Mathematical models of magmatic sulfide ore formation: Applications to the exploration and evaluation of mineral resources

Abstract

Sulfide ores that formed by magmatic segregation processes currently account for about 60% of mankind's supply of nickel, 98% of the platinum group metals, and substantial quantities of copper, cobalt, and other elements. The first stage in the generation of such an ore is the separation of an immiscible sulfide liquid from a mafic or ultramafic silicate magma. The sulfide acts as a collector of the ore metals and its tenor is determined by the concentrations of the metals in the parent magma, the degree to which the metals partition into the sulfide phase, and the relative proportions of sulfide, silicate liquid, and crystalline phases that equilibrate. Deposits of an economically exploitable grade represent metal concentrations of at least an order of magnitude greater than those in the parent magmas, and so sulfide saturation in itself does not lead to the formation of an ore. It is necessary that some process such as gravitative settling or flowage differentiation operate in the magma to accumulate the exsolved sulfide. Ultimately the ore grade reflects both the metal tenor of the sulfide phase and the efficiency of the accumulation process.