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• 1. [Image] Drilling plan: Raft River Geothermal Exploratory Hole No. 3

  	The program, plans, and procedures to be used in drilling and completion of the Raft River Geothermal Exploratory Hole No. 3(RRGE-3) are described. RRGE-3 will be located in the Raft River valley of south ...
  	Citation × Citation Citation Abstract Copy Title: Drilling plan: Raft River Geothermal Exploratory Hole No. 3 Author: Industrial Applications Division , Nevada Operations Office Year: 1976 The program, plans, and procedures to be used in drilling and completion of the Raft River Geothermal Exploratory Hole No. 3(RRGE-3) are described. RRGE-3 will be located in the Raft River valley of south central Idaho, southeast of Burley, and approximately 16 miles south of Malta, Idaho. The third exploratory hole will be drilled to provide data to further investigate and evaluate the geothermal reservoir, as well as to optimize the location of possible future resource and/or injection wells, and to develop methods to reduce the cost of geothermal wells. Plans call for drilling to a total depth of approximately 6,000 ft., or to the depth at which it is either indicated from temperature and test flow data and from logs that an acceptable hot water resource is available or that the hole is accepted as a possible reinjection well. (LBS) Title: Drilling plan: Raft River Geothermal Exploratory Hole No. 3 Author: Industrial Applications Division , Nevada Operations Office Year: 1976 The program, plans, and procedures to be used in drilling and completion of the Raft River Geothermal Exploratory Hole No. 3(RRGE-3) are described. RRGE-3 will be located in the Raft River valley of south central Idaho, southeast of Burley, and approximately 16 miles south of Malta, Idaho. The third exploratory hole will be drilled to provide data to further investigate and evaluate the geothermal reservoir, as well as to optimize the location of possible future resource and/or injection wells, and to develop methods to reduce the cost of geothermal wells. Plans call for drilling to a total depth of approximately 6,000 ft., or to the depth at which it is either indicated from temperature and test flow data and from logs that an acceptable hot water resource is available or that the hole is accepted as a possible reinjection well. (LBS) Close

• 2. [Image] Geothermal Energy: Residential Space Heating

  	The purpose of this study, which was carried out under the auspices of the DGRST, was to determine the best way to use geothermal hot water for residential space heating. It quickly became apparent that ...
  	Citation × Citation Citation Abstract Copy Title: Geothermal Energy: Residential Space Heating Author: Delegation Generale a la Recherche Scientifique et Technique 35 rue Saint-Dominique, 75007 Paris Year: 1977 The purpose of this study, which was carried out under the auspices of the DGRST, was to determine the best way to use geothermal hot water for residential space heating. It quickly became apparent that the type of heating apparatus used in the housing units was most important and that heat pumps could be a valuable asset, making it possible to extract even more geothermal heat and thus substantially improve the cost benefit of the systems. Many factors play a significant role in this problem. Therefore, after a first stage devoted to analyzing the problem through a manual method which proved quite useful, the systematic consideration of all important aspects led us to use a computer to optimize solutions and process a large number of cases. The software used for this general study can also be used to work out particular cases: it is now available to any interested party through DGRST. This program makes it possible to: (1) take climatic conditions into account in a very detailed manner, including temperatures as well as insolation. 864 cases corresponding to 36 typical days divided into 24 hours each were chosen to represent the heating season. They make it possible to define the heating needs of any type of housing unit. (2) simulate and analyze the behavior in practice of a geothermal heating system when heat is extracted from the well by a simple heat exchanger. This simulation makes it possible to evaluate the respective qualities of various types of heating apparatus which can be used in homes. It also makes it possible to define the best control systems for the central system and substations and to assess quite accurately the presence of terminal controls, such as radiators with thermostatically controlled valves. (3) determine to what extent the addition of a heat pump makes it possible to improve the cost benefit of geothermal heating. When its average characteristics and heating use conditions (price, coefficient of performance, length of utilization, electrical rates, etc.) are taken into account, the heat pump should not be scaled for maximum heating power. Consequently, the program considers several possible sizes, with different installation schemes, and selects for each case the value which corresponds to the lowest cost of heating Title: Geothermal Energy: Residential Space Heating Author: Delegation Generale a la Recherche Scientifique et Technique 35 rue Saint-Dominique, 75007 Paris Year: 1977 The purpose of this study, which was carried out under the auspices of the DGRST, was to determine the best way to use geothermal hot water for residential space heating. It quickly became apparent that the type of heating apparatus used in the housing units was most important and that heat pumps could be a valuable asset, making it possible to extract even more geothermal heat and thus substantially improve the cost benefit of the systems. Many factors play a significant role in this problem. Therefore, after a first stage devoted to analyzing the problem through a manual method which proved quite useful, the systematic consideration of all important aspects led us to use a computer to optimize solutions and process a large number of cases. The software used for this general study can also be used to work out particular cases: it is now available to any interested party through DGRST. This program makes it possible to: (1) take climatic conditions into account in a very detailed manner, including temperatures as well as insolation. 864 cases corresponding to 36 typical days divided into 24 hours each were chosen to represent the heating season. They make it possible to define the heating needs of any type of housing unit. (2) simulate and analyze the behavior in practice of a geothermal heating system when heat is extracted from the well by a simple heat exchanger. This simulation makes it possible to evaluate the respective qualities of various types of heating apparatus which can be used in homes. It also makes it possible to define the best control systems for the central system and substations and to assess quite accurately the presence of terminal controls, such as radiators with thermostatically controlled valves. (3) determine to what extent the addition of a heat pump makes it possible to improve the cost benefit of geothermal heating. When its average characteristics and heating use conditions (price, coefficient of performance, length of utilization, electrical rates, etc.) are taken into account, the heat pump should not be scaled for maximum heating power. Consequently, the program considers several possible sizes, with different installation schemes, and selects for each case the value which corresponds to the lowest cost of heating Close

