A study on kriging small blocks

CIM Bulletin, Vol. 82, No. 923, 1989

Margaret Armstrong and Normand Champigny, Centre de Géostatistique, France

In order to define the ore/waste boundaries as finely as possible, mine planners often insist on kriging very small blocks (relative to the spacing of the available sample grades). These kriged estimates for very small blocks are over-smoothed. For several simple sampling patterns the relation between the block size and the variogram range, and the kriging results were studied. Meaningful estimates of individual blocks are obtained when the variogram range is large compared to the block size and the sample spacing. For a variogram range less than half the sample spacing, the kriged block estimates were found to be uncorrelated with the actual grades. The over-smoothed estimates should not be used for calculating recoverable reserves.
Keywords: Geostatistics, Ore reserve estimation, Kriging