Geochemical exploration for gold: a new approach to an old problem

Abstract

Of the huge sum of money allocated to gold exploration, only a small proportion has been spent on geochemical surveys. A major reason for the lack of emphasis on geochemical methods lies in the unique geochemical characteristics of Au, namely the problem of sample representativity and analytical reproducibility caused by the uneven distribution of discrete Au particles in nature. Although this problem can be addressed by collecting large samples, this approach is expensive and inconvenient. In regional exploration programs in China over the past ten years, an approach has been developed to bypass these problems. Numerous stream sediment surveys using a gold analytical method with a detection limit of 0.2 ppb show that gold mines and groups of gold mines can be outlined by regional anomalies using a threshold of 2 to 4 ppb. Within the regional anomalies, “concentration centers” with gold values exceeding a threshold of 4 to 8 ppb furnish areas for follow-up. These low-threshold anomalies are very reproducible on resurveying, because they rely on low levels of ultrafine gold rather than particulate gold. Use of these surveys has allowed geochemistry to become the primary method of reconnaissance gold exploration in China, and has led to the discovery of hundreds of new gold occurrences, some of which are or will soon be producing mines.