Hyperenrichment of gold in pyrite induced by solid-state transportation

The hyperenrichment of gold is critical for the formation of high-grade gold deposits in orogenic systems, where gold enrichment can reach several percent. However, many details on the nature of the hyperenrichment mechanism remain unclear. Here we show a "self-purification " model that could explain the hyperenrichment of gold from nanoparticles to veinlets in deformed pyrite. The three-dimensional spatial relationship and coexistence of gold nanoparticles and veinlets indicate a direct transformation from the former to the latter in solid-state. Theoretical evaluation reveals that this transformation involves a thermodynamically favorable self-purification process. We thus propose that deformation/thermo drives the transport of gold nanoparticles towards veinlets in pyrite through atomic diffusion. This deformation/thermo-driven model is applicable to any deformed nano-gold-bearing pyrite and explains how solid-state transport can effectively concentrate gold to a very high grade. Similar mechanisms may have broad implications in both ore-forming and beneficiation processes.