• 3. [Image] Evaluation and Design of Downhole Heat Exchangers for Direct Application; Annual Report, May 1, 1976 - July 1, 1977

  	Progress in an experimental and analytical research program to evaluate and improve the design of downhole heat exchangers (DHEs) for direct applications of geothermal energy is reported. Significant progress ...
  	Citation × Citation Citation Abstract Copy Title: Evaluation and Design of Downhole Heat Exchangers for Direct Application; Annual Report, May 1, 1976 - July 1, 1977 Author: Culver, G.G. Year: 1977 Progress in an experimental and analytical research program to evaluate and improve the design of downhole heat exchangers (DHEs) for direct applications of geothermal energy is reported. Significant progress has been achieved in characterizing flows in wells and without perforated casings and DHEs installed, determination of energy extraction rates for conventional DHEs in both cased and uncased wells, and utilization of information obtained to develop and substantiate models of heat transfer within the well. Flow characterization was obtained by experimentally measuring temperature and velocity profiles. In uncased wells, there was a relatively large vertical temperature gradient (approximately 0.5{sup 0}C/m) and insignificant measured vertical flow, while for the same wells when cased the temperature gradient was essentially zero (approximately 0.03{sup 0}C/m) and a large vertically upward flow was measured (9 to 14 cm/s as measured with a hot-film anemometer). These show that a significant connection cell is established after installation of the casing. The energy extraction rates for a conventional DHE both before and after casing of a 60 m deep well was experimentally measured. In the uncased well up to 300 kW was obtained while the cased well produced over 500 kW. Analytical heat transfer models were developed for the cased well both with and without DHEs. For the cased well without a DHE, the model predicts flow rates that agree with the measured value within about 30 percent. Further, the energy extraction rates predicted by the models agree even better with the measured values. These models allow the energy extraction rates of design parameter variations to be evaluated. At this stage, only trends can be shown but with additional substantiation they should produce optimum energy extraction designs Title: Evaluation and Design of Downhole Heat Exchangers for Direct Application; Annual Report, May 1, 1976 - July 1, 1977 Author: Culver, G.G. Year: 1977 Progress in an experimental and analytical research program to evaluate and improve the design of downhole heat exchangers (DHEs) for direct applications of geothermal energy is reported. Significant progress has been achieved in characterizing flows in wells and without perforated casings and DHEs installed, determination of energy extraction rates for conventional DHEs in both cased and uncased wells, and utilization of information obtained to develop and substantiate models of heat transfer within the well. Flow characterization was obtained by experimentally measuring temperature and velocity profiles. In uncased wells, there was a relatively large vertical temperature gradient (approximately 0.5{sup 0}C/m) and insignificant measured vertical flow, while for the same wells when cased the temperature gradient was essentially zero (approximately 0.03{sup 0}C/m) and a large vertically upward flow was measured (9 to 14 cm/s as measured with a hot-film anemometer). These show that a significant connection cell is established after installation of the casing. The energy extraction rates for a conventional DHE both before and after casing of a 60 m deep well was experimentally measured. In the uncased well up to 300 kW was obtained while the cased well produced over 500 kW. Analytical heat transfer models were developed for the cased well both with and without DHEs. For the cased well without a DHE, the model predicts flow rates that agree with the measured value within about 30 percent. Further, the energy extraction rates predicted by the models agree even better with the measured values. These models allow the energy extraction rates of design parameter variations to be evaluated. At this stage, only trends can be shown but with additional substantiation they should produce optimum energy extraction designs Close

