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<p>In the Coastal Cordillera of northern Chile, iron oxide-copper-gold (IOCG) deposits are spatially associated with Early Cretaceous intrusive rocks, though their genetic relationship remains enigmatic. We present zircon U–Pb dating and trace element analysis of intrusions in the world-class Mantoverde district to elucidate the magmatic evolution and controls on mineralization. Zircon geochemistry data indicate magmatism occurred in three main stages: Stage I (~ 138–134&#xa0;Ma), Stage II (~ 131–125&#xa0;Ma), and Stage III (~ 119–98&#xa0;Ma). Stage I is interpreted as a precursor magmatic episode, with low Eu/Eu* values (~ 0.25), low ΔFMQ (–0.1), crystallization temperatures between 650 and 720&#xa0;°C, and (Dy/Yb)<sub>N</sub> ratios of ~ 0.16. Stage II magmatism is characterized by distinctively low Eu/Eu* values (&lt; 0.2), reduced conditions (ΔFMQ = − 1.4 to 0), higher temperatures (&gt; 700&#xa0;°C), and higher (Dy/Yb)<sub>N</sub> ratios (~ 0.2). The reduced nature of the Stage II magmas may be attributed to segregation of magnetite during an early iron oxide-apatite (IOA)-type mineralization. A sharp contrast is observed in Stage III, which is broadly coeval with copper mineralization at Mantoverde. This stage displays zircon Eu/Eu* values of &gt; 0.4, oxidized signatures (ΔFMQ &gt; + 0.8), lower temperatures (630–700&#xa0;°C), and lower (Dy/Yb)<sub>N</sub> ratios (~ 0.1), i.e., typical of those found in porphyry copper intrusions. The change in magmatic conditions facilitated transport of copper and sulfur to form IOCG-type mineralization. The reported changes in magmatism are coeval with a regional tectonic reconfiguration to a more compressive setting, which likely influenced magmatic differentiation. As a result, conditions shifted from a shallower reservoir with low water accumulation to deeper levels characterized by multi-stage stagnant magmas with increased hydration levels. Our results provide further evidence that Andean IOCG deposits were the result of a two-stage process: an IOA-style mineralization related to reduced, water-poor magmatism, followed by an oxidized, water-rich magmatism responsible for the main copper mineralization.</p>

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Fingerprinting magmatic fertility in Andean IOCG deposits: a case study of the Mantoverde district, Chile

  • 期刊论文

  • 发表日期：

    2025年10月21日

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  • Rurik Romero,
  • Fernando Barra,
  • Martin Reich,
  • María José Tapia,
  • Andrés Ojeda,
  • Nikki M. Seymour

摘要

In the Coastal Cordillera of northern Chile, iron oxide-copper-gold (IOCG) deposits are spatially associated with Early Cretaceous intrusive rocks, though their genetic relationship remains enigmatic. We present zircon U–Pb dating and trace element analysis of intrusions in the world-class Mantoverde district to elucidate the magmatic evolution and controls on mineralization. Zircon geochemistry data indicate magmatism occurred in three main stages: Stage I (~ 138–134 Ma), Stage II (~ 131–125 Ma), and Stage III (~ 119–98 Ma). Stage I is interpreted as a precursor magmatic episode, with low Eu/Eu* values (~ 0.25), low ΔFMQ (–0.1), crystallization temperatures between 650 and 720 °C, and (Dy/Yb)N ratios of ~ 0.16. Stage II magmatism is characterized by distinctively low Eu/Eu* values (< 0.2), reduced conditions (ΔFMQ = − 1.4 to 0), higher temperatures (> 700 °C), and higher (Dy/Yb)N ratios (~ 0.2). The reduced nature of the Stage II magmas may be attributed to segregation of magnetite during an early iron oxide-apatite (IOA)-type mineralization. A sharp contrast is observed in Stage III, which is broadly coeval with copper mineralization at Mantoverde. This stage displays zircon Eu/Eu* values of > 0.4, oxidized signatures (ΔFMQ > + 0.8), lower temperatures (630–700 °C), and lower (Dy/Yb)N ratios (~ 0.1), i.e., typical of those found in porphyry copper intrusions. The change in magmatic conditions facilitated transport of copper and sulfur to form IOCG-type mineralization. The reported changes in magmatism are coeval with a regional tectonic reconfiguration to a more compressive setting, which likely influenced magmatic differentiation. As a result, conditions shifted from a shallower reservoir with low water accumulation to deeper levels characterized by multi-stage stagnant magmas with increased hydration levels. Our results provide further evidence that Andean IOCG deposits were the result of a two-stage process: an IOA-style mineralization related to reduced, water-poor magmatism, followed by an oxidized, water-rich magmatism responsible for the main copper mineralization.