Several field-based studies have proposed that late-stage magmatic aqueous brines may be responsible for the transportation and redistribution of platinum-group elements (PGE) in mafic-ultramafic igneous systems. We experimentally studied the solubility of Pt in high-temperature aqueous brines as a function of oxygen fugacity (ƒO₂), temperature (T), pH and total chloride concentration (Cl_total) in a S-free system. Experiments were conducted at 800-1000 °C and 200 MPa in an externally-heated rapid-quench Molybdenum-Hafnium Carbide (MHC) pressure vessel assembly. We employed the synthetic fluid inclusion (SFI) technique to trap and sample pre-equilibrated, high-salinity brines in quartz cylinders subjected to in situ fracturing during experimental run conditions. Platinum solubility was observed to have a positive correlation with ƒO₂, temperature, fluid acidity and Cl_total (salinity). A log Pt versus log ƒO₂ diagram derives a weighted-error linear regression slope (m) = 0.48 ± 0.04 which demonstrates that Pt is present in the 2+ oxidation state over the studied ƒO₂ range. At relatively oxidizing conditions, 1.44 log units above the Ni-NiO oxygen buffer (NNO+1.44), aqueous brines (containing 63 NaCl eq. wt.%) with a mildly acidic fluid composition (pH = 6.03) can dissolve up to ∼100 µg/g Pt at 900 °C and 200 MPa. Aqueous brines with identical fluid compositions yield a solubility of 4–13 µg/g Pt under more reducing conditions (NNO–0.41 to NNO–1.42). Thermodynamic model calculations suggest that both PtCl₂ and PtCl₃^– are the dominant Pt(II)-chloride complexes which facilitate the transport of Pt in high-temperature aqueous vapors and brines. In fluid compositions with Cl_total >32m (mol/kg H₂O), PtCl₃^– complex is expected to be the dominant Pt species. In natural mafic-ultramafic systems, high-salinity, orthomagmatic aqueous brines may be important transporting agents if such magmatic fluids can participate in the dissolution of Pt-enriched base-metal sulfides or react with discrete insoluble Pt phases imposing a relatively high activity of Pt (i.e., Pt₃Fe). Furthermore, precipitation of Pt from aqueous brines is promoted by a decrease in ƒO₂, temperature, acidity and Cl_total.

几项基于实地的研究表明，晚期岩浆含水盐水可能是镁铁质-超镁铁质火成岩系统中铂族元素 (PGE) 的运输和重新分布的原因。我们通过实验研究了 Pt 在高温盐水水溶液中的溶解度作为无 S 系统中氧逸度 (ƒO ₂ )、温度 ( T )、pH 和总氯化物浓度 (Cl _total )的函数。实验在 800-1000 °C 和 200 MPa 下在外部加热的快速淬火碳化铪 (MHC) 压力容器组件中进行。我们采用合成流体包裹体 (SFI) 技术在石英圆柱体中对预平衡的高盐盐水进行了捕集和采样，并进行了原位处理。在实验运行条件下压裂。观察到铂溶解度与 ƒO ₂、温度、流体酸度和 Cl_总量（盐度）呈正相关。log Pt 与 log ƒO ₂图得出加权误差线性回归斜率 ( m ) = 0.48 ± 0.04，这表明 Pt 在研究的 ƒO ₂中以 2+ 氧化态存在范围。在相对氧化的条件下，比 Ni-NiO 氧缓冲液 (NNO+1.44) 高 1.44 log 单位，具有弱酸性流体成分 (pH = 6.03) 的含水盐水（含有 63 NaCl eq. wt.%）最多可溶解约 100 µg/g Pt 在 900 °C 和 200 MPa 条件下。具有相同流体成分的盐水在更多还原条件下（NNO–0.41 至 NNO–1.42）产生 4–13 µg/g Pt 的溶解度。热力学模型的计算表明，这两个氯铂酸₂和氯铂酸₃ ^-是其促进Pt的高温的水蒸汽和盐水的运输的主导的Pt（II） -氯化物络合物。在 Cl_总量>32m (mol/kg H ₂ O) 的流体组合物中，PtCl ₃ ^–复合物有望成为主要的 Pt 物种。在天然镁铁质-超镁铁质系统中，如果这种岩浆流体可以参与富含 Pt 的贱金属硫化物的溶解或与离散的不溶性 Pt 相反应，从而使 Pt 具有相对较高的活性，那么高盐度、正交岩浆的含水盐水可能是重要的输送剂(即，Pt ₃ Fe)。此外，降低 ?O ₂、温度、酸度和 Cl_总量会促进 Pt 从盐水中的沉淀。