Deposition of highly crystalline graphite from moderate-temperature fluids

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 XCO(2)/(XCO(2) + XCH(4)) ratio of 0.69, thus indicating temperatures of similar to 500 degrees 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.