Abstract Hydrodynamic and thermodynamic modeling of fluid evolution in shallow magmatic hydrothermal systems based on phase equilibria for the system H2O-NaCl predicts that the fluid becomes halite saturated at some point in its evolution. A review of the published fluid inclusion data also supports halite saturation in these systems. In this study, we synthesized fluid inclusions at known pressure-temperature-composition (PTX) conditions in the H2O-NaCl and H2O-NaCl-KCl systems such that vapor + halite or liquid + vapor + halite existed at the time of trapping. Our results show that fluid inclusions trapped in the liquid + vapor + halite field in experiments along an evolving temperature path best match the phase ratios and thermometric behavior of fluid inclusions commonly reported in magmatic-hydrothermal systems (particularly in porphyry-style deposits). These results are consistent with the hypothesis that magmatic-hydrothermal fluids in porphyry settings are commonly trapped under conditions of liquid + vapor + halite equilibrium, which in turn has consequences for fluid flow and mineralization. Our results also show that the presence of KCl in the system significantly improves the agreement between microthermometric behaviors reported in natural systems and experimental results. The major effect of adding KCl is to increase the thermodynamic variance (degrees of freedom) of coexistence of liquid + vapor + halite from univariant in the system H2O-NaCl to divariant (occupying an area, rather than a line, in pressure–temperature space). Simulations based on the system H2O-NaCl predict that halite saturation occurs predominantly in the vapor + halite field with localized halite precipitation during the transition from the liquid + vapor to the vapor + halite field. By rendering the liquid + vapor + halite coexistence space as divariant, the addition of KCl also prevents an abrupt termination of liquid stability upon intersecting the liquid + vapor + halite boundary. Simulations using the system H2O-NaCl commonly predict pressure–temperature pathways constrained to the univariant liquid + vapor + halite curve, owing to volumetric and latent heat constraints. In contrast, the presence of KCl relaxes these constraints and expands the ranges of pressure and temperature over which liquid, vapor and halite can coexist. This phenomenon has major implications for the chemical and hydrological evolution in magmatic-hydrothermal systems as related to the ability of fluids to transport metals (ore deposition) and the potential loss of porosity/permeability as a result of salt and quartz precipitation.

中文翻译：

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合成流体包裹体 XXII：水蒸气和盐饱和条件下捕获的 H2O-NaCl±KCl 流体包裹体的特性，重点是 KCl 对相平衡的影响

摘要 基于 H2O-NaCl 系统相平衡的浅层岩浆热液系统流体演化的流体动力学和热力学模型预测，流体在演化过程中的某个时刻变成岩盐饱和状态。对已发表的流体包裹体数据的回顾也支持这些系统中的岩盐饱和度。在这项研究中，我们在 H2O-NaCl 和 H2O-NaCl-KCl 系统中在已知压力-温度-成分 (PTX) 条件下合成流体包裹体，使得在捕集时存在蒸汽 + 岩盐或液体 + 蒸汽 + 岩盐。我们的结果表明，在沿着温度演化路径的实验中，在液体 + 蒸汽 + 岩盐场中捕获的流体包裹体与岩浆-热液系统（特别是在斑岩型沉积物）中常见的流体包裹体的相比和测温行为最匹配。这些结果与斑岩环境中的岩浆热液流体通常被困在液体 + 蒸汽 + 岩盐平衡条件下的假设一致，这反过来又会对流体流动和矿化产生影响。我们的结果还表明，系统中 KCl 的存在显着提高了自然系统中报告的微温行为与实验结果之间的一致性。添加 KCl 的主要作用是将液体 + 蒸汽 + 岩盐共存的热力学方差（自由度）从系统 H2O-NaCl 中的单变量增加到双变量（在压力-温度空间中占据一个区域，而不是一条线） ）。基于 H2O-NaCl 系统的模拟预测，岩盐饱和主要发生在蒸气 + 岩盐场中，在从液体 + 蒸气到蒸气 + 岩盐场的过渡期间，会出现局部的岩盐沉淀。通过将液体 + 蒸汽 + 岩盐共存空间呈现为二变体，添加 KCl 还可以防止液体稳定性在与液体 + 蒸汽 + 岩盐边界相交时突然终止。使用 H2O-NaCl 系统进行的模拟通常预测压力-温度路径受限于单变量液体 + 蒸汽 + 岩盐曲线，由于体积和潜热的限制。相比之下，KCl 的存在放松了这些限制，并扩大了液体、蒸汽和岩盐可以共存的压力和温度范围。这种现象对岩浆-热液系统中的化学和水文演化具有重要意义，因为它与流体输送金属的能力（矿石沉积）以及盐和石英沉淀导致的孔隙度/渗透率的潜在损失有关。