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

geothermometry for waters containing higher calcium, chloride, and sulfate
concentrations are believed unreliable due to possible mixing, dissolution of
gypsum,
and cation exchange reactions with clay in the basin-fill sediments.
Na-K-Ca geothermometry assumes that temperature-dependent equilibrium with
silicate minerals in the reservoir has occurred and that no additional reactions
have changed the ratios of sodium, potassium, and calcium after the
thermal water leaves the deep reservoir (Fournier and others, 1974).
Figure
30 is a map of the Bowie area showing the distribution of the Na-K-Ca geothermometer
temperatures.
Wells with the highest Na-K-Ca temperatures may
overlie fractured basement, which is leaking thermal water into shallow
«600 m) aquifers. Additional studies are required to confirm the high Na-K­
Ca geothermometer temperatures obtained using the low magnesium,
sodium bicarbonate
waters because the sodium, potassium and calcium ratios may also
reflect shallow nontemperature-dependent dissolution of silicate minerals
in a high dissolved carbon dioxide environment (Paces, 1975).
Structure and Stratigraphy
Geophysical studies by Eaton (1972)
and drillers' logs provide a basis
to describe the subsurface geology in the Bowie area.
Eaton (1972) published
a subsurface model of structure based upon an accompanying gravity profile.
Figure 31 shows Eaton's structural model and gravity profile.
His profile
locations are shown in Figure 32, Gravity interpretation by Eaton (1972) shows a
graben, which is about five miles wide and filled with up to 760 m of clastic
sediment.
Tertiary volcanic rock, 300 to 600 m thickness, are modeled to
underlie the basin-fill sediments.
Drillers' logs published in 'fuite (1963) and White and Smith (1965) show
the stratigraphy of the upper portion of the basin-filling sediments in the
Bowie graben (see drillers' logs in the appendix),
A "blue clay" strata,
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