Mineralogical and isotopic characterization of graphite 2 deposits from the Anatectic Complex of Toledo, central Spain

Abstract

Graphite is found dispersed in high-grade metapelitic rocks of the Anatectic Complex of Toledo 15 (ACT) and was mined during the mid twentieth century in places where it has been concentrated 16 (Guadamur and la Puebla de Montalbán mines). Some samples from these mines show variable but 17 significant alteration intensity, reaching very low-T hydrothermal (supergene) conditions for some 18 samples from the waste heap of the Guadamur site (<100 ºC and 1kbar). Micro-Raman and XRD data 19 indicate that all the studied ACT graphite is of high crystallinity irrespectively of the degree of hydrothermal alteration. Chemical differences were obtained for graphite δ 13 20 C composition. ACT granulitic graphite shows δ 13 21 CPDB values in the range of -20.5 to -27.8‰, indicating a biogenic origin. 22 Interaction of graphite with hydrothermal fluids does not modify isotopic compositions even in the 23 most transformed samples from mining sites. The different isotopic signatures of graphite from the 24 mining sites reflect its contrasted primary carbon source. The high crystallinity of studied graphite 25 makes this area of central Spain suitable for graphitic exploration and its potential exploitation, due to 26 the low carbon content required for its viability and its strategic applications in advanced technologies, 27 such as graphene synthesis.