The role of potassium in lode gold mineralization: insights from ab initio molecular dynamics and geochemical modeling

Abstract

Potassium ions (K+) are abundant in ore fluids of lode gold deposits, largely illustrated by pervasive potassic alteration and commonly expressed as K-feldspar and muscovite on both sides of individual gold lodes. However, their potential roles in gold mineralization remain elusive. Here, we present results from ab initio molecular dynamics simulation and geochemical modeling to address this question. Molecular dynamics simulation results show that the ability of K+ pairing with Au(HS)2– complex over a wide temperature–pressure range has a negative linear correlation to fluid density. In high-density liquid-like fluids, little K+ is coordinated with the Au(HS)2– complex. In contrast, this complex can be nearly neutralized by ion association with K+ in low-density, vapor-like fluids, but such a neutral complexation is not very stable, even if under conditions typical of lode gold mineralization. Thus, K+ has a limited role in the complexing and transporting of Au in hydrothermal fluids forming lode gold deposits. We conducted geochemical modeling that integrates geological context and mineral paragenesis. The results reveal that potassic alteration in lode gold deposits, characterized by the transition from K-feldspar to muscovite, occurs alongside decreasing temperature, pH, and oxygen fugacity of the ore-forming fluids. Among these factors, the drop in temperature is the most significant mechanism driving potassic alteration, while also causing the destabilization of Au-bisulfide complex and spatially associated deposition of gold. These results suggest that gold mineralization during potassic alteration is primarily driven by the cooling of ore fluids, which also explains the transition from K-feldspar to muscovite alteration. The combination of molecular simulation and geochemical modeling indicates that the role of potassic alteration in lode gold mineralization reflects the influence of fluid evolution particularly fluid cooling on gold precipitation, rather than a direct control of K+ on Au transport in lode gold deposits. Therefore, potassic alteration can serve as an effective indicator for lode gold exploration and has been widely applied in practical fieldwork.