Mercury geochemical, groundwater geochemical, and radiometric geophysical signatures at three geothermal prospects in northern Nevada

Groundwater sampling, desorbed mercury soil geochemical surveys and a radiometric
geophysical survey were conducted in conjunction with geological mapping at
three geothermal prospects in northern Nevada. Orientation sample lines from 610 m
(2000 ft.) to 4575 m (15,000 ft.) in length were surveyed at right angles to known and suspected faults. Scintillometer readings (gamma radiation measured in total
counts/second) were also recorded at each soil sample station.
At the Reese River prospect, a 60-station sample line crossed a pull-apart basin in
the northern Shoshone Range. The eastern third of the sample line crossed a
514°C/km (33°F/100 ft.) heat flow anomaly defined by previous drilling. Desorbed
mercury anomalies in the 0.5 ppb to 1.0 ppb range correlate well with the location of
known and suspect faults. Radiometric data, while useful at this prospect, were not as effective a tool as mercury data for mapping structure because of the masking effect of widespread alluvial deposits.
At the Salt Wells prospect, the 26-station sample line crossed a previously
mapped basin/playa bounding fault and a suspected buried fault indicated by the
location of a warm spring. Elevated mercury concentrations and anomalous radioactivity were detected along the fault trace and in the vicinity of the spring.
At the Silver Peak prospect, a basin/playa bounding fault was defined by both
mercury vapor and radioactivity anomalies along the 14 station sample line. Mercury
anomalies in the 2.0 to 6.0 ppb range and radioactivity anomalies in the +500 CPS
range marked both the location of the fault and associated sub-cropping hot springs
sinter (mixed travertine–silica) deposits. A detailed radiometric survey along 4.5 km
of strike of the basin bounding fault detected three dormant hot spring vent areas.