Grade and geological continuity in high-nugget effect gold–quartz reefs: implications for resource estimation and reporting

Abstract

High-nugget effect gold-quartz reefs are one of the most challenging styles of mineralisation to evaluate and exploit. The estimation of mineral resources, and subsequent ore reserves, forms a critical base for exploitation. The understanding and application of grade and geological continuity issues during estimation is of importance. Most reporting codes make specific references to grade and geological continuity issues. Within the high nugget environment, confidence in the tonnage estimate is variable depending upon geological continuity, though it is usually higher than the confidence in the grade estimate. Estimation of grade is problematic as a result of the erratic and low continuity of gold values and gold-bearing domains. Detailed geological interpretation supported by 3D modelling to produce either 'conceptual' or 'visual' continuity models is critical. The inherent risk associated with the estimation of mineral resources and ore reserves and subsequent classification can be reduced by a strong understanding of geological and grade continuity.The level of investment required to acquire this information is generally substantial, and will almost certainly involve underground development supported by close-spaced diamond drilling and bulk sampling/trial mining.