Continental-scale kriging of gold-bearing commodities

This paper focuses on continental-scale kriging on the African continent using the gold-bearing commodities of the Gondwana Geoscience Indexing Database. The mineral layer contains over 20 000 commodities, each containing information on its ordinal interval size value. Boundaries between class intervals across the database are, however, not uniform. We perform spatial interpolation on a continental scale using the commodity gold as the binary variable. First, we select an appropriate distance metric in order to krige on an essentially spherical surface. We use this metric to implement a valid covariance function. Second, the ordinal size classes of the commodities are combined into a unique size classification. In addition, the commodity size classification is used as a proxy for data reliability and is incorporated by using a weighted variogram. The geology is used to stratify Africa into geologically homogeneous strata, leading to stratified kriging. The best model in each stratum is used to produce a map of gold commodities of Africa including the spatial uncertainties. By integrating advanced techniques with high-quality data, a state-of-the-art map of gold commodities was obtained for Africa, including the spatial uncertainties.