Field Mapping At Long Valley Caldera Geothermal Area (Sorey, 1985)

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Exploration Activity: Field Mapping At Long Valley Caldera Geothermal Area (Sorey, 1985)

Exploration Activity Details
Location Long Valley Caldera Geothermal Area
Exploration Technique Field Mapping
Activity Date 1974 - 1985

Usefulness useful
DOE-funding Unknown

 
Exploration Basis
The caldera geology, distribution of active hydrothermal surface manifestations, and relict features associated with past hydrothermal activity were summarized by Sorey (1985), and have been described by numerous studies dating back to 1974.
 
Notes
Existing geothermal surface expressions at Long Valley include a few scattered fumaroles, mudpots, and mineral deposits on the western flanks of the resurgent dome, where the land elevation is higher. Hot-springs with surface discharge temperatures of 79-93 oC occur primarily at Casa Diablo, Hot Creek gorge, Little Hot Creek, and along the south side of the resurgent dome. Additional warm- and cold-spring discharges occur in the eastern part of the caldera between Hot Creek and Lake Crowley where the surface elevation is relatively low, promoting surface flow of geothermal fluids, as exemplified at Fish Hatchery springs. The distribution, quantity, and age of borate minerals in Searles Lake, located some 200 km south of Long Valley indicate that hydrothermal activity associated with the caldera has persisted for the past 300 ka, with the establishment of the present hydrothermal system with the past 40 ka (Sorey, 1985). These results are in good agreement with previous estimates of the occurrence of peak hydrothermal activity at approximately 300 ka based on pervasive hydrothermal alteration in lacustrine deposits southeast of the resurgent dome, which are interbedded with Hot Creek moat rhyolite erupted at about 280 ka (Bailey et al., 1976). More exact age constraints on recent hydrothermal activity at Long Valley were obtained through age determinations of silica and carbonate hot-spring deposits using the 230Th/234U disequilibrium (Keith 1986), and 230Th/232Th versus 234U/232Th ratio least-squares linear regression methods (keith 1986), and yielded an age range of < 6.4 ka to > 310 ka.


Additional References