This study combines structural mapping, petrographic analysis, and U-Pb zircon geochronology of low-grade metamorphic rocks from the Iberian Pyrite Belt (IPB), located in the westernmost domains of the South Portuguese Zone (SPZ). At Ilha do Pessegueiro beach, the Cercal volcanic-sedimentary complex (VSC) rocks, assigned to the Late Devonian in previous studies, exhibit a dominant S 1 slaty cleavage overprinted by S 2 crenulation cleavage. This ductile deformation has been attributed to contractional tectonics. However, new structural data indicate that older ductile structures formed in relation to a low-grade extensional shear zone (D 1 -E) and were tectonically transported to the east-southeast. The new age of the Cercal VSC felsic metatuffs (ca. 364-363 Ma) is consistent with VSC ages from other areas of the IPB, enabling us to bracket the D 1 -E deformation event between the Tournaisian and the Bashkirian. After the D 1 syn-convergent extension, a subsequent contractional deformation event (D 2 -C), resulting from the latest events of the Gondwana-Laurussia oblique convergence, caused inversion of the Carboniferous synorogenic basins and the formation of a thrust-and-fold belt. Recent data for the late Devonian-early Carboniferous geology of the IPB appear to support a correlation between the SPZ and the Meguma terrane.

The increasing production of biodiesel has led to a surplus of glycerol, a polluting by-product in need of valorization. In this study, we demonstrate that Citrobacter telavivensis T1.2D-1, an extremophile bacterium isolated from the Iberian Pyrite Belt, effectively converts glycerol into valuable compounds via dark anaerobic fermentation. Genomic and bioinformatic analyses confirmed the presence of the dha and pdu operons, responsible for 1,3-propanediol (1,3-PDO) synthesis, and the hyc operon and fdhF gene involved in hydrogen (H2) production. Batch fermentations revealed that optimal yields of both H2 (0.94mol.mol-glycerol-1) and 1,3-PDO (0.66mol‧mol-glycerol-1) were achieved at 25°C using 2gL-1 of supplied glycerol. Optimum yield of ethanol (1mol‧mol-glycerol-1) was achieved using 12.5gL-1 of supplied glycerol. Interestingly, 1,3-PDO and H2 production inversely correlated with ethanol formation, suggesting metabolic competition. Antibiotic sensitivity profiling revealed susceptibility to multiple antibiotics, supporting future genetic engineering efforts. We suggest opperating with reactors at low concentrations to produce 1,3-PDO and H2 with high yields, and at medium concentrations to generate ethanol. Our findings support C. telavivensis T1.2D-1 as a promising venue for the sustainable biotechnological production of biohydrogen and bio-based 1,3-PDO from glycerol, offering a dual solution to both energy demands and industrial waste management.

Nitrate reduction and iron (II) oxidation by subsurface bacteria from the Iberian Pyritic Belt: Insights into the biogeochemical cycles in this environment.

Accumulation of harmful metal(loid)s in acidic pit lakes (APLs) is a serious environmental issue in mining districts. This lab-based study evaluated a novel method to stimulate dissimilatory sulfate reduction to promote the formation of sparingly soluble metal(loid)-sulfide minerals in the permanently stratified deep layer of Cueva de la Mora (CM), an APL in the Iberian Pyrite Belt in Spain. Solid-phase biomass was selected because it can be pressed into high-density forms that are dense enough to settle into the deep layer of a lake. This "direct delivery" of electron donor overcomes the current "indirect method" to stimulate algae growth in the upper layer and wait for algae to die and settle into the deep layer. We added the microalgae Coccomyxa onubensis (predominant in CM), Euglena gracilis (another acid-tolerant microalgae), and Lemna obscura (duckweed), as well as model biocomponents (amino acids, monosaccharides, and lipids) as substrates to stimulate biological sulfide production (biosulfidogenesis). We found that compared with biocomponents, high-density biomass required a shorter lag time before it was utilized. Temporal patterns of the production of sulfide and volatile fatty acids with high-density biomass were similar to patterns with amino acids, suggesting that amino acids may be the preferred substrate among the biocomponent monomers for the microbial community. Biosulfidogenesis led to the complete removal of metal(loid)s (Zn and As) contaminants from solution, mimicking the chemical composition of the deep layer. Desulfosporosinus, the only acid-tolerant sulfate-reducing bacteria (SRB) identified in situ, was significantly enriched in the laboratory setup and presumably responsible for biosulfidogenesis.IMPORTANCERemediation of high concentrations of harmful metal(loid)s in acidic pit lakes is challenging. This research presents a novel strategy by supplying high-density biomass as a carbon source and electron donor to stimulate biological dissimilatory sulfate reduction in acidic pit lakes in the Iberian Pyrite Belt. The formation of biogenic sulfide precipitates dissolved metal(loid)s in the acidic pit lakes. This approach is feasible in meromictic acidic pit lakes, where precipitated metal(loid)s would remain sequestered in bottom sediments. However, the deep layer of acidic pit lakes is often oligotrophic with respect to organic carbon. Pelletized high-density biomass can be added to the top layer of the lake and transported to the deep layer. This strategy offers practical and adaptable guidance for the bioremediation of persistent metal(loid) contamination in acidic pit lakes.

