past or which currently support mining activity naturally rank high, but more and more, exploration is extending into virgin areas which are selected on theoretical geological grounds. Areas are chosen which are believed to possess geological environments similar to those known to have produced deposits of the desired minerals elsewhere either in the immediate neighbourhood, in other parts of Australia or overseas. This approach places great value on knowledge of the distinctive geological characteristics of these empirically proven favourable environments. These characteristics may involve fundamental aspects of sedimentation, vulcanism, intrusive activity, meta-morphism and structure. It places equally great value on knowledge of local geological environments which is necessary for the selection of areas with matching characteristics.

The search for nickel in the Kalgoorlie region illustrates the application, in various degrees of refinement, of the concept of geological environments as a guide to exploration. Prior to the discovery of nickel at Kambalda there had been developing a growing recognition by geologists of similarities between the Western Australian Archaean and the Canadian Archaean which is proving to be so productive of large base metal deposits. Included amongst these are the nickel sulphide deposits found in association with ultramafic rocks in the Manitoba nickel belt.

Interest by Western Mining Corporation in the nickel possibilities of the Kalgoorlie region was focused on the Kambalda area as a result of examination of nickel-bearing limonitic material brought in by prospectors.

The subsequent discovery of nickel sulphide ore bodies at Kambalda in ultramifics associated with metabasalts (Woodall and Travis,1969), touched off a rush to take up exploration holdings over virtually all the known greenstone belts containing ultramafics in the Kalgoorlie district. Applications for the large-area Temporary Reserve type of holding soon threatened to exhaust the areas of greenstones available and this led to the placing of an embargo by the Mines Department on issuing any more holdings of this type. Coverage of the remaining known areas of ultramafics was accomplished by the pegging of a multitude of the much smaller (300 acres or less) Mineral Claims.

Exploration activity on these holdings is continuing at a high level and while it is too early for the history of the discoveries so far made to be recounted, it is evident that successes have been achieved by methods which have covered a wide range of sophistication, from simple recognition of outcropping oxidized ore by prospectors, to saturation prospecting by large exploration teams using all available methods of geology, geophysics and geochemistry, together with direct exploration by trenching, test pitting and drilling. Initial identification of ultramafic belts been greatly facilitated by the regional mapping carried out by the Western Australian Geological Survey and by the regional aeromagnetic surveys made by the Bureau of Mineral Resources, which cover parts of the region.

The discovery at Kambalda marks a most significant breakthrough in mineral exploration in the Archaean.