The valuation of dianlondiferous deposits depends on (i) the density distribution, (ii) the size distribution of stones and (iii) the selling price structure prevailing at a particular time. In the density distribution the stochastic variable is defined as the number of individunl stones found per sample unit irrespective of the stone size. The density distribution is discrete and allows for barren sample umts. As diamonds often occur in clusters, a Poisson mixture distribution is derived which is entirely new, as
existing discrete distributions cannot represent the stone number frequencies found in nature.
For the si"WI of d iamonds, which are measured by weight, a new compound logarithmic DOrmal distribution
is developed.