Gold particle clustering: a new consideration in sampling applications

Abstract

Recent research indicates that an enhanced coarse gold problem may be present in some gold deposits. This can be due to the presence of gold particle clusters that give the effect of individual coarse-gold particles and leads to a high constitution heterogeneity (CH). These clusters, which may be distributed on the centimetre-scale or greater, give rise to high assay variability in field samples. However, once a sub-sample is pulverised, the effect of the clusters may be removed if the individual gold particles making up the clusters are liberated. Thus any resulting pulp will tend to have a low variability, unless true coarse-gold particles exist. Clusters are readily recognised in coarse gold deposits where they accentuate existing high nugget effect and CH. Clusters may however also occur in fine gold deposits where they produce an apparent coarse gold style. This is signaled by an unexpectedly high nugget effect from variography and poor correlation between field sample duplicates. The Gy sampling equation is applied to model coarse and fine gold deposits with clustered and non-clustered gold grains. Case studies illustrating observed effects of clustering are presented. If clustered particles exist, then proper protocol design at the field and early laboratory stage is paramount. The sample characterisation stage should include an assessment of possible gold particle clustering, in addition to the standard descriptions of the gold particle size distribution.