A comprehensive literature review reflecting fifteen years of debate regarding the representativity of reverse circulation vs blast hole drill sampling

Blast hole sampling is widely used for grade control by the mining industry all over the world, both in precious and base metal open pit mining. Blast hole (BH) samples are often regarded as inferior in comparison to “proper drill sampling” like reverse circulation (RC) and diamond (core) drilling (DD), and are accused of lacking representativity by the sampling community. The present paper aims at collecting all peer reviewed publications from 2000 onwards that concern open pit mine sampling performance of BH, RC and/or DD drill sampling. This will form a comprehensive literature review reflecting on the debate between the representativity of the different sampling methods. The literature review collected a total of 31 publications (two were more or less duplicates and one consisted of an abstract only). The main source for publications on RC and BH drill sampling were dedicated sampling conferences, other mining conferences and some publications were found in peer-reviewed journals. From the gathered publications, it is not possible to draw a general overall conclusion as to the superiority of one drill sampling method over another. Both RC and BH have advantages and disadvantages and the choice of system needs to be related to the ore type and to the mining conditions. The overall conclusion is that it is always necessary to evaluate the specific sampling system to be used in light of the Theory of Sampling (TOS) (and with respect to the characteristics of the ore to be mined). It is always necessary to ascertain that the specific drilling sampling system contemplated does not lead to hidden losses that could have been avoided or missed profits that could be gained with a more relevant and representative sampling system. It would appear that the mining industry is doomed to continue to follow local,
often economy-driven objectives and sampling solutions even if these can be documented as inferior when seen in the light of the representativity imperative. A call is made for universal adherence to the principles laid down by TOS for representativity in the primary sampling stage, before economic, logistical or other (local) factors are allowed to intervene. What is the objective to analyse and to make decisions in the mining industry, based on samples that can be documented not to be representative?