Revisiting the age of magmatism and ductile deformation in the Iberian Pyrite Belt: evidence of Carboniferous syn-convergent extensional tectonics

Subvolcanic rocks from hybrid zones provide insights into the parental magmas present in calc-alkaline arc systems. Determining the composition and formation conditions of the parental magma is essential for linking plutonic and volcanic rocks to a common source. Here, we investigate the genetic relationships between plutonic rocks from the bimodal Seville Sierra Norte Batholith (SSNB) and coeval bimodal volcanic rocks from the Iberian Pyrite Belt, one of the largest massive sulfide provinces on Earth, hosted by the Volcanic–Sedimentary Complex in the South Portuguese Zone (Iberian Variscan Belt). Metadata analysis of geochemical signatures from the SSNB and the Volcanic–Sedimentary Complex indicates a common arc-like magma source. The Gerena hybrid zone, located in the southern section of the SSNB, provides evidence of a genetic link between mafic and felsic end members of this magmatism. Experiments on the hybrid zone, performed at 300 MPa and 1000°C, and subsequently quenched, produced a liquid composition consistent with the Andean cotectic. Furthermore, the crystallization ages of the granodiorites (356 ± 1 Ma) and quartz-diorites from the Gerena hybrid zone (368 ± 3 Ma) overlap the age range of volcanic felsic rocks from the Iberian Pyrite Belt. We propose that: (i) the quartz-diorite of the Gerena hybrid zone corresponds to the missing Late Famennian plutonic roots of the Iberian Pyrite Belt; and (ii) the Late Famennian–Tournaisian arc-like magmatism in the South Portuguese Zone was related to the termination of subduction of the Rheic oceanic lithosphere. Our findings can help in understanding the links between magmatic systems and metallogenic provinces.

In the South Portuguese Zone (Iberian Massif), thin-skinned tectonics linked to the collision with the Ossa-Morena Zone produced the inversion of previous extensional basins in Carboniferous times. Its central domain, namely the Iberian Pyrite Belt, underwent two deformation phases at mostly low-grade metamorphic conditions linked to a progressive deformation migrating upwards from a basal detachment and from north to south. The Puebla de Guzmán Antiform is one of the most outstanding cartographic structures in the Iberian Pyrite Belt, representing a imbricate fan thrust system developed during the second regional deformation phase. In the Puebla de Guzmán Antiform, the first deformation phase gave rise to a penetrative slaty cleavage (S 1 ), which is also recognized in the whole Iberian Pyrite Belt and constitutes the main foliation all over the region. Its genesis is possibly linked to the coetaneous development of thrusts at deeper crustal levels and SSW-vergent folds at all levels above these thrusts. First phase structures were deformed by large-scale imbricated thrust systems with lateral (NNE–SSW) and frontal (WNW–ESE) ramps, which constitute the most relevant regional cartographic structures. This second deformation phase generated thrusts, two set of folds with WNW–ESE and NNE–SSW-oriented axes, as well as two related axial plane crenulation cleavages. These relatively brittle to ductile-brittle second phase structures have been identified in many areas of the Iberian Pyrite Belt, and especially in the southern limb of the Puebla de Guzmán Antiform. The second phase thrusts reported from the Puebla de Guzmán Antiform have not been folded according to both the geological map of the area and the analysis of maximum shortening and stretching axes.

The Rio Tinto project area is located in the South Portuguese Zone, in the eastern part of the Iberian Pyrite Belt. The Iberian Pyrite Belt (IPB) is one of the world’s best-known ore provinces hosting volcanogenic massive sulphide deposit, formed in the latest Famennian (ca. 360 Ma) and subsequently folded and metamorphosed during the Variscan orogeny (330–300 Ma). The study area is located in the Rio Tinto syncline, with Carboniferous metasediments (Culm) in its core. The volcanic sedimentary complex (VSC) is overthrusted in the central part of the syncline forming the Rio Tinto anticline outcrop (an antiformal stack). The aim of this work was to construct a 3D geological model of the Rio Tinto mine area. To achieve this data compilation has been done including new geological mapping and structural interpretations, petrological and petrophysical sampling, drill hole logging, and geophysical data interpretation (gravimetric, magnetic and radiometric data). Complex surfaces were constructed using large data sets analysed by suitable geometrical techniques. The obtained 3D model shows the relationships between several lithologies, tectonic surfaces and mineralization zones, and is an example of reconstruction of complex geological units within the Iberian Pyrite Belt. In addition, in the Rio Tinto area it was possible to derive a predictive model defining four areas of high ore potential based on detailed geological field work, fracture analyses and geophysical studies related to the possible presence of massive sulphides and stockwork zones.

