Rye Patch Geothermal Area

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Rye Patch Geothermal Area

Area Overview

Geothermal Area Profile

Location: Pershing County, Nevada

Exploration Region: Northwest Basin and Range Geothermal Region

GEA Development Phase: Operational"Operational" is not in the list of possible values (Phase I - Resource Procurement and Identification, Phase II - Resource Exploration and Confirmation, Phase III - Permitting and Initial Development, Phase IV - Resource Production and Power Plant Construction) for this property.

Coordinates: 40.535°, -118.2683333°

Resource Estimate

Mean Reservoir Temp: 213°C486.15 K
415.4 °F
875.07 °R

Estimated Reservoir Volume: 4.71 km³4,710,000,000 m³
1.13 mi³
166,332,080,255.91 ft³
6,160,447,415.49 yd³
4,710,000,000,000 L

Mean Capacity: 12.5 MW12,500 kW
12,500,000 W
12,500,000,000 mW
0.0125 GW
1.25e-5 TW

USGS Mean Reservoir Temp: 205°C478.15 K
401 °F
860.67 °R

USGS Estimated Reservoir Volume: 9 km³ [3]

USGS Mean Capacity: 90 MW [3]

Rye Patch Geothermal Area is located in Pershing County, Nevada between Winnemucca and Lovelock. The area can be found 190 km northeast of Reno along I-80 and is bounded by the Midas Lineament to the North (trends northeast) and a sinistral strike-slip fault zone to the South. [4] [5]

Rye Patch is located within the Basin and Range Province in the Northern and Central Great Basin. The overall tectonics of the area changed from compression to extension when, 30 Ma, the angle of Farallon plate subduction steepened and thus narrowed the related continental calc-alkaline volcanic arc. Block faulting began 20-10 Ma, but mostly occurred <15 Ma. In the late Cenozoic, there was a transition from a magmatic arc/subduction zone to extension. The area contains valley grabens, half-grabens, mountain horsts, and tilted blocks that formed during this time period. [6] [7] [8]

Rye Patch area has a tilt in the east/southeast direction that is perpendicular to the strike of Cenozoic strata and the trend of the elongate mountain ranges. In the north/northeast direction, tilt is parallel to the strike of the Cenozoic strata and the trend of mountain ranges. There are west/northwest transverse zones that bound the anticlines and synclines.[6]

Rye Patch Known Geothermal Resource Area (KGRA) contains two blind geothermal anomalies: Humboldt House anomaly and Rye Patch anomaly. Humboldt House is a high temperature (>200° C) geothermal anomaly to the North, and it underlies a series of coalescing alluvial fans descending from the western flank of the Humboldt Range. Rye Patch is a moderate temperature geothermal anomaly to the South. In these anomalies, there is deep hydrothermal circulation in the shallow crust. [9] [7] [10] [4]

History and Infrastructure

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Power Production Profile

Gross Production Capacity:

Net Production Capacity:

Owners  :

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Other Uses:

• The siliceous and calcareous sinter deposits south and east of Humboldt House were first discovered by Croffut in 1872. The deposits contain gypsum, sulfur, and some mercury. [11]

• Geothermal exploration was slow from 1962 to 1973, focusing on deeper drilling. The Geothermal Steam Act of 1970 permitted future leasing and development on federal lands, but federal lands were unavailable for geothermal leasing until 1974. [10]

• In 1974, a regional shallow temperature-gradient drilling program (<20 m) was conducted by Phillips Petroleum Company in order to identify Humboldt House and Rye Patch geothermal anomalies. A sub-surface water temperature of 260° C was predicted for the near-surface thermal anomaly. [10] [4]

• The first geothermal production well was drilled in November 1977 in the Rye Patch anomaly area. The well, Campbell E-1, was drilled to 560 m depth and, producing from an unconsolidated zone of alluvial limestone boulders. Campbell E-1 produced a 183° C fluid at 6050 l/s USGS subsequently deemed the area Rye Patch KGRA, meaning that the geothermal resource is viable for monetary expenditures. [4] [10]

• An audiomagnetotelluric study was completed by Long and Batzle in 1976, in which resistivity values for various frequencies were found. A U.S. Geological Survey A.M.T. Data Log and audiomagnetotelluric station map of Rye Patch KGRA were created. Their prediction was that no geothermal reservoir exists in the horst block, but rather exists in the graben block and contains all sinter deposits. [4] [12]

• Two more production wells were drilled in 1978 and 1979. Union Oil Company’s Campbell No. 1 well was drilled in Humboldt House geothermal anomaly to a depth of 2080 m; temperatures reached 205° C but only at 0.17 l/s. Phillips Petroleum Company’s Campbell E-2 well-- north of Campbell E-1—was drilled as a dry hole to 2450 m depth. In addition, 40 temperature gradient and stratigraphic wells were drilled to depths of 90-610 m. [4] [10]

• In 1981, Sibbett and Glenn used cutting and well log descriptions from Phillips Petroleum Company’s Campbell E-2 well and predicted a cross section extending from west to east of the well into the Humboldt Range. [13]

