Temperature Gradient Surveys
                     
                 
  A new spin on an old technique: the Great Basin Center is perfecting a method to rapidly measure temperatures at a two meter depth, below the zone of daily temperature variation. The method consists of pounding 1/2" hollow steel rods into the ground using a demolition hammer, inserting a resistive temperature device (RTD) into the rod, and then measuring the temperature after a short equilibration time (see Coolbaugh and others, 2007 and Sladek and others, 2007). This method works well in areas with thick soil horizons, such as alluvial valleys, but the rods have difficulty penetrating through cobbly soils or bedrock.    
                 
                     
                 
DESERT QUEEN  A pilot study was conducted in the Desert Queen geothermal area east of Desert Peak in T22-T23N, R28E, where a temperature gradient hole drilled in 1974 had identified a thermal aquifer at ~70 m depth. A survey conducted over nine days during October and November of 2006 delineated a strong, consistent temperature anomaly at 2 meter depth in the vicinity of the temperature gradient hole. Peak temperatures reached 43o C against a background of less than 23oC.

Click here for a closeup of the Desert Queen picture.

Click here for a description of the survey in Coolbaugh and others, 2007

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    TUNGSTEN MOUNTAIN  Mineral exploration holes drilled in 2004 and 2005 in T21N R38E of the Edwards Creek Valley encountered hot water with fluid geochemistry indicating high reservoir temperatures (see GRC Bulletin article). No hot springs or wells are known in the area. A two meter temperature survey conducted during 2007 identified an associated thermal anomaly in the vicinity of these drill holes along a hydrothermally altered range front fault.

Click here for a detailed view of the Tungsten Mountain anomaly

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TEELS MARSH  DISCOVERY The Teels Marsh playa hosts borate minerals and once was the site of a thriving borate mine, which suggests a possible association with geothermal fluids, as first proposed by Coolbaugh and others (2006) and Kratt and others, (2006). Follow-up investigations identified cold springs with fluid geochemistry suggestive of high geothermal reservoir temperatures (Coolbaugh and others, 2006).

Direct evidence of an active geothermal system in the Teels Marsh area has recently been gathered by researchers at the Great Basin Center for Geothermal Energy, University of Nevada, Reno and the Desert Research Institute.  This evidence comes from mapping anomalously high temperatures at a depth of 2 meters below the surface (see adjacent map): these temperatures are as high at 35°C compared to background temperatures of approximately 16-18°C.  The temperature anomalies occur in two separate zones, both of which are adjacent to a Quaternary fault on the western margin of Teels Marsh basin.  The two temperature anomalies have a combined strike length parallel to the fault of almost 4 km.


No hot springs or wells are known in the Teels Marsh valley.  The shallow temperature anomalies are believed caused by geothermal groundwater upwelling along Quaternary fault(s).  After reaching the groundwater table, these fluids likely flow down-gradient and mix with non-thermal groundwaters before reaching the Teels Marsh playa, where a portion of such fluids exit to the surface to form cold springs with anomalous geothermometer temperatures and borate-rich evaporite crusts.

 
       
      Deeper Probe Measurements Validate Geothermal Origin of Temperature Anomaly at Teels Marsh:  To verify if the shallow temperature anomaly at Teels Marsh is produced by geothermal groundwaters, the site was revisited in May, 2008.  Near the point of the highest measured 2-meter-deep temperatures, a probe was inserted to a depth of 31 feet (9.5 meters), where a temperature of 65°C (148 F) was measured, and the temperatures are increasing rapidly with depth. Click here to see a graph of the data.

Click here for a detailed view of the Teels Marsh anomaly

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RHODES MARSH DISCOVERY  Similar to Teels Marsh, the Rhodes Marsh playa hosts borate minerals that were mined during the 1870s, which led Coolbaugh and others (2006) and Kratt and others (2006) to investigate the potential for geothermal energy.  Reconnaissance field investigations and mapping of borate minerals with remote sensing techniques led to the identification of warm artesian wells, one of which yielded a quartz geothermometer temperature of 162°C and an Mg-corrected Na-K-Ca geothermometer of 155°C (the well water contains 360 ppm Cl, suggesting minimal contamination with evaporite fluids).  Several outcrops of opalized sands were subsequently identified immediately east of the playa at the foot of the adjacent Pilot Mountains.

The mapping of shallow temperatures by researchers from the Great Basin Center for Geothermal Energy and the Desert Research Institute is still in progress (see adjacent map).  A significant temperature anomaly has been detected immediately upslope of the opalized sand occurrences.  The anomaly is elongate in a NNE-SSW direction.  As currently mapped, the anomaly is more than 2.5 km long, and its northern and southern limits have not yet been defined.  Additional temperature mapping is planned for late May, 2008.

Click here for a detailed view of the Rhodes Marsh reconnaissance survey.

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