METALLOGENESIS AND TRANSPRESSION: THE OSSA-MORENA ZONE (SW IBERIA) CASE STUDY

Transpressional deformation regimes characterize the tectonic evolution of the Ossa-Morena Zone during the collisional Variscan orogeny. This is due to the impingement of a promontory in NW Gondwana onto Laurussia. Development of lithospheric scale strike-slip structures greatly enhanced magma ascent and emplacement and hydrothermal circulation, thus providing unique conditions for generation of various types of ore-forming processes and deposits. A selection of these includes:

Antimony (i.e. the San Antonio mine, the largest antimony deposit in the Iberian Peninsula) and gold mineralizations are spatially and genetically related to the Badajoz-Córdoba shear zone (BCSZ), which is a major left-lateral shear zone (suture) separating the Central Iberian and Ossa Morena zones, and is one of the sinistral transpressional belts in which deformation was accommodated as a result of highly oblique convergent process of continental collision. The gold concentrations are located following the antithetic NW-trending faults connected to the main shear zone.

Variscan to late-Variscan mineralizations are characteristic of an active continental margin setting with mineral deposits related to early plutonism (i.e. Fe- skarns at Burguillos) and to late collisional granitoids (i.e. Pb-Zn-Ag-Va veins at Santa Marta granodiorites) and the Ni-Co-Bi-Ag-U, Pb-Zn-Cu-F-Ba, Sb-As-Zn-W, Cu-Zn-Pb-F-Ba late-Variscan veins (i.e. Pedroches, Azuaga, and Cerro Muriano in the Córdoba province).

W-Sn-Bi-Mo-(Au) porphyry-Sn-greisen deposits are in close relationship with highly evolved epizonal leucogranites.

During the final extensional (transtensional) period, along regional fracture zones convective cells of hydrothermal circulation produced epithermal deposits (Hg-Ba-Pb-Sb).

Finally, the geometry of the host-structures induced by continued left-lateral transpression was important in focusing mineral precipitation in specific fractures/shear zones (targets) and may play a major role in the future exploration of the whole area.