A History of Geothermal Energy Research and Development in the ...

EXPLORATION
Figure 2. Photograph of the Cove Fort-Sulphurdale geothermal power plant, Utah
Geologic studies at Cove Fort-Sulphurdale discovered large-scale gravitational
glide blocks, soled (bounded below) by low-angle faults, and composed
of volcanic rocks that formed a cap rock over the geothermal system.
Figure 3 is a geologic map of the Cove Fort-Sulphurdale geothermal
area, and Figure 4 is a schematic conceptual model of the area. 7
Over much of the system, the exposed geology was not a good indicator of
what lies vertically below. The steam cap, fed by a deeper liquid-dominated
resource, occurred in fractured sandstone above the water table. Areas of
surface leakage were characterized by anomalously high thermal gradients,
pronounced soil-mercury anomalies, intense acid leaching and deposits of
native sulfur. Extrapolation of the measured shallow thermal gradients to the
depth of the water table suggested that temperatures may be high enough to
cause boiling under atmospheric conditions, but the gradients provided no
information on the true reservoir temperature. Such large-scale gravitational
glide blocks in geothermal fields, and their influence on shallow temperature
measurements, had not previously been documented, although they were well
known to mining companies exploring the Basin and Range province.
20 A History of Geothermal Energy Research and Development in the United States | Exploration