Transport and deposition of copper in the Earth’s crust are mainly controlled by the solubility of Cu-bearing phases and the speciation of Cu in magmatic-hydrothermal fluids. To improve our understanding of copper mobilization by hydrothermal fluids, we conducted an experimental study on the interaction between Cu-bearing phases (metallic copper, Cu2O, CuCl) and aqueous chloride solutions (H2O ± NaCl ± HCl; with Cl concentrations of 0 to 4.3 mol kg-1). The experiments were run in rapid heat/rapid quench cold-seal pressure vessels at 800 °C, 200 MPa, and logfO2 ~ NNO+2.3. Either Cu or Au capsules were used as containers. The reaction products were sampled in situ by the entrapment of synthetic fluid inclusions in quartz. Fluid composition was subsequently determined by analyzing individual fluid inclusions using a freezing cell and laser ablation inductively coupled plasma-mass spectrometry. Our results show that large isolated and isometric inclusions, free of late-stage modifications, can be preserved after the experiment even when using a high cooling rate of 25 K s-1. The obtained results demonstrate that: (1) reaction between native Cu, NaCl solution, and quartz (± silica gel) leads to the coexistence of fluid inclusions and Na-bearing silicate melt inclusions. Micrometerto submicrometer-sized cuprite (Cu2O) crystals have been observed in both types of the inclusions, and they are formed most probably due to the dissociation of CuOH. (2) When Cu0 reacts with HCl and CuCl solutions, or Cu+ reacts with NaCl solution, nantokite (CuCl) formed due to oversaturation has been found in fluid inclusion. Copper concentration in the fluid shows a strong positive dependence on the initial chlorine content, with Cu/Cl molal ratios varying from 1:9 to 1:1 in case 1 and case 2, respectively. When Cl is fixed to 1.5 m, initial fluid acidity has a major control on the Cu content, i.e., 0.17 ± 0.09 and 1.29 ± 0.57 m Cu were measured in fluids of case 1 and case 2, respectively. Cu solubility in pure water and in 1.5 m NaCl solutions are 0.004 ± 0.002 and 0.16 ± 0.07 m, respectively. The main responsible Cu-bearing complexes are CuOH(H2O)x in water, NaCuCl2 in NaCl solutions and HCuCl2 in alkali-free solutions. These results provide quantitative constraints on the mobility of Cu in hydrothermal solutions and confirm that Cl is a very important ligand responsible for Cu transport. The first observation that silicate melt can be generated in the fluid-dominated and native-copper-bearing system implies that transitional thermosilicate liquids can coexist with metalrich fluids and may enhance Cu mobility in magmatic-hydrothermal systems. This may have important implications for the formation of Cu deposits in the systems with low S activities.

中文翻译：

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800°C 和 200 MPa 下含铜矿物与热液流体的反应：合成流体包裹体的约束

铜在地壳中的迁移和沉积主要受含铜相的溶解度和岩浆热液中铜的形态控制。为了加深我们对热液对铜迁移的理解，我们对含铜相（金属铜、Cu2O、CuCl）和氯化物水溶液（H2O ± NaCl ± HCl；Cl 浓度为 0 至 4.3）之间的相互作用进行了实验研究mol kg-1)。实验在 800 °C、200 MPa 和 logfO2 ~ NNO+2.3 的快速加热/快速淬火冷密封压力容器中进行。Cu或Au胶囊用作容器。通过在石英中捕获合成流体包裹体，对反应产物进行原位取样。随后通过使用冷冻室和激光烧蚀电感耦合等离子体质谱法分析单个流体包裹体来确定流体成分。我们的结果表明，即使使用 25 K s-1 的高冷却速率，也可以在实验后保留没有后期修改的大型孤立和等距夹杂物。所得结果表明：（1）天然Cu、NaCl溶液和石英（±硅胶）反应导致流体包裹体和含钠硅酸盐熔体包裹体共存。在两种类型的夹杂物中都观察到了微米到亚微米大小的赤铜矿 (Cu2O) 晶体，它们的形成很可能是由于 CuOH 的解离。(2) 当Cu0与HCl和CuCl溶液反应，或Cu+与NaCl溶液反应时，在流体包裹体中发现了由于过饱和而形成的 nantokite (CuCl)。流体中的铜浓度显示出对初始氯含量的强烈正依赖性，Cu/Cl 摩尔比在案例 1 和案例 2 中分别从 1:9 到 1:1 不等。当 Cl 固定为 1.5 m 时，初始流体酸度对 Cu 含量有主要控制，即在案例 1 和案例 2 的流体中分别测量到 0.17 ± 0.09 和 1.29 ± 0.57 m Cu。Cu 在纯水和 1.5 m NaCl 溶液中的溶解度分别为 0.004 ± 0.002 和 0.16 ± 0.07 m。主要负责的含铜配合物是水中的 CuOH(H2O)x、NaCl 溶液中的 NaClCuCl2 和无碱溶液中的 HCuCl2。这些结果为 Cu 在热液溶液中的迁移提供了定量约束，并证实 Cl 是负责 Cu 传输的非常重要的配体。第一个观察到硅酸盐熔体可以在流体主导和天然含铜系统中产生，这意味着过渡热硅酸盐液体可以与富含金属的流体共存，并可能增强岩浆-热液系统中铜的流动性。这可能对在低硫活性系统中形成铜沉积物具有重要意义。