Drill Holes and Blastholes

Abstract

The following is a geostatistical study of copper measurements on samples from diamond drill holes and blastholes. Both measurements are formally compared, leading to a model where a blasthole can be considered a regularization of the drill information up to a nugget effect characteristic of the blastholes. This formal link makes it possible to build a cokriging system that takes into account the different supports and leads to a block model based on blast- and drill holes. The model is tested on a realistic simulation where the true block grades, which are known, are compared to their estimate obtained by:

• Kriging using only drill holes

• Kriging using only blastholes

• Cokriging using drill and blastholes together

A preliminary conclusion is that the best estimates are obtained when only blasts or, alternatively, blast- and drill holes are used; there is no significant difference between the two, which is due to the great amount of blast information. This result justifies the usual practice of basing short-term planning on blasts only. But another conclusion may be drawn when kriging is compared to a moving average (another common practice), both based on blasts: depending on the number of data used in the neighborhood, the moving average produces a strong conditional bias. As a byproduct, we also show how it is possible to filter the blast error by kriging and to make a deconvolution to estimate point-support values using blast measurements.