F.J. Luque, L. Ortega, J.F. Barrenechea, D. Millward, O. Beyssac, J-M. Huizenga; Deposition of highly crystalline graphite from moderate-temperature fluids. Geology 2009; 37 (3): 275-278. doi: 10.1130/G25284A.1
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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.