Propylitic alteration, characterized by the occurrence of chlorite and epidote, is typically the most extensive and peripheral alteration facies developed around porphyry ore deposits. However, exploration within this alteration domain is particularly challenging, commonly owing to weak or nonexistent whole-rock geochemical gradients and the fact that similar assemblages can be developed in other geologic settings, particularly during low-grade metamorphism. We document and interpret systematic spatial trends in the chemistry of chlorite and epidote from propylitic alteration around the E48 and E26 porphyry Cu-Au deposits of the Northparkes district, New South Wales, Australia. These trends vary as a function of both distance from hydrothermal centers and alteration paragenesis. The spatial trends identified in porphyry-related chlorite and epidote at Northparkes include (1) a deposit-proximal increase in Ti, As, Sb, and V in epidote and Ti in chlorite, (2) a deposit-distal increase in Co and Li in chlorite and Ba in epidote, and (3) a pronounced halo around deposits in which Mn and Zn in chlorite, as well as Mn, Zn, Pb, and Mg in epidote, are elevated. Chlorite Al/Si ratios and epidote Al/Fe ratios may show behavior similar to that of Mn-Zn or may simply decrease outward, and V and Ni concentrations in chlorite are lowest in the peak Mn-Zn zone. In comparison to porphyry-related samples, chlorite from the regional metamorphic assemblage in the district contains far higher concentrations of Li, Ca, Ba, Pb, and Cu but much less Ti. Similarly, metamorphic epidote contains higher concentrations of Sr, Pb, As, and Sb but less Bi and Ti. These chlorite and epidote compositional trends are the net result of fluid-mineral partitioning under variable physicochemical conditions within a porphyry magmatic-hydrothermal system. They are most easily explained by the contribution of spent magmatic-derived ore fluid(s) into the propylitic domain. It is envisaged that such fluids experience progressive cooling and reduction in 𝑓s2 during outward infiltration into surrounding country rocks, with their pH controlled by the extent of rock-buffering experienced along the fluid pathway.

中文翻译：

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斑岩矿系统中的绿泥石和绿帘石矿物化学：澳大利亚新南威尔士州北帕克斯区的案例研究

以绿泥石和绿帘石的赋存为特征的丙纹岩蚀变是斑岩矿床周围发育最广泛、最外围的蚀变相。然而，在这个蚀变区域内的勘探特别具有挑战性，这通常是由于全岩地球化学梯度较弱或不存在，以及在其他地质环境中可以开发类似组合的事实，特别是在低品位变质作用期间。我们记录并解释了来自澳大利亚新南威尔士州 Northparkes 区 E48 和 E26 斑岩铜金矿床周围青绿岩蚀变的绿泥石和绿帘石化学的系统空间趋势。这些趋势随着距热液中心的距离和蚀变共生作用而变化。在 Northparkes 与斑岩相关的绿泥石和绿帘石中确定的空间趋势包括 (1) 绿帘石中 Ti、As、Sb 和 V 以及绿泥石中 Ti 的矿床近端增加，(2) Co 和 Li 矿床远端增加绿帘石中的绿泥石和 Ba 中的含量，以及 (3) 沉积物周围的明显晕圈，其中绿泥石中的 Mn 和 Zn 以及绿帘石中的 Mn、Zn、Pb 和 Mg 升高。绿泥石 Al/Si 比率和绿帘石 Al/Fe 比率可能表现出与 Mn-Zn 相似的行为或可能只是向外减少，并且绿泥石中 V 和 Ni 的浓度在峰值 Mn-Zn 区最低。与斑岩相关样品相比，该地区区域变质组合中的绿泥石含有高得多的 Li、Ca、Ba、Pb 和 Cu，但 Ti 含量要少得多。同样，变质绿帘石含有较高浓度的 Sr、Pb、As、和 Sb 但较少 Bi 和 Ti。这些绿泥石和绿帘石组成趋势是在斑岩岩浆-热液系统中不同物理化学条件下流体-矿物分配的最终结果。它们最容易通过废岩浆衍生的矿液对青橄榄岩域的贡献来解释。可以设想，这些流体在向外渗透到周围的围岩中的过程中会经历逐渐冷却和 𝑓s2 的减少，其 pH 值由沿流体路径经历的岩石缓冲程度控制。它们最容易通过废岩浆衍生的矿液对青橄榄岩域的贡献来解释。可以设想，这些流体在向外渗透到周围的围岩中的过程中会经历逐渐冷却和 𝑓s2 的减少，其 pH 值由沿流体路径经历的岩石缓冲程度控制。它们最容易通过废岩浆衍生的矿液对青橄榄岩域的贡献来解释。可以设想，这些流体在向外渗透到周围的围岩中的过程中会经历逐渐冷却和 𝑓s2 的减少，其 pH 值由沿流体路径经历的岩石缓冲程度控制。