• Schaefer 1986 produced a Bouguer gravity anomaly map containing the depth to the bedrock, 30 shallow temperatures based on the gravity readings, and 6 seismic lines. [14]

• In 1991, there was commercial development of the KGRA. A successful production well (44-28) (one of the 40 wells from Phillips Petroleum Company) led to construction of a 12.7 MW power plant in 1993 by Ormat. Wells 68-21, 52-28, 72-28, and E-1 were produced to supply the plant. Seven production wells were drilled concurrently with the plant in the same area as the successful well, but these were unsuccessful due to low temperature or lack of fluid flow. Well 72-28, a shallow, low-temperature well, was successful on the basis of production of additional thermal gradient wells. Moreover, USGS set up 172 gravity stations in 1991 along four major transects and several offshoots across the valley between the Humboldt Range (east) and the Trinity and Antelope Ranges (west). [4] [5] [9]

• In 1997, a Vertical Seismic Profiling (VSP) study was completed by DOE Lawrence Berkeley National Laboratory (LBNL), The Industrial Corporation (TIC), and Transpacific Geothermal Inc. (TGI) to 1) apply seismic imaging methods for the geothermal reservoir, 2) determine the seismic reflectivity of the reservoir horizons, and 3) obtain reservoir velocity information. The success of these results lead to a 3D seismic reflection survey proposed by TGI to cover a more extended region. [5] [15]

• In 1998, the 3D surface seismic reflection survey was completed over 3 square miles with 12 north/south receiver lines and 25 east/west source lines with a spacing of 245. A single-level, high temperature, hydraulic well-locking, three-component seismometer was installed at 3900 ft. depth in well 46-28 and used vibrosis to record waves generated by all surface sounds. A high-temperature geophone was installed in an original VSP well at depth of 3900 ft., which recorded all seismic waves generated by surface sources in addition to the seismic-reflection data at a frequency of 25 Hz for arriving waves. The seismic data was processed by two contractors: SECO of Pasadene, CA, and Trend Technology of Midland, TX. SECO provided 1) a report outlining the permits, surveying, and data acquisition and processing, 2) a binder with sample 2D sections from processed 3D volumes, and 3) a log describing the corrected field tapes that were sent to LBNL. Trend Technology provided LBNL with the final stack, final migration in time and depth, and final stacking velocities used. Neither refraction nor reflection static corrections helped improve the data quality. [15] [5]

• In 1999, Teplow produced a report of 3D seismic reflection data. Included was a gravity survey that calculated the Bouguer residual from 334 stations. Also, Feighner et al., 1999 presented results of the 3D seismic survey and revealed that possible faulting at depth was based on surface seismic-reflection studies as well as surface-to-surface tomographic-time-travel investigations. [15]

• In 2000, Mt Wheeler Power received a grant from DOE Geothermal Resource Exploration and Definition (GRED) Projects to evaluate the productivity of Rye Patch fault intersection with the other east/west striking fault. Rye Patch was a GRED I project that was completed in April 2002, with the award given to Presco Energy, LLC. Well 78-28 had previously lost-circulation, but re-drilling and use of a polyurethane foam cement showed success for this project, and the well was deepened from 298 m to 643 m. This successful plugging lowered the point of lost circulation to 643 m. Temperatures in the well range from 150-179°C, indicating high productivity. The well’s long-term sustained production was 111,800 lb/hr; it could be maintained at 1,500,000 lb/hr for 27 years. [4] (Warpinski et al., 2004) (Mansure et al., 2001)

• Presco Energy, LLC acquired Rye Patch from Mt Wheeler Power in 2001. Presco is the current owner of Rye Patch.

• In 2002, Michels reported on the hydrogeochemistry of thermal waters. 82 sets of analyses were produced from 9 wells to be evaluated. [16]

• In 2003, University of Nevada Reno Great Basin Center for Geothermal Energy received a grant from DOE to work with Presco Energy LLC and Florida Canyon Mine to research and drill more wells to expand development onto Florida Canyon Mine property. From May-July 2003, 5 wells were drilled: one to 152 m, three to 305 m, and the last one to 457 m. 564 m of core were obtained from the wells, along with lithology descriptions, gamma ray logs, and temperature logs. Core logging and analysis were completed by Johnson 2003 and Johnson et al., 2004. Scanning Electron Microscopy (SEM) was completed to determine mineral phase relationships; Inductively Coupled Plasma-Mass Spectroscopy (ICP-MS) for whole rock geochemistry was completed to determine trace elements. Petrographic study of fluid inclusions, laser ablation, and x-ray diffraction were completed for clay identification. Furthermore, Davis 2011 re-logged, described, and sampled core. There are photographed core sets and samples for 3 wells.[4] [17] [18]

