Hydrothermal fluid is essential for transporting metals in the crust and mantle. To explore the potential of Cu isotopes as a tracer of hydrothermal-fluid activity, Cu isotope fractionation factors between Cl-bearing aqueous fluids and silicate magmas (andesite, dacite, rhyolite dacite, rhyolite, and haplogranite) were experimentally calibrated. Fluids containing 1.75 to 14 wt.% Cl were mixed together with rock powders in Au₉₅Cu₅ alloy capsules, which were equilibrated in cold-seal pressure vessels for 5 to 13 days at 800 to 850°C and 2 kbar. The elemental and Cu isotopic compositions of the recovered aqueous fluid and solid phases were analyzed by (LA-) ICP-MS and MC-ICP-MS, respectively. Our experimental results show that the fluid phases are consistently enriched in heavy Cu isotope (⁶⁵Cu) relative to the coexisting silicates. The Cu isotope fractionation factor (Δ⁶⁵Cu_FLUID-MELT) ranges from 0.08±0.01‰ to 0.69±0.02‰. The experimental results show that the Cu isotopic fractionation factors between aqueous fluids and silicates strongly depend on the Cu speciation in the fluids (e.g., CuCl(H₂O), CuCl₂^– and CuCl₃²⁻) and silicate melts (CuO_1/2), suggesting that the exsolved fluids may have higher δ⁶⁵Cu than the residual magmas. Our results suggest the elevated δ⁶⁵Cu values in Cu-enriched rocks could be produced by addition of aqueous fluids exsolved from magmas. Together with previous studies on Cu isotopes in the brine and vapor phases of porphyry deposits, our results are helpful for better understanding Cu mineralization processes.

中文翻译：

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含氯流体与硅酸盐岩浆的铜同位素分馏实验：对流体出溶和斑岩铜矿床的影响

热液流体对于在地壳和地幔中运输金属是必不可少的。为了探索 Cu 同位素作为热液流体活动示踪剂的潜力，对含 Cl 水性流体和硅酸盐岩浆（安山岩、英安岩、流纹岩英安岩、流纹岩和单长花岗岩）之间的 Cu 同位素分馏因子进行了实验校准。含 1.75 至 14 wt.% Cl 的流体与 Au ₉₅ Cu _{5 中的}岩粉混合在一起合金胶囊，在 800 至 850°C 和 2 kbar 的冷密封压力容器中平衡 5 至 13 天。回收的水相和固相的元素和铜同位素组成分别通过 (LA-) ICP-MS 和 MC-ICP-MS 进行分析。我们的实验结果表明，相对于共存的硅酸盐，流体相始终富含重铜同位素 ( ⁶⁵ Cu)。Cu 同位素分馏因子 (Δ ⁶⁵ Cu _FLUID-MELT ) 范围从 0.08±0.01‰ 到 0.69±0.02‰。实验结果表明，水性流体和硅酸盐之间的 Cu 同位素分馏因子在很大程度上取决于流体中的 Cu 形态（例如，CuCl(H ₂ O)、CuCl ₂ ^–和 CuCl₃ ²⁻ ) 和硅酸盐熔体 (CuO _1/2 )，表明溶出流体的 δ ⁶⁵ Cu可能高于残余岩浆。我们的结果表明，富铜岩石中δ ⁶⁵铜值升高可以通过添加从岩浆中溶出的含水流体产生。结合之前对斑岩矿床卤水和蒸汽相中铜同位素的研究，我们的结果有助于更好地了解铜矿化过程。