Downward Continuation of Temperature Gradients at MacFarlane's Hot Spring, Northern Nevada

Abstract

MacFarlane's Hot Spring is located on the eastern margin of the Black Rock Desert of northwest Nevada. Detailed temperature logs from thirty eight shallow boreholes (500 feet) and six intermediated shallow boreholes (1500-2000 feet) have been used to construct a temperature gradient contour map covering approximately 144 square miles, both within the adjacent to the geothermal area. These temperature gradients were then continued downward through a detailed conductivity model to complete the three dimensional thermal picture. The principal results are as follows: (1) the maximum measured temperature is 178°F at 2,000 feet, and depths are not likely to exceed the 250-350°F range. (2) the area of hydrothermal activity is confined to the western front of a structural platform bounded by two roughly parallel normal faults. (3) the anomaly is best explained in terms of a simple groundwater flow model. The groundwater flows west through the structural platform and ascends when it intersects the conduit provided by the fault. The faults on the eastern side of the platform permit recharge to the system.