The Highland Valley Copper porphyry Cu (±Mo) district is hosted in the Late Triassic Guichon Creek batholith in the Canadian Cordillera. Fracture-controlled sodic-calcic alteration is important because it forms a large footprint (34 km²) outside of the porphyry Cu centers. This alteration consists of epidote ± actinolite ± tourmaline veins with halos of K-feldspar–destructive albite (1–20 X_An) ± fine-grained white mica ± epidote. The distribution of sodic-calcic alteration is strongly influenced by near-orthogonal NE- and SE-trending fracture sets and by proximity to granodiorite stocks and porphyry dikes. Multiple stages of sodic-calcic alteration occurred in the district, which both pre- and postdate Cu mineralization at the porphyry centers.The mineral assemblages and chemical composition of alteration minerals suggest that the fluid that caused sodic-calcic alteration in the Guichon Creek batholith was Cl bearing, at near-neutral pH, and oxidized, and had high activities of Na, Ca, and Mg relative to propylitic and fresh-rock assemblages. The metasomatic exchange of K for Na, localized removal of Fe and Cu, and a paucity of secondary quartz suggest that the fluid was thermally prograding in response to magmatic heating. Calculated δ¹⁸O_fluid and δD_fluid values of mineral pairs in isotopic equilibrium from the sodic-calcic veins and alteration range from 4 to 8‰ and −20 to −9‰, respectively, which contrasts with the whole-rock values for least altered magmatic host rocks (δ¹⁸O = 6.4–9.4‰ and δD = −99 to −75‰). The whole-rock values are suggested to reflect residual magma values after D loss by magma degassing, while the range of hydrothermal minerals requires a mixed-fluid origin with a contribution of magmatic water and an external water source. The O-H isotope results favor seawater as the source but could also reflect the ingress of Late Triassic meteoric water. The ⁸⁷Sr/⁸⁶Sr_inital values of strongly Na-Ca–altered rocks range from 0.703416 to 0.703508, which is only slightly higher than the values of fresh and potassic-altered rocks. Modeling of those data suggests the Sr is derived predominantly from a magmatic source, but the system may contain up to 3% seawater Sr. Supporting evidence for a seawater-derived fluid entrained in the porphyry Cu systems comes from boron isotope data. The calculated tourmaline δ¹¹B_fluid values from the sodic-calcic domains reach 18.3‰, which is consistent with a seawater-derived fluid source. Lower tourmaline δ¹¹B_fluid values from the other alteration facies (4–10‰) suggest mixing between magmatic and seawater-derived fluids in and around the porphyry centers. These results imply that seawater-derived fluids can infiltrate batholiths and porphyry systems at deep levels (4–5 km) in the crust. Sodic ± calcic alteration may be more common in rocks peripheral to porphyry Cu systems hosted in island-arc terranes and submarine rocks than currently recognized.

中文翻译：

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加拿大不列颠哥伦比亚省高地山谷铜矿区钠钙变化的矿物学和同位素特征：斑岩铜矿体系中流体源的意义

高地谷铜斑岩铜（±Mo）区位于加拿大山脉山脉的晚三叠纪Guichon Creek基岩中。断裂控制的苏打-钙化蚀变很重要，因为它在斑岩型铜中心外形成了较大的足迹（34 km ²）。这种变化包括附子±阳起石±电气石脉和钾长石破坏性钠长石（1–20 X _An）±白云母细粉±附子。苏打钙化蚀变的分布受到近正交NE和SE趋势断裂集以及接近花岗闪长岩和斑岩脉的影响。该地区发生了钠钙质变化的多个阶段，在斑岩中心的铜矿化之前和之后都发生过。蚀变矿物的矿物组成和化学成分表明，导致Guichon Creek基岩发生钠钙质变化的流体是含Cl的溶液在接近中性的pH值下会被氧化，并且相对于丙稀酸和新鲜岩石组合具有较高的Na，Ca和Mg活性。K与Na的交代交换，局部去除Fe和Cu以及少量的次生石英表明，流体在响应岩浆加热时正在热膨胀。从钠钙钙矿到同位素平衡的矿物对的¹⁸ O_流体和δD_流体值，其变化范围分别为4至8‰和-20至-9‰，这与变化最小的岩浆岩体的全岩石值形成对比岩（δ ¹⁸ O = 6.4-9.4‰和δD= -99至-75‰）。建议将整个岩石的值反映为由于岩浆脱气而导致的D损失后的剩余岩浆值，而热液矿物的范围则需要混合流体成因，并贡献岩浆水和外部水源。OH同位素的结果偏爱海水作为水源，但也可能反映了晚三叠世的大气水的侵入。在⁸⁷ SR / ⁸⁶锶_initalNa-Ca强烈改变的岩石的值范围为0.703416到0.703508，仅略高于新鲜和钾改变的岩石的值。这些数据的模型表明，Sr主要来自岩浆来源，但该系统可能包含高达3％的海水Sr。斑岩型Cu系统夹带的海水衍生流体的支持证据来自硼同位素数据。所计算出的δ电气石¹¹乙_流体从含钠钙质域值达到18.3‰，这与一个海水衍生的流体源相一致。下电气石δ ¹¹乙_流体其他蚀变相的值（4-10‰）表明斑岩中心及其附近的岩浆和海水衍生流体之间混合。这些结果表明，海水的流体可以渗入地壳深层（4-5 km）的岩床和斑岩系统。在岛弧地层和海底岩石中斑岩型铜系统外围的岩石中，苏打±钙质变化可能比目前公认的更为普遍。