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Metamorphic Fluids and their Relationship to the Formation of Metamorphosed and Metamorphogenic Ore Deposits

By
I. Cartwright
I. Cartwright
Victorian Institute of Earth and Planetary Sciences, Department of Earth Sciences, Monash University, Clayton, Victoria 3168, Australia
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N. H. S. Oliver
N. H. S. Oliver
Economic Geology Research Unit, Department of Earth Sciences, James Cook University, Townsville, Queensland, Australia
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Published:
January 01, 1998

Abstract

Metamorphic rocks produce fluids as devolatilization occurs during prograde metamorphism or as melts (which act as temporary repositories for fluids) crystallize during the early stages (>650°C) of cooling in high-grade metamorphic terranes. Metamorphosed shales and graywackes, which make up much of the sedimentary component of the upper crust, initially contain approximately 4 wt percent H2O, which may be liberated during the metamorphic cycle. These fluids may combine with others derived from external sources (e.g., synmetamorphic igneous intrusions or surface-derived fluids), and have the potential to transport heat, cause metasomatism, alter the rheology of the rocks, or form ore deposits. Metamorphic fluid flow in the crust is probably initially widespread, as fluids are derived from much of the rock mass, and then becomes increasingly channeled as fluids are focused along higher-permeability layers or along structures such as faults or shear zones. This type of flow path promotes ore genesis as metals can be scavenged from a large volume of rocks, with deposition occurring where fluids are focused and flowing down temperature. Most metamorphic fluids are dominated by H2O, with variable CO2 and minor amounts of other species (e.g., F, Cl, B, and S). At high to moderate metamorphic grades, H2O and CO2 are miscible at all XCO2 values unless significant salt is present. Such fluids transport some metals (e.g., Cu, Au, Ag) relatively efficiently but not base metals. Thus, the variety of metamorphogenic ore deposits will be limited unless input of saline fluid from other sources (e.g., igneous bodies) occurs, or the terrane is composed of significant volumes of meta-evaporites. However, remobilization of preexisting orebodies may occur during metamorphism and deformation.

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Contents

Reviews in Economic Geology

Metamorphic and Metamorphogenic Ore Deposits

Frank M. Vokes
Frank M. Vokes
Volume Editor
Department of Geology and Mineral Resource Engineering Norwegian University of Science and Technology Trondheim, Norway
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Brian Marshall
Brian Marshall
Volume Editor
Department of Applied Geology University of Technology Sydney NSW 2007 Australia
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Paul G. Spry
Paul G. Spry
Volume Editor
Department of Geological and Atmospheric Sciences Iowa State University Ames, Iowa 50011 USA
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Society of Economic Geologists
Volume
11
ISBN electronic:
9781629490182
Publication date:
January 01, 1998

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