• In 2004, University of California Santa Cruz and DOE completed HyMAP hyperspectral imagery and Optech light detection and ranging (LiDAR) imaging of the Humboldt River basin to test fault patterns, surface mineral alteration from hydrothermal alteration, and mud volcanoes in the Humboldt/Rye Patch district. The goals of the project were to gain clearer view of faults, to determine which fault segments have been hydrothermally active, and to ascertain whether mud diapirism in the region could be caused by seismic shaking. The HyMAP data was from 19 north/south flight lines, which covered 500 square km at 2000-5000 m above ground level, and was subsequently processed using the RSI commercial software package ENVI. The mineralogy distribution for Humboldt House was mapped over a 4 km by 8 km area northwest of Florida Canyon Mine and east of Humboldt River. With the above information, faults and paleo-shorelines of Lake Lahontan were identified (elevation of 1290 m, age 12500 ± 500) and abundant hot spring and fumarole deposits were found in the Humboldt River Valley, rather than near the mountain ranges. The linear distribution of the hot springs and fumaroles implied structurally controlled deposition. [4] (MacKnight et al., 2005) (Silver et al., 2011)

• Sanyal et al., 2006 made a conceptual model of Rye Patch geothermal field via lithological, geophysical, and temperature logs in addition to production, injection, and pressure data from 8 production wells. The east/west structure was mapped more to the northeast than it had been previously. [9]

• In 2008, Presco Energy completed an aeromagnetic survey with gravity and ground-based magnetic anomalies. The aeromagnetic survey consisted of 539 line-miles that covered 65 square miles, and ultralight flew at 150 m terrain clearance. Results show the lateral limits of where the flow is likely to occur. Presco Energy used the 2D VPS wells 51-21 and 68-21 (receiver wells) and 44-28 (validation well). An attempt was made to dynamically cool the wellbore to decrease temperatures below the limits of the sensors, but rapid receiver well reheating limited the vertical aperture and imaging was limited in the horizontal dimension due to heterogeneity and poor reflectivity. Rye Patch was awarded DOE “innovative technology” grant in 2009. [19] [4]

• Infrared spectrometry by Calvin et al., 2010 was completed from well 3-1 to identify temperature dependent mineral assemblages from 198-306 m depth, including layered silicates, zeolites, opal, calcite, and iron oxides and hydroxides. The identification results from Calvin et al., 2010 included weakly altered mafics, illite/chlorite, hydrated quartz/opal, kaolinite, and jarosite. [20]

• In 2011, Presco Energy deepened well 44-28 from 1059 m depth to 1275 m to research the high enthalpy zone below Natchez Pass clastic layer. Flow rate was 2385 l*m 1 and the temperature was 200° C after 20 hours of pumping. Furthermore, Silver et al., 2011 identified two sand volcanoes and a field of low-carbonate mounds (from recent and paleo-seismicity that initiated liquefaction). This is likely to be associated with highstands of Lake Lahontan when ground was saturated, rather than with recent events. [4]

• In 2013, McDonald completed gravity and ground-based magnetic surveys-- augmented with existing seismic, aeromagnetic, remote sensing, and geochemical data-- to delineate approximate fault locations, lengths, trends, and dip angles. Gravity anomalies were present from Rye Patch Fault and from the southeast fault and show high dip angles (~80°). The southeast fault might represent a southern divide or barrier. Geothermometry showed that the temperature of the geothermal source is 200-250° C. [4]

Regulatory and Environmental Issues

The Rye Patch area is lacking in rainfall. Typically the area only receives 5.76 inches annually, though it can range from 4-16 in/yr. Due to water scarcity, there is seasonal and long-term regulation of Humboldt River to increase the amount of water available. Water for the Humboldt Project can be obtained from the Battle Mountain area, as well as from the Pitt-Taylor Reservoirs. As a result of this lack of water, water injection in an EGS system would be problematic for Rye Patch KGRA. [7][21]

Future Plans

In general, more/better data is necessary to improve understanding of the Rye Patch geothermal area. More seismic information and more data on rock densities would improve the control on the models. Higher resolution of gravity meter readings might improve results of trending features/faults. An improved quality of the seismic 3D reflection technology would improve the fault interpretations, such that the Rye Patch fault width, strike, dip, and strength could be determined. Better vertical resolution could be acquired for more accurate tomographic travel time inversions. [15] [4] [5]

Moreover, more tests need to be completed in general. Flow tests, pressure tests, and production histories could be used to help verify that the barriers to lateral fluid flow exist at the observed reflection discontinuities.

Finally, more funding is needed from industry sponsors to pay for the field work. There is abandoned vector-wavefield reflection data that was going to be used to examine surface noise, but the project was discontinued due to an economic decline in the oil industry in the 90s (instead, the seismic method was employed).

Exploration History

First Discovery Well

Completion Date:

Well Name: Campbell E-1


Depth: 560m0.56 km
0.348 mi
1,837.27 ft
612.422 yd

Initial Flow Rate: 100 kg/s6,000 kg/min
360,000 kg/hour
8,640,000 kg/day
100 L/s
1,585.032 gal/min

Flow Test Comment:

Initial Temperature: 183°C456.15 K
361.4 °F
821.07 °R

In the VSP study, there were two prominent, coherent reflectors seen at 680 ms and 880 ms in the two-way travel time. The upper reflector correlates with the sandstone/siltstone clastic unit of the Natchez Pass Formation at a depth of 3000 ft., and the reflection continues for 180 ft. northwest of the well before truncation. The deeper reflector is in the lower member of the Natchez Pass Formation and may occur at a limestone/siltstone interface. This process confirmed the regional trend of a North/South strike and a dip to the West, in addition to indicating the presence of an east/west structure that might be a normal fault with an elevated interface between the carbonate basement and the overlying sedimentary sequence. VSP identified eastward dipping layers west of the well field potentially as a series of antithetic faults. All faults discovered prior were westward dipping. [4] [15] [5]

