Engineering & Mining Journal

When compared with the world’s largest nickel/copper sulphide districts, various sources rank the Duluth Complex as third largest in nickel content, second in copper and second in PGM content. There are presently 13 known nickel/copper sulphide deposits in the Duluth Complex that combined, could host a theoretical resource of 4.4 billion tons of copper/nickel ore averaging 0.66% Cu and 0.20% Ni using a cutoff grade of 0.50% Cu equivalent. Not surprisingly, its economic potential has attracted a number of players.

The NorthMet project is by far the most advanced of its type in the area, but other companies are avidly pursuing exploration and development of additional polymetallic deposits throughout the Complex. Franconia Minerals Corp., an Alberta, Canada, company with its head office in Spokane, Washington, USA, holds more than 15,000 acres in the area and is focusing on its Birch Lake copper-nickel-PGM deposit located in the north-central part of the mineral belt. According to the company’s latest figures, Birch Lake contains resources of more than 100 million t grading 0.59% Cu, 0.19% Ni and 0.14 g/t Au, 0.65 g/t Pd and 0.32 g/t Pt. The company’s Maturi deposit, 3 miles to the north of Birch Lake, contains another 83.1 million t of similar but lower-grade mineralization, and its Spruce Road property is estimated to contain 124 million t of underground-minable and 376 million t of surface-minable inferred resources. Pre-feasibility studies are presently aimed at evaluating the viability of separate mines at Birch Lake and Maturi that would feed a single processing complex built near the Birch Lake deposit.

Another company active in the area is Ontario, Canada-based Duluth Metals, which reports that current estimated resources at its Nokomis deposit in the western portion of its Maturi Extension properties in the Duluth Complex consists of 347 million t of indicated resources grading 0.62% Cu, 0.20% Ni, and 0.52 g/t of platinum+palladium+gold (total precious metals, or TPM), plus an additional 108 million t of inferred resources grading 0.64% Cu, 0.18% Ni, and 0.70 g/t of TPM. In mid-January 2008, the company announced it had acquired a Platsol technology license from the process patent owner, International PGM Technologies Ltd., for future processing of these metals extracted from its properties along the Complex.