Gold transport during magmatic degassing: Model experiments

Abstract

Interaction of metallic gold with (Na, K)Cl salt melts was investigated by the weight-loss method at 700–1000°C using silica glass ampoules. Interaction was not detected in hermetic evacuated ampoules over the whole temperature interval and even after the addition of 5 wt % Na₂SO₄ as a possible oxidizer to the salt. Gold solubility increased sharply in open ampoules, but this was accompanied by the evaporation of salt melt and, possibly, AuCl_x. The limiting gold solubility in the salt melt at 860°C was estimated as 1 wt % or 10000 ppm. The model of gold transport in a gas phase during magmatic degassing invokes shallow gold extraction by salt melt, melt evaporation, and removal of precipitated metallic particles by the gas phase.