The goal of the 3D surface seismic survey was to use seismic tomographic analysis of first arrival times to better understand near surface heterogeneity. 3D seismic reflection data was acquired for depths below 500 ft., while the tomographic travel time inversion produced results down to 500 ft. This 3D surface seismic survey showed the presence of at least one dominant fault responsible for the migration of fluids in the reservoir (controling geothermal production); it might be part of a fault system that includes a graben structure along receiver line 7, bound by two faults to the South and North. Results of the aeromagnetic survey show the lateral limits of where the flow is likely to occur. There is a velocity high between 300 and 400 ft. depth along receiver line 11, correlating to SP and magnetic results; possibly this is a result of fluid mineralization from migration upwards along intersection of two faults. The fault strike and dip is N76W/73. [4] [15] [19]

Gritto et al., 2002 interpreted an anomaly on the residual map as an excess of the uniform sloping plane of the Triassic basement rocks. Mass excess could either be the result of hydrothermal mineralization or the result of an uplift of high-density basement rocks relative to lower density overlying sediments.[4]

Michels 2002 found that sodium, potassium, chloride, lithium, and boron concentrations were uniform, which possibly indicated a common heat source with temperatures of 274° C. The reservoir was found to be depleted of silica, which precipitated out; in addition, the limestone reservoir near the cap had been partially dissolved. This indicated hydraulic isolation of the “active” reservoir, creating a stacked reservoir system. The active reservoir is the principle source of water (2100-2440 m); it is overpressured due to sealing from the cap and the side. There is meager recharge to the bottom of the active reservoir; circulation is driven by density gradients associated with cooling at the cap and some through fracture zones. This gives the potential of drilling through the upper, isolated zone to reach the hotter, original source underneath. [16] [4]

U.C. Santa Cruz found Holocene sediments overlying all Lake Lahontan (Pleistocene) deposits. The fault conduits have since sealed; hot springs are no longer active at the surface. Hydrothermal circulation is probably still active at depth with sufficient permeability. While there are no signs of surface alteration in Rye Patch anomaly area, there is abundant evidence of alteration, including jarosite, hematite, montmorillonite, carbonate, siliceous sinter.[4]

In Sanyal et al., 2006, the thermal fluid migrates up-dip in the permeable clastic unit and reaches an upper medium-enthalpy aquifer, but the pathway is diverted by a fault to the southwest well 44-28 from the east/southeast-east/northeast along a relatively narrow channel. Mapping of the Humboldt Mountain fault was completed in three segments; the normal fault dips northwest. The Rye Patch Fault, Humboldt Mountain Fault, Standard Mountain Fault, and a small fault northwest of the Florida Canyon mine were mapped. LiDAR allowed viewing of detailed relationships between their escarpments and the latest Pleistocene shorelines from Lake Lahontan. Faults are not associated with surface mineral alteration but showed widespread alteration in the Humboldt House district. Intrusion features were possibly triggered by nearby seismic events. The results show at least two mud volcanoes and a large field of low-carbonate mounds. [9](Silver et al., 2011)

Well Field Description

Well Field Information

Development Area:

Number of Production Wells:

Number of Injection Wells:

Number of Replacement Wells:

Average Temperature of Geofluid:

Sanyal Classification (Wellhead):

Reservoir Temp (Geothermometry):

Reservoir Temp (Measured):

Sanyal Classification (Reservoir):

Depth to Top of Reservoir: 579 m0.579 km
0.36 mi
1,899.606 ft
633.2 yd

Depth to Bottom of Reservoir: 1219 m1.219 km
0.757 mi
3,999.344 ft
1,333.111 yd

Average Depth to Reservoir: 899 m0.899 km
0.559 mi
2,949.475 ft
983.155 yd

The prospects of the geothermal well field at Rye Patch can be characterized by initial success followed by increasing frustration in exploration.

A regional shallow temperature-gradient-hole drilling program was undertaken in 1974 by Phillips Petroleum Company. The Humboldt House and Rye Patch near-surface thermal anomalies were outlined, recently extinct siliceous and calcareous spring deposits were noted, and warm (76*C) saline water was discovered flowing at a rate of 19l/s from an old mineral exploration well. Silica and Na-K-Ca geothermometery performed on this well gives reservoir temperatures of 232C to 254C. This is the highest predicted subsurface temperature in Nevada, but no wells in the area have exhibited temperatures close to this. [10] (Desormier, 1979) [22]

Phillips Petroleum Company drilled the first geothermal production well at the Rye Patch Geothermal Area in November 1977. This well, Campbell E-1, was drilled to a depth of 560 m and was cased until the final 25 m. Campbell E-1 had a maximum production potential of about 6050 l/min of fluid with a maximum temperature of 183C as determined by an initial flow test. The fluid produced was a dilute saline water with a total dissolved solids content of about 5000 ng/l. The geochemistry of the fluid is very similar to that of the old shallow mineral exploration well described previously. (Desormier, 1979)

