The Selectivity of the Distributions and “The Second Principle of Geostatistics”

The definition of the recoverable reserves is nearly connected with two effects of a purely physical nature: a support effect, and an information effect. For the reserves depend on the support of the selection, that is on the size of the minimal units which can be separately sent either to the mill or to waste. Similarly, they also depend on the ultimate information, that is on the nature of the sampling which will be available when the final destination of each unit will be decided. This is not at all an estimation problem, although, naturally, estimation problems will also arise, but it involves the definition of the “true” or “really” recoverable reserves themselves. In any case, we must expect that an increase of the size of the support, or decrease of the ultimate information will result in a distortion or adulteration of the true grade/tonnage curves. And very often this distortion will be much more important than any estimation error. This “second principle” of Geostatistics seems absolutely general, and it deserves a precise formulation which was given in [3] although the basic idea goes back to D.G. Krige [5].