The volcanic-hosted massive sulphide deposits of the Iberian Pyrite Belt - Review and preface to the Thematic Issue

The Iberian Pyrite Belt (IPB) has, over the past decade, been an area of renewed mining activity and scientific research that has resulted in a wealth of new data and new geological and metallogenic concepts that are succinctly presented in this Thematic Issue. The reason for this interest in the IPB, which forms part of the Hercynian orogenic belt. is that its Late Devonian to Middle Carboniferous rocks host a huge quantity of volcanic-hosted massive sulphide (VMS) mineralization (1700 Mt of sulphides, totalling 14.6 Mt Cu, 13.0 Mt Pb, 34.9 Mt Zn, 46100 t Ag and 880 t Au). The mineralization and its environment display a number of typical signatures that can be related to the mineralogy and zoning of the sulphide orebodies, to the lead isotopes of the mineralization, to the geochemical and mineralogical variations in the hydrothermal alteration halos surrounding the orebodies, to the geochemical characteristics of the bimodal volcanics hosting the VMS, to the complex structural evolution during the Hercynian orogeny, to the presence of palaeofaults and synsedimentary structures that acted as channels and discharge traps for the metalliferous fluids, and to the gossans developed over VMS. Discriminant geological criteria have been deduced for each domain which can be helpful in mineral exploration, complementing the more traditional prospecting techniques. Although the question of the IPB's geodynamic setting is still under debate, any interpretation must now take into account some incontrovertible constraints: for example the geochemical characteristics of a large part of the basic lavas are comparable to those of mantle-derived basalts emplaced in extensional tectonic settings, and the associated acidic rocks were produced by melting of a basic crustal protolith at low-to medium-pressures and a steep geothermal gradient, thus, the sulphide-bearing volcanosedimentary sequence differs strongly from recent are-related series. It is considered here that the tectonic setting was extensional and epicontinental and that it developed during the Hercynian plate convergence, that culminated in thin-skinned deformation and accretion of the South Portuguese terrane to the Iberian Paleozoic continental block.