%0 Journal Article
%A Luque Del Villar, Francisco Javier
%A Ortega Menor, Lorena
%A Fernández Barrenechea, José María
%A Huizenga, Jan-Marten
%A Millward, David
%T Key factors controlling massive graphite deposition in volcanic settings: an exampleof a self-organized critical system
%D 2012
%@ 0016-7649
%U https://hdl.handle.net/20.500.14352/42463
%X Massive graphite deposition resulting in volumetrically large occurrences in volcanic environmentsis usually hindered by the low carbon contents of magmas and by the degassing processes occurringduring and after magma emplacement. In spite of this, two graphite deposits are known worldwide associatedwith volcanic settings, at Borrowdale, UK, and Huelma, Spain. As inferred from the Borrowdale deposit,graphite mineralization resulted from the complex interaction of several factors, so it can be considered asan example of self-organized critical systems. These factors, in turn, could be used as potential guides forexploration. The key factors influencing graphite mineralization in volcanic settings are as follows: (1) anunusually high carbon content of the magmas, as a result of the assimilation of carbonaceous metasedimentaryrocks; (2) the absence of significant degassing, related to the presence of sub-volcanic rocks or hypabyssalintrusions, acting as barriers to flow; (3) the exsolution of a carbon-bearing aqueous fluid phase; (4) thelocal structural heterogeneity (represented at Borrowdale by the deep-seated Burtness Comb Fault); (5) thestructural control on the deposits, implying an overpressured, fluid-rich regime favouring a focused fluidflow; (6) the temperature changes associated with fluid flow and hydration reactions, resulting in carbonsupersaturation in the fluid, and leading to disequilibrium in the system. This disequilibrium is regarded as thedriving force for massive graphite precipitation through irreversible mass-transfer reactions. Therefore, theformation of volcanic-hosted graphite deposits can be explained in terms of a self-organized critical system.
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