AUTHORS: Christoph Heinrich, Marcel Guillong, Thomas Pettke, Claudia Pudack, Jung Hun Seo
High concentrations of Cu, As and Au analysed in vapour inclusions of porphyry-type ore deposits have been used to claim that magmatic vapour may be an essential ingredient for the formation of rich epithermal precious-metal deposits. Thermodynamic data show that magmatic vapour can homogeneously contract to a gold-rich aqueous liquid, if it cools at elevated pressure and contains enough sulphur for gold complexation. This paper confirms these predictions with two sets of new data. First, we demonstrate that metal-rich magmatic vapours are indeed sufficiently sulphur-rich to support the required Cu-S and Au-S complexes. Second, we present the first fluid inclusion analyses of exceptionally metal-rich epithermal liquids, consistent with vapour contraction at the porphyry-to-epithermal transition.
KEYWORDS: Porphyry, epithermal, copper, gold, sulphur, vapour, contraction, fluid inclusions, Famatina
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