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<p>Porphyry copper deposits (PCDs) are the primary global source of copper, with Cenozoic PCDs in the Chilean Andes being notable for their large size and high ore grades. The Cretaceous PCDs of the Coastal Cordillera in northern Chile are comparatively smaller and predominantly sub-economic. This study investigated zircon geochemical signatures in ore‐related and barren Cretaceous intrusive rocks to assess whether magmatic fertility fingerprints differentiate between large and small PCD systems. Ore-related intrusive rocks from Early Cretaceous PCDs (116–108&#xa0;Ma), including Tricolor, Dos Amigos, Cachiyuyo, and Pajonales, are characterized by high Eu/Eu* ratios (&gt; 0.4) and relatively oxidized conditions (ΔFMQ ~ 0 to + 1). On the other hand, barren intrusive rocks emplaced during the Late Cretaceous period (98–93&#xa0;Ma) display lower Eu/Eu* ratios (&lt; 0.4) and have ΔFMQ ~ –1 to + 1. In comparison, supergiant Cenozoic PCDs of the Andean Cordillera, e.g., El Salvador, Chuquicamata, and El Teniente display high Eu/Eu* ratios (&gt; 0.4), and are more oxidized (ΔFMQ ~ + 1 to + 3). Results from this study show that the Yb<sub>N</sub>/Dy<sub>N</sub> and (Eu/Eu*)/(Dy<sub>N</sub>/Yb<sub>N</sub>) ratios can effectively discriminate between different PCDs settings. Deposits related to magmatic differentiation with a high-water content at relatively shallow to intermediate levels (&lt; 40&#xa0;km), such as those from the Early Cretaceous, are characterized by Yb<sub>N</sub>/Dy<sub>N</sub> values of ~ 10–18 and (Eu/Eu*)/(Dy<sub>N</sub>/Yb<sub>N</sub>) ratios of ~ 6–14. In contrast, deposits where magmatic differentiation occurred at greater depth within the crust (&gt; 40&#xa0;km), like the large Cenozoic deposits in the Andes, show Yb<sub>N</sub>/Dy<sub>N</sub> values of ~ 3–12 and (Eu/Eu*)/(Dy<sub>N</sub>/Yb<sub>N</sub>) ratios of ~ 1.5–6. Furthermore, our data highlight the crucial role of geodynamic conditions, such as horizontal tectonic stress, the depth of magmatic differentiation, which may determine the size of porphyry Cu systems.</p>

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Large versus small Andean porphyry Cu deposits: insights from zircon petrochronology of porphyry Cu–Mo ± Au deposits from the Coastal Cordillera, northern Chile

  • 期刊论文

  • 发表日期：

    2025年3月26日

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  • María José Tapia,
  • Fernando Barra,
  • Martin Reich,
  • Rurik Romero,
  • Andrés Ojeda

摘要

Porphyry copper deposits (PCDs) are the primary global source of copper, with Cenozoic PCDs in the Chilean Andes being notable for their large size and high ore grades. The Cretaceous PCDs of the Coastal Cordillera in northern Chile are comparatively smaller and predominantly sub-economic. This study investigated zircon geochemical signatures in ore‐related and barren Cretaceous intrusive rocks to assess whether magmatic fertility fingerprints differentiate between large and small PCD systems. Ore-related intrusive rocks from Early Cretaceous PCDs (116–108 Ma), including Tricolor, Dos Amigos, Cachiyuyo, and Pajonales, are characterized by high Eu/Eu* ratios (> 0.4) and relatively oxidized conditions (ΔFMQ ~ 0 to + 1). On the other hand, barren intrusive rocks emplaced during the Late Cretaceous period (98–93 Ma) display lower Eu/Eu* ratios (< 0.4) and have ΔFMQ ~ –1 to + 1. In comparison, supergiant Cenozoic PCDs of the Andean Cordillera, e.g., El Salvador, Chuquicamata, and El Teniente display high Eu/Eu* ratios (> 0.4), and are more oxidized (ΔFMQ ~ + 1 to + 3). Results from this study show that the YbN/DyN and (Eu/Eu*)/(DyN/YbN) ratios can effectively discriminate between different PCDs settings. Deposits related to magmatic differentiation with a high-water content at relatively shallow to intermediate levels (< 40 km), such as those from the Early Cretaceous, are characterized by YbN/DyN values of ~ 10–18 and (Eu/Eu*)/(DyN/YbN) ratios of ~ 6–14. In contrast, deposits where magmatic differentiation occurred at greater depth within the crust (> 40 km), like the large Cenozoic deposits in the Andes, show YbN/DyN values of ~ 3–12 and (Eu/Eu*)/(DyN/YbN) ratios of ~ 1.5–6. Furthermore, our data highlight the crucial role of geodynamic conditions, such as horizontal tectonic stress, the depth of magmatic differentiation, which may determine the size of porphyry Cu systems.