Nanoscale distribution of elements in gold: examples from contrasting deposit types

Quantifying the distribution and nature of trace elements in native gold is a novel approach to understanding the genesis of gold deposits and has implications for metallogenic processes, mineral exploration, and metallurgical processing. Most previous research on the formation of gold deposits has utilized proxies for gold, rather than gold itself, to infer its source, transport, and depositional mechanisms, despite the difficulty in establishing unequivocal relationships among the proxies and gold. This approach has left many questions regarding the formation of high-grade coarse gold. This contribution presents results on the composition and distribution of trace elements in native gold using electron probe microanalysis and, for the first time, atom probe tomography. Gold grains selected are from a deformed and metamorphosed Archean orogenic gold deposit (Preston Mine) and a young, undisturbed epithermal gold deposit (McLaughlin mine) which are endmembers in terms of deposit type and geologic time. Results show that Cu, Ag, and Hg are homogenously distributed in gold while Sb is not, which raises questions regarding the substitution mechanisms of large radii metallic elements in gold. These data provide new insights into the incorporation of trace elements in gold, as well as primary and secondary processes related to the formation of high-grade gold deposits through time.