Abstract Knowledge of speciation and thermodynamic properties for aqueous gold complexes are important for both the understanding and numerical modelling of the formation of hydrothermal gold deposits. While gold speciation in chlorine- and sulfur-rich hydrothermal fluids has been investigated by considerable theoretical and experimental studies, the complexation of gold with other ligands that may be important for transporting gold in hydrothermal fluids, such as hydroxyl (OH−) and ammonia (NH3) complexes, have received limited attention so far. In this study, we conduct ab initio molecular dynamics (MD) simulations to calculate the coordination structures of Au(I)–OH and Au(I)–NH3 complexes. Our simulations show linear structures of Au(I) complexes with two bonded ligands (OH−/NH3/H2O), consistent with previous experimental and theoretical studies of Au(I) complexation (e.g., Liu et al., 2014). The new speciation models show that Au(I)–OH−/NH3/H2O complexes are stable in hydrothermal fluids and vapors. We also use thermodynamic integration to determine the formation constants of these species at temperatures up to 350 °C and at water-saturated pressures; furthermore, we extrapolate these properties to wider temperatures and pressures range based on the Modified Ryzhenko–Bryzgalin equation of state parameters. In particular, this study, for the first time, reports the speciation and formation constants of mix-ligand [Au(NH3)(OH)]0(aq) complexes. The derived formation constants show that the stability of Au(I)–NH3 complexes decreases progressively with increasing temperature. The quantitative modelling of gold solubility based on the new thermodynamic data shows that gold can be transported as Au(I)–OH−/NH3 complexes in sulfur-poor and ammonia-rich hydrothermal fluids. In sulfur-bearing ore fluids, ammonia is only likely to transport small amounts of gold as [Au(NH3)(OH)]0(aq) in hydrothermal fluids in the near-neutral to alkaline fluids under extremely reduced conditions.

中文翻译：

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金在碱性和富含氨的热液中的溶解度：来自从头分子动力学模拟的见解

摘要 水相金配合物的形态和热力学性质的知识对于热液金矿床形成的理解和数值模拟都很重要。虽然大量的理论和实验研究已经研究了富含氯和硫的热液中的金形态，但金与其他配体的络合可能对在热液中传输金很重要，例如羟基 (OH-) 和氨。 NH3) 络合物，到目前为止受到的关注有限。在这项研究中，我们进行了从头分子动力学 (MD) 模拟来计算 Au(I)-OH 和 Au(I)-NH3 配合物的配位结构。我们的模拟显示了具有两个键合配体 (OH−/NH3/H2O) 的 Au(I) 配合物的线性结构，与之前 Au(I) 络合的实验和理论研究一致（例如，Liu 等，2014）。新的形态模型表明 Au(I)–OH−/NH3/H2O 复合物在热液流体和蒸汽中是稳定的。我们还使用热力学积分来确定这些物质在高达 350 °C 的温度和水饱和压力下的形成常数；此外，我们基于修正的 Ryzhenko-Bryzgalin 状态参数方程将这些特性外推到更宽的温度和压力范围。特别是，这项研究首次报告了混合配体 [Au(NH3)(OH)]0(aq) 复合物的形态和形成常数。导出的形成常数表明，Au(I)-NH3 配合物的稳定性随着温度的升高而逐渐降低。基于新热力学数据的金溶解度定量模型表明，金可以作为 Au(I)-OH-/NH3 复合物在贫硫和富氨热液流体中传输。在含硫矿流体中，氨仅可能以 [Au(NH3)(OH)]0(aq) 的形式在近中性至碱性流体中的热液流体中在极端还原的条件下传输少量金。