Regional-scale targeting for gold in the Yilgarn Craton: part 1 of the Yilgarn Gold Exploration Targeting Atlas

The Yilgarn Craton of Western Australia is well known for its gold endowment (more than 324 Moz, or 9730 t), including the giant Golden Mile deposit at Kalgoorlie (67.3 Moz, or more than 2000 t). Despite considerable success in the identification of near-surface gold during the periods 1890–1910 and 1985–2005, the discovery rate for gold in the Yilgarn has since slowed, a situation that is commonly attributed to exhaustion of economic near-surface resources. This view has led to a greater focus on exploration for ‘blind’ orebodies with tonnages and grades in excess of modern nearsurface resources. Exploration for blind orebodies relies on identification of a geophysical expression of subsurface ore, a geochemical expression of the ore in overlying transported sediments or sedimentary rock, or a conceptual approach that predicts the presence of ore on the basis of the geological controls of known near-surface mineralization. Although each approach has both advantages and limitations, this Atlas focuses on the conceptual approach. Eighteen targeting criteria for gold exploration at regional scale are addressed in the Atlas, with individual criteria ranging from well-established geological controls such as intersecting faults to more recent suggestions (e.g. proximity to late-stage basins). Each criterion (and sub-criteria, in some cases) is examined in relation to gold distribution, at scales ranging from craton to domain, using a GIS platform. The results of the spatial analyses are summarized in the form of maps, and histograms (containment analyses) or curves (proximity analyses) showing ounces per square kilometre and deposits per square kilometre. Full results of the spatial analyses are presented in the Appendix. \ud \ud The results of this study suggest that the four most effective targeting criteria for gold in the Yilgarn Craton are proximity to intrusions of Mafic Group granites, elevated fault density, proximity to regional fault bends, and the well-known preference for gold to be found in greenstone belts rather than in intervening areas of granite. A fuzzy logic approach has been used to combine and weight the results of spatial analyses for these four criteria to produce spatial arrays of prospectivity values that have then been used to produce regional prospectivity maps for gold in the Yilgarn Craton and in the Eastern Goldfields Superterrane. Correlation coefficients relating gold endowment to prospectivity values range from 0.38 to 0.78, depending on the parameter used to measure endowment. The results for the Yilgarn Craton as a whole are better than those for the Eastern Goldfields Superterrane, and results expressed in terms of deposit density are better than those expressed as ounces per square kilometre. Although spatial analyses for domes (containment) and late-stage basins (proximity) suggest a relationship to gold mineralization, prospectivity maps produced after their addition to the previous fuzzy logic analysis compromised the correlation between gold endowment and prospectivity value. \ud \ud This report forms the first part of a three-part Atlas. Parts two and three deal with district-scale and deposit-scale targeting, respectively