Borax Spring (NE¼ Sec. 14, Tl7N, R30E) at the northwest end of the Eightmile Flat part of the Salt Wells Basin 29 km southeast of Fallon had a reported temperature of 81°C (Stearns and others, 1937; Russell, 1885, pl. 8). Also, an exploration drill hole for saline minerals in NW¼ NW¼ Sec. 12, Tl7N, R30E reportedly hit very hot water at 120 m. The drill hole is in playa and lake sediments to a total depth of 152 m (NBMG unpub. data). Borax spring could not be located ca. 1980 (Trexler, Koenig, Flynn, and others, 1981, Table E2) or in summer 2002 (oral commun., Chris Sladek, 2002), but it was located by Mark Coolbaugh on a cold day in February 2005 (temperature of 81.6°C), along with 18 additional hot and warm springs in the area.
Prior to AMP Resources, LLC taking over the Salt Wells project, the Nevada Division of Minerals issued a geothermal project area permit to Nevada Geothermal Specialists, LLC for this project. It anticipated development of six production wells, four injection wells, and ten observation wells. One of the first wells drilled under this project was the Industrial Production Well PW-2 drilled by AMP Resources, LLC in the spring of 2005 to a depth of 471 feet. Static temperature surveys showed a peak temperature of 145°C and a flowing temperature of 140°C. The well was flowed at a rate of 2500 gpm for 46 hours with no drawdown. (Nevada Division of Minerals, 2005) A transmission line to the site of a proposed 26-MW power plant has been completed.
In March 2007, Enel North America, Inc. purchased AMP Resources, LLC from AMP Capital Partners and a minority investor. The Nevada Division of Minerals has issued a geothermal project area permit to Enel Salt Wells, LLC to drill up to eight production wells and eight injection wells. The project area is located in Secs. 23, 24, 25, 266, 35, and 36 of T17N, R30E.
Opal-cemented sands occur in the area (oral commun., Chris Sladek, 2002). Presumably these are the same as the sinter deposits reported by Edmiston and Benoit (1984) from an area of inactive hot springs that were reportedly active in the late 19th century (probably Borax Spring). A detailed map and description of the opalized Quaternary sediments is provided by Coolbaugh et al. (2004).
A cold NaCl spring yielded a Na-K-Ca geothermometer temperature of 207°C (Edmiston and Benoit, 1984). Morrison (1964, p. 92) reported siliceous sinter along a postulated east-striking fault near Salt Wells (probably N½ Sec. 2, T17N, R30E, based on Plate 3 of Morrison, 1964). Morrison (1964, p. 36) also reported sinter-cemented sand in eastern Wyemaha Valley, about 3 km north of Salt Wells. Many of these geothermal indications are located along or near the southern projection of the Rainbow Mountain fault, which bounds the east side of Rainbow Mountain to the north of U.S. Highway 50. This fault had movement during 1954 earthquakes (see Bell, 1984 and references therein). Morrison (1964, p. 35-36) also reported sinter-cemented sands in Sec. 26, T17N, R30E on the east flank of the Bunejug Mountains west of a geothermal well drilled in 1985 (see below).
Geothermal heat-flow studies have defined a geothermal anomaly on the western margin of the Salt Wells Basin (the western margin of Eightmile Flat). The anomaly extends from the community of Salt Wells south 12 km to the Simpson Pass area of the Cocoon Mountains (Edmiston and Benoit, 1984; GeothermEx, 2004, Fig. SAW00-1). About half of the 46 km2 anomaly is underlain by aquifers at depths of less than 100 m having temperatures greater than 100°C. Large-diameter geothermal wells drilled by Anadarko Production Company in 1980 and 1985 at the south end of this anomaly (SW¼ NW¼ Sec. 36, T17N, R30E and SW/NW¼ Sec. 25, T17N, R30E, respectively) reported temperatures as high as 181°C (2,587-m well) and 128°C (at 400 m) (NBMG geothermal files; Edmiston and Benoit, 1984). A shallow geothermal aquifer is in fractured basalt, which is being recharged by upwelling from deeper reservoirs (Edmiston, 1993). Morrison (1964, p. 36) also reported sinter-cemented sands northeast of the Cocoon Mountains, probably southeast of Rock Springs. Hoover and others (1977) reported telluric data and Peterson and Kaufmann (1977) reported principal gravity facts for the Salt Wells geothermal area.