[1] Our paper [Onezime et al., 2003] was basically aimed at providing a new, and thus debatable, geodynamic interpretation at a regional scale of the South Portuguese Zone, of which the Iberian Pyrite Belt (IPB) is part. Our study relied mainly on new structural data and facies analysis, with some emphasis on the volcanic and related facies of the Volcano-Sedimentary Complex (VSC) of the IPB, on which Boulter’s [2005] comments concentrate. Boulter complains that his ideas about the IPB and more specifically his interpretations of the VSC volcanic and volcaniclastic facies [Boulter, 1993a, 1993b, 1996] were not correctly rendered and were partly misinterpreted in our paper. A huge literature exists about the IPB geology, and various authors have dealt in more or less detail with the volcanological aspects of this belt. There was reasonably no room in our paper for an in-depth discussion of all relevant previous interpretations on this topic, including Boulter’s sill-sediment model. Some other workers in the IPB have already stressed the poor consistency of this model with the field observations at the regional scale [e.g., Carvalho et al., 1999], and recent reviews of the IPB geology and metallogeny do not rely much on this model [e.g., Leistel et al., 1998; Saez et al., 1996, 1999]. We restrict our reply to the issues raised by Boulter in his comment. [2] We acknowledge the fact that Boulter [2005] reported extrusive volcaniclastics and resedimented volcanic deposits in the VSC. We thus acknowledge that our quoting of his model as ‘‘a complete intrusive model’’ was a bit loose in this regard. However, the claim by Boulter that ‘‘he did recognize the importance of stratified volcaniclastic rocks in the Pyrite Belt’’ does not give any support to the sillsediment model he in fine continues to defend. It rather tends to weaken his case since such volcaniclastic facies are not normal components of intrusive magma-sediment systems. Boulter interprets them as mostly ‘‘extrusive hydroclastic breccias’’ derived from disruption, eventually explosive, of the sediment cover above the high-level intrusive system. In this interpretation, there is implicit assumption that such volcaniclastic deposits should be volumetrically trivial in the VSC, if this is still to be described as a sill-sediment system. We thus envisioned the extrusive component as being subsidiary in Boulter’s model and not worth to be quoted in our paper. It is concerning, and rather contradictory to his claim, that Boulter himself states that ‘‘the majority of the volcanic facies in the Rio Tinto district were peperitic intrusions that did not supply detritus to the sedimentary basin.’’ [3] Boulter [2005] pretends to understand that we are unaware of the possible formation of volcaniclastic rocks in intrusive conditions. This is rather unfair misreading of our writing. The exact wording of his comment is ‘‘Despite important amounts of volcaniclastic ‘‘deposits’’ (quotation marks added), a complete intrusive model has been proposed. . .’’. ‘‘Volcaniclastic deposits’’ in our writing referred to material that has been transported and deposited (either pyroclastic or resedimented), according to the common meaning. It was not to refer to the intrusive autoclastic facies reported and emphasized by Boulter in his papers. Intrusive (and extrusive as well) autoclastic facies in submarine environment of relevance here are mostly formed by quench fragmentation (granulation in our paper). We have made due recognition of such facies in the VSC (e.g., Figure 8 of our paper, our ‘‘autoclastic brecciated facies’’). Although locally conspicuous at the outcrop scale, they do not represent a prominent volumetric part of the volcanic province as a whole. [4] The issues raised by Boulter [2005] and discussed above should not obscure some more significant differences between his description of the VSC and ours. A major point is the evidence gained from our fieldwork that volcaniclastic deposits, both primary and resedimented, are, along with volcanogenic sedimentary deposits, a major component of the VSC in terms of volume. The volcaniclastic deposits are dominated by sandstones and lapillistones. In the perspective of the issues raised by Boulter in his comment, it is clear that this evidence does not match with the sillsediment hypothesis. There is obvious contradiction between a model where volcanics are dominated by intrusions, TECTONICS, VOL. 24, TC1010, doi:10.1029/2004TC001775, 2005