Waste deposits from the Iberian Pyrite Belt that are rich in pyrite are a valuable secondary resource for getting back sulphide minerals and important metals that go with them. This study assessed the efficacy of a Multi-Gravity Separator (MGS) in concentrating pyrite and related polymetallic minerals from sulphide waste material sourced from the Alonso mining district (Huelva, Spain). Bench-scale MGS tests were done on two particle size fractions (−500 µm and −50 µm) to see how the speed of the drum rotation, the angle of the tilt, and the flow rate of the wash water affected the separation efficiency. Mineral Liberation Analysis (MLA) showed that both size fractions had about 65.8 wt% pyrite, but the −50 µm fraction was much more liberated. Under the best operating conditions, the MGS was able to recover about 58% of the pyrite from the −500 µm fraction and about 64% from the −50 µm fraction. The mass recoveries were about 38% and 42%, respectively. There was also a better recovery of related metals like Co, Cu, Zn, and Mn, especially for the finer fraction. This shows the improvement of the liberation and stratification behaviour. The results show that MGS is a good way to pre-concentrate fine-grained pyrite-rich waste. The performance is heavily influenced by the size distribution of the particles and the operating parameters. These results suggest that improvements in gravity separation may offer a long-term pathway for the recycling of sulphide mine waste within a circular economy.

Procambarus clarkii represents an invasive species of crayfish common in the rivers of the Iberian Peninsula, which replaced a previous invasive species of crayfish (Austropotamobius pallipes) and is now being replaced by a new invasive species (Pacifastacus leniusculus) in northern rivers. Leaving aside the ecological problems that these invasive species can cause, these organisms can be excellent candidates to act as environmental indicators in pollution processes that involves the interface water-sediment. In this work, the potential role of Procambarus clarkii as a bioindicator of pollution processes of mining origin is evaluated. Unlike previous research, which often focuses on snapshot assessments of contamination levels, our approach integrates historical data and continuous monitoring to provide a dynamic perspective on the impact of Hg and other metals on biotic and abiotic media over an extended period. A total of 330 crayfish were collected from 10 sites in Valdeazogues river, grouped by size, and analyzed for Hg, Pb, Cd, Cu, Zn, As, and Sb in abdominal muscle and hepatopancreas, with a complete characterization of sediment and water media. Crayfish data have shown that hepatopancreas and muscle present the highest average content of Zn (1,325 and 377mgkg-1, respectively) and Cu (1,297 and 179mgkg-1 respectively). Levels of Hg were higher in muscle (1.6mgkg-1) than hepatopancreas (1.0mgkg-1), with all muscle samples exceeding the EU maximum permissible level of 0.5mgkg-1 for food. The sensitivity of P. clarkii has been sufficient to identify different sources of Hg, Pb and Zn contamination in the drainage system, and even agricultural sources of Cd downstream of the mining district. This versatile capability can be of application to large mining areas in the south of the Iberian Peninsula, especially throughout the Iberian Pyrite Belt.

Abandoned mine waste is both a significant environmental liability and a potential secondary source of critical raw materials (CRMs). This study provides an integrated geochemical and mineralogical assessment of two contrasting waste deposits from the Trimpancho mining complex (Iberian Pyrite Belt, SW Europe). Bulk chemical analyses, XRD and TEM/SEM-EDX mineralogy, and sequential extraction were combined with UAV-derived volumetric estimates to evaluate contaminant mobility and CRM recovery potential. The sulfide-rich Nuestra Señora del Carmen (NSC) dump, integrating the Trimpancho mining complex, is dominated by Fe and S, with marked chemical heterogeneity and high concentrations of As, Cu, Pb, and Zn. Mineralogical analyses revealed abundant sulfide alteration products (jarosite and goethite) and clay minerals, which influence potential contaminant retention and mobilization. Sequential extraction results showed high potential mobility for Mn, Zn, Cu, and, locally, As and Pb, translating into mobilizable loads in the order of 104t. In contrast, the Volta Falsa (VF) dump, composed mainly of roasted pyrite slag and Fe oxides, displayed lower S contents, greater homogeneity, and negligible mobilizable contaminant loads, consistent with its more stable mineral assemblage. From a resource perspective, only NSC exhibits significant CRM potential, primarily for Cu (∼175-246t), with minor contributions from Co, Sb, and LREEs. VF, despite locally elevated Cu concentrations, is constrained by its limited volume. These findings highlight the dual significance of mine waste as both environmental hazards and potential secondary mineral resources. Integrated strategies that couple risk mitigation with selective CRM recovery represent a promising pathway for sustainable management of mining legacies and align with international efforts toward circular resource use.

Dispersed alkaline substrate passive treatment technology for highly contaminated acid mine drainage: 20 years of successful application.

