Use of the specific surface to measure the efficiency of grids of drillholes and classify the resources of a set of 2D mineral deposits
Résumé
The hole spacing is an essential element that controls the precision of estimated
resources, hence their categorisation. Generally, with a regular sampling grid, the
smaller the grid cell, the better the precision. However, for a given grid, the precision also depends on the spatial continuity, typically the variogram of the target
variable. The specific surface (specific volume in 2D) has been designed to measure
the efficiency of a grid cell, depending on this variogram. This further allows to
approximate the precision of the resources contained in volumes made by blocks
centered on the grid and having the size of the grid cell. Classification of resources
can be deduced by considering a number of blocks corresponding to a nominal, for
example annual, production. It provides an objective method to evaluate the level
of confidence of resources, then to make comparison of different projects.
This concept of specific surface has been used by Orano, a leader of uranium
mining industry, for the classification of the resources of a set of deposits at various
stages of regular sampling. The present paper illustrates the methodology in the
example of one such deposit. It also shows how the method can be used to make a
synthetic comparison of different projects at the level of a mining company.
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