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Geochemical variations of precursor and ore-related intrusive rocks associated with porphyry copper deposits in Sonora, northwestern Mexico
Journal of South American Earth Sciences ( IF 1.8 ) Pub Date : 2021-01-01 , DOI: 10.1016/j.jsames.2020.102823
Cecilia Santillana-Villa , Martín Valencia-Moreno , Rafael Del Rio-Salas , Lucas Ochoa-Landín

Abstract The present study analyzes the geochemical composition of samples of both, pre- and ore-related intrusive rocks collected from five porphyry copper deposits of Sonora, Mexico. These deposits are included in the porphyry copper belt of the western North American Cordillera, and particularly in the great porphyry copper cluster of Arizona, New Mexico and Sonora, recognized as one of the most important copper provinces at world level. The ore systems were emplaced during the Late Cretaceous-Eocene, under very particular geotectonic conditions. The sampled sites are El Pilar, Buenavista del Cobre, La Caridad, Suaqui Verde and Piedras Verdes. This work focuses on an evaluation of major and trace element changes in the interphase of the late stage cooling of the main porphyry copper associated pluton and the extraction of the mineralizing porphyritic stock. The age variation between each pair of samples are normally less than 2 Ma and of ~5 Ma in Buenavista del Cobre, the largest deposit in Sonora. The results indicate that both intrusive pulses are very similar in most senses, suggesting a calc-alkaline source linked to a magmatic arc emplaced in continental crust above the North America/Farallon subduction zone. Major oxide elements and most trace elements suggest that the ore-related stocks are relatively more differentiated than the precursor plutons. The most remarkable findings indicate that the REE were differentially fractionated, showing a regular decrease of these elements in the porphyritic phase. This is coupled with an inversion of the Eu anomaly, from clearly negative in the precursor plutons to positive in the ore-related stocks. Moreover, there is a relatively more concave shape in the HREE segment of the chondrite-normalized patterns. Although preliminary, we conclude that all these features suggest that the conditions of the magma during the stage that generated the mineralized porphyritic stocks occurred in equilibrium with a mineral association including hornblende-clinopyroxene-sphene, and a change in the oxidation conditions leading to a more reducing environment. This conclusion appears to be also applicable for the porphyry copper deposits of Arizona, in which the elemental spectra have a similar behavior.

中文翻译:

墨西哥西北部索诺拉与斑岩铜矿床相关的前驱体和与矿石有关的侵入岩的地球化学变化

摘要 本研究分析了从墨西哥索诺拉的五个斑岩铜矿床中采集的与矿体相关的侵入岩样品的地球化学组成。这些矿床包括在北美科迪勒拉西部的斑岩铜矿带中,特别是亚利桑那州、新墨西哥州和索诺拉州的大斑岩铜矿群,被认为是世界上最重要的铜产区之一。矿石系统是在晚白垩世-始新世期间在非常特殊的大地构造条件下形成的。采样地点是 El Pilar、Buenavista del Cobre、La Caridad、Suaqui Verde 和 Piedras Verdes。这项工作的重点是评估主要斑岩铜伴生岩体后期冷却和矿化斑状岩浆提取的中间相中的主要和微量元素变化。在索诺拉州最大的矿床 Buenavista del Cobre,每对样品之间的年龄差异通常小于 2 Ma 和 ~5 Ma。结果表明,这两种侵入脉冲在大多数意义上都非常相似,这表明钙碱性源与位于北美/法拉隆俯冲带上方大陆地壳中的岩浆弧有关。主要氧化物元素和大多数微量元素表明与矿石相关的储量比前体岩体更加分化。最显着的发现表明 REE 被差异分馏,显示这些元素在斑状相中有规律地减少。这与 Eu 异常的反转相结合,从前体岩体的明显负值到矿石相关库存的正值。此外,球粒陨石归一化模式的 HREE 段有一个相对更凹的形状。虽然是初步的,但我们得出的结论是,所有这些特征表明,在产生矿化斑状岩库存的阶段,岩浆的条件与包括角闪石-斜辉石-钆在内的矿物组合处于平衡状态,氧化条件的变化导致更多减少环境。这一结论似乎也适用于亚利桑那州的斑岩铜矿床,其中元素光谱具有类似的行为。这与 Eu 异常的反转相结合,从前体岩体的明显负值到矿石相关库存的正值。此外,球粒陨石归一化模式的 HREE 段有一个相对更凹的形状。虽然是初步的,但我们得出的结论是,所有这些特征表明,在产生矿化斑状岩库存的阶段,岩浆的条件与包括角闪石-斜辉石-钆在内的矿物组合处于平衡状态,氧化条件的变化导致更多减少环境。这一结论似乎也适用于亚利桑那州的斑岩铜矿床,其中元素光谱具有类似的行为。这与 Eu 异常的反转相结合,从前体岩体的明显负值到矿石相关库存的正值。此外,球粒陨石归一化模式的 HREE 段有一个相对更凹的形状。虽然是初步的,但我们得出的结论是,所有这些特征表明,在产生矿化斑状岩库存的阶段,岩浆的条件与包括角闪石-斜辉石-钆在内的矿物组合处于平衡状态,氧化条件的变化导致更多减少环境。这一结论似乎也适用于亚利桑那州的斑岩铜矿床,其中元素光谱具有类似的行为。球粒陨石归一化模式的 HREE 段有一个相对更凹的形状。虽然是初步的,但我们得出的结论是,所有这些特征表明,在产生矿化斑状岩库存的阶段,岩浆的条件与包括角闪石-斜辉石-钆在内的矿物组合处于平衡状态,氧化条件的变化导致更多减少环境。这一结论似乎也适用于亚利桑那州的斑岩铜矿床,其中元素光谱具有类似的行为。球粒陨石归一化模式的 HREE 段有一个相对更凹的形状。虽然是初步的,但我们得出的结论是,所有这些特征表明,在产生矿化斑状岩库存的阶段,岩浆的条件与包括角闪石-斜辉石-钆在内的矿物组合处于平衡状态,氧化条件的变化导致更多减少环境。这一结论似乎也适用于亚利桑那州的斑岩铜矿床,其中元素光谱具有类似的行为。我们得出的结论是,所有这些特征表明,在产生矿化斑状岩库存的阶段,岩浆的条件与包括角闪石-斜辉石-钆在内的矿物组合处于平衡状态,氧化条件的变化导致环境更加还原。这一结论似乎也适用于亚利桑那州的斑岩铜矿床,其中元素光谱具有类似的行为。我们得出的结论是,所有这些特征表明,在产生矿化斑状岩库存的阶段,岩浆的条件与包括角闪石-斜辉石-钆在内的矿物组合处于平衡状态,氧化条件的变化导致环境更加还原。这一结论似乎也适用于亚利桑那州的斑岩铜矿床,其中元素光谱具有类似的行为。
更新日期:2021-01-01
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