• 4. [Image] Heat Flow of Oregon

  	An extensive new heat flow and geothermal gradient data set for the State of Oregon is presented on a contour map of heat flow at a scale of 1:1,000,000 and is summarized in several figures and tables. ...
  	Citation × Citation Citation Abstract Copy Title: Heat Flow of Oregon Author: Blackwell, D.D. Year: 1978 An extensive new heat flow and geothermal gradient data set for the State of Oregon is presented on a contour map of heat flow at a scale of 1:1,000,000 and is summarized in several figures and tables. The 1:1,000,000 scale heat flow map is contoured at 20 mW/m/sup 2/ (0.5 HFU) intervals. Also presented are maps of heat flow and temperature at a depth of 1 km averaged for 1/sup 0/ x 1/sup 0/ intervals. Histograms and averages of geothermal gradient and heat flow for the State of Oregon and for the various physiographic provinces within Oregon are also included. The unweighted mean flow for Oregon is 81.3 +- 2.7 mW/m/sup 2/ (1.94 +- 0.06 HFU). The average unweighted geothermal gradient is 65.3 +- 2.5/sup 0/C/km. The average heat flow value weighted on the basis of geographic area is 68 +- 5 mW/m/sup 2/ (1.63 +- 0.12 HFU) and the average weighted geothermal gradient is 55.0 +- 5/sup 0/C/km Title: Heat Flow of Oregon Author: Blackwell, D.D. Year: 1978 An extensive new heat flow and geothermal gradient data set for the State of Oregon is presented on a contour map of heat flow at a scale of 1:1,000,000 and is summarized in several figures and tables. The 1:1,000,000 scale heat flow map is contoured at 20 mW/m/sup 2/ (0.5 HFU) intervals. Also presented are maps of heat flow and temperature at a depth of 1 km averaged for 1/sup 0/ x 1/sup 0/ intervals. Histograms and averages of geothermal gradient and heat flow for the State of Oregon and for the various physiographic provinces within Oregon are also included. The unweighted mean flow for Oregon is 81.3 +- 2.7 mW/m/sup 2/ (1.94 +- 0.06 HFU). The average unweighted geothermal gradient is 65.3 +- 2.5/sup 0/C/km. The average heat flow value weighted on the basis of geographic area is 68 +- 5 mW/m/sup 2/ (1.63 +- 0.12 HFU) and the average weighted geothermal gradient is 55.0 +- 5/sup 0/C/km Close

• 5. [Image] Geologic Characteristics of a Portion of the Salton Sea Geothermal Field

  	The examination of drill cuttings and core samples from the Magmamax Nos. 2 and 3 and Woolsey No. 1 wells indicate that the sequence of sedimentary rocks in the Salton Sea geothermal field from the surface ...
  	Citation × Citation Citation Abstract Copy Title: Geologic Characteristics of a Portion of the Salton Sea Geothermal Field Author: Tewhey; J.D. Year: 1977 The examination of drill cuttings and core samples from the Magmamax Nos. 2 and 3 and Woolsey No. 1 wells indicate that the sequence of sedimentary rocks in the Salton Sea geothermal field from the surface to below 4000 ft can be divided into three categories Title: Geologic Characteristics of a Portion of the Salton Sea Geothermal Field Author: Tewhey; J.D. Year: 1977 The examination of drill cuttings and core samples from the Magmamax Nos. 2 and 3 and Woolsey No. 1 wells indicate that the sequence of sedimentary rocks in the Salton Sea geothermal field from the surface to below 4000 ft can be divided into three categories Close

• 6. [Image] Field Electrochemical Measurements of Corrosion Characteristics of Materials in Hypersaline Geothermal Brine

