The Yilgarn craton is one of the world's major nickel provinces, containing 31.5 million tonnes (Mt) of Nimetal with an in situ value of about $350 billion on a pre-mining basis, amounting to 13.6 percent of the world'scurrently known Ni resources. This entire resource inventory has been discovered since 1966. This chapterpresents an analysis of the 40-year discovery history, which isideal as a province-scale case study in mineralexploration.

The province experienced a major peak in exploration activity between 1966 and 1971, the "nickel boom," which accounted for more than half of all NiS deposits, and all of the giant (>1 Mt Ni) NiS deposits so far discovered. Almost 70 percent of those discoveries were related to direct surface prospecting methods, commonly based on recognition of magnetic ultramafic rocks as favorable hosts. Since the end of the nickel boom, the dominant discovery method has been follow-up exploration around significant known mineralization. From about the mid-1990s, electromagnetic (EM) surveying, which had been considered ineffective during the nickel boom phase, became a demonstrably successful technique for the detection of sulfide deposits. An improved understanding of geologic processes and controls has played an important role in sustaining exploration success since the end of the early, surface-prospecting phase of the nickel boom.

Most nickel laterite deposits were first found during the nickel boom but not considered at that time to be economically significant. A large surge in exploration activity, much of it focused on resource delineation rather than true green-fields exploration, occurred between 1996 and 2001, triggered by the advent of the Pressure Acid Leach (PAL) technology in the mid-1990s.

The discovery record of the Yilgarn province exhibits many patterns typical of an exploration province: early discovery of both the largest deposits and most of the metal and generally increasing discovery costs as the province matures. The average discovery costs for nickel in the Yilgarn have been 5.2 c/lb for sulfide nickel and 0.6 c/lb for laterite nickel.

The Yilgarn province offers two examples of exploration expenditure booms arising from the coincidence of an upturn in commodity price with the opening up of new exploration parameter spaces. These are the initial discovery of komatiite-hosted nickel sulfide at Kambalda in 1966, and the mid-1990s recognition of the potential of PAL technology to treat laterite ore deposits.