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Department of Geology, University of Wales College of Cardiff, PO Box 914, Cardiff CF1 3YE, UK
Statistical studies of a portion of the Boulby potash seam revealed that distinct subareas are present in which stationarity could be shown to exist and which are characterized by statistically distinct populations of seam thickness and % KCl. Semivariogram modelling in these sub-areas allowed the definition of the axes of anisotropism in each case and hence the dimensions and orientation of the search ellipses for ore reserve purposes. Inverse distance weighting was then applied to evaluate individual ore blocks and the efficiency of the method tested by cross-validation of actual borehole values. Considering the problems induced by the sampling method applied (low angle deflection of in-seam drill holes), the results were generally satisfactory and form the basis for a more detailed comparative study of inverse distance and kriging techniques at Boulby.