  	A flow cell (with appropriate accessories) was developed for use in short-term testing of the corrosion behavior of materials in approximately 100{sup 0}C, hypersaline geothermal brine. The apparatus was ...
  	Citation × Citation Citation Abstract Copy Title: Field Electrochemical Measurements of Corrosion Characteristics of Materials in Hypersaline Geothermal Brine Author: Harrar, J.E. Year: 1977 A flow cell (with appropriate accessories) was developed for use in short-term testing of the corrosion behavior of materials in approximately 100{sup 0}C, hypersaline geothermal brine. The apparatus was designed to accommodate commercial (Petrolite) corrosion measurement equipment and conducted experiments on-line at the Lawrence Livermore Laboratory Test Station in the Salton Sea Geothermal Field. The apparatus also permitted direct readings of corrosion potentials, solution redox potential (E{sub h}), brine flow rate, pH, and temperature. Estimates of general corrosion rates were obtained by the linear polarization resistance technique and from measurements of complete potentiodynamic polarization curves. The latter also afforded predictions of pitting susceptibilities of active-passive type materials. Twenty-two alloys (with various heat treatments) were tested and readily grouped according to general corrosion resistances in acidified hypersaline (approximately 4 M chloride) brine. Especially promising in regard to corrosion resistance-vs-cost is the series of low Cr--Mo steels. Prescaling of materials in unacidified (pH approximately 5.7) brine prior to exposure to acidified (pH 2 to 4.5) brine was found to be beneficial in reducing corrosion rates at 100{sup 0}C Title: Field Electrochemical Measurements of Corrosion Characteristics of Materials in Hypersaline Geothermal Brine Author: Harrar, J.E. Year: 1977 A flow cell (with appropriate accessories) was developed for use in short-term testing of the corrosion behavior of materials in approximately 100{sup 0}C, hypersaline geothermal brine. The apparatus was designed to accommodate commercial (Petrolite) corrosion measurement equipment and conducted experiments on-line at the Lawrence Livermore Laboratory Test Station in the Salton Sea Geothermal Field. The apparatus also permitted direct readings of corrosion potentials, solution redox potential (E{sub h}), brine flow rate, pH, and temperature. Estimates of general corrosion rates were obtained by the linear polarization resistance technique and from measurements of complete potentiodynamic polarization curves. The latter also afforded predictions of pitting susceptibilities of active-passive type materials. Twenty-two alloys (with various heat treatments) were tested and readily grouped according to general corrosion resistances in acidified hypersaline (approximately 4 M chloride) brine. Especially promising in regard to corrosion resistance-vs-cost is the series of low Cr--Mo steels. Prescaling of materials in unacidified (pH approximately 5.7) brine prior to exposure to acidified (pH 2 to 4.5) brine was found to be beneficial in reducing corrosion rates at 100{sup 0}C Close

• 7. [Image] An Experimental Investigation of the Permeability of Kayenta and St. Peter Sandstones to Hypersaline Brine in the Temperature Interval 70 to 90 C at 10. 3-MPa Confining Pressure

  	Permeabilities of 10.2 cm in length, 2.5 cm in diameter Kayenta (porosity, 20.7, +- 1.66%) and St. Peter (porosity, 13.6, +- 0.13%) sandstones to Magmamax No. 1 brine containing suspended solids were determined ...
  	Citation × Citation Citation Abstract Copy Title: An Experimental Investigation of the Permeability of Kayenta and St. Peter Sandstones to Hypersaline Brine in the Temperature Interval 70 to 90 C at 10. 3-MPa Confining Pressure Author: Piwinskii, A.J. Year: 1977 Permeabilities of 10.2 cm in length, 2.5 cm in diameter Kayenta (porosity, 20.7, +- 1.66%) and St. Peter (porosity, 13.6, +- 0.13%) sandstones to Magmamax No. 1 brine containing suspended solids were determined from 70 to 90/sup 0/C at 10.3-MPa confining pressure. Measurements were performed without filters, with one 10-..mu..m filter, and with two 10-..mu..m filters inserted upstream of the core sample. In all cases, there was a dramatic decrease in permeability within the first hour of flow or few hundred pore volumes of flow through the core. Experiments conducted without filters or with one filter yield permeabilities that represent both the rock and the 2- to 3-mm amorphous silica-iron layer on the top face of the core. The experimental results show that if the Salton Sea Geothermal Field (SSGF) were composed of porous, sedimentary formations similar to Kayenta sandstone, long-term injection of unmodified Magmamax brine would not be feasible. In the case of acidified brine, most of the permeability decline may result from the mobilization of calcite Title: An Experimental Investigation of the Permeability of Kayenta and St. Peter Sandstones to Hypersaline Brine in the Temperature Interval 70 to 90 C at 10. 3-MPa Confining Pressure Author: Piwinskii, A.J. Year: 1977 Permeabilities of 10.2 cm in length, 2.5 cm in diameter Kayenta (porosity, 20.7, +- 1.66%) and St. Peter (porosity, 13.6, +- 0.13%) sandstones to Magmamax No. 1 brine containing suspended solids were determined from 70 to 90/sup 0/C at 10.3-MPa confining pressure. Measurements were performed without filters, with one 10-..mu..m filter, and with two 10-..mu..m filters inserted upstream of the core sample. In all cases, there was a dramatic decrease in permeability within the first hour of flow or few hundred pore volumes of flow through the core. Experiments conducted without filters or with one filter yield permeabilities that represent both the rock and the 2- to 3-mm amorphous silica-iron layer on the top face of the core. The experimental results show that if the Salton Sea Geothermal Field (SSGF) were composed of porous, sedimentary formations similar to Kayenta sandstone, long-term injection of unmodified Magmamax brine would not be feasible. In the case of acidified brine, most of the permeability decline may result from the mobilization of calcite Close