The Iberian Pyrite Belt (IPB) hosts world-class massive sulphide deposits, such as Neves-Corvo in Portugal and Rio Tinto in Spain. In Portugal, the Palaeozoic Volcanic-Sedimentary Complex (VSC) hosts these ore deposits, extending from the Grândola-Alcacer region to the Spanish border with a NW–SE to WNW–ESE trend. In the study area, between the Neves-Corvo mine region and Alcoutim (close to the Spanish border), the VSC outcrops only in a small horst near Alcoutim. Sparse exploration drill-hole data indicate that the depth to the top of the VSC varies from several 100 m to about 1 km beneath the Mertola Formation Flysch cover. Mapping of the VSC to the SE of Neves-Corvo mine is an important exploration goal and motivated the acquisition of six 2D seismic reflection profiles with a total length of approximately 82 km in order to map the hidden extension of the VSC. The data, providing information deeper than 10 km at some locations, were integrated in a 3D software environment along with potential-field, geological and drill-hole data to form a 3D structural framework model. Seismic data show strong reflections that represent several long Variscan thrust planes that smoothly dip to the NNE. Outcropping and previously unknown Late Variscan near-vertical faults were also mapped. Our data strongly suggest that the structural framework of Neves-Corvo extends south-eastwards to Alcoutim. Furthermore, the VSC top is located at depths that show the existence within the IPB of new areas with good potential to develop exploration projects envisaging the discovery of massive sulphide deposits of the Neves-Corvo type.

The 250 × 20–70 km Iberian Pyrite Belt (IPB) is a Variscan metallogenic province in SW Portugal and Spain hosting the largest concentration of massive sulphide deposits worldwide. The lowermost stratigraphic unit is the early Givetian to late Famennian-Strunian (base unknown) Phyllite-Quartzite Group (PQG), with shales, quartz-sandstones, quartzwacke siltstones, minor conglomerate and limestones at the top. The PQG is overlain by the Volcanic Sedimentary Complex (VSC), of late Famennian to mid-late Visean age, with a lower part of mafic volcanic rocks, rhyolites, dacites and dark shales, hosting VHMS deposits on top (many times capped by a jasper/chert layer), and an upper part, with dark, purple and other shales and volcanogenic/volcaniclastic rocks, carrying Mn oxide deposits. The VSC is covered by the thousands of meters thick Baixo Alentejo Flysch Group of late Visean to Moscovian age. The VSC comprises a bimodal submarine volcanic succession, with VHMS deposits spatially associated to dacites and rhyolites corresponding to effusive/explosive lava-cryptodome-pumice cone volcanoes. The lava/domes consist of coherent lithofacies surrounded by clast-rotated hyaloclastite breccia and minor autobreccia, with massive VHMS ore at the top of the felsic effusive units and stockworks in the autoclastic and pyroclastic breccias. The eastern IPB rocks are intruded by the voluminous Sierra Norte Batholith (tonalite-trondhjemite-granodiorite, TTG series). Felsic volcanic rocks (dacite to high-silica rhyolite) predominating over basalts and dolerites, belong to the calc-alkaline series and plot mostly in the within-plate field in tectonic discriminative diagrams. Several periods of volcanism, from 384 to 359 Ma are recognized. Dacites and rhyolites exhibit Nd and Sr enrichment, typical of a crustal signature, and their overall geochemistry suggests generation by fractionation/partial melting of amphibolites at low pressure. Trace elemental modelling of the basic rocks, involving tholeiitic lavas and alkaline basaltic lavas and dolerites, points to mixing between E- and N-MORB and assimilation of crustal material. Variscan NW-SE/W-E-trending and SW- or S-verging folds (with NE- or N-dipping planar cleavage) and thrusts, occur in west-central and eastern IPB, respectively. In late to post-Variscan time strike-slip oblique faults formed, either N-S to NNW-SSE or NE-SW to ENE-WSW, dextral or sinistral (both extensional), respectively. The first set hosts late Variscan Cu-Pb-Ba veins and Mesozoic(?) dolerite dykes. IPB contains over 90 VHMS deposits, estimated before erosion at >1700 Million tonnes (Mt), with 14.6 Mt Cu, 34.9 Mt Zn, 13.0 Mt Pb, 46,100 t Ag, 880 t Au and many other metals, particularly Sn. Eight of these are giant (≥100 Mt) VHMS deposits, namely Rio Tinto, Tharsis, Aznalcollar-Los Frailes, Masa Valverde, Sotiel-Migollas and La Zarza (Spain) and Neves Corvo and Aljustrel (Portugal). The VHMS deposits are of the felsic-siliclastic type and mostly of the Zn–Pb–Cu and Zn–Cu–Pb metal content types. The deposits range in thickness from 1 m to tens of meters (plus increase from tectonic stacking) and up to a few kilometers in extension, and many are underlain by large stockwork zones. Their age is either Strunian (palynological age) in the southern IPB or mostly Tournaisian in the northern IPB. The major massive ore minerals are pyrite, sphalerite, chalcopyrite, galena (and cassiterite at Neves Corvo), also present with dominant quartz-chlorite-sericite-carbonate in the stockwork ore. Sericite and chlorite were also formed from additional alteration in the hanging wall rocks. Metal zonation in most VHMS deposits consists of a Cu-rich stockwork and base of the massive ore, with Zn–Pb massive ore above and extending laterally. S-, O-, H- and C-isotope data indicate that ore-forming fluids contain predominant or exclusive modified seawater. A magmatic fluid contribution to the dominant seawater has been proposed for some deposits. The deposits are exhalative or formed by shallow subsurface replacement of either muds/shales or coherent felsic volcanic rocks.

<p>The Iberian Pyrite Belt (IPB) in Portugal and Spain is a world-class metallogenic province that contains more than 1800 Mt of massive sulfide ore in over 100 deposits. The orebodies are hosted by submarine lithologies comprising felsic and mafic volcanic rocks and sedimentary units from the Volcanic-Sedimentary Complex (VSC) of Devonian-Carboniferous age. This study reports preliminary geological, mineralogical, and geochemical results from the Sesmarias prospect.</p><p>The Sesmarias VMS prospect is a blind discovery (~100 m of Tertiary cover) with the first lens intersected by drilling in 2014 (10.85 meters @ 1.81% Cu, 2.57% Pb, 4.38% Zn, 0.13% Sn, and 75.27 g/t Ag). Recent drilling has encountered 39.2 meters @ 0.44% Cu, 0.71 g/t Au, 27.1 g/t Ag, 2.07% Zn, and 0.79% Pb and 36.45 meters @ 0.72% Cu, 0.36 g/t Au, 0.82% Pb, and 21 g/t Ag in separate holes, and has extended the mineralization further to the SE. Through all phases of drilling, the company intersected copper-zinc massive sulfide mineralization in various lenses over a strike length of about 1.7 km; however, this value may easily increase with the continuation of the drilling program.</p><p>The Sesmarias massive sulfide system is heavily folded and strongly modified by several post-mineralization deformation events. The VSC at Sesmarias comprises black shales and felsic volcanics that are the primary hosts of the massive and semi-massive sulfide mineralization and a younger thick sequence of mafic volcanics (including intrusives) which overlap grey/green shales. Macroscopic observations complemented by petrographic studies and bulk rock chemistry of the volcanic rocks allowed to distinguish two main groups of volcanics rocks. The-mafic rocks are composed of plagioclase, relics of amphibole and pyroxene (±quartz), and are dominated by an alteration assemblage that includes chlorite, calcite, dolomite, epidote, (±quartz), and iron (hydro-)oxides. The felsic rocks include lavas and associated volcaniclastic rocks that are composed of quartz, plagioclase and are altered to muscovite ± chlorite. Compositionally, all major elements except for Na<sub>2</sub>O, K<sub>2</sub>O, and Al<sub>2</sub>O<sub>3</sub>, show roughly negative correlations with SiO<sub>2</sub> and allow the discrimination of mafic from felsic rocks; however, the trends of magmatic differentiation are compromised due to secondary alteration. The results show that the VSC at Sesmarias is dominated by mafic rocks of basaltic composition (alkaline basalts) which are strongly spilitized. In contrast, the felsic rocks that host the mineralization are manly rhyodacites and dacites. Overall the magmatism at Sesmarias is more mafic in comparison with other mineralized areas such as Aljustrel and Neves Corvo, where the volcanism is predominantly rhyolitic.</p>

