Wires laid by Quantec Geoscience will provide a picture of subsurface mineral deposits in the Patagonia Mountains. Photo by Robert Gay

In Feb. and March 2021, Quantec Geoscience LLC, under contract to South32, conducted ground-based field work for an exploration technique that analyzes electronically collected data to produce a spatial model of underground masses that could be “minerals of interest.” This high-tech method will create subsurface modeling of the area near the Hermosa Project in the Patagonia Mountains. 

Approximately five miles of electric wire was laid along upper Flux Canyon Rd. and Harshaw Rd. The three-plus mile segment on Harshaw Rd. extended south from within the Hermosa Project to Guajolote Flats Rd., then about a mile west toward Soldier Basin. Both segments of wire run through areas of several historic mines, including Flux, Humboldt, Endless Chain, and Blue Nose mines. 

Quantec is an international geophysical surveying firm headquartered in Ontario that serves the mining, geothermal and gas sectors in many countries. For mineral exploration, the company’s studies are generally used to refine targets and expand deposits for future exploration, generally by core drilling. The Quantec toolbox offers ten types of ground-based geophysical survey techniques.

According to Hermosa Project’s Melanie Lawson, the method being used for South32 is called Spartan MT. Quantec describes the method as “a magnetotelluric (ground magnetism) resistivity mapping approach for both 2D and 3D geologic scenarios.” In an email, Larson wrote, “Our goal is to better understand the rock types in the area, such as limestone to volcanic, and doesn’t identify new deposits.” 

Lawson stressed that Quantec’s exploration method is non-invasive: “The program allows us to do some exploring with minimal disturbance. The technology does not impact wildlife, both flora and fauna, and the areas are reclaimed after the survey is complete.” She added that the project areas lie within the company’s patented and unpatented claims (approximately 1300 claims, averaging 20 acres each). South32’s claims cover approximately 26,500 aces, extending around private inholdings, from the Forest Service boundary nearest to Patagonia to the vicinity of Duquesne Road. 

Near the Hermosa Project site, the only areas South32 is not entitled to explore for mineral presence, under current laws, would be the Sunnyside Project’s approximately 5220 acres and the 31 acres of the privately held Harshaw Townsite. 

How does ground-based prospecting work? The electrical resistivity of the planet’s natural electromagnetic field varies from spot to spot, both above and below ground, and different densities and types of rock can be inferred from the naturally caused variations in electrical resistance. In the Spartan MT method, a temporary ground array of sensors collects electromagnetic data from many frequencies and sends it to a 10-channel recorder for storage and later analysis. 

The method can “see” ten kilometers (6.2 miles) into the earth, several times deeper than South32’s currently presented model of the Clark and Taylor deposits, which bottoms out roughly 1 km (5/8 of a mile) below the Project’s surface. 

Once a static 3D model is made from data acquired from a field survey like this, it can be tinted and animated to give a dramatic portrayal of mineral zones of interest. Besides guiding future drilling, the resulting still pictures and videos can be used to guide future physical explorations, inform the public, attract investors or convince government or business entities to support the project for economic reasons.