Recent induced-polarisation (IP) surveys by PolarX at its Humboldt Range claims area in Nevada have identified several geophysical anomalies coinciding with surface gold anomalies and mapped faults within both its Black Canyon and Fourth of July projects.
At Black Canyon, the company surveyed seven east-west IP traverse lines of variable lengths ranging from 1.3 to 1.7km across known mineralisation trends for 10.2 line kilometres and identified a 1.7km-long IP chargeability anomaly south of the Star Canyon prospect. It is interpreted to extend from the surface to a depth of 250m.
PolarX’s Ridgeline prospect is a target previously identified through mapping and surface geochemistry programs. It comprises multiple gold-mineralised north/north-east-trending veins that extend in outcrop for 1km, immediately north of the IP survey area.
Armed with the new survey information, the company has outlined an anomalous gold-IP zone that now extends for 2.7km and which is coincident with a strong resistivity anomaly, soil gold anomalism, mapped mineralised veins and the extensive Rochester Rhyolite Formation – a recognised host rock for gold-silver mineralisation that outcrops at surface.
IP is an electrical geophysical method used extensively in mineral exploration and mine operations. Resistivity and IP methods are often applied on the ground surface using multiple four-electrode sites.
At Black Canyon, the coincidence of chargeability and resistivity anomalies fits the expected IP response for mineralisation observed in the region. It is typical of the area’s finely-disseminated metal sulphides that are conductive and of strong siliceous alteration that is resistive.
Previous Star Canyon drilling results have revealed a mineralisation style PolarX describes as hosted within finely-disseminated arsenic and iron sulphides that are typically crystals of arsenopyrite and pyrite, respectively.
With anomalies coinciding with previously-established surface geochemical gold anomalies and known faults, the merits of the IP technique for exploration to modest depths offer a solid level of confidence to drill target areas identified by the method.
In addition to the Black Canyon survey, four east-west IP traverse lines were run across the Fourth of July project, about 5km south of Black Canyon. The IP lines measured between 3km and 3.5km in length 13.6 line kilometres, which the company says signalled several strong chargeability anomalies.
It says the anomalies are strongest near the surface and in similar mode to Black Canyon, are coincident with soil gold anomalism and known north-west-trending fault structures. But management says they don’t appear to indicate the same depth penetration as the Black Canyon results and are considered a lower-priority drill target.
The Black Canyon claims at the northern end of Humboldt Range are less than 3km east from the operating 5-million-ounce Florida Canyon gold mine, while the 4-million-ounce Spring Valley gold project is just 9km away. The Rochester Mine, with 400 million ounces of silver and 3 million ounces of gold, is also only 15km south of Fourth of July.
PolarX’s two projects indisputably lie in what is often described in explorers’ parlance as “elephant country”, in the sense of possessing a “good geological address. It seems logical that exploration focussed on identifying mineralised targets within the regional Rochester Rhyolite Formation is justified based on the area’s strong history of large-scale commercial resources.
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By Doug Bright
