Novel geophysics technology identifies deep drill targets in Athabasca

Two of the Athabasca basin’s junior explorers have made a significant advance in geophysics that could aid exploration for deep deposits. And the implications of the technology — which uses electric and magnetic signals induced by lightning — could go well beyond uranium exploration in Saskatchewan.

A novel geophysics technology, MagnetoTelluric (MT) Deep Resistivity Sounding, has been used by Golden Valley Mines (GZZ-V, GLVMF-O) and Ditem Explorations (DIT-V, DTEMF-O) to identify deep (700-metre) drill targets on their Beartooth Island uranium project in the Athabasca basin. The ground survey was carried out by Toronto-based Quantec Geoscience, which uses the trade name Spartan MT for this technology. Golden Valley and Ditem are currently busy with a drilling program of three 800-metre holes on the property.

Michael Rosatelli, vice-president of exploration for Golden Valley, says the company initially commissioned an airborne Mega- TEM survey to look for conductors. The survey outlined some responses that merited further investigation. Beside conductors, the survey also identified alteration halos. To get a better indication of the geophysical anomalies, Golden Valley decided to carry out a magnetotelluric deep resistivity sounding and hired Quantec Geoscience to conduct the survey. The idea was to look for resistivity lows, suggestive of conductors. Another reason for choosing this technology was that the unconformity on the property is deep (600 metres plus), and the MT technology is particularly suitable for deeper targets.

Rosatelli says the survey returned high-resolution results, which helped Golden Valley select targets for the drilling program. Asked where the MT deep resistivity sounding could be useful, Rosatelli says that the technology can be used to detect resistivity lows, locate deep targets, provide high-resolution survey results, investigate conductive zones or alteration halos, and identify structures and faults. However, he suggests that the MT technology should not be used on its own, but rather as a follow-up on results from another geophysics technology, such as MegaTEM.

Peter Legein, manager of corporate sales for Quantec Geoscience, explains how the MT system operates. An array of dipole receivers and magnetic coils is placed on a property. The dipole receivers record voltage signals while the magnetic coils record magnetic field signals. These signals are induced by lightning storms elsewhere on the planet. The two kinds of signals are processed to give an apparent resistivity value, and the resistivity is correlated to a depth based on signal frequency. The higher the frequency, the nearer to the surface the site is. So the test produces a series of resistivities corresponding to different depths, and a resistivity anomaly is an indication of a geological anomaly such as a conductor, fault, alteration, etc.

On Beartooth Island, sensors were inserted into the lake through holes in the ice, but they can also be inserted into the ground. Legein says that although the Beartooth Island project was a detailed survey, the system is even more suitable for regional-scale surveys. The MT technology can be combined with an induced-polarization (IP) test: the MT survey is carried out during the night, while IP is used during the day.

Legein says that the good depth penetration of MT can help discover conductors underneath large, near-surface conductive sediments such as mudstone, which MegaTEM can have difficulty penetrating. The MT technology has been used in the past in oil exploration, as well as exploration for copper porphyries, volcanogenic massive sulphides (VMS), nickel sulphides, and iron oxide-copper-gold (IOCG). It was also used to find a new 1-km-deep zone at Northgate Minerals’ (NGX-T,

NXG-X) Kemess gold-copper project, in B. C. And an MT survey was carried out at Debswana’s Jwaneng diamond mine, in Botswana, based on the resistivity in the contact zone between the kimberlite and surrounding rock.

What is so significant about MT geophysics is that it comes at just the right time, when explorers are forced to search for deeper deposits. Fewer and fewer large, near-surface deposits with outcrops are being discovered, and explorers need deeper penetrating geophysics such as magnetotelluric deep resistivity sounding.

The Beartooth Island project is 100% owned and operated by Golden Valley Mines. Ditem Explorations is earning a 50% interest by spending $1 million on exploration over three years. Thereafter, it can earn a further 10% interest by spending $2 million in the fourth year.