Metamorphic fluids and their relationship to the formation of metamorphosed and metamorphogenic ore deposits

Cartwright, I., and Oliver, N.H.S. (2000) Metamorphic fluids and their relationship to the formation of metamorphosed and metamorphogenic ore deposits. In: Spry, G., Marshall, B., and Vokes, F., (eds.) Metamorphosed and Metamorphogenic Ore Deposits. Reviews in Economic Geology, 11 . Society of Economic Geologist, Littleton, Colorado, pp. 81-96.

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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 H20, 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 H20, with variable C02 and minor amounts of other species (e.g., F, Cl, B, and S). At high to moderate metamorphic grades, H20and C02 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.

Item ID: 14295
Item Type: Book Chapter (Research - B1)
ISBN: 978-1-629495-69-9
Date Deposited: 30 Aug 2017 04:00
FoR Codes: 04 EARTH SCIENCES > 0403 Geology > 040307 Ore Deposit Petrology @ 100%
SEO Codes: 97 EXPANDING KNOWLEDGE > 970104 Expanding Knowledge in the Earth Sciences @ 100%
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