Copper Isotope Fractionation Used to Identify Supergene Processes
Ryan Mathur, Spencer Titley, Fernando Barra, Susan Brantley, Marc Wilson, Allison Phillips, Francisco Munizaga, Victor Makseav, Jeff Vervoort, Garret Hart, 2009. "Copper Isotope Fractionation Used to Identify Supergene Processes", Supergene Environments, Processes, and Products, Spencer R. Titley
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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.