total depth: 1944 feet limestone; Truckee Formation ┬╗tuff, fine grained and soft, light green in color diatomite with some tuffaceous material and gravel ash, brown to amber colored and soft basalt with th in interbedded lakebeds; Chloropagus Formation diatomite with some clay interbedded basalts and clays rhyolite tuff, generally blue with a soft altered matrix; quartz, biotite, magnetite and feldspar are present. The cuttings are very poor basalt dike (?)

location: SW/2 NE/4 S23, T22N, R27E

Churchill County, Nevada started: April 27, 1977 completed: May 6, 1977

FIGURE 22. Lithologie log of Desert Peak stratigraphie test no. 7.

discovered which resulted in decreasing the depth of this anomaly to between 1000 and 3000 feet. The anomaly was now obviously too shallow to reflect a reservoir and still fit the known temperature distribution. As the drilling pad for well B23-1 had already been constructed and the temperature data from strat. test no. 7 were encouraging, the site was not moved.

Later analysis of the MT survey reconfirmed that the quality of the raw data is excellent; however, some of the mode selections appeared to be in error (Charles Swift, personal commun., 1978). As a result of this discovery the Desert Peak MT survey was thoroughly reevaluated (John Maas, personal commun., 1979) and some of the refined data are presented in this report. Three slice maps which show the minimum apparent resistivity at depths of 1000, 4000, and 8000 feet are shown as plates 7, 8, and 9.

The apparent resistivity at a depth of 1000 feet (pi. 7) is, with the exception of one point, very low, and the contours show little character. In T22N.R28E there is a single-point resistivity high which may be the result of the site being located on a young, resistant ash-flow sheet (pi. 13). The very low nature of the apparent resistivities is unexpected, as much of the survey area is underlain by volcanic bedrock near the surface and the water table is generally more than 150 feet below the surface; occasionally it is 500 feet deep. Plate 8 shows the apparent resistivity at a depth of 4000 feet, which is an approximate known depth of the top of the reservoir. The contour pattern shows several small apparent resistivity highs and lows, most of which are singlepoint anomalies. The most interesting feature is the resistivity high containing wells B21-1 and B21-2. Generally, in geothermal exploration hot saline reser-

collar elevation : 4240 feet __

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