In 1978, Union Oil Company drilled the Campbell No. 1 well to the north of Campbell E-1, in the Humboldt House geothermal anomaly. The well was drilled to a depth of 2080 m and had measured temperatures in excess of 205C. The well was drilled into thick Triassic shales, slates, and phyllites which are too incompetent to maintain fracture permeability. Fluid mobility was inhibited by this lack of fracture permeability, and the well only produced 0.17 l/s. [10]

In 1979, Phillips Petroleum Company drilled the 2450m deep Campbell E-2 well to the north of Campbell E-1. This well also entered the Triassic strata with limited fracture permeability, and was essentially a dry hole. In 1979, Phillips Petroleum also drilled 40 temperature gradient and/or stratigraphic wells to depths of 90 to 610 m across the Geothermal Area. On the basis of the findings of this survey, a successful production well was drilled. . [10] (Desormier, 1979) [22]

In 1991, Ormat Energy Services, Inc. drilled 44-28, a successful production well with temperatures near 205C and a flow rate of 50 l/s, in the southern portion of the Rye Patch Geothermal Area. This well confirmed the potential for commercial geothermal power generation and led to the construction of a power plant by Ormat Energy. Seven additional wells were drilled as part of the establishment of the power plant. These wells proved either too cold or virtually dry. This spotty production well success is likely an indicator that reservoir fluid distribution and movement is controlled by fractures and faulting of limited extent. (Gritto 2003) [15]

Mt. Wheeler Power drilled 5 thermal gradient wells to a depth of 500 ft. These wells better characterized the position of the shallow upflow to the Rye Patch fault. Another semi-successful production well, 72-28, was drilled to a depth of 636m on the basis of these 5 gradient wells. The well had a test flow rate of 225 l/s and exhibited temperatures near 145C. [22] [4]

Research and Development Activities

Extensive previous research in the Rye Patch Geothermal Area is documented in the exploration history section. The Department of Energy has previously supported research in the Rye Patch through the Geothermal Resource Exploration and Definition Projects program to study productivity at fault intersections (2001) and through a grant awarded to The University of Nevada, Reno Great Basin Center for Geothermal Energy to expand geothermal development on to Florida Canyon Mine property (2003). [18](Mansure et al., 2001) (Warpinski et al., 2004) (Nevada Bureau of Mines and Geology, 2005)

As previously stated, a 12.7 MW capacity power plant was installed by Ormat Energy Services, Inc. However, the new wells drilled to supply the plant were either too cold or did not produce sufficient geothermal fluids and the project was abandoned just as the plant was nearing completion. (Gritto, 2003)

Recent Geophysical investigations have shed more light on subsurface structure in the geothermal area, but as of now, no development of the resource is ongoing. [19][4]

Technical Problems and Solutions

Many of the wells drilled in the Rye Patch Geothermal Area have been essentially dry wells. Saynal, 2006 suggests that these wells were drilled into thick Triassic shales, slates and phyllites which are too incompetent to maintain fracture permeability. Fluid mobility was likely inhibited by this lack of fracture permeability, and resulted in flow rates from the wells as low as 0.17 l/s. Most of the wells in the field that are producing are much colder than suggested by various geothermometry calculations. Previous work has suggested that the hydrothermal fluids in the Rye Patch Geothermal Area move along structural surfaces with very limited areal extent. This explanation accounts for dry or cold wells occurring in close proximity to hotter, producing wells. [22] [4] [19]

Geology of the Area

Regional Setting

The Rye Patch Geothermal Area is located within the Great Basin, part of the northern Basin and Range Province. Cenozoic extensional tectonics of the northern Basin and Range Province caused large-scale normal faulting and crustal thinning. This resulted in high heat flow and general low upper mantle seismic wave velocities in the region. [4][23]

The Humboldt Range and Humboldt River Valley are an adjacent horst and graben structural block system typical of Basin and Range extensional tectonics. They are separated by an active system of range front faults along which the most recent activity occurred post-Holocene. The Rye Patch Geothermal Area is located in the elongate Humboldt River Valley between the Humboldt Range to the east and the Rye Patch Reservoir to the west. [4] [23]


The oldest exposed rocks in the Humboldt Range area are the Lower Triassic volcanics of the Koipato Group. These consist of the Limerick Greenstone- a succession of andesitic flows and breccias, the Rochester Rhyolite- altered rhyolitic tuffs and flows, and the Weaver Formation- younger rhyolitic tuffs and flows. [24]

Unconformably overlying the Koipato Group are the marine platform carbonates of the Star Peak Group. These consist of the Prida and Natchez Pass Formations. The Prida Formation has a basal clastic unit, a middle unit of medium bedded limestone interbedded with calcareous shales and siltstones, and an upper unit of thin to medium bedded limestone and dolomite with dark chert lenses. The Natchez Pass Formation consists of mafic flows, tuffs, and breccias in the lower part of the formation overlain by massive dolomite and limestone and more thinly bedded silty limestones. [24]

