Deposition of highly crystalline graphite from moderate-temperature fluids
- 1Departamento de Cristalografía y Mineralogía, Facultad de Geología, Universidad Complutense de Madrid, 28040 Madrid, Spain
- 2British Geological Survey, Murchison House, West Mains Road, Edinburgh EH9 3LA, UK
- 3Laboratoire de Géologie, CNRS, Ecole Normale Supérieure, 24 rue Lhomond, 75005 Paris, France
- 4Department of Geology, University of Johannesburg, P.O. Box 524, Auckland Park 2006, University and Kingsway (Auckland Park Kingsway Campus), Johannesburg, South Africa
- *E-mail: jluque{at}geo.ucm.es.
Abstract
Recognized large occurrences of fluid-deposited graphite displaying high crystallinity were previously restricted to high-temperature environments (mainly granulite facies terranes). However, in the extensively mined Borrowdale deposit (UK), the mineralogical assemblage, notably the graphite-epidote intergrowths, shows that fully ordered graphite precipitated during the propylitic hydrothermal alteration of the volcanic host rocks. Fluids responsible for graphite deposition had an average X CO2/(XCO2 + X CH4) ratio of 0.69, thus indicating temperatures of ~500 °C at the fayalite-magnetite-quartz buffered conditions. Therefore, this is the first reported evidence indicating that huge concentrations of highly crystalline graphite can precipitate from moderate-temperature fluids.
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- Received 26 June 2008.
- Revision received 4 November 2008.
- Accepted 6 November 2008.
- © 2009 Geological Society of America
