Recognizing Propylitic Alteration Associated with Porphyry Cu-Mo Deposits in Lower Greenschist Facies Metamorphic Terrain of the Collahuasi District, Northern Chile--Implications of Petrographic and Carbon Isotope Relationships
| Autor: | Christian Ihlenfeld, Esteban Urqueta, Christopher J. Oates, Kurt Kyser, Merline L. Djouka-Fonkwé, Alan H. Clark |
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| Rok vydání: | 2012 |
| Předmět: | |
| Zdroj: | Economic Geology. 107:1457-1478 |
| ISSN: | 1554-0774 0361-0128 |
| DOI: | 10.2113/econgeo.107.7.1457 |
| Popis: | The Collahuasi district is a porphyry Cu-Mo subprovince located on the Andean high plateau of northern Chile. Late Eocene-early Oligocene mineralization in the district involved hydrothermal alteration of the upper Paleozoic to Lower Triassic Collahuasi Group granodiorites, diorites, andesites, dacites, and rhyolites, which had previously experienced regional lower greenschist facies metamorphism as well as uneconomic porphyry-style mineralization and associated sericitic alteration. Alteration mapping represents an effective technique for prospecting for hydrothermal deposits, but, in low-grade metamorphic terrains, recognition of propylitic assemblages that represent the boundary of the mineralizing system is hampered by their resemblance to metamorphic mineral assemblages. Our results from Collahuasi indicate that petrographic criteria can distinguish propylitic alteration from the effects of lower greenschist facies metamorphism, but distinctions vary with rock type. Mafic, intermediate, and felsic rocks with varying degrees of propylitic alteration can be distinguished from background metamorphism mainly by the presence of calcite. However, propylitic alteration can also be distinguished by high whole-rock δ 13C values and carbon contents (−19.1 to −1.4‰ and up to 0.79 wt %, respectively) that result from the incorporation of magmatic CO2 during the mineralizing events. Lower δ 13C values (−32.7 to −13.1‰) and carbon contents ( |
| Databáze: | OpenAIRE |
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