The upper Triassic Auld Lang Syne Group conformably overlies the Koipato Group and in this area contains the Grass Valley and Dun Glen Formations. The Grass Valley Formation consists of mudstones interbedded with thin units of fine-grained sandstone. These deposits are variably recrystallized to argillite, slates, and quartzite. The Dun Glen Formation gradationally overlies the Grass Valley Formation and is composed of thick-bedded limestone and dolomite with thin interbeds of sandstone and argillite. [9]

Paleogene and Neogene valley infill unconformably overlies the Auld Lang Syne Group. This contact may be an eroded land surface with karst features. The unnamed volcanics, sands, gravels, silts, clays, and minor limestones act as an impermeable cap enhanced by sinter deposits above the underlying Triassic rocks. [16][9]

Quaternary alluvial, floodplain, playa lake, and aeolian sand deposits make up the uppermost valley infill. There is a highly vesicular, dark gray to black Quaternary Basalt flow located northeast of the geothermal plant. (Johnson, 1977)

Intrusive dikes, sills, and plugs are present throughout the Mesozoic rocks of the Humboldt Range, and it is likely that local manifestations of these features served as basalt feeders for the previously mentioned Quaternary basalt flow in the valley. [24]


The Humboldt Range is structurally controlled by high-angle normal faults associated with the extensional tectonics that produced the present day block-faulted basins and ranges of Nevada. The area is seismically active; there is significant Holocene age faulting. The Rye Patch geothermal area is located west of a major fault that bounds the Humboldt Range. ([4][19]

Miocene and younger east-west trending transform faults form the north and south boundaries of the geothermal area. These transform faults cut the north-south trending range front faults (Rye Patch Fault and Range Front Fault) that bound the Basin and Range horst and graben structures. Piedmont faults occur in the alluvial valleys parallel to the North-South trending faults. An antithetic fault system also parallels the range front faults until it converges and is truncated in the north by the east-west trending transform fault known as the “Midas Transform.” To the South, the antithetic fault system is truncated by convergence with the Rye Patch Fault and a recently discovered transform fault. [4] [19]

The younger Paleogene, Neogene and Quaternary age deposits of the Rye Patch Geothermal Area are nearly horizontal. The unconformable contact between these younger rocks and the underlying Mesozoic rocks dips approximately 30 to the Northwest. The Mesozoic rocks dip to the west-northwest 20-40. [24] [9]

Hydrothermal System

Convection of water, as opposed to steam, is the main transport mechanism for heat. Surface water, connate water, magmatic water, and meteoric water circulate to depth and rise back to the surface. Hydrothermal circulation and repeated intrusions of crust by magma result in the transport and deposition of ore minerals during compression and extension phases of the province, which likely affects the flow. [7] (Flynn and Buchanan, 1990) [19] [4]

The hydrothermal resource stems from the extensional regime. The lithosphere is stretched and invaded by magma, faults are fragmented, and the brittle, shallow crust comes to have enhanced permeability. Production and permeability appear to vary widely within short distances. The distribution of reservoir fluid is thus controlled by fractures and faulting. The Range Front Fault controls outflow in the area of the Florida Canyon Mine, while the Rye Patch Fault (a splay off of the Range Front Fault system) controls outflow to the South and may contain an active conduit. Structurally controlled upwelling probably occurs along faults that have been recently seismically active. Over time, the flow paths become restricted or sealed by mineral deposition. Geothermal recharge from mountain runoff flows down these faults and fractures, and are then heated and returned to the surface. Thus geothermal recharge may have been greater during the Pleistocene when there was greater precipitation. [4] [7] [19] [5]

Richards and Blackwell, 2002 have proposed three scenarios for shallow geothermal fluid movement in the Basin and Range to create the varied surface effects from the different interactions of hot fluids along faults with the water table. All three scenarios (cases) of Richards and Blackwell are operating. Holocene sinter deposits in the Humboldt House area indicate hot springs, which indicate Case A. The linear nature of the sinter deposits shown from LiDAR suggests that they are structurally controlled by piedmont or antithetic faults in the area. The sinter deposits have a tendency to reduce permeability and seal flow paths. Case B is present from the shallow, laterally-flowing outflow discharge plumes in the Florida Canyon mine. Case C is indicated by the fumaroles close to Humboldt Range identified by Croffut in 1872. The surficial hot spring and fumarolic deposits at Humboldt House were structurally deposited along a series of four normal faults, active post Lake Lahontan. Holocene seismicity created permeability along the faults, allowing fluids from geothermal reservoir to reach the surface. Conduits have sealed at the surface but are permeable at depth, explaining the laterally flowing discharge plumes. Therefore, Rye Patch consists of three geothermal zones, various convective and conductive zones above and below the impermeable layer, and separation of low- and medium-enthalpy wells as a result of the postulated impermeable cap. [4] (MacKnight et al., 2005) [22] [19]

Heat Source

The Basin and Range is characterized by thin crust and high heat flow. High heat flow is due to near-surface sources of heat, such as magma chambers or hot, recently solidified and emplaced rock. Most of the area’s magmatic activity is older than 10 Ma and would be cooled, therefore not contributing significantly to the heat in geothermal systems. However, there are quaternary volcanics scattered through the Basin and Range, including in an outcrop along the northern edge of Humboldt Range plant. [4]

