Colloids and Nanoparticles: Implications for Hydrothermal Precious Metal Ore Formation

Abstract

Abstract Research on nanoscale processes is expanding in many scientific and technical disciplines, and economic geology is no exception. The idea that colloidal gold particles (or nanoparticles) may have played a significant role in ore formation was initially based on textural evidence from high-grade epithermal veins. More recently, the discovery of gold nanoparticles in some present-day geothermal systems and several orogenic gold deposits suggests that their formation could be a common process in gold-supersaturated hydrothermal solutions. Rare laboratory studies indicate that gold nanoparticles typically aggregate to form dendritic clusters. Over time, these dendrites perhaps can evolve to form coarser-grained crystals as subsequent annealing and recrystallization occurs. Due to the ephemeral nature and later recrystallization of dendrites, evidence of their former existence is commonly obscured. However, newer nanoscale imaging technologies have resulted in an increased recognition of their presence in hydrothermal gold ores, and thus their role in ore-forming processes merits further research. In particular, does their nucleation and deposition lead to forming higher-grade ores?