In porphyry ore deposit models, the propylitic alteration facies is widely interpreted to be caused by convective circulation of meteoric waters. However, recent field-based and geochemical data suggest that magmatic-derived fluids are likely to contribute to development of the propylitic assemblage. In order to test this hypothesis, we determined the oxygen and hydrogen isotope compositions of propylitic mineral separates (epidote, chlorite, and quartz), selected potassic mineral separates (quartz and magnetite), and quartz-hosted fluid inclusions from around the E48 and E26 deposits in the Northparkes porphyry Cu-Au district, New South Wales, Australia. In addition, the strontium isotope composition of epidote was determined to test for the potential contribution of seawater in the Northparkes system given the postulated island-arc setting and submarine character of some country rocks.Oxygen isotope geothermometry calculations indicate potassic alteration occurred between ~600° and 700°C in magmatic/mineralized centers, persisting to ~450°C upon lateral transition into propylitic alteration. Across the propylitic facies, temperature progressively decreased outward to <250°C. These temperature estimates and additional data from chlorite geothermometry were utilized to calculate the oxygen and hydrogen isotope composition of the fluid in equilibrium with the sampled minerals. Results show that propylitic fluids spanned a range of compositions with δ¹⁸O between 0.5 and 3.7‰ and δD between –49 and –17‰. Comparison of these results with the modeled compositions of meteoric and/or magmatic fluids during their evolution and isotopic exchange with local country rocks shows that a magmatic fluid component must exist across the propylitic halo during its formation. Strontium isotope data from propylitic epidote provide initial (based on formation at ~450 Ma) ⁸⁷Sr/⁸⁶Sr values in the range of 0.704099 to 0.704354, ruling out the presence of seawater as a second fluid in the system. Although we cannot exclude magmatic-meteoric mixing, especially toward the fringes of the system, our results support a model in which magmatic-derived fluid is the primary driver of propylitic alteration as it undergoes cooling and chemical equilibration during outward infiltration into country rocks. This is consistent with chemical mass transfer calculations for Northparkes and published chemical-thermodynamic models that only require a magmatic fluid for the production of propylitic assemblages. In view of this and supporting data from other deposits, we suggest that magmatic fluids are essential drivers of propylitic alteration in porphyry systems.

中文翻译：

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涉及早生蚀变形成的岩浆流体：来自澳大利亚新南威尔士州Northparkes斑岩Cu-Au区的氧，氢和锶同位素约束

在斑岩型矿床模型中，普遍认为丙炔蚀变相是由对流水的对流循环引起的。但是，最近的野外和地球化学数据表明，岩浆衍生的流体很可能会促进丙炔组合的发展。为了检验该假设，我们确定了E48和E26周围的丙炔矿物分离物（e石，绿泥石和石英），选定的钾矿物分离物（石英和磁铁矿）以及石英基流体包裹体的氧和氢同位素组成矿床位于澳大利亚新南威尔士州Northparkes斑岩Cu-Au区。此外，考虑到假定的岛弧环境和某些乡村岩石的海底特征，确定了附子的锶同位素组成，以测试海水在Northparkes系统中的潜在作用。岩浆/矿化中心的碳，在横向转变为丙炔化蚀变时持续至〜450°C。在整个乙炔相中，温度逐渐向外下降至<250°C。这些温度估计值和来自亚氯酸盐地热法的其他数据被用于计算与采样矿物平衡的流体中的氧和氢同位素组成。结果表明，丙炔流体的δ组成范围广泛 氧同位素地热法计算表明，岩浆/矿化中心的钾素蚀变发生在〜600°至700°C之间，在横向过渡为丙炔化蚀变时持续到〜450°C。在整个乙炔相中，温度逐渐向外下降至<250°C。这些温度估计值和来自亚氯酸盐地热法的其他数据被用于计算与采样矿物平衡的流体中的氧和氢同位素组成。结果表明，丙炔流体的δ组成范围广泛 氧同位素地热法计算表明，岩浆/矿化中心的钾素蚀变发生在〜600°至700°C之间，在横向过渡为丙炔化蚀变时持续到〜450°C。在整个乙炔相中，温度逐渐向外下降至<250°C。这些温度估计值和来自亚氯酸盐地热法的其他数据被用于计算与采样矿物平衡的流体中的氧和氢同位素组成。结果表明，丙炔流体的δ组成范围广泛 这些温度估计值和来自亚氯酸盐地热法的其他数据被用于计算与采样矿物平衡的流体中的氧和氢同位素组成。结果表明，丙炔流体的δ组成范围广泛 这些温度估计值和来自亚氯酸盐地热法的其他数据被用于计算与采样矿物平衡的流体中的氧和氢同位素组成。结果表明，丙炔流体的δ组成范围广泛¹⁸ O在0.5至3.7‰之间，而δD在–49至–17‰之间。将这些结果与流变和/或岩浆流体的演化过程中的模型组成以及与当地乡村岩石的同位素交换进行比较表明，岩浆流体在形成过程中必须存在于整个丙炔环中。丙炔化石的锶同位素数据提供了初始值（基于〜450 Ma的形成）⁸⁷ Sr / ⁸⁶Sr值在0.704099至0.704354的范围内，排除了海水作为系统中第二流体的存在。尽管我们不能排除岩浆-岩浆混合，特别是向系统边缘的岩浆-岩浆混合，但我们的结果支持了一个模型，在这种模型中，岩浆源性流体是丙烯质蚀变的主要驱动力，因为它在向乡村岩石的向外渗透过程中经历冷却和化学平衡。这与Northparkes的化学传质计算和已公开的化学热力学模型相一致，后者仅需要岩浆流体即可生产丙炔化合物。考虑到这一点和其他矿床的支持数据，我们认为岩浆流体是斑岩系统中质性改变的重要驱动力。