine and 12 km southwest of the Dixie production zone, the DF 45-14 well was drilled in 1979 in alluvium near the margin of fanglomerate. It was drilled “to a depth of 2750 m (9022 ft) penetrating 335 m of unconsolidated basin-fill sediments, 457 m of Tertiary volcanic rocks, and 1982 m of Upper Triassic metasedimentary rocks locally intruded by gabbro/diorite sills and dikes (Mackay Minerals Research Institute, 1980). The well was cased and fluids entered the well near the bottom of the hole. Temperature surveys show a maximum temperature of 196°C at total depth. The well has been discharging intermittently (surging) through a pipe into a pond surrounded by desert shrubs on the eastern side of the wellhead since it was drilled.
The wellhead was opened in April 1998 and a mini separator was attached to obtain fluid and gas samples at a separation temperature of 125°C (Goff et al., 2002). The brine contains high concentrations of SiO2, As, B, Br, and Li, and low concentrations of Ca and Mg. The Cl content is 481 ppm. Of all thermal waters outside the immediate area of the Dixie production zone, DF 45-14 water is the most similar in general composition to deep reservoir waters. Although the compositions are similar, chloride variation plots generally show that the DF 45-14 fluid is not derived from or part of the 245°C reservoir. Because sampling conditions were unstable, the gas sample is not considered completely representative (28 mol-% air contamination). None-the-less, the sample is relatively rich in CO2, H2S, H2, and CH4, typical of high-temperature geothermal gases. Chemical geothermometers indicate a subsurface equilibration temperature of about 200°C for DF 45-14 fluids, essentially identical to the measured BHT.” (Blackwell et al., 2006 (in review))