Prediction of gold grade potential in erratic vein-hosted deposits using a geochemical discrimination index

摘要

The erratic and localized occurrence of gold is a feature of many gold-bearing veins. The term 'nuggety' is often used to describe such deposits, where it refers to the erratic high gold values that may accompany low grades (low relative to the mean). The effect is a consequence of localized geologically controlled enrichment and the inclusion or exclusion of sparse gold grains because of the nature of the sampling process. Nuggety deposits do not always contain visible or coarse gold (e.g. >100 #mu#m) and may be characterized by erratically distributed fine-grained gold. High-grade regions are generally extremely erratic with a low spatial continuity, but may make mineralization economic. Economic grades are generally contained within discrete oreshoots, which are surrounded by barren to low-grade material.A measure of 'gold grade potential' based on trace-element ratios has been developed that allows the user to discriminate between barren, low-, medium- and high-grade mineralization. A preliminary report on the development of this discrimination index, the Gold Proxy Index (GPI), is presented here and the discussion of gold sampling in previous work by Dominy et al. is extended.