On the role of alkanethiol Au complex in the formation of gold deposits; an in-silico approach

Abstract

The association of organic matter with ore minerals has been observed for many years. Over decades, many speculations have been proposed to define the possible roles that organic matter might have played in the ore genesis. In this paper, we performed a series of electronic calculations, and molecular dynamic simulations to investigate the behaviour of organic matter in ore-forming environments. Ab initio calculations revealed that variation in the length of alkane tails has a limited impact on the geometry of the Au-ligand, and the strength of Au–S bonds. MD and metadynamics simulations proved that the organic Au-ligand could be dissolved in the organic phase but it mostly pose at the interface of the organic-inorganic phase, in a way that its ionic head place in the aqueous solution and its alkane tails dissolved in organic matter. These observations suggest the organic-gold ions (and organic ligands of some other metals) are preferentially accumulated in the narrow interface of the aqueous/petroleum phase. Overall, although experimental results suggest that organic matter might have a role in gold transport, this study proves that organic gold ligand is concentrated only at the interface between the organic and aqueous phases and therefor, the organic phase alone cannot carry gold. This finding is also consistent with field observations, which suggest that gold concentrations in oil are relatively low.