The Rouyn-Noranda mining district of Quebec contains 20 Cu-Zn (±Au ±Ag) volcanogenic massive sulfide (VMS) deposits, including the giant and gold-rich Quemont and Horne deposits. Mineralized epigenetic veins are also present, but their origin and relative timing remain enigmatic. The nature and extent of their alteration signatures and the effect of their superposition on district-scale alteration patterns is unknown. The VMS-related quartz-sulfide Cu-Zn-Ag veins have δ¹⁸O_quartz values of 8.5 ± 0.8‰, reflecting δ¹⁸O_fluid compositions of –0.4 to 3.1‰ (250°–350°C) that are typical of Archean seawater. They are associated with a proximal Fe-rich chlorite alteration and marginal spotted sericite-chlorite alteration with whole-rock δ¹⁸O values of 2.9 to 5.9‰ and are interpreted to have formed within the structurally controlled discordant upflow zones of a VMS hydrothermal system. Younger gold-bearing quartz-carbonate veins were emplaced along mechanical anisotropies created by mafic dikes during north-south compression and the formation of regional E-trending faults, folds, and cleavage. They are characterized by δ¹⁸O_quartz values of 11.3 ± 0.8‰, reflecting δ¹⁸O_fluid compositions of 2.4 to 5.9‰ (250°–350°C), typical of a metamorphic fluid, possibly mixed with a lower δ¹⁸O upper crustal fluid. They are associated with ankerite, calcite, muscovite, chlorite, albite, and quartz ± hematite alteration with whole-rock δ¹⁸O values of 5.8 to 10.3‰. Chemical abrasion-isotope dilution-thermal ionization mass spectrometry (CA-ID-TIMS) U-Pb zircon ages for two tonalite intrusions constrain the maximum age of the Cu-Zn-Ag veins to 2697.6 ± 0.7 Ma and the minimum age to 2695.3 ± 1.0 Ma, which is also the maximum age of the gold quartz-carbonate veins. Superposition of alteration related to the gold quartz-carbonate veins on previously chlorite- and sericite-altered rocks has resulted in mixed alteration signals with whole-rock δ¹⁸O values of ~6 to 8‰ that have perturbed and masked regional alteration patterns related to older VMS mineralization, such as those found in the Quemont and Horne deposits. These results indicate that defining alteration vectors in camps that have superimposed hydrothermal systems requires full consideration of the hydrothermal history of the camp, and if such constraints are lacking, whole-rock δ¹⁸O values should not be used as a stand-alone exploration method.

中文翻译：

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魁北克鲁安-诺兰达矿区与表观遗传基础和贵金属矿脉系统相关的叠加蚀变辨别；对古代火山区勘探的意义

魁北克省的 Rouyn-Noranda 矿区拥有 20 个铜锌 (±Au ±Ag) 火山成因块状硫化物 (VMS) 矿床，其中包括巨大且富含金的 Quemont 和 Horne 矿床。矿化的表观遗传静脉也存在，但它们的起源和相对时间仍然是个谜。它们的蚀变特征的性质和程度以及它们对地区规模蚀变模式的叠加影响尚不清楚。与 VMS 相关的石英硫化物 Cu-Zn-Ag 矿脉的 δ ¹⁸ O_石英值为 8.5 ± 0.8‰，反映太古代典型的δ ¹⁸ O_流体成分为 –0.4 至 3.1‰ (250°–350°C)海水。它们与近端富铁绿泥石蚀变和边缘点状绢云母-绿泥石蚀变有关，全岩 δ ¹⁸ O 值为 2.9 至 5.9‰，并被解释为形成于 VMS 热液系统结构控制的不一致上流区域内。较年轻的含金石英碳酸盐脉沿着南北挤压期间镁铁质岩脉产生的机械各向异性以及区域东向断层、褶皱和解理的形成而形成。它们的特征是 δ ¹⁸ O_石英值为 11.3 ± 0.8‰，反映 δ ¹⁸ O_流体成分为 2.4 至 5.9‰ (250°–350°C)，是典型的变质流体，可能与较低的 δ ¹⁸ O 上部混合。地壳流体。它们与铁白云石、方解石、白云母、绿泥石、钠长石和石英±赤铁矿蚀变有关，全岩 δ ¹⁸ O 值为 5.8 至 10.3‰。化学磨损同位素稀释热电离质谱 (CA-ID-TIMS) 两个英英闪长岩侵入体的 U-Pb 锆石年龄将 Cu-Zn-Ag 矿脉的最大年龄限制为 2697.6 ± 0.7 Ma，最小年龄为 2695.3 ± 1.0 Ma，这也是金石英碳酸盐脉的最大年龄。与金石英碳酸盐脉相关的蚀变叠加在先前绿泥石和绢云母蚀变岩石上，导致了全岩 δ ¹⁸ O 值约为 6 至 8 ‰ 的混合蚀变信号，扰乱并掩盖了与较古老的 VMS 矿化体，例如在 Quemont 和 Horne 矿床中发现的矿化体。这些结果表明，在具有叠加热液系统的营地中定义蚀变矢量需要充分考虑营地的热液历史，如果缺乏这样的约束，则不应该使用全岩δ ¹⁸ O值作为独立的勘探方法。