Using Unfolding to Obtain Improved Estimates in the Murrin Murrin Nickel-Cobalt Laterite Deposit in Western Australia

Nickel and cobalt are key additives to modern alloys. The largest worldwide nickel-cobalt resources occur in surface laterite deposits that have formed during chemical weathering of ultramafic rocks at the Earth’s surface. Geologically young deposits have formed by rapid weathering processes in tropical environments while older deposits that have formed in drier climates. At the Murrin Murrin mine in Western Australia the dry climate laterite deposits occur as laterally extensive, undulating blankets of mineralisation with strong vertical anisotropy and near normal nickel distributions. This deposit structure presents an estimation challenge for both classical and geostatistical resource estimation methods. In this paper, ordinary kriging and multiple indicator kriging estimation methods are applied to both the in situ and unfolded structural cases to obtain estimates for nickel and cobalt. Improvement in point grade estimation following the unfolding of the laterite blanket by vertical data translation prior to grade estimation is assessed in the light of close spaced grade control data. The results indicate that unfolding, particularly when combined with indicator kriging, improves both the nickel and cobalt estimates albeit only slightly in the case of cobalt.