Basic rocks from the Filón Norte open pit (Tharsis, Iberian Pyrite Belt) are hydrothermally altered and
crosscutted by a stockwork which is composed by carbonate filled veins and clastic dikes. Both, dykes and
veins, show carbnonate selvages. Clastic dykes include black shale, basic rock and siliceous fragments that
exhibit angular to lobulate shape and grain size up to 40 cm in diameter. Palynomorphs recovered from
black shales of the clastic dykes give an uppermost Devonian age (LN Biozone).
Dykes and veins belong to a fracture system representing the escape pathways of fluids trapped within the
footwall muddy sediments when the basic sill was intruded. Black shale sedimentation, emplacement of
the basic sills, fracturation and carbonate alteration, and filling of veins and dykes constitute a succession
of nearly coeval events, all of them related with the uppermost Devonian crisis of the South Iberian Basin
