Journal of the international association for mathematical geology
In the usual geostatistical practice, global estimation of a deposits is made by running the estimated values obtained by kriging for each individual block in the deposits. When all blocks are identical in size it is equivalent to simply accepting the average of all the estimated values as the global estimated value. Variance of this estimator is expressed by a complicated formula. This explain why numerous approximations have been proposed; they use different hypotheses for distribution of samples in space or for noncorrelation of individual kriging errors. These are not practical hypotheses and actual calculation of the global estimation variance has always been considered a difficult and uncertain step in the estimation.