Rye Patch has three main observed geothermal zones (aquifer systems). The first, an unconfined aquifer, is a shallow, low-enthalpy outflow zone 65-95° C in Valley Fill sediments at depths of hundreds of meters. The second, a confined aquifer, is a medium-enthalpy zone (150-175° C) at the interface between Triassic “bedrock” and Tertiary volcanics at 550-640 m. The third is a high-enthalpy zone with flowing temps >200° C in a clastic unit in the Triassic Natchez Pass at 1040 m depth (42-28 well). The Natchez Pass Formation is the main permeable clastic unit that supplies the thermal fluids to the Rye Patch wells [15] [19][4]

The three geothermal enthalpy zones have a common heat source with temperatures >270° C at 2100-2440 m depth. Convection of high enthalpy fluids are designed to target fault intersections with fractured Triassic limestones and volcanic rocks at these deeper depths. Recharge occurs or did occur along the Range Front Fault, which circulates to depth and subsequently rises along other faults or conduits. The Rye Patch Fault feeds the three geothermal zones. [19] [4]

Geofluid Geochemistry


Salinity (low):

Salinity (high):

Salinity (average): 461

Brine Constituents: Na, K, Li, B, and Cl

Water Resistivity:

Twelve wells have been drilled in the Rye Patch Geothermal Area, and nine of them have produced thermal water for geochemical analysis.

A geochemical analysis of geothermal fluids at the Rye Patch Geothermal Site was conducted by Michels in 2002. Results of the 82 sets of analyses from 9 wells showed little variation in Na, K, Li, B, and Cl concentrations as well as significant silica depletion. Based on the uniformity of the findings, Michels concluded that all wells appeared to be tapping a resource with the same initial hydrogeochemical character. The depleted silica concentrations of the resource were attributed to deposition of the material in fluid transfer pathways. This deposition likely occluded the pathway apertures, inhibiting fluid transfer within fractures and bedding structures, and contributed to the overall chemical isolation and hydrogeochemical similarities of the fluids.[16]

Calcium/sodium/potassium geothermometry performed by The Nevada Bureau of Mines and Geology in 2012 found resource temperatures from several wells ranging from 209C to 247C. Using quartz geothermometry, much lower resource temperatures (ranging from 166C to 226C) were outlined. (Nevada Bureau of Mines and Geology, 2012)

NEPA-Related Analyses (0)

Below is a list of NEPA-related analyses that have been conducted in the area - and logged on OpenEI. To add an additional NEPA-related analysis, see the NEPA Database.

CSV No NEPA-related documents listed.

Exploration Activities (0)

Below is a list of Exploration that have been conducted in the area - and cataloged on OpenEI. Add.png Add a new Exploration Activity

No exploration activities listed on OpenEI.


