Coal basins in the Cantabrian Mountains, northwestern Spain

The Cantabrian Mountains, containing about 70% of the total coals of the country and 95% of the anthracitic and bituminous resources, is the most important coal-mining district of Spain. Coal-bearing successions are Late Carboniferous in age and their deposition took place in a syn-orogenic context during the Hercynian activity, mainly in three different time-successive locations: foreland basins, intrathrust basins and intramontane fault-controlled basins. Foreland deposition occurred in strongly asymmetrical basins located ahead of thrust sheets units. Intrathrust basins resulted from folding and tightening of these units during or after their emplacement. Intramontane and fault-controlled basins were developed along lineaments with strike-slip movements and as a result of fold and fault reactivation. Peat mires in foreland and intrathrust coal basins mainly occupied broad areas on abandoned delta and fan delta lobes. Coals in intramontane and fault-controlled basins were related with alluvial fan and lacustrine environments. Coal ranks vary from high volatile bituminous coals to anthracite, depending on the structural location of the coalfields. Hydrothermal activity seems to be the most important factor in coal evolution.