Isotopic Analysis-Fluid At Long Valley Caldera Geothermal Area (McKenzie & Truesdell, 1977)

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Exploration Activity: Isotopic Analysis-Fluid At Long Valley Caldera Geothermal Area (McKenzie & Truesdell, 1977)

Exploration Activity Details
Location Long Valley Caldera Geothermal Area
Exploration Technique Isotopic Analysis- Fluid
Activity Date 1976 - 1977
Usefulness useful
DOE-funding Unknown

Exploration Basis
The study investigated corrections that could be applied to the sulfate geothermometer (Fournier, 1976) to account for the effects of subsurface boiling and dilution, in order to increase the effective temperature range of the geothermometer from 100-200°C to 140-350°C. This range encompasses the temperature range of greatest interest in geothermal exploration/production. Analysis and geothermometry are described as applied to the Yellowstone, WY, Long Valley, CA, and Raft River, ID geothermal systems.
Spring and well water samples were collected by Lawrence M. Willey during a geochemical sampling survey published in 1976 (Mariner and Willey, 1976). Details of sampling practices and field treatment are detailed in the text. Water samples were passed through a 0.7x4 cm column containing a Bio-Rad AG1-8x, 50-100 mesh, chloride form anion exchange resin. The resin was treated with 100 mL of 0.5 M sodium chloride in order to remove [barium] sulfate, which was precipitated by standard gravimetric methods, dried, and then weighed. The extracted barium sulfate was converted to carbon dioxide by the graphite reduction method (Rafter, 1976) modified for internal resistance heating (Mizutani, 1971; Sakai and Krouse, 1971) prior to analysis by mass spectrometry. Water samples were analyzed for their oxygen isotope ratios using the carbon dioxide-equilibration method. Waters analyzed from the Long Valley Caldera include samples taken from the Casa Diablo Magma-Ritchie No. 5 geothermal well, Hot Creek spring, and unnamed hot spring GT 31. All of these waters were apparently of mixed composition between thermal water and dilute near-surface meteoric water, and so application of the sulfate isotope geothermometer yielded minimum reservoir temperature estimates from 184° to 246°C, with the highest temperature estimate obtained from the Magma-Ritchie No. 5 well.

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