This paper aims to discuss the structural evolution of the Iberian Pyrite Belt during the Variscan Orogeny. It provides new structural data, maps and cross sections from the eastern part of the Iberian Pyrite Belt. Regional geology of the South Portuguese Zone and lithostratigraphy of the Iberian Pyrite Belt are first briefly summarised. Three roughly homoaxial deformation phases are distinguished, and are mainly characterised by south-verging multi-order folds, axial planar cleavages and thrusts. Three structural units are distinguished: the La Puebla de Guzman and Valverde del Camino antiforms are rooted units related to the propagation of southward-directed thrust systems that may branch onto the lower decollement level of the South Portuguese Zone; El Cerro de Andevalo is a structurally higher unit, mainly composed of allochthonous D1 thrust nappes. No evidence of sinistral transpression has been found in the transected cleavage and the strike of S3 with respect to S2. Better evidence of transpression is the moderately to steeply westerly plunging folds that show S-type asymmetry in down-plunge view. Variscan deformation in the Iberian Pyrite Belt is defined as the combination of a dominant southwards shear and a sinistral E-shear caused by oblique continental collision between the South Portuguese plate and the Iberian Massif.

Structural evolution of the southernmost segment of the West European Variscides: the South Portuguese Zone (SW Iberia)

The South Portuguese Zone (SPZ) constitutes the southernmost segment of the Variscan Iberian Massif. It is bounded to the north by the Beja‐Acebuches Ophiolitic Complex and related accretionary wedge. To the south lie the Iberian Pyrite Belt (IPB) and flysch deposits forming the southern extent of the zone. Structural analysis within the Spanish side of the SPZ supports continuous south propagating deformation, evolving from early synmetamorphic thrusting in the internal zone to thin‐skinned tectonics in the southern external domain. The accretion of the SPZ to the Ossa Morena Zone is also witnessed by the presence of various mélanges, observed throughout the investigated area. Part of the mélanges observed in the IPB are related to the volcanics and mineralizations setting. A key point to understand the IPB mineralizations genesis is to constrain the volcanogenic model. One underestimated feature is the large amount of submarine calc‐alkaline ignimbritic facies, implying the presence of caldera structures within the province. Such correlation between caldera environment and ore deposits strongly suggests that the IPB developed in a continental arc. Our geodynamic model proposes an early north directed subduction associated with the obduction of the oceanic crust toward the south. Southward, this episode is immediately followed by the development of the accretionary prism, while farther south, a second subduction zone responsible for the arc setting of the IPB initiates. Subsequent Visean continental collision is associated with the deposit of the south propagating flysch and the present geometry of the SPZ.

Recognizing metasedimentary sequences potentially hosting concealed massive sulfide accumulations in the Iberian Pyrite Belt using geochemical fingerprints

Felsic volcanic rocks exposed in the Frasnian Gafo Formation, in the Azinhalinho area of Portugal, display very similar geochemical signatures to volcanic rocks from the Iberian Pyrite Belt (IPB). located immediately to the south. The similarities include anomalously low high field-strength elements (HFSE) concentrations, possibly caused by low-temperature crustal melting, which translate into classification problems.A geochronological study, using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) analyses of zircon grains from these rocks, has provided concordia ages of 356±1.5 Ma and 355±2.5 Ma for two samples of rhyodacite porphyry, and 356±1.4 Ma for a granular rhyodacite. These results show that volcanism at Azinhalinho was broadly contemporaneous with IPB volcanism, widely interpreted as being of Famennian to Visean age. Considering that the host rocks of the Azinhalinho volcanic rocks are Frasnian, and therefore deposited synchronously with the Upper Devonian Phyllite-Quartzite Group sedimentation in the IPB basin, the radiometric ages imply that the Azinhalinho felsic rocks are intrusive and likely represent conduits or feeders to the volcanism of the IPB.