Abstract The Lousal Mine (Iberian Pyrite Belt, Portugal) was operated from 1900 to 1988 for the extraction of massive sulphides and was later rehabilitated as a science museum. It was selected as a test site for underground muon tomography applied to geophysical surveys, as part of the LouMu project. This study focuses on seismic tomography to analyse the subsurface above the mine gallery, primarily surveyed by a muography telescope, which was developed specifically for this site by the Laboratory of Instrumentation and Experimental Particle Physics. To validate the muon tomography results, an initial approach using conventional 2D seismic refraction failed to reach the Waldemar gallery depth, due to limited seismic ray coverage. Therefore, an innovative setup using surface shots and in-gallery geophones was implemented, providing full ray coverage. A 3D velocity model was then produced using the ATOM3D code, which enabled the integration of this configuration and performed travel-time inversion for velocity calculation. A regional dextral strike-slip fault, the Corona Fault (CF), crosses the surveyed area, and served as the main focus of this investigation. The 3D velocity model successfully detected this structure, that corresponded to the boundary between positive anomalies of the Volcano-Sedimentary Complex (VSC) and negative anomalies of the Phyllite-Quartzite Group (PQG). The absolute velocity distribution showed a distinct offset around the Corona Fault (CF), indicating a dextral strike-slip mechanism. A subvertical extension of secondary faults was observed, reflecting deformation similar to that of the main tectonic context. Previous data from the gallery confirmed that these results are consistent with the known geology and can serve as a reference for the muon tomography interpretations.

Abstract The long-term environmental legacy of mining in sulfide-rich regions remains a critical concern due to the persistent generation of acid mine drainage (AMD) and the mobilization of potentially toxic elements (PTEs). This study presents a comprehensive, site-specific assessment of mine waste from two contrasting geochemical zones, Nuestra Señora del Carmen (NSC) and Volta Falsa (VF), within the historically under-characterized Trimpancho Mining Complex, located in the Iberian Pyrite Belt (IPB). A multidisciplinary approach combining mineralogical characterization, physicochemical and geochemical analyses, multivariate statistics, and contamination indices, provided insights into the behavior, mobility, and ecological risk of key PTEs such as Cu, As, and Zn. The NSC zone is dominated by pyrite and secondary sulfates, promoting acidic conditions (pH values ranging from 2.42 to 3.60) and high Cu mobility, whereas VF waste materials show a more heterogeneous mineralogy, higher pH (ranging from 2.77 to 5.05), and broader PTE enrichment. Principal Component Analysis revealed distinct geochemical regimes shaped by the presence of sulfides or silicates. Contamination indices underscored significant ecological risk in both zones, but with distinct pollution signatures. This integrated framework supports site-specific environmental risk management and remediation strategies and applies to other AMD-impacted volcanogenic massive sulfide (VMS) mining environments facing renewed exploration pressures.

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.

Inventory of the mining wastes located at the Iberian Pyrite Belt (IPB)

This study represents an exploration of the geochemistry of sulphide minerals from prominent shale-hosted volcanogenic massive sulphide deposits of the Iberian Pyrite Belt, including Sotiel-Migollas, Tharsis, Neves Corvo and Lousal using the non-traditional heavy stable isotopes of Fe and Cu along with the S light isotope. Sampling encompassed a diverse range of styles of mineralization, including the dominant fine-grained massive sulphides sometimes exhibiting sedimentary layering, carbonate-rich mounds dominated by sulphides-siderite and formed by the superposition of microbial mats in anoxic bottoms, underlying subseafloor feeder structures (stockworks) and disseminated pyrite within the altered host shales. The δ 56 Fe IRMM-014 values of pyrite exhibit a range from −2.62 to +2.58 ‰, while those of pyrrhotite range from −1.93 to −0.40 ‰. Chalcopyrite δ 65 Cu SRM-976 signature varies between −1.11 and + 0.95 ‰, while the measured δ 34 S V-CDT values fluctuate from −45.0 to +9.4 ‰ in pyrite, −6.8 to +2.1 ‰ in pyrrhotite, and − 10.1 to +6.2 ‰ in chalcopyrite. Notably, pyrite grains within massive sulphides consistently exhibit more negative and variable δ 56 Fe and δ 34 S values than those in the hydrothermally altered host shales (apart from Neves Corvo) and stockworks. These findings strongly imply that the exhalative mineralization incorporated substantial amounts of iron derived from the dissimilatory reduction of aqueous Fe +3 , attributable to low-temperature (<100–120 °C) microbial reduction and contemporaneous with biogenic sulphate reduction. Consequently, Fe in pyrite is likely inherited from both the reduced hydrothermal fluids venting on the seafloor and the microbial reduction of oxidized iron dissolved in ambient seawater. While the microbial influence on Cu isotope signatures is less evident, we infer its potential significance. Superimposed hydrothermal refining during the late percolation of hot hydrothermal fluids reveals a non-biogenic kinetic fractionation, with partial overprinting of the early mineralization and neoformation of sulphides depicting isotopically heavy δ 56 Fe, δ 65 Cu, and δ 34 S signatures that are interpreted as of deep derivation. • