Analyses under the curve, identifying how invisible gold is held in pyrite

Summary: Invisible gold refers to gold occurring either within the lattice of a host sulfide or as discrete nanoparticles within a host that are only observable when imaged at very high magnifications. The physical form of invisible gold is partially controlled by the concentration of arsenic in the host sulfide, and stability fields for different forms of gold are defined by an empirical solubility curve. Analysis of a sample from the Olympic Dam Cu-U-Au-Ag deposit in South Australia shows that more than 50% of pyrites contain measurable gold and arsenic, and they plot below the solubility curve. Gold and arsenic are geochemically associated with other elements such as tellurium, bismuth, lead, silver, and tin.