<p>A regional South Portuguese Zone (SPZ) mapping and stratigraphic program in SW Iberia is presented. It is being developed by LNEG and IGME and financed by the GEO_FPI Project (www.geo-fpi.eu).</p><p>The SPZ is the southwesternmost geotectonic unit of the Variscan Orogeny in Iberia. The following domains are considered: Pulo do Lobo (early Frasnian -late Famennian); Iberian Pyrite Belt (IPB, late Famennian-late Visean), Baixo Alentejo Flysch Group (late Visean-late Moscovian) and Southwest Portugal (late Strunian-mid Bashkirian). The mapping program also includes the Mesozoic sequences of the Lusitanian, Santiago do Cacém, and Algarve basins and the Cenozoic Lower Tagus, Alvalade and Guadalquivir/Algarve basins. Proper research was conducted in the IPB, considered one of the most important metallogenetic VHMS deposit provinces worldwide with significant Cu, Zn, Pb, Ag, Au, Sn, In, Se and Ge resources. Currently, mining is being undertaken both in Portugal (Aljustrel, Neves-Corvo) and Spain (Las Cruces, Aguas Teñidas, La Magdalena, Sotiel, Riotinto). Field surveys were done using common stratigraphic and GIS database methodologies, developed in cooperation involving the Portuguese and Spanish Geological Surveys. A joint fieldwork was carried out in the border region (Guadiana and Chança river sections), allowing a better integration and correlation of geological data. Palynological studies performed at LNEG allowed dating of 113 Palaeozoic sediment samples in outcrop and drill hole sections. The same approach was used for U/Pb zircon geochronology using 31 samples of plutonic and volcanic rocks. Rock dating results obtained are important to constrain the geological structures of the IPB Volcano-Sedimentary Complex (VSC) that host the massive sulphide and stockwork mineralization. Key ore horizons, important to identify, are dated late Famennian (late Strunian) age in felsic volcanic and in sedimentary sequences and Tournaisian age felsic volcanic sequences. For upper VSC, zircon ages ca. 340–330 Ma were reported for the first time, suggesting new geodynamic interpretations. The main project outputs are the first 1/200.000 scale cross border and the 1/400.000 scale SPZ Geological Maps. The latter covers SW Iberia from Lisbon to Seville along 330 km. This scale was also considered in the following thematic maps developed by LNEG, IGME and JA: mineral occurrences, mining, and geological heritage. Another project activity was the development of a drill hole database and equipment acquisition for the Aljustrel (LNEG) and Peñarroya (IGME) drill core sheds. LNEG and Aljustrel Municipality also promoted mining and geological studies in the Algares (Aljustrel) mine sector on gossan, underground gallery mapping and mineral characterization. GEO_FPI Project has improved the geological knowledge of the cross border region and promoted IPB as a key mining region in Europe. Therefore, since 2010, exploration campaigns led to the discovery of the Semblana, Monte Branco, La Magdalena, Sesmarias, Lagoa Salgada Central and Elvira deposits. Regional surveys carried out to promote a common approach to SW Iberia and improve new business initiatives focused on mineral resources and territory management. These activities could predict a larger mapping program to be developed in central and northern sectors of the Portuguese-Spanish border. Acknowledgement: EU/Interreg-VA/Poctep/0052_GEO_FPI_5_E Project/ funded by European Regional Development Fund/ERDF.</p>

The lithostratigraphic sequence in the Rosário–Neves Corvo antiform comprises the Phyllite–Quartzite Group, whose top is of Famennian age, the Volcanic Sedimentary Complex, of Strunian to upper Visean age, and the Mértola Formation (the lower unit of the Baixo Alentejo Flysch Group) of upper Visean age. The volcanic sedimentary complex comprises a lower sequence of Strunian (Late Famennian) age and an upper sequence of lower to upper Visean age. Detailed mapping of the antiform towards NW of the Neves Corvo mine, supported by palynological dating, identified two new lithostratigraphic units: the Barrancão member (upper Famennian) ascribed to the Phyllite–Quartzite Group and made up of laminated dark shales with siliceous lenses and nodules, and the Ribeira de Cobres Formation of the Volcanic Sedimentary Complex, containing shales, siltstones and fine volcaniclastic rocks. Based on zircon U–Pb isotope dating, five discrete felsic magmatic events were identified at approximately 354, 359, 365, 373 and 384 Ma. This suggests that the volcanic activity in the area has extended for about 30 Ma, in a context of high regional heat flow as indicated by the geochemical signatures of the felsic volcanic rocks. The characteristics of magmatism and the depositional environment indicated by the sedimentary record should therefore have been highly favourable for massive sulphide formation. However, evidence of massive sulphide mineralization in the study area is still to be found. Moreover, reconstruction of the volcanic facies architecture demonstrated that the volcanic units in the Rosário area are strongly dominated by coherent facies typical of the inner part of thick lavas/domes. In fact, most of their external part, the more favourable location for possible massive sulphide mineralization, is missing. Palynological dating indicates a significant hiatus, recognised between the lower and upper sequences of the volcanic sedimentary complex, which implies erosion of the top of the volcanic centre, where VHMS deposits could possibly have formed. However, lateral areas of this volcanic centre, eventually preserved at depth, have good potential to host massive sulphide mineralization.

