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Sulphide magma as a source of metals in arc-related magmatic hydrothermal ore fluids

Nature Geoscience volume 3, pages 501505 (2010) | Download Citation

Abstract

As magma ascends in subduction zones, decreasing pressure and temperature cause it to separate into two or more phases in a process known as exsolution. Hydrothermal ore fluids and metal-rich sulphide melts may be products of this exsolution. Conventionally, the ore fluids are thought to acquire their metal content directly from the parent magma. However, it is probable that the ore fluids and sulphide melts interact after exsolution, and therefore possible that the sulphide melts are an important source of metals for the ore fluids. Here we use petrographic analyses of erupted sulphide melts and compositional analyses of volcanic gases emitted immediately after an eruption at Merapi Volcano, Indonesia, to show that magmatic hydrothermal fluids can derive their metals from dissolution of sulphide melts. We find that the volcanic gases exhibit metal ratios that are comparable to those in the erupted sulphide melts. Furthermore, we show that gases sampled immediately after the eruption have metal concentrations that are orders of magnitude higher than those of gases emitted during periods of quiescence. We propose that the metal content of ores forming in volcanic arc environments is established by exsolution accompanying injections of primitive magma immediately before explosive eruptions.

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Acknowledgements

Reviews by J. Mungall, M. J. Rutherford and B. Scaillet contributed significantly to improving the manuscript. This study was funded by scholarships to O.N. by the Natural Sciences and Engineering Research Council (NSERC) and the Fond Québécois de la Recherche sur la Nature et les Technologies (FQRNT), and research grants to A.E.W-J. and J.S. from NSERC and FQRNT.

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Affiliations

  1. Department of Earth & Planetary Sciences, McGill University, 3450 University Street, Montreal, Quebec, H3A 2A7, Canada

    • Olivier Nadeau
    • , Anthony E. Williams-Jones
    •  & John Stix

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Contributions

This paper is the product of research conducted by O.N. during his Ph.D. O.N. made the petrographic observations and undertook the chemical analyses. A.E.W-J. participated in the field work and all three authors contributed to the interpretation of the data and to the writing of the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Olivier Nadeau.

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DOI

https://doi.org/10.1038/ngeo899

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