Caracterización geológica de las mineralizaciones de hierro de la Sierra del Teleno (León, NO de España)

Resum

The eastern iron belt in NW Spain represents a mineralised band that extends through Galicia, Asturias and León. In the latter, the primary mineralisation extends along 80 km and forms one of the largest mining districts in the Iberian Peninsula: the Ponferrada-Astorga District. The genesis of these iron ore deposits has received significant attention, and their presence linked to the formation of oolitic irons in the middle Ordovician series. However, small-scale deposits related to a great variety of metallogenesis processes have aroused little interest due to their low economic value. Still, the current attention in this type of ores focusses on its historical implications and remarkable heritage value. In this work, we study and characterise the irons associated with the Ordovician series of the Sierra del Teleno, analysing the metallogenesis processes that have given rise to extensive mineralisations and its correlation with different geological events. For this purpose, an X-ray fluorescence characterisation has been carried out, analysing the various ore deposits present in the area. The results show four different types of iron ores leading to primary or secondary occurrences. Two types are associated with hydrothermal fluids filling veins and fractures, where iron coexists with quartz veins, and iron-cemented breccias; they form stockwork ores in the lower Ordovician quartzites (Armorican Quartzite). Secondary iron deposits are the result of sulphides weathering in the quartzices and secondary transformation of chlorite into goethite and mainly appear at the base of the middle Ordovician slates. These iron ores have played an important historical role, exploited since antiquity, whose vestiges preserved throughout the area as shafts, adits and rock emptying.