The Iberian Pyrite Belt (IPB), which is located in the South Portuguese Zone (SPZ) of the Iberian Massif, is one of the most prominent sections of the Variscan orogenic belt in Western Europe. It extends over about 250 km in length and a width of 60 km forming an arc-shaped belt comprising several series of asymmetric basins that are tectonically controlled. These basins reflect the process of heterogeneous continental thinning triggered by left-lateral transpressive convergence with the Iberian Terrane.Economically, it is an important European mining region with over 90 massive sulphides deposits shared between Portugal and Spain. It is home to world-famous and huge deposits such as Neves-Corvo, Aljustrel, Rio Tinto, Tharsis, Aznalcollar-Los Frailes, Las Cruces, among others. These mining activities show the economic dimension of the province based on the resources of Cu, Zn, Pb, Ag, Au, and Sn. The deposition of massive sulphides was related to the felsic volcanism and the black shales of the IPB volcano-sedimentary complex (VSC), which overlies the siliclastic sediments of the phyllite-quartzite group.Nevertheless, many aspects are still poorly understood, especially those related to the deep lithospheric structure and the extent of the IPB to the southwest. The growing interest in the search for mineral deposits has led to many geophysical surveys being carried out over the years. However, most of them are limited to the first hundred meters in local areas or have a low spatial resolution, so a complete and global picture of the IPB extent isn't possible.We present the preliminary results of a 3D resistivity model focusing on the lithospheric structure of the IPB down to a depth of 40 km. The model was calculated using data from 60 broadband Magnetotelluric (BBMT) stations, combining previous and newly acquired data, arranged in a 10x10 km grid along the IPB in Portuguese Terrain. The BBMT method provides a comprehensive resistivity image of the lithosphere, which is essential to decipher the geometry of the tectonic structures at depth. These structures play a key role in controlling the spatial distribution of many massive sulphide ore systems and offer potential insights into identifying new areas with deposits suitable for exploitation. AcknowledgmentThis work is supported by the Portuguese Fundação para a Ciência e Tecnologia, FCT, I.P./MCTES through national funds (PIDDAC): UID/50019/2025 and LA/P/0068/2020 https://doi.org/10.54499/LA/P/0068/2020).ReferencesVozoff, K. (1991). The magnetotelluric method: Electromagnetic methods. In M. N. Nabighian (Ed.), Applied Geophysics (pp. 641–712).Kelbert, A., Meqbel, N., Egbert, G. D., & Tandon, K. (2014). ModEM: A modular system for inversion of electromagnetic geophysical data. Computers & Geosciences, 66, 40–53. https://doi.org/10.1016/j.cageo.2014.01.010.Miensopust, M. P. (2017). Application of 3-D electromagnetic inversion in practice: Challenges, pitfalls and solution approaches. Surveys in Geophysics, 38(5), 869–933. https://doi.org/10.1007/s10712-017-9435-1.Matos, J.X. et.al - Geophysical surveys in the Portuguese sector of the Iberian Pyrite Belt: a global overview focused on the massive sulphide exploration and geologic interpretation. In: Comunicações Geológica (2020), vol.107, Fasc. Especial III, p. 41-78.de Oliveira, Daniel et.al - Mineral sustainability of the Portuguese sector of the Iberian Pyrite Belt. In: Comunicações Geológica (2020) vol.107, Fasc. Especial III, p. 11-20.