Colloidal gold dispersions in orogenic gold from the Barberton greenstone belt, South Africa

The mechanisms of gold grain growth, as a necessary precursor to gold hyper-accumulation and the formation of high-grade ore deposits, remain equivocal. This is particularly true for orogenic gold deposits where primary growth textures may be poorly preserved due to episodic fault re-activations during successive seismic events. A sample collected from the Fairview Mine in the Barberton Greenstone Belt (South Africa) and subjected to non-destructive SELFRAG sample preparation and subsequent scanning electron microscopy provides rare capture of images of millimeter-scale gold grains associated with dispersed spheroidal gold colloids and nanoparticles (<5 nm to >1 mu m diameter). Although the ultimate provenance of these gold spheroids remains equivocal, textural evidence suggests a net addition of mass to the adjacent gold grains. We suggest that Ostwald ripening (a process of particle growth or coarsening by diffusion) and coalescence may contribute to gold grain growth in this sample.