By: Brian Harrisson
This article appeared in the Journal of the Australasian Institute of Mining and Metallurgy, No. 6 December, 2009 at, P24.
A recent technical paper has challenged one of the golden rules of exploration namely that angled drill holes detect dipping targets more effectively than vertical holes.
The paper has its origin in the Central Victorian goldfields where the author was a member of the management team in a small mining company exploring for gold in the Rheola/Moliagul district. In this district where gold forms narrow veins, is nuggetty and difficult to find, the golden rule is of little practical value. In fact a search of the geo-scientific literature did not find any papers or texts that provided a convincing
theoretical justification for the golden rule so the author developed a detection model from scratch based on conventional probability concepts. The model showed that based on data for the area being explored vertical drilling has a higher chance of detecting a target than angled drilling irrespective of its geometry or orientation. It further showed that this outcome will not be limited to the particular conditions that apply in the Central Goldfields, but will apply to exploration in general.
While these conclusions are at odds with the golden rule the paper also shows that the golden rule is flawed and promotes less than optimal drilling strategies. Where chance is influential significant improvements can be expected by putting drilling on a sounder theoretical basis.
All relevant information is contained in the technical paper: B. K. Harrisson, “Detection effectiveness of angled versus vertical drilling”, Mining Technology, 2009, vol. 119 no. 1, 13-24, published in Section A of the AustIMM/IOM3 Transactions.