Application of median indicator kriging in the analysis of an iron mineralization

Abstract

This paper presents an application of median indicator kriging in the analysis of iron mineralisation data from the Chadormalu iron mine in Yazd province, Iran. The sample data used in this study consist of exploration drilling data, suitably composited. The data set is sparse, irregularly spaced, and has a bimodal distribution. It is important to use an estimation method that deals with the nature of the distribution appropriately. Since none of the grade distributions are normal or log-normal, a non-linear estimator is ideal. The indicator kriging method is considered to provide a better way of estimating an element with a bimodal distribution. Indicator semivariograms were modelled for nine cut offs, the deciles. Semivariograms were standardised by dividing each semivariogram by the total sill, and a single spherical structure plus nugget was fitted in each case. All data were treated as point data in three-dimensional space rather than block data. The grade tonnage curves were calculated on the assumption that each estimate is representative of a block of size 20 m by 20 m by 12.5 m centred on the location of the datum.