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Copper Isotope Fractionation Used to Identify Supergene Processes

By
Ryan Mathur
Ryan Mathur
Department of Geology, Juniata College, Huntingdon, Pennsylvania 16652
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Spencer Titley
Spencer Titley
Department of Geosciences, University of Arizona, Tucson, Arizona
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Fernando Barra
Fernando Barra
Department of Geosciences, University of Arizona, Tucson, Arizona
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Susan Brantley
Susan Brantley
Department of Geosciences, Pennsylvania State University, State College, Pennsylvania
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Marc Wilson
Marc Wilson
Carnegie Museum of Natural History, Pittsburgh, Pennsylvania
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Allison Phillips
Allison Phillips
Department of Geology, Juniata College, Huntingdon, Pennsylvania 16652
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Francisco Munizaga
Francisco Munizaga
Departamento de Geología y Geofísica, Universidad de Chile, Santiago, Chile
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Victor Makseav
Victor Makseav
Departamento de Geología y Geofísica, Universidad de Chile, Santiago, Chile
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Jeff Vervoort
Jeff Vervoort
Department of Geology, Washington State University, Pullman, Washington
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Garret Hart
Garret Hart
Department of Geology, Washington State University, Pullman, Washington
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Published:
January 01, 2009

Abstract

We examined the copper isotope ratio of primary and secondary copper mineralization of porphyry copper deposits. Distinct Cu isotope reservoirs exist for high-temperature hypogene, enrichment, and leach cap minerals. Chalcopyrite from high-temperature primary mineralization forms a relatively tight cluster of δ65Cu values of +1 to –1 per mil, whereas secondary minerals formed by low-temperature reveal a range of δ65Cu values from –16.96 to +9.98 per mil. Secondary chalcocite is relatively heavy, with δ65Cu varying from –0.3 to +6.5 per mil. Leach cap minerals dominated by Fe oxides (jarosite, hematite, and goethite) are relatively light, ranging from –9.9 to +0.14 per mil. A distinct pattern of heavier copper isotopes in supergene samples and a lighter isotopic signature exists in the leach cap and oxidation zone minerals. The pattern presents an excellent tool for using Cu isotopes for exploration through providing the following information: (1) identification of highly fractionated copper isotope ratios in copper sulfide and Fe oxide samples that indicate supergene processes and the extent of leaching and enrichment of copper, and (2) identification of highly fractionated copper isotope ratios in surface and/or groundwaters that indicate the active weathering of copper sulfides that experienced significant enrichment.

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Contents

Special Publications of the Society of Economic Geologists

Supergene Environments, Processes, and Products

Spencer R. Titley
Spencer R. Titley
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Society of Economic Geologists
Volume
14
ISBN electronic:
9781629490380
Publication date:
January 01, 2009

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