The Composition of Canadian Sulphide Ore Deposits
Canadian sulphide deposits generally have characteristic compositions. Metal associations in ore deposits and in igneous rocks are similar. Nickel: sulphur ratios, copper-nickel ratios, and nickel :cobalt ratios in copper-nickel sulphide ores are characteristic for most orebodies. Nickel, as sulphide, is highest in ores associated with ultrabasic rocks, whereas copper is highest in ores associated with gabbros. Cobalt is relatively constant. The metal ratios in copper-nickel ores are due, first, to the composition of the related igneous rock or magma; second, to the partition ratios of the metals into the sulphides when separating from the silicate rock or magma; and third, to the conditions at the time of deposition. Each factor is discussed and the evidence indicates the Frood orebody is a magmatic segregation in place and Falconbridge is an injected sulphide melt. Many Canadian orebodies containing copper, zinc, or lead also have relatively constant compositions. Copper and zinc are concentrated in gabbro and diorite, and copper-zinc ores in northwestern Quebec are spatially related to gabbros and diorites. The same three factors controlling metal ratios in. copper-nickel deposits should control the metal_ ratios in copper-zinc deposits if the metals come from the gabbro-diorite intrusions. The ratios of hase metals in common sedimentary rocks are not similar to the ratios in orebodies. Base metal elements are mobilized during high-grade metamorphism, but much fundamental research is needed before the relating between metamorphism and ore deposits can be established on a sound basis. The distribution of elements in sulphide orebodies suggests that copper, zinc, and lead are deposited simultaneously .in relatively constant proportions rather than successively in a paragenetic sequence. Zoning may be due to different ratios of metals being deposited under changing temperature, pressure, and chemical environment, or may be the result of other processes.