In 1970, an oil exploration well drilled in northern Fish Springs Valley reported a bottom-hole temperature of 159°C at a depth of 2,775 m (Garside and Schilling, 1979).This well (Nevada Oil and Minerals V.R.S. No. 1 Well; SW¼ SW¼ NE¼ Sec. 16, T1S, R36E) in northern Fish Lake Valley encountered hot water during drilling. A temperature log of the well shows a steady temperature increase from 101°C at 457 m to 123°C at 2,775 m. However, the bottom-hole temperature reported in the electric log was 159°C (Nevada Oil and Gas Conservation Commission, unpub. data). Water flows from the well to soaking and swimming pools, which have temperatures of about 40ºC (Williams, 1996). The tops of the major lithologic units in the well are listed below:
In addition to the Nevada Oil and Minerals well, several other springs and water wells in Fish Lake Valley have higher than normal temperatures. Gap Spring, an unnamed spring about 2.4 km northeast of Gap Spring, Fish Spring, and Sand Spring have temperatures of 22.8-27.2°C and small discharges. At Gap Spring, a small spot of a few square meters at the spring outlet is slightly radioactive. The running water has the highest radioactivity, suggesting that the water may contain radon (Garside, 1973). Four water wells in the northern part of Fish Lake Valley have water temperatures of 23.3-25°C. Gap spring and several other springs in the area were visited in July 2005. Three samples were collected, including one from a well filling a swimming pool. The county developed the area for recreational use, including construction of camp sites. Several other springs could not be sampled in July (e.g., those south and southwest of the pool) because they had gone dry.
Surface valley fill 1,524 m volcanics 1,882 m limestone 1,935 m shale 2,004 m dolomite 2,015 m metasedimentary(?) rocks 2,475 m limestone 2,530 m metavolcanic(?) rocks 2560 m mudstone 2,621 m metavolcanic rocks
Exploration in the area by Steam Reserve Co. (a division of Amex Exploration) in the mid 1980s found >200°C fluids at a depth of 2,485 m (The Geyser, 1984), and temperatures as high as 157°C at 135 m were reported by Edmiston and Benoit (1984). Temperature-gradient well data has defined an area of thermal water over an area of 25 km2 or more centered on the NW¼ of T1S, R35E and the adjacent part of T1N, R36E. A large-diameter well drilled in Sec. 11, T1S, R35E, in 1984 has been described as a discovery well and a power plant was proposed in adjacent Sec. 14 (NBMG files). Tertiary sedimentary rocks are reported to depths of about 1,000 m; below that, fractured lower Cambrian phyllite and sandstone (Harkless Formation) are found (NBMG files). Extensive geologic, geophysical, and geochemical data sets are available in the private sector. Drilling includes 30 shallow temperature-gradient drill holes, five stratigraphic tests as deep as 1,200 m, and five large-diameter wells to as deep as 3,078 m (Alex Schriener, written commun., 2002). A small fumarole is reported from Sec. 6, T1S, R35E (GeothermEx, 2004), and middle Pleistocene sinter, opal-cemented sands, and siliceous root casts are reported from center, S½ Sec. 17, T1S, R36E (Reheis and others, 1993, p. 959-961).
Emigrant Prospect. Approximately 13 km east of the Steam Reserve anomaly, near the corners of T1N, T1S, and R36 and 37E (5 km southwest of Emigrant Pass), Fish Lake Green Power Co. reported temperatures up to 109ºC in mineral exploration and temperature gradient drill holes ~60-300 m deep (Emigrant prospect; GeothermEx, 2004; Hulen and others, 2005a, b). Thermal gradients for these drill holes are as high as 700ºC/km. The subsurface thermal anomaly extends over an area of >5 km2, mainly in Sec. 31, T1N, R37E and parts of Secs. 4, 5, 8, and 9, T1S, R37E (all protracted on the Goldfield 30x60-minute quadrangle). The only surface manifestation is a fumarole with crusts of manganese oxides and native sulfur on fractures. Argillization and local silicification and quartz veining are present, mainly in outcrops of Pliocene and Pleistocene sedimentary rocks, but also in Tertiary volcanic rocks and pre Tertiary metasedimentary rocks. The area of alteration is over 11 km2, but only a minor amount of the alteration can be unambiguously attributed to the present geothermal system (Hulen and other, 2005). Borate minerals have been mined from Pliocene lacustrine sedimentary rocks in the area of the geothermal anomaly. Ulexite is found as cottonball nodules and veinlets in the sedimentary rocks (Papke, 1976). Deep fluid flow is apparently controlled by north- to northeast-striking high-angle faults; however, shallow aquifers may be related to low-angle normal faults. Silica geothermometry suggests reservoir temperatures may be in the 150-170ºC range, but mixing cannot be discounted and higher temperatures are possible (Hulen and others, 2005a, b).
Photos
Fish Lake Valley 81-13 Well