• 8. [Image] Geothermal Energy Resource Assessment

  	This report covers the objectives and the status of a long-range program to develop techniques for assessing the resource potential of liquid-dominated geothermal systems. Field studies underway in northern ...
  	Citation × Citation Citation Abstract Copy Title: Geothermal Energy Resource Assessment Author: Wollenberg, H.A. Year: 1975 This report covers the objectives and the status of a long-range program to develop techniques for assessing the resource potential of liquid-dominated geothermal systems. Field studies underway in northern Nevada comprise a systematic integrated program of geologic, geophysical, and geochemical measurements, necessary to specify a drilling program encompassing heat flow holes, deep calibration holes, and ultimately, deep test wells. The status of Nevada field activities is described. The areas under study are in a region characterized by high heat flow where temperatures at depth in some geothermal systems exceed 180 C. Areas presently being examined include Beowawe Hot Springs in Whirlwind Valley. Buffalo Valley Hot Springs, Leach Hot Springs in Grass Valley, and Kyle Hot Springs in Buena Vista Valley. Geologic studies encompass detailed examinations of structure and lithology to establish the geologic framework of the areas. The geothermal occurrences are characterized by zones of intense fault intersection, which furnish permeable channelways for the introduction of meteoric water into regions of high temperature at depth Title: Geothermal Energy Resource Assessment Author: Wollenberg, H.A. Year: 1975 This report covers the objectives and the status of a long-range program to develop techniques for assessing the resource potential of liquid-dominated geothermal systems. Field studies underway in northern Nevada comprise a systematic integrated program of geologic, geophysical, and geochemical measurements, necessary to specify a drilling program encompassing heat flow holes, deep calibration holes, and ultimately, deep test wells. The status of Nevada field activities is described. The areas under study are in a region characterized by high heat flow where temperatures at depth in some geothermal systems exceed 180 C. Areas presently being examined include Beowawe Hot Springs in Whirlwind Valley. Buffalo Valley Hot Springs, Leach Hot Springs in Grass Valley, and Kyle Hot Springs in Buena Vista Valley. Geologic studies encompass detailed examinations of structure and lithology to establish the geologic framework of the areas. The geothermal occurrences are characterized by zones of intense fault intersection, which furnish permeable channelways for the introduction of meteoric water into regions of high temperature at depth Close

• 9. [Image] Petrology of the Quaternary Volcanics of the Roosevelt KGRA, and Adjoining Area, Utah. Final Report, Volume 1

