Reappraisal of arsenic-gold interaction in pyrite: insights from ab initio simulations

Geochemical evidence suggests that arsenic is a key accelerator reinforcing gold mineralization in pyrite. The systematic presence of Au-bearing arsenian pyrite in hydrothermal systems highlights the coupled Au-As geochemical behaviors in various physio-chemical conditions. However, there is a lack of understanding of elemental interactions at the atomic scale during gold mineralization.

Here, we employ ab initio simulations to detect the atomic-scale mechanisms governing gold incorporation in arsenian pyrite. By computing crystal unit cell volume, incorporation energy, and detailed electronic properties, we demonstrate the fundamental role of arsenic in gold occurrence, which effectively leads us to revisit the Au-As coupling.

We obtain that the Au-As substitution is one of the most favorable double substitutions into pyrite. The incorporation of As induces the expansion of the unit cell, which facilitates the substitution of the Au atom to the Fe-site. Lattice distortions of pyrite caused by other elements (including the common trace elements in pyrites) promote this process on a smaller scale. Among several calculated double substitutions, the valence shell of As and the volume of the [FeAs_xS_6-x] polyhedra provide a unique preferential environment that can easily accommodate incompatible elements, such as Au.

Our study provides a novel insight of the co-evolutionary process between Au-As coupling in pyrite during gold mineralization, and propose a fresh approach to detect the dynamic evolution between varying trace elements occurring in different mineralization system.