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

the uplift is approached. Late Cretaceous sediments are observed unconformably
overlapping both the Precambrian rocks on the uplift and Paleozoic rocks
on the uplift margins.
Due to the widespread cover to Tertiary sediment and
volcanic rocks, the actual extent of the uplift is not known with certainty.
It is believed the uplift trends west-northwest in conformance with the trend
of Mesozoic sedimentation patterns and tectonic features inferred to comprise
elements of the Texas Zone. Figure 5 is a generalized map of the Tertiary
basement in southeast Arizona and southwestern New Mexico.
Inspection of
the map shows that the Pinaleno Mountains may be part of a western extension
of the Burro uplift. However, this is not certain because the Pinaleno Mountains
are not known to expose late Cretaceous sediment unconformably overlying
Precambrian granite. Tertiary low-angle faulting may have tectonically removed
the Paleozoic rocks since the Pinaleno Mountains are a Tertiary "metamorphic
core complex" (Davis and Coney, 1979). The geothermal implications
and description of "metamorphic core complex" are discussed later in this
section.
Basement Structure of the Northern Safford-San Simon Basin
The "Laramide" orogeny, 75 m.y. to 50 m.y., involved uplift, volcanism,
intense compressive deformation and plutonism in that order (Coney, 1978;
Shafiqullah and others, 1980).
In the northern Safford-San Simon Basin area,
the "Laramide" orogeny is recorded in the Gila Mountains.
Andesite and felsic
tuff is intruded by small silicic to intermediate composition stocks, which
are associated with local porphyry copper deposits.
These volcanic and intrusive
rocks range in age from 53 to 58 m.y.
(Dunn, 1978; Robinson and Cook,
1966; and Livingston and others, 1968). Intense shear zones and dike swarms
trending northeast transect these rocks and they are frequently highly altered
and mineralized.
Drill holes up to 4,000 feet have failed to reach the
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