Genesis and rank distribution of Upper Carboniferous coal basins in the Cantabrian Mountains, Northern Spain

18 pages, 14 figures, 3 tables.-- Printed version published on Nov 3, 2008.The Cantabrian Mountains located in the NW of the Iberian Peninsula constitute the most important coal-mining district of Spain. Anthracitic and bituminous coals (high and medium rank coals) have been mined in the area since the end of the nineteenth century and they currently account for about 70% of the total coal resources of the country. The region forms part of the Cantabrian and West Asturian–Leonese Zones of the Iberian Variscan Fold Belt and is strongly deformed by a set of imbricate thrusts, coeval folds and high-angle faults. Coal-bearing successions are Westphalian and Stephanian (Pennsylvanian) in age and are exposed in numerous coalfields of variable size arranged roughly parallel to the tectonic structures.Coal rank varies from medium-rank bituminous D coals (Rr ≥ 0.5%) to high-rank anthracites A coals (Rr < 6.0%). The regional rank distribution can be correlated with the increase in the thermal effect observed from Westphalian to the Stephanian coals, and from the Cantabrian Zone to the West Asturian–Leonese Zone. These rank variations are related to the thermal processes caused by the emplacement of some major faults, and granitoids and mafic rocks in upper crustal levels and the subsequent development of the regional methamorphic contact aureoles.The authors express their gratitude to the mining companies, the Spanish power plants and the INCAR (CSIC, Spain) for providing facilities and supplying essential information related to the Carboniferous coal seams. Financial support for this research was provided from Junta de Castilla y León (Proyects SA021/04 and SA005/01) and from the Spanish Ministerio de Educación y Ciencia (Proyect CGL2004-02645/BTE). J. R. Montes from the INCAR-CSIC, (Spain) is also acknowledged for his help in preparing and analysing some coal samples.Peer reviewe