Based on the theory and method of thermodynamics, this paper discusses the effect of CO2-H2O fluid immiscibility on the solubility of Au. The results indicate that the ore-forming fluid in the Shuiyindong gold deposit was a kind of volatiles-rich (f∞2=707.946bar),acid (pH=3.71),reducing (fo2=5.012×10-36bar),mid-temperature (267℃) and overpressure (1800bar) gold-bearing fluid (a∑Au=3.744×10-8mol/L). When the closed layer of overpressure fluid was destroyed by the fault, pressure suddenly decreased (285～353bar), CO2-H2O fluid immiscibility occurred, and a large amount of CO2 overflowed. The fugacity of CO2 and O2 decreased (f∞2=8.054bar ,fo2=2.512×10-41bar), pH increased (pH=4.32), and temperature decreased too (224℃) with the fluid immiscibility. This led to the solubility of Au in ore-forming hydrothermal solution(a∑Au=3.790×10-9mol/L), rapid precipitation of Au, and the formation of ore deposit.%运用热力学原理和方法,研究了CO<,2>-H<,2>O流体不混溶作用对Au的溶解度的影响.结果表明,贵州水银洞金矿床的成矿流体是一种富含挥发分(fco<,2>=70.79MVa)、酸性(pH=3.71)、还原性(fo<,2>=0.50x10<'-36>MPa)、中温(267℃)、具有超压(180MPa)性质的含Au(a<,∑Au>=3.744x10<'-8>mol/L)流体.当超压流体的封闭层--炭质页岩因断裂作用而被破坏时,热液体系的压力发生骤降(28.50～35.30MPa),CO<,2>-H<,2>O流体发生不混溶作用,并有大量CO<,2>溢出.CO<,2>的流失可使成矿溶液的CO<,2>逸度和O<,2>逸度降低(foo<,2>=0.80MPafo<,2>=2.512x10-<,42>MPa),酸碱度升高(pH=4.32),同时伴随温度的下降(224℃),成矿热液中Au溶解度的降低(a<,∑Au>=3.790x10-gmol/L),从而快速沉淀下来成矿.
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