Gold–quartz reefs are often characterized by localized, erratic high grades and, in many cases, coarse free gold. They typically display a high to extreme nugget effect, and the sampling of these deposits for resource evaluation presents a corresponding challenge. Core drilling is generally an effective measure of geological continuity, but reliable grade data and confirmation of its continuity can only be obtained from underground development. Generally it will be possible to estimate only an inferred mineral resource from drill data alone; underground development with closely spaced infill drilling and bulk sampling will be required to delineate indicated and measured mineral resources. Three case studies are presented that show that bulk sampling provides an effective—though costly—way of assessing likely minable grades.
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