  1. 1.0 1.1 1.2 1.3 S.K Sanyal, J.R McNitt, S. J. Butler, C. W. Klein, and R.E. Elliss. 2006. Assessing the Rye Patch Geothermal Field, a Classic Basin-and-Range Resource. GRC Transactions. 30(1):97-104.
  2. Geothermex Inc.. 2004. New Geothermal Site Identification and Qualification. Richmond, CA: California Energy Commission. Report No.: P500-04-051. Contract No.: 500-04-051.
  3. 3.0 3.1 3.2 U.S. Geological Survey. 2008. Assessment of Moderate- and High-Temperature Geothermal Resources of the United States. USA: U.S. Geological Survey. Report No.: Fact Sheet 2008-3082.
  4. 4.00 4.01 4.02 4.03 4.04 4.05 4.06 4.07 4.08 4.09 4.10 4.11 4.12 4.13 4.14 4.15 4.16 4.17 4.18 4.19 4.20 4.21 4.22 4.23 4.24 4.25 4.26 4.27 4.28 4.29 4.30 4.31 M. McDonald. 2013. Geophysical Investigation and Assessment of the Rye Patch Known Geothermal Resource Area, Rye Patch, Nevada [Dissertation]. [University of North Dakota]: University of North Dakota.
  5. 5.0 5.1 5.2 5.3 5.4 5.5 5.6 R. Gritto, T.M. Daley, E.L. Majer. 2002. Integrated seismic studies at the Rye Patch geothermal reservoir. Geothermal Resources Council Transactions. 26:431-445.
  6. 6.0 6.1 J.H. Stewart. 1998. Regional characteristics, tilt domains, and extensional history of the Late Cenozoic Basin and Range Province, Western North America, in: Accommodation Zones and Transfer Zones and the Regional Segmentation of the Basin and Range Province. Geological Society of America Special Paper. 47-74.
  7. 7.0 7.1 7.2 7.3 7.4 G.P. Eaton. 1979. Regional geophysics, Cenozoic tectonics and geologic resources of the Basin and Range Province and adjoining regions. Proceedings of Basin and Range Symposium and Great Basin Field Conference; Denver, CO: Rocky Mountain Association of Geologists.
  8. C.B. Hunt. 1979. The Great Basin, an overview and hypotheses of its history, in: Newman, G.W., and Goode, H.D. Proceedings of Basin and Range Symposium and Great Basin Field Conference; Denver, CO: Rocky Mountain Association of Geologists.
  9. 9.0 9.1 9.2 9.3 9.4 9.5 9.6 Sanyal, S.K., McNitt, J.R., Butler, S.J., Klein, C.W., and Ellis, R.K.. 2006. Assessing the Rye Patch geothermal field, a classic Basin-and-Range Resource: Geothermal Resources Council Transactions. In: Geothermal Resources Council Transactions. GRC Annual Meeting; (!) ; (!) . (!) : (!) ; p. 97-104
  10. 10.0 10.1 10.2 10.3 10.4 10.5 10.6 10.7 W.R. Benoit, R.W. Butler. 1983. A review of high-temperature geothermal developments in the Northern Basin and Range Province. (!) : Geothermal Resources Council. Report No.: 13.
  11. Crofutt, G.A. 1872. Crofutt's Transcontinental Tourist's Guide. New York, NY: (!) . 153p.
  12. Long, C.L., and Batzle, M.L. Station location map and audio-magnetotelluric data log for Rye Patch known geothermal resource area. [Map]. Place of publication not provided. U S. Geological Survey. 1976. Available from: http://pubs.er.usgs.gov/publication/ofr76700C.
  13. B.S. Sibbett, W.E. Glenn. 1981. Lithology and well log study of Campbell E-2 geothermal test well, Humboldt House geothermal prospect, Pershing County, Nevada. (!) : University of Utah Research Institute. Report No.: 53.
  14. D.H. Schaefer. Bouguer gravity anomalies, depth to bedrock, and shallow temperature in the Humboldt House geothermal area, Pershing County, Nevada. [Map]. Online. U.S. Geological Survey. 1986. Scale 1:250,000. Available from: http://pubs.er.usgs.gov/publication/i1701.
  15. 15.0 15.1 15.2 15.3 15.4 15.5 15.6 15.7 M.A. Feighner, R. Gritto, T.M. Daley, H. Keers, E.L. Majer. 1999. Three dimensional seismic imaging of the Rye Patch geothermal reservoir. Online: Lawrence Berkeley National Laboratory. Report No.: LBNL-44119.
  16. 16.0 16.1 16.2 16.3 D. Michels. 2002. Rye Patch geothermal development, hydro-chemistry of thermal water applied to resource definition. (!) : Presco Energy.
  17. D.D. Davis. 2011. Descriptive logs, skeletonized samples, and photographs of core from Presco Energy's thermal gradient wells P3-1, P10-1, and P32-2 in the Rye Patch area, Pershing County, Nevada. (!) : Nevada Bureau of Mines and Geology. Report No.: Open-File Report 11-10.
  18. 18.0 18.1 Johnson, J.L., Tempel, R.N., and Shevenell, L.A.. 2004. Characterization of past hydrothermal fluids in the Humboldt House geothermal area, Pershing County, Nevada - geochemical and paragenetic studies of core samples. In: (!) ; (!) ; (!) . (!) : Geological Society of America Abstracts with Programs; p. 148
  19. 19.00 19.01 19.02 19.03 19.04 19.05 19.06 19.07 19.08 19.09 19.10 R.K. Ellis. 2011. A restated conceptual model for the Humboldt House-Rye Patch geothermal resource area, Pershing County, Nevada. Geothermal Resources Council Transactions. 35:769-776.
  20. W. Calvin, A. Lamb, C. Kratt. 2010. Rapid characterization of drill core and cutting mineralogy using infrared spectroscopy. Geothermal Resources Council Transactions. 34:761-764.
  21. Humbolt Project [Internet]. 2011. U.S. Department of the Interior. [updated 2014;cited {{{WebCiteDate}}}]. Available from: https://www.usbr.gov/projects/Project.jsp?proj_Name=Humboldt%20Project
  22. 22.0 22.1 22.2 22.3 22.4 A. Waibel, D.D. Blackwell, R.K. Ellis. 2003. The Humboldt House-Rye Patch geothermal district: an interim view. In: Geothermal Resources Council Transactions. GRC Annual Meeting; 2003/10/15; Morelia, Mexico. Online: Geothermal Resources Council Transactions; p. 33-36
  23. 23.0 23.1 G.A. Davis. 1979. Problems of intraplate extensional tectonics, Western United States, with special emphasis on the Great Basin. Proceedings of Basin and Range Symposium and Great Basin Field Conference; Denver, CO: Rocky Mountain Association of Geologists.
  24. 24.0 24.1 24.2 24.3 Hastings, J.S., Burkhart, T.H., and Richardson, R.E.. 1993. Geology of the Florida Canyon gold deposit, Pershing County, Nevada, in: Gold and Silver Deposits of Western Nevada. (!) : Geological Society of Nevada 1993 fall field trip guidebook. Report No.: Special Publication no. 18.

List of existing Geothermal Resource Areas.

Some of the content on this page was part of a case study conducted by: UND Team 3

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