Abstract
Major- and trace-element compositions of zircons and whole rocks from 14 barren and seven ore-bearing calc-alkaline intrusions from the Chuquicamata-El Abra porphyry copper belt of northern Chile have been measured in situ by excimer laser ablation (ELA) ICP-MS. These data permit the Ce(IV)/Ce(III) ratio within zircon to be calculated using a lattice-strain model for mineral-melt partitioning of Ce(IV) and Ce(III). Zircon Ce(IV)/Ce(III) and EuN/EuN* ratios, and by inference magmatic oxidation states, generally increase from older, mafic to younger, felsic units. Within this sequence, porphyry copper mineralization is directly associated only with intrusions with zircon Ce(IV)/Ce(III)>300 and EuN/EuN*>0.4. Such trends can be understood in terms of interdependent relations between oxygen fugacity, sulfur speciation and solubility, and chalcophile element partitioning in silicate magmas. Because zircon occurs in most calc-alkaline intrusions and is resistant to subsolidus alteration, zircon Ce(IV)/Ce(III) ratios provide a useful tool for evaluating the economic potential of such rocks for magmatic-hydrothermal Cu±Au mineralization. The approach is general and may provide a means to infer relative oxidation state in a wide range of intermediate to felsic igneous rocks.
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27 April 2023
The original article has been updated: the name of second author has been corrected in the electronic version.
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Ballard, J.R., Palin, J.M. & Campbell, I.H. Relative oxidation states of magmas inferred from Ce(IV)/Ce(III) in zircon: application to porphyry copper deposits of northern Chile. Contrib Mineral Petrol 144, 347–364 (2002). https://doi.org/10.1007/s00410-002-0402-5
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DOI: https://doi.org/10.1007/s00410-002-0402-5