Magmatic vapor contraction and the transport of gold from the porphyry environment to epithermal ore deposits
- 1Department of Earth Sciences, Swiss Federal Institute of Technology, ETH Zentrum NO, 8092 Zürich, Switzerland
Abstract
Fluid-phase stability relations combined with thermodynamic modeling using fluid-inclusion analyses and new gold-solubility experiments lead to an integrated geological interpretation linking epithermal gold mineralization and porphyry-style ore formation to the cooling of hydrous magma chambers. The essential chemical requirement for gold transport to low temperatures is an initial excess of sulfide over Fe in the magmatic fluid, which is best achieved by condensing out Fe-rich brine from a buoyant, low- to medium-salinity vapor enriched in volatile S. This vapor can contract directly to an aqueous liquid, by cooling at elevated pressure above the critical curve of the salt-water fluid system. Physical and chemical conditions are matched when magmatic fluid is released through a gradually downward-retracting interface of crystallizing magma beneath a porphyry stock, predicting the consistent zoning and overprinting relations of alteration and mineralization observed in magmatic hydrothermal systems.
Footnotes
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↵*Heinrich—also at Faculty of Mathematics and Natural Sciences, University of Zürich, Winterthurerstrasse 190, 8057 Zürich, Switzerland; heinricherdw.ethz.ch. Present address: Stefánsson—Science Institute, University of Iceland, Dunhagi 3, 107 Reykjavik, Iceland
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↵GSA Data Repository item 2004132, Table DR1, species and sources of thermodynamic data for parts of the chemical system Na-K-Al-Si-Fe-Au-Cl-S-O-H at 500 bar and 25–400 °C with comments about modeling approach, is available online at www.geosociety.org/pubs/ft2004.htm, or on request from editinggeosociety.org or Documents Secretary, GSA, P.O. Box 9140, Boulder, CO 80301-9140, USA.
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- Accepted May 20, 2004.
- Received March 19, 2004.
- Revision received May 20, 2004.
- Geological Society of America