  	The Roosevelt KGRA (Known Geothermal Resource Area) located near Milford, Utah, is associated with a suite of quaternary silicic volcanics distributed for 15 km along the crest and western flank of the ...
  	Citation × Citation Citation Abstract Copy Title: Petrology of the Quaternary Volcanics of the Roosevelt KGRA, and Adjoining Area, Utah. Final Report, Volume 1 Author: Nash, W.P. Year: 1976 The Roosevelt KGRA (Known Geothermal Resource Area) located near Milford, Utah, is associated with a suite of quaternary silicic volcanics distributed for 15 km along the crest and western flank of the Mineral Mountains, a large tertiary granite batholith. The volcanics are high-silica rhyolites and occur as domes, flows and tuffs. Initial eruptions resulted in two flows of low viscosity, phenocryst-poor rhyolite. Later activity consisted of pyroclastic eruptions and the emplacement of at least 9 viscous domes. In addition to abundant glass the rhyolites contain alkali feldspar, plagioclase, biotite, iron-titanium oxides and small amounts of hornblende, allanite, apatite, zircon, sphene and topaz. Magmatic temperatures were about 700C and water fugacities ranged from 350 to 3450 bars. Based on water fugacity calculations it is concluded that there may have been one or more shallow magma chambers in the Mineral Range at depths of about 1.6 km. Title: Petrology of the Quaternary Volcanics of the Roosevelt KGRA, and Adjoining Area, Utah. Final Report, Volume 1 Author: Nash, W.P. Year: 1976 The Roosevelt KGRA (Known Geothermal Resource Area) located near Milford, Utah, is associated with a suite of quaternary silicic volcanics distributed for 15 km along the crest and western flank of the Mineral Mountains, a large tertiary granite batholith. The volcanics are high-silica rhyolites and occur as domes, flows and tuffs. Initial eruptions resulted in two flows of low viscosity, phenocryst-poor rhyolite. Later activity consisted of pyroclastic eruptions and the emplacement of at least 9 viscous domes. In addition to abundant glass the rhyolites contain alkali feldspar, plagioclase, biotite, iron-titanium oxides and small amounts of hornblende, allanite, apatite, zircon, sphene and topaz. Magmatic temperatures were about 700C and water fugacities ranged from 350 to 3450 bars. Based on water fugacity calculations it is concluded that there may have been one or more shallow magma chambers in the Mineral Range at depths of about 1.6 km. Close

• 10. [Image] Stratigraphy and Alteration, 15 Shallow Thermal Gradient Holes, Roosevelt Hot Springs KGRA and Vicinity, Millard and Beaver Counties, Utah

  	Fifteen shallow thermal gradient drill holes were recently completed by Geothermal Power Corporation (GPCR) in the vicinity of the Roosevelt Hot Springs KGRA. Five holes penetrated Tertiary granitic rocks ...
  	Citation × Citation Citation Abstract Copy Title: Stratigraphy and Alteration, 15 Shallow Thermal Gradient Holes, Roosevelt Hot Springs KGRA and Vicinity, Millard and Beaver Counties, Utah Author: Hulen, J.B. Year: 1978 Fifteen shallow thermal gradient drill holes were recently completed by Geothermal Power Corporation (GPCR) in the vicinity of the Roosevelt Hot Springs KGRA. Five holes penetrated Tertiary granitic rocks and Precambrian gneiss east of the KGRA. Seven holes completed entirely in alluvium near the southwestern corner of the KGRA encountered a near-surface marker horizon of Pleistocene pumice and perlite. Maximum calculated alluvial sedimentation rates since initial deposition of this pumice and perlite range from 1 foot in 12,500 years to 1 foot in 2,300 years. Three holes east of the Mineral Mountains penetrated late Cenozoic basaltic andesite beneath a thin veneer of alluvium. All 15 GPCR drill holes appear to be peripheral to a central zone of anomalously high thermal gradient and low resisitivity delineated by previous investigations. GPCR-8 and -14, however, are characterized by high heat flow and relatively abundant manganese oxide mineralization, which may reflect a favorable hydrologic system controlling thermal fluid flow at depth. These holes thus seem most encouraging for discovery of a deeper high-temperature geothermal resource Title: Stratigraphy and Alteration, 15 Shallow Thermal Gradient Holes, Roosevelt Hot Springs KGRA and Vicinity, Millard and Beaver Counties, Utah Author: Hulen, J.B. Year: 1978 Fifteen shallow thermal gradient drill holes were recently completed by Geothermal Power Corporation (GPCR) in the vicinity of the Roosevelt Hot Springs KGRA. Five holes penetrated Tertiary granitic rocks and Precambrian gneiss east of the KGRA. Seven holes completed entirely in alluvium near the southwestern corner of the KGRA encountered a near-surface marker horizon of Pleistocene pumice and perlite. Maximum calculated alluvial sedimentation rates since initial deposition of this pumice and perlite range from 1 foot in 12,500 years to 1 foot in 2,300 years. Three holes east of the Mineral Mountains penetrated late Cenozoic basaltic andesite beneath a thin veneer of alluvium. All 15 GPCR drill holes appear to be peripheral to a central zone of anomalously high thermal gradient and low resisitivity delineated by previous investigations. GPCR-8 and -14, however, are characterized by high heat flow and relatively abundant manganese oxide mineralization, which may reflect a favorable hydrologic system controlling thermal fluid flow at depth. These holes thus seem most encouraging for discovery of a deeper high-temperature geothermal resource Close