Constellation, le dépôt institutionnel de l'Université du Québec à Chicoutimi

Résumé

Determining the number of gold grains in till is a widely used exploration technique in glaciated terrain. Nonetheless, there is no existing reference material to assess the quality of either the recovery or the counting of gold particles in samples from glaciated sites. We manufactured a reference material (AuGC-1) by mixing a gold-free heavy mineral concentrate with gold grains recovered from mine tailings. The reference material contains 38 gold grains, with a standard deviation of 10 grains, in 1.5 g of heavy mineral concentrate. Of the 38 gold grains, 24 grains are >50 μm (optically determined), and 14 grains are <50 μm (using SEM). This grain concentration is considered optimal, well above Canadian Shield till background and sufficient for obtaining reproducible statistics. Gold grain reference materials can be improved further by ensuring that i) the grain size distribution of gold is similar to that of the matrix; ii) gold grains in the sample originate from different sources or a source having a great variation in gold grain composition; iii) a slightly larger number of gold grains are present in the samples (closer to 50 grains) to reduce the standard deviation; and iv) a larger sample size is used to improve mixing of the high-density gold grains with the mineral matrix.