geothermal resource potential of the safford-san simon basin, arizona

Buena Vista Area
Introduction
More than eight irrigation wells, which are all less than 213 meters
deep, discharge thermal water from 30 to 49 0 C.
These thermal waters, previously
reported by Muller and. others (1973) as the "Larson anomaly", have
sodium chloride-sulfate chemistry with TDS less than 1,200 mg/1 (Table 2).
Three of these wells sampled during the study have artesian flows which exceed
an estimated 100 gpm during the winter months.
Pumped flow rates
measured by the U.S. Geological Survey range between 900 and 1,600 gpm (files,
USGS,
Tucson).
Geochemistry
Thermal waters in the Buena Vista area are readily distinguished from
local non-thermal waters by their low calcium «20 mg/1) and magnesium
«8.0 mg/1) concentration and their high fluoride (>4.0 mg/1) concentrations.
Fluoride concentration up to 14.0 mg/1 are reported for thermal waters in
this area (Figure 9). Dissolved silica in these thermal waters is supersaturated
with respect to quartz and chalcedony at measured discharge temperatures.
Dissolution of alumino-silicate minerals is tentatively suggested
as the primary control of dissolved silica because the highest silica concentrations
are observed in waters with the highest dissolved carbon dioxide
concentration (Figure 10).
Carbon dioxide reacts with sodium and potassium
feldspars to form clay while adding dissolved sodium, potassium and silica
to ground water (Garrels and Mackenzie, 1967; Stumm and Morgan, 1970).
Subsurface mixing of non-thermal waters and thermal waters may occur
because Muller and others (1973, p. 55) report a conversation with Mr. Moroni
Larson of Solomonsvi11e, who states that wells on the "east side of the road
(San Jose Road) gradually cooled after pumping." This cooling suggests that
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