- © 2002 Canadian Institute of Mining, Metallurgy and Petroleum
There are two main issues stemming from Vallée’s (2002) comments on Dominy et al. (2001b). First, he raises the importance of quality assurance/quality control (QA/QC) during resource estimation programs, and second, he indicates that the resolution and understanding of continuity (grade and geological) issues are paramount in the classification of resources. In particular, continuity is critical at the boundary between the Inferred and Indicated Mineral Resource categories. The original contribution agrees with the importance of these points, and the principal author offers the following discussion and clarification. Further comment is also provided on the reporting of grade uncertainty through grade ranges.
It is worth remembering that vein-gold deposits (e.g., shear-zone, lode-gold, mesothermal types etc.), particularly those containing coarse gold particles (e.g., >100 μm), generally show large variations in grade and an erratic grade distribution. In most cases, diamond drilling is a good measure of geological continuity (depending on drill spacing), but a poor measure of grade and its distribution. High-nugget effect deposits rank among the most difficult deposit types in terms of producing an accurate and precise resource estimate, and clearly represent a distinct deposit type.
Quality Assurance/Quality Control
The issue of quality assurance (QA) and quality control (QC) during exploration, estimation/evaluation and exploitation has been at the forefront of industry perceptions since the Bre-X affair in the late 1990s. The need for QA/QC programs is paramount in any mining/minerals project (Vallée, 1998a, 1998b, 2002).
Quality is a critical issue at all stages of a minerals project. For example, QA/QC of analytical and test data, and the corroboration of geological data within the resource/reserve estimation process must now be considered mandatory. Indeed, the Canadian National Instrument 43–101 requires mandatory QA/QC programs (CSA, 2001). The 1999 JORC Code does not prescribe QA/QC programs but, for example, QA/QC for sampling/assaying is …