Vancouver — There’s gold in them thar Churchill-Superior Boundary zone rocks. The discovery, by
Historically the Thompson region has been the focus of massive sulphide exploration, but this latest discovery is refocusing exploration along the zone.
Says International Curator Chairman Michael McInnis: “What appealed to us first was that we had some hits of economic grade, though, at the time, it wasn’t gold but zinc. Also, we knew that if we could find more economic mineralization, there would be a entire region that could evolve into a mining camp.”
Vice-President Richard Bailes says Homestake Mining had recognized this as an elephant-country-type gold area because of the Thompson lineament and the banded iron formations. “In the mid-1980s, Homestake flew a low-level airborne mag and electromagnetic survey. All our ground geophysical anomalies are identified by that airborne survey.”
The Churchill-Superior Boundary zone, between Superior and Churchill Provinces, is the southern element of the Trans-Hudson Orogen, Earth’s earliest continental collision zone. It is thought to represent the suture between the two ancient continental fragments, one of which is 3 billion years old; the other, 2.5 billion years. The southern boundary of the suture is the Assean Lake shear zone, which lies 1 km south of the Hunt mineralized zone. Recently, Tim Corkery, Christian Bohm and Larry Heaman of the Manitoba Geological Survey mapped a large orthogneiss of 3.2-billion-year-old granodiorite and tonalite on the northwestern side of Assean Lake. The Hunt zone is in Proterozoic rocks enfolded with this orthogneiss.
The Hunt-Tex property, along the northwestern side of Assean Lake, covers a 20-km strike length of the Superior Boundary zone. Sparse outcrop occurs mainly along the lakeshore. Some 2-10 metres of Manitoba clay covers bedrock, and the vegetation cover is sparse scrub spruce forest.
Gold was discovered on the property in the 1930s, when three narrow high-grade gold-bearing quartz veins were found on the shoreline of Assean Lake. Dan Ziehlke, who vended the property to Curator, was attracted to the area by a 1951 letter. An unknown prospector had trenched and sampled material that assayed about a third of an ounce of gold over 40 ft. from a trench near the Assean property. Later, interest in the property shifted to a zinc prospect known as the Tex, a massive sulphide body discovered by Hudson Bay Exploration & Development in the mid-1960s.
By early 2001, a large, low-level gold mobile metal ion (MMI) geochemical anomaly had been outlined in soils on the Hunt Peninsula. The anomalous area trends north-northeast and is about 1 km long and 200-300 metres wide. MMI gold values in the anomalous zone are 3-7 times background of 0.0001 gram per tonne, the detection limit of the method.
The mineralized rocks contained disseminated sulphides, so induced-polarization (IP) surveys were carried out. “We have since done IP surveys over the Hunt zone and there is a fairly low-level but distinct anomaly directly over the zone,” says Bailes. The anomaly is attributed to disseminated sulphides (about 2-3%) in the mineralized rocks; in contrast, the country rocks lack sulphides. In February 2001, steep-angle diamond drilling was begun to test the MMI anomalies, which led directly to discovery of the Hunt zone in March 2001.
International Curator has drilled 56 holes (for a total 7,684 metres) on the Hunt and Tex properties. The Hunt zone mineralization was intersected in 24 holes. The best grade drilled to date is 9.4 grams per tonne over 8.2 metres.
Rocks intersected in the drilling are strongly foliated, dark mafic schist and gneiss with a strong penetrative schistosity. They consist of tremolite-actinolite, biotite, calcite and chlorite, and have up to 10% quartz. The quartz forms veinlets, lozenges and boudins, to 1 cm thick, contained within the foliation.
High-grade shoot
Fine-grained native gold grains, 0.1-0.2 mm across, occur in the quartz. Disseminated sulphides associated with it make up about 2% by volume; they include galena, pyrrhotite, pyrite and chalcopyrite. Sphalerite and arsenopyrite occur rarely.
The shear zone strikes north-northeast and dips 80 south-southwest. Mineralization appears to be confined to the shear zone. The system is traced for about 500 metres on surface, that it was drilled to a depth of 150 metres and that mineralization is concentrated in a higher-grade shoot. This shoot was intersected by drilling over 100 metres along strike and to a depth of 200 metres, as measured along the plunge of the shoot. The higher-grade shoot plunges westward at 50 within the mineralized shear zone.
The current winter program, budgeted at $600,000, will entail 5,000 metres of diamond drilling. Its main objective is to test the extension of the Hunt zone to a depth of 350 metres. One rationale is that shear-hosted gold deposits typically have a comparatively short strike length compared with their depth extent.
About 2,000 metres of the current drilling will focus on other geochemical and geophysical targets. Two diamond drills started up in mid-February and are expected to continue to the end of March.
Bailes sums up his company’s approach thus: “We outlined an MMI anomaly, we drilled it, and we found the zone, so we’re now going after MMI anomalies. We wanted to be able to distinguish the target within the anomalies, so we ran very-low-frequency electromagnetics and mag, and now we’ve run IP. As a result, we think we can go inside an MMI anomaly and pick the better target.”
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