Reinaldo Sáez

Geological constraints on massive sulphide genesis in the Iberian Pyrite Belt

Abstract The Iberian Pyrite Belt (IPB), SW Iberian Peninsula, Spain and Portugal, one of the most famous and oldest mining districts in the world, includes several major concentrations of massive sulphides, unique on Earth (e.g., Riotinto, Neves Corvo), as well as a large number of smaller deposits of this same type. All these deposits, in spite of their general similarities, show significant differences in geological setting, age, relations to country rocks, hydrothermal alteration, mineralogy and geochemistry. As a consequence of a review of the available data in the IPB, together with new findings on volcanism, hydrothermal alteration and ore mineralogy, we propose a modified genetic scenario, that can account particularly for the diversity of the geological situations in which sulphide deposits occur, as well as for their mineralogical and petrological diversity. It is concluded that there is no direct genetic relationship between felsic volcanic activity and massive sulphide deposition in the IPB, and that most of the massive sulphide bodies, including all of the giant ones, are closely related to hydrothermal vents, being therefore proximal. The available isotopic data yield additional genetic information: (a) Homogeneous lead isotope values indicate a single (or homogenized) metal source; (b) sea and connate water are the fluid reservoirs for hydrothermal input, and (c) bacterial reduction of sulphur is the most probable cause of differences in δ 34 S between stockwork and massive sulphide mineralizations. Finally, current geodynamic models suggested for the IPB are discussed. It is suggested that an intracontinental, ensialic rift or pull-apart environment is the most probable genetic environment for the IPB mineralizations.

U–Pb dating of stockwork zircons from the eastern Iberian Pyrite Belt

Zircons found in the stockwork zones of the massive sulphide Los Frailes deposit, Iberian Pyrite Belt, are interpreted to have grown during the hydro-thermal alteration of host felsic volcanic rocks. Ion microprobe (SHRIMP) dating gives a206Pb/238 U age of 345.7 ± 4.6 Ma (2σ) and together with published spore data from the deposit suggest an age of uppermost Devonian to lowermost Carboniferous. Stockwork zircons offer the possibility of precisely defining the emplacement ages of these giant sulphide accumulations over the whole Pyrite Belt and from this will emerge estimates of the thermal budget necessary to generate the deposits.

Ore genesis age of the Tharsis Mining District (Iberian Pyrite Belt): a palynological approach

Massive sulphide deposits of the Tharsis Mining District (Iberian Pyrite Belt) are included in a black shaly series that is stratigraphically conformable with the underlying Phyllite–Quartzite Group. Well-preserved palynomorph assemblages have been obtained from this shaly series. The miospore assemblages are assigned to the LN Biozone, indicating a latest Devonian age. This is consistent with the Re–Os age of 348.6 ± 12.3 Ma from both massive sulphides and stockwork mineralization. Palynological and isotopic results from elsewhere in the Pyrite Belt are similar, suggesting that mineralization was synchronous throughout the region.

Combination of sequential chemical extraction and modelling of dam-break wave propagation to aid assessment of risk related to the possible collapse of a roasted sulphide tailings dam

The Sotiel-Coronada abandoned mining district (Iberian Pyrite Belt) produced complex massive sulphide ores which were processed by flotation to obtain Cu, Zn and Pb concentrates. The crude pyrite refuses were roasted for sulphuric acid production in a plant located close to the flotation site, and waste stored in a tailing dam. The present study was focused on the measurements of flow properties, chemical characterization and mineralogical determination of the roasted pyrite refuses with the aim of assessing the potential environmental impact in case of dam collapse. Chemical studies include the determination of the total contaminant content and information about their bio-availability or mobility using sequential extraction techniques. In the hypothetical case of the tailing dam breaking up and waste spilling (ca. 4.54Mt), a high density mud flow would flood the Odiel river valley and reach both Estuary of Huelva (Biosphere Reserve by UNESCO, 1983) and Atlantic Ocean in matter of a couple of days, as it was predicted by numerical simulations of dam-break waves propagation through the river valley based on quasi-2D Saint-Venant equations. The total amount of mobile pollutants that would be released into the surrounding environment is approximately of 7.1.10(4)t of S, 1.6.10(4)t of Fe, 1.4.10(4)t of As, 1.2.10(4)t of Zn, 1.0.10(4)t of Pb, 7.4.10(3)t of Mn, 2.2.10(3)t of Cu, 1.5.10(2)t of Co, 36t of Cd and 17t of Ni. Around 90-100% of S, Zn, Co and Ni, 60-70% of Mn and Cd, 30-40% of Fe and Cu, and 5% of As and Pb of the mobile fraction would be easily in the most labile fraction (water-soluble pollutants), and therefore, the most dangerous and bio-available for the environment. This gives an idea of the extreme potential risk of roasted pyrite ashes to the environment, until now little-described in the scientific literature.

Evidence for catastrophism at the Famennian-Dinantian boundary in the Iberian Pyrite Belt

Abstract Terrigenous shelf sedimentation during the Devonian created a homogeneous basin in the Iberian Pyrite Belt. This shallow south-Iberic basin changed into a mosaic of horsts and graben at the Famennian-Dinantian boundary and subsequent evolutionary history can be explained in terms of locally increased rates of subsidence. Deposits commonly related to highly energetic processes characterize this change (fan-deltas, sediment gravity flows, rapid basin-shallowing). These resulted from convulsive/catastrophic events related to the Bretonic phase of the Hercynian Orogeny.

La estructura sísmica de la corteza de la Zona de Ossa Morena y su interpretación geológica

El experimento de sismica de reflexion profunda IBERSEIS ha proporcionado una imagen de la corteza del Orogeno Varisco en el sudoeste de Iberia. Este articulo se centra en la descripcion de la corteza de la Zona de Ossa Morena (OMZ), que esta claramente dividida en una corteza superior, con reflectividad de buzamiento al NE, y una corteza inferior de pobre reflectividad. Las estructuras geologicas cartografiadas en superficie se correlacionan bien con la reflectividad de la corteza superior, y en la imagen sismica se ven enraizar en la corteza media. Esta esta constituida por un cuerpo muy reflectivo, interpretado como una gran intrusion de rocas basicas. La imagen de las suturas que limitan la OMZ muestra el caracter fuertemente transpresivo de la colision orogenica varisca registrada en el sudoeste de Iberia. La Moho actual es plana y, en consecuencia, no se observa la raiz del orogeno.