On the Use of MultiGaussian Kriging for Grade Domaining in Mineral Resource Characterization

In the mining sector, grade domains are often considered, following the modelling of geologic domains, to further control the distribution of grades during resource estimation. This is usually achieved by wireframe modelling on sections displaying grade assays or composites, indicator kriging, and/or via boundary modelling using radial basis functions. This paper proposes an alternative approach to conventional grade domaining, an approach that is based on MultiGaussian kriging. The method consists of estimating grades using MultiGaussian kriging; however, instead of back transforming to obtain a grade estimate at each location, the probability to exceed certain grade thresholds are determined and grade domains are categorized accordingly. This permits uncertainty assessment of grade domains by post-processing for various grade thresholds. An example to a gold deposit is shown, with visual comparisons to grade shells based on radial basis functions that were used to facilitate explicit domain wireframing for resource estimation. Results show the MultiGaussian kriging approach to grade domains can yield comparable shells to existing implicit modelling approaches such as radial basis function. The method and model parameters are data-driven, resulting in an approach that is tractable and repeatable, with the added benefit of quantifying a measure of confidence associated to the resulting grade shells.