| Title | Preliminary Characterization of the Geothermal System at Stanley, Idaho, for Possible Resource Utilization |
|---|---|
| Authors | Welhan, John; Autenrieth, Kathleen; Ginsbach, Michael; Koster, Adam; Ohly, Rebecca; Armstrong, Trent; Heath, Gail; McCurry, Michael; Mink, Leland "Roy"; Beckwith, Robert |
| Year | 2012 |
| Conference | Geothermal Resources Council Transactions |
| Keywords | Thermal springs; Idaho batholith; shallow thermal gradient; magnetic survey; soil temperature survey; 3D visualization |
| Abstract | The geothermal system in the Stanley area is characterized by deep circulation of meteoric water along multiple faults and fracture zones in which conductive heating occurs under either a modest regional geothermal gradient of ca. 30 oC/km or a locally elevated gradient and higher than average heat flow due to high uranium and thorium concentrations in the granitic rocks of the Idaho batholith and Tertiary igneous and volcanic rocks in the Stanley area. These thermal waters acquired their unusual alkaline, sodium-carbonate and low dissolved solids character due to closed-system dissolution of granite under high waterrock ratios at maximum temperatures of ca. 85-115 oC. Magnetic surveys in the Stanley area have detected evidence of mineralized zones beneath the valley floor that align with a pair of NE and NW-striking faults that intersect beneath the Stanley terrace. Two test wells drilled in 1986 that intersected one of these faults produced in excess of 200 gpm of artesian flow at a depth of 200-300 feet. In addition to discharge from thermal springs and seeps on the terrace, these faults appear to be capable of supplying more than 250 gallons per minute of water hotter than 40o C. Elevated soil temperatures and high thermal gradients observed in shallow wells on the terrace and in the fluvial sediments and bedrock of the Salmon River valley indicate that considerably more thermal fluid may discharge from the two faults into the sedimentary overburden at the bedrock interface. The inferred geometry of the faults suggests that drilling is likely to intersect the thermal upflow zones at relatively shallow depth (1000-2000 ft) and permit hydraulic testing of long-term productivity, temperature and reinjection potential. |