Sudbury Deposits

copper and nickel deposits in Canada; one of the richest ore fields in the world, located in western Ontario. Total reserves are estimated at 360 million tons, with an average nickel content of 1.5 percent (1971). The deposits were discovered in 1883 during construction of the transcontinental Canadian Pacific Railway.

The ore field is of the same age as a norite massif that lies amid a complex of Proterozoic rocks with a total thickness of more than 10 km. The rocks occur in a system of gentle folds and broken faults. The encompassing metamorphic rocks are in the form of metamorphic facies of greenstone and almandine-amphibolite. The ore-bearing norite massif is in the shape of an oval dish measuring 60 × 25 km. Its foundation is composed of black norites that change gradually as one moves toward the roof into gabbro-norites, gabbro, and quartz gabbro, and finally into granophyres. Two generations of norites are distinguished: an early one, which constitutes the primary massif, and a late one, which was introduced along the floor after the massif recrystallized. The deposits of rich, massive ores are related to the later generation and to the Precambrian rocks directly beneath. The deposits gravitate toward the periphery of the massif and form a broken ring of ore bodies that can be traced to a depth of 1,500 m. The ore bodies are composed of sulfide copper-nickel ore in complex deposits, lenses, and irregular veins.

The ores contain 64 minerals, the most important of which are pyrrhotite, pentlandite, chalcopyrite, and cubanite. They were formed as a result of the recrystallization of a sulfide melt, which separated out during the cooling of the magma that formed the norite massif. Recrystallization of the upper part of the massiv occurred at a depth of 2 to 3 km, and the lower part recrystallized at a depth of 10–15 to 20–25 km below the earth’s surface at that time.

The geological position of this massif may possibly be a result of the intersection of two large, deep fractures. Another hypothesis relates the massif to an astrobleme formed by the impact of a large meteorite in Proterozoic times.

Mining of the Sudbury deposits began in 1889. Since then a total of approximately 12 billion dollars worth of nickel, copper, cobalt, selenium, tellurium, platinum metal, gold, silver, sulfuric acid, and iron-ore concentrate has been extracted. In 1971 the 40 Sudbury mines produced 220,000 tons of nickel, constituting 41.4 percent of the extraction in the developed capitalist and developing countries. In the same year 300,000 tons of copper and 13.5 tons of platinum metals were extracted.