Base metal exploration comes out of the shadows

After a long period in the shadow of the precious metals, the base metals appear to be regaining some of their past glory in exploration in the Canadian Shield.

Three projects in northwestern Ontario offer a picture of how base metal exploration has changed since the golden age of airborne surveys.

In the Rainy River area west of Fort Frances, a long campaign of overburden drilling by Nuinsco Resources (NWI-T) — mainly aimed at finding gold mineralization — has defined an apparent caldera complex. The complex, which occupies an area about 2.5 km by 3 km, is a south-dipping sequence of intermediate to felsic volcanic rocks overlying mafic volcanic rocks; all are intruded by a late-stage porphyry body. The volcanic sequence in the caldera is girdled by mafic volcanic rocks, except on the east where it is intruded by a granitic stock.

Earlier work in the area had concluded, based on limited bedrock exposure, that the dominant structural grain of the area was east to northeast. The overburden drilling program has made it possible to map bedrock units more systematically, and there is now strong evidence that the bedrock units strike roughly easterly, and that there are a number of northwesterly striking faults that may mark the caldera margin.

While gold remains Nuinsco’s main interest at Rainy River, the company is giving the area’s base metal potential more weight. Diamond drilling on several targets in Richardson Twp. intersected sulphide mineralization grading up to 13% zinc, in what appears to have been stratabound zones.

Moreover, the volcanic rocks in some of the cores were rich in magnesium and poor in sodium, two characteristics that have long been considered typical of the footwall rocks of massive sulphide deposits.

An early spring breakup forced Tri Origin Exploration (TOE-T) to cut short its 800-metre drill program at the Confederation Lake base-metal property, situated 40 km southeast of Red Lake. Two of the three holes Tri Origin completed cut disseminated sulphides, with one 1-metre intersection grading 0.74% copper. Two other holes had to be abandoned after the overburden proved to be deeper than expected.

Tri Origin, having added 288 claims to its property in the early part of the year, now controls about 60 sq. km in the Confederation Lake area. Once the ice is out, the company plans geological mapping and geophysical and geochemical surveys. It expects to move a drill back on to the property in the late summer.

Across the border in Manitoba, Canadian Shield Exploration (CSP-A) is completing the acquisition of a property in the Rice Lake greenstone belt, near Bissett.

Zinc-copper showings had been reported from the area since the late 1920s, when Selkirk Canadian Mines drilled a few holes. Teck (TEK-T) optioned the property from Tulsa Resources, a private company, in 1992, and carried out rock geochemical surveys that revealed large areas where the rocks were low in sodium and high in magnesium.

Electromagnetic surveys located 18 conductors, seven of them coincident with the depletion zones found by the geochemical survey. Teck dropped its option in 1994 after seven drill holes encountered values up to 0.53% copper and 0.76% zinc, but no significant mineralization; a large number of the geophysical conductors are still untested.

Overburden drilling in 1996 indicated seven areas with zinc and copper in glacial drift, some of which are near targets that Teck did not test.

Linecutting is under way, in preparation for new electromagnetic and magnetic surveys, and a rock-geochemical survey is planned for the summer.