Palaeozoic magmatic-related hydrothermal activity in the Almadén syncline, Spain: a long-lasting Silurian to Devonian process?

Almaden (central Spain) is the most remarkable mercurymining district in the world, having produced one-third of the total world output of this element. The mercury orebodies are hosted by sedimentary and volcanic rocks belonging to a Lower Palaeozoic sequence that unconformably overlies the pre-Ordovician basement of the Central Zone of the Iberian Variscan Chain2,3 (Fig. 1). The Almaden rocks and mineralization pose an intriguing problem because in addition to the classic Lower Silurian strata-bound mineralization (e.g. Almaden and El Entredicho) other deposits are found higher in the stratigraphic sequence in both Silurian and Devonian