The Walker Lane shear zone straddles the border between Nevada and California and has a long history of exploration and mining, dating back to the discovery of the famous Comstock Lode in the late 1850s. The Walker Lane is notable for its numerous occurrences of volcanic-hosted epithermal gold and silver deposits.
The majority of gold deposits occur in the Walker Lane shear zone, which is a 100-km wide, NW-trending structural corridor extending southeast from Reno towards Las Vegas. This strike-slip system contains a series of deep-seated, right-lateral shears and associated normal faults. The rock outcrop is mostly Tertiary volcanics with an assortment of Mesozoic intrusions of mostly monzonitic or granodioritic composition. The basement is made up of strongly folded and thrusted Palaeozoic sedimentary rocks.
The area covered by the Walker Lane study is about 140,000 square kilometres. To date, approximately 50 million ounces of gold have been discovered in this area. Our data mining study was commissioned by Newmont Mining Corporation as part of a regional survey for gold in this area. The available exploration data sets included regional geology and structure, airborne magnetics and radiometrics, isostatic residual gravity, stream sediment geochemistry, Landsat and digital elevation. Most of these data sets were obtained from sources such as the Nevada Bureau of Mines and the National Geophysical Data Center. One exception was regional structure which was based on a proprietary in-house compilation belonging to Newmont.
The known deposits layer is the most critical, since it is used for training the process against all the other data sets. In producing this layer, all known gold deposits exceeding 50,000 ounces were carefully plotted from air photographs, detailed publications, or field visits with a GPS.
Data Mining Results
Since the Walker Lane is a competitive exploration area, the final target map is too sensitive to be shown in full. Part of the study area falling inside the Nevada Test Site, however, can be shown. After four decades of nuclear weapons testing, this is permanently off-limits to gold mining.
The lower figure shows an area of about 2500 square km in the northwest corner of the Test Site, with the TM image on the top and the geology on the bottom. The target favorability map in the middle is based on all the exploration data sets except for geochemistry, which was not collected in the Test Site.
The study produced two interesting targets. Target A coincides with a color anomaly in the TM data, indicating the presence of alteration associated with mineralization. Target B coincides with a circular feature in both the TM and the geology. Further interest is added by the small, orange-colored formation labeled `Ta3′, which outcrops at the center of this probable caldera. This is a Tertiary andesite well known to Nevada geologists for hosting many of the larger volcanic-hosted gold deposits in the Great Basin. Both of these targets would certainly be followed up if access were permitted to this area.