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

Abstract

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.