Case Studies - Mineral Exploration

Voisey's Bay Ovoid Zone, Labrador

The Ovoid Zone of the Voisey's Bay deposit consists of 31.7 Mt of near-massive to massive sulphides, mainly pyrrhotite, pentlandite and chalcopyrite. It is approximately 70% massive sulphide, grading roughly 2.8% Cu, 1.7% Ni, 0.1%Co. The Ovoid is about 900m long, 500m wide, and is over 100m thick at the center. The top is 2.5 to 30m below surface.

Total Magnetic Field

The zones which comprise the Western Extension have about 29.6 Mt of indicated and inferred resources. These occur as thin lenses of massive sulphides. This part of the deposit is discontinuous and approximately 1600m long, 150m wide, and 20 to 70m thick.

The responses of both zones to the DIGHEM^V survey flown by Fugro Airborne Surveys are very strong EM anomalies, indicating very large, very conductive targets. (No big surprise!)

The apparent resistivity map, calculated from the 900Hz frequency, shows the curved anomaly of the Ovoid, and the linear Western Extension. On all lines crossing the Ovoid, the strength of the response was extremely high, and indicated the apparent width of the deposit along the flight line path (up to 500m). The conductivity-thickness products calculated range as high as thousands of Siemens. The apparent resistivity calculated over the Ovoid was far below 1 ohm-m, and below the resistivity which would be calculated for the salt water in the area.

900 Hz Apparent Resistivity

There is a moderate magnetic anomaly apparent over the deposit. The strong anomaly expected from the high percentage of pyrrhotite in the Ovoid zone is apparent on profile 604900. However, the anomaly due to the deposit is partially concealed in the map view by the strong background response due to the mafic troctolite hosting the deposit. While the deposit has a higher magnetic susceptibility than the troctolite, the much greater volume of the troctolite creates a stronger anomaly.

Digital Profile- Line 604900 Ovoid

The profile of line 604900 across the Ovoid shows the strength and width of the EM anomaly over that deposit. The width and thickness of the deposit at this point are so great that the deposit appears as a half-space to the DIGHEM^V system. The S.E. Extension is not apparent on this profile, because it is approximately 200m east of the flight line.

The profile across the Discovery Hill deposit (603800) where the deposit is thinner, yields a slightly weaker EM response. The width and amplitude of the response are less. The apparent resistivity is less than the true resistivity of the deposit, because it no longer resembles a half-space to the EM system. Of course the anomaly is still very large, and unmistakable in the data.

Digital Profile- Line 603800 Discovery Hill

West of the Discovery Hill zone, the DIGHEM^V survey discovered the previously unknown Reid Brook zone, buried as deep as 90 metres. The profile from line 602100 over this zone shows a very weak anomaly on the coaxial 900Hz data (CXI900) and a small anomaly on the coplanar 900 Hz data (CPI900). The apparent resistivity data, however, shows a very strong anomaly, which could not be missed.

Digital Profile- Line 602100 Reid Brook Zone

DIGHEM^V surveys were flown by Fugro Airborne Surveys over the Voisey's Bay deposit and surrounding properties for Diamond Fields and Inco Ltd. to search for more deposits like the Ovoid. These data were shown courtesy of Inco and Voisey's Bay Nickel. We also wish to thank Voisey's Bay Nickel for their geological information.