Abstract

Inflections in temperature-depth profiles from forty 150 m thermal gradient holes define a shallow thermal flow system in the Whirlwind Valley near the Beowawe Geysers. U.S. Geological Survey hydrologic data reveal the vertical and west-to-east components of cold water flow at the water table above the thermal flow system. The temperature inflections break most abruptly in areas with a downward component of flow at the water table. The inflections are thought to indicate the level where the buoyant thermal water maintains a dynamic equilibrium with the overlying cold water. Combining these geophysical and hydrologic data suggests areas away from The Geysers where thermal water may rise from the deep reservoir into the alluvium. These leakage areas may be viable geothermal exploration targets. Even if the temperatures of the leakage were subeconomic, knowledge of where upwelling occurs could be helpful in assessing the potential for energy production. The systematic acquisition of hydrologic data is recommended as a standard component of hydrothermal resource exploration programs.Measurements of thermal conductivity from chip samples from the shallow holes and from Chevron Resources Company's Ginn 1-13 geothermal exploration hole (2917 m T.D.) enable inferences based on heat flow. The average heat flow east of the Dunphy Pass fault zone, 110 mW/m 2 , may be representative of background in this portion of the Battle Mountain high heat flow province. Thermal gradient and conductivity data from the deep well have a wide range of values (65-144 degrees C/km, 1.59-5.95 Wm (super -1) K (super -1) ) but produce a relatively constant heat flow of 235 mW/m 2 above a depth of 1600 m. The shallow data indicate that the area with similarly high surficial heat flow extends as far east as the Dunphy Pass fault zone, suggesting that this Miocene rift boundary may form the eastern margin of the Beowawe hydrothermal system.

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