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Book Chapter

The role of metamorphic fluids in the formation of ore deposits

By
Bruce W. D. Yardley
Bruce W. D. Yardley
School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK
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James S. Cleverley
James S. Cleverley
CSIRO Earth Science & Resource Engineering, Australian Resources Research Centre, Kensington, Western Australia 6152, Australia
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Published:
January 01, 2015

Abstract

Many ore deposits are hosted by metamorphic rocks, and metamorphic fluids have been invoked as a source for various deposits, especially gold deposits. Metamorphic fluid compositions reflect original sedimentary environment: continental shelf sequences yield saline metamorphic fluids with little dissolved gas while metasediments from accretionary and oceanic settings host less saline fluids with significant CO2 contents.

The principal difficulty in reconciling ore deposits with a metamorphic origin is that many form quickly (c. 1 Ma), whereas metamorphic heating is slow (c. 10–20 °/Ma). Gravitational instability means that fluid cannot be retained. Metamorphic ores may nevertheless form by: (a) segregation leading to enrichment of pre-existing concentrations; (b) infiltration of water-rich fluids from schists into marbles at high temperature overstepping decarbonation reactions and allowing fast reaction that locally draws down temperature; and (c) rapid uplift driving dehydration reactions owing to pressure drop.

Some orogenic lode gold deposits fit well with a purely metamorphic origin during rapid uplift, but others are problematic. At Sunrise Dam, Western Australia, anomalies in Sr-isotope ratios and in apatite compositions indicate a partial mantle/magmatic source. Low salinity, H2O–CO2 fluids commonly associated with hydrothermal gold reflect the effect of salt on gas solubility, not the origin of the fluid.

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Contents

Geological Society, London, Special Publications

Ore Deposits in an Evolving Earth

G. R. T. Jenkin
G. R. T. Jenkin
University of Leicester, UK
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P. A. J. Lusty
P. A. J. Lusty
British Geological Survey, UK
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I. Mcdonald
I. Mcdonald
Cardiff University, UK
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M. P. Smith
M. P. Smith
University of Brighton, UK
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A. J. Boyce
A. J. Boyce
Scottish Universities Environmental Research Centre, UK
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J. J. Wilkinson
J. J. Wilkinson
Natural History Museum and Imperial College London, UK
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Geological Society of London
Volume
393
ISBN electronic:
9781862396692
Publication date:
January 01, 2015

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