Isotopic Analysis- Fluid At Long Valley Caldera Geothermal Area (Sorey, Et Al., 1991)

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Exploration Activity: Isotopic Analysis- Fluid At Long Valley Caldera Geothermal Area (Sorey, Et Al., 1991)

Exploration Activity Details
Location Long Valley Caldera Geothermal Area
Exploration Technique Isotopic Analysis- Fluid
Activity Date 1985 - 1988
Usefulness useful
DOE-funding Unknown

Exploration Basis
Sorey et al. (1991) integrated information from previous scientific and private industry investigations with new data obtained from fluid sampling, test drilling, and geological and geophysical studies conducted between 1985-1988 into a comprehensive conceptual model of the present-day hydrothermal flow system at Long Valley caldera. Lithology and temperature gradient data from wells drilled prior to 1988 are summarized in detail in the compilation, which includes information from numerous wells described in previous studies, and data from many of the wells are available online through the U.S. Geological Survey (Farrar et al., 2010). Thermal conductivity, XRD, and isotopic analyses of core cuttings from several of the wells discussed have been completed in several studies, and seem to prove useful in most cases (Flexser, 1991; Goff et al., 1991; Smith and Suemnicht, 1991). Results from these studies are also summarized in Sorey et al. (1991). Relevant data from chemical and isotopic studies published during the same year are also considered in the review.
Interpretation of the isotopic data obtained through analysis of the sampled waters was useful in a variety of reservoir characterization goals. As noted in previous studies, the deuterium versus O18 ratios for select hydrologic features show progressive depletions in the isotopic content of cold meteoric water, from isotopically heavy waters along the caldera's western rim to isotopically lighter waters approaching the eastern rim (Mariner and Willey, 1976; Sorey et al., 1978; White et al., 1990). New data collected from thermal wells at Casa Diablo (MBP) and Chance Meadow (CW-2) in the south moat, wells RDO-8 and 44-16 in the west moat, and cold-water wells (WD) and springs (VR) on the southeast flank of Mammoth Mountain show a similar distribution with respect to their isotopic contents (Sorey et al., 1991). Spring and well water samples follow a general mixing trend, with thermal waters sampled in the west and south moat zones occupying one end and cold meteoric waters sampled from the south and east moat zones occupying the other. Dilution of thermal waters with meteoric groundwater is indicated by progressively lighter isotopic values with distance eastward from Casa Diablo. In the vicinity of Casa Diablo, near-surface boiling causes an observable shift in the deuterium versus O18 isotopic ratio between the average value for the single-phase liquid samples collected from the MBP wells and the spring samples from Casa Diablo Geyser (CDG) and Colton Spring (CS). Tritium concentrations in the thermal wells generally show an inverse correlation with the chloride contents measured in the sampled waters.

Additional References