Estudio preliminar de las mineralizaciones de la mina de oro romana de Llamas de Cabrera (Leon, NO de España)

Abstract

The mine of Llamas de Cabrera (Leon, Spain) is a gold deposit operated during the Roman Empire, in which primary and secondary gold ores coexist. The primary gold ores were hosted mainly in the upper layers of the Armorican Quartzite. They are lodes, being very abundant those hosted in N180°E/70-85°E tensional fractures and rare the ones associated to N70°E and N125°E fractures. They are formed by quartz and arsenopyrite very dominant over pyrite, galena, gold, chalcopyrite, bismuthinite, tetrahedrite and covellite. The accompanying hydrothermal alteration is silicification, sericitization and chloritization. The determined supergene minerals are scorodite, goethite and anglesite. The operated gold is free gold located generally in microfractures in arsenopyrite or quartz. Its content in silver varies from 1,99 to 7,62%, whereas the copper content is very low, remaining below the limit of instrumental detection. This study shows the existence of two phases of mineralization, deposited during two hydrothermal events of hercinian age, in addition to the supergenic phase. The secondary gold ores, operated in alluvial and colluvial sediments, were deployed by the action of the exogenous cycle on the primary gold deposits. We consider that the total volume of material moved at roman time ascended to 2 Mm³.