Cinnabar, metacinnabar, sulfur, and minor pyrite were reported at the Senator Mine (Senator Fumaroles) in the northern end of Dixie Valley. The fumaroles are located along the N30°E fault that bounds the eastern edge of the Stillwater Range (Lawrence, 1971). The fumaroles are located in SW¼ NW¼ Sec. 32, T25N, R36E. The mercury mineralization was discovered in 1968.
No hot springs are present at the site, as it was about 18 m to the water table in the 1970s. Cinnabar was apparently depositing in the 1970s around two main fumaroles that are 90 m east of the main deposit. Small amounts of sulfur and pyrite have also been deposited, and considerable solfataric alteration has taken place. Small volumes of steam with some hydrogen sulfide were being emitted at the vents, and preliminary work indicated that the cinnabar was being deposited from a vapor phase at the surface (Lawrence, 1971). The fumaroles were the only surface indication of subsurface geothermal activity, as no hot springs were known from the area. Sinter is known from an area about 5 km southwest of the fumaroles (Sec. 15, T24N, R36E; Waibel, 1987). Also, thin bands of sinter are found in alluvial fan deposits adjacent to the Dixie Valley frontal fault about 10 km to the southwest (Al Waibel, oral commun., 1983) of the fumaroles.
Considerable work has been conducted in the area beginning in the 1980s when exploration activities were conducted. A power plant was constructed at the site in 1988, and it produces 66 MW of electricity from a resource that was initially 250°C at depths between about 2,400 to 3,050 m. The amount of research that has been conducted at this site is extensive and cannot be fully summarized here. Summaries of recent work supported by the Department of Energy, as well as a list of published work at Dixie Valley, can be found at the following web site: www.unr.edu/geothermal/meetingsandpresentations/meetings_pres.html. Additional information on the geothermal area is available in GeothermEx (2004).
The Caithness Dixie Valley plant, the largest single geothermal power plant in Nevada, was purchased from Oxbow Geothermal Corp. in 2000. A pilot study has shown that high-quality silica can be extracted from the geothermal fluid; this process could both reduce silica scaling and produce a valuable mineral product (Lin and others, 2000). Pressure augmentation has included combining post-flash brine with water from a shallower local water well (Goerenger Well) prior to re-injection The production zone at 2-3 km depth is believed to be related to highly permeable fractures in and adjacent to the Dixie Valley fault, the major range-bounding fault on the west margin of Dixie Valley. It is uncertain whether the Dixie Valley fault is a single fault or several faults (see web site noted previously, Blackwell and others, 2000, and Smith and others, 2001); if it is interpreted as single fault, the dip is about 50°E (Benoit, 1999). Fluid flow is apparently up the fault from depth, and into fractured Mesozoic metaigneous rocks and overlying Tertiary volcanic rocks (e.g., Desormier, 1987).
Nearby and to the west of the main producing area are the “oldest known spring deposits in the Dixie Valley region are those currently associated with the Dead Travertine (Cottonwood Travertine) springs about 2 km upstream of the mouth of Cottonwood Canyon” (see Appendix 5, of Blackwell et al., 2006). “The deposit drapes the northeast side of the canyon wall over an elevation range of 275 m and is roughly 400 m wide at the base (along the dirt road), 150 m wide at the crown, and 550 m long horizontally. The deposit is fault controlled because Jurassic quartzite is faulted down to the northwest against Jurassic gabbro in a narrow, northeast trending window within the travertine (F. Goff and C.J. Janik, unpublished mapping, 1999). This fault extends beyond the deposit to the northeast up the canyon wall. Rocks within the window and just above the crown of the deposit are highly fractured and contain numerous calcite veins. A sample of dense, honey-colored calcite from one of these veins yielded U/Th disequilibrium and protactinium-231 ages of 182 ± 4 ka and 161 ± 15 ka, respectively (Goff et al., 2002). More recently, Dixon et al. (2003) reported a preliminary U/Th isochron age of 100 ka from four layered travertine samples obtained throughout the deposit. Determination of whether or not these deposits were formed from spring waters of compositions and temperatures different from the cold seeps of today would require considerable additional work. However, it appears that carbonate-rich fluids have discharged in this area for 150 ka or more.” (Blackwell et al., 2006 (in review))
Photos
Federal 65-18 well flow test, Dixie Valley, Nevada. The geothermal plant at Dixie Valley is operated by Caithness Dixie Valley LLC, 9790 Gateway Drive, Ste. 200, Reno, NV 89521
Photo of cooling units at the Dixie Valley Power Plant. The geothermal plant at Dixie Valley is operated by Caithness Dixie Valley LLC, 9790 Gateway Drive, Ste. 200, Reno, NV 89521
Dixie Valley S.W. Lamb No. 3 well (Sunoco Energy Development Co.) flow test. The geothermal plant at Dixie Valley is operated by Caithness Dixie Valley LLC, 9790 Gateway Drive, Ste. 200, Reno, NV 89521
Dixie Valley S.W. Lamb No. 3 flow demonstration. The geothermal plant at Dixie Valley is operated by Caithness Dixie Valley LLC, 9790 Gateway Drive, Ste. 200, Reno, NV 89521
Dixie Valley Senator Fumaroles - silicified rock. The geothermal plant at Dixie Valley is operated by Caithness Dixie Valley LLC, 9790 Gateway Drive, Ste. 200, Reno, NV 89521
Dixie Valley Senator Fumaroles - sulfur. The geothermal plant at Dixie Valley is operated by Caithness Dixie Valley LLC, 9790 Gateway Drive, Ste. 200, Reno, NV 89521
Schematic cross section at Dixie Valley, showing single and double fault models. From Blackwell and others, 1999. The geothermal plant at Dixie Valley is operated by Caithness Dixie Valley LLC, 9790 Gateway Drive, Ste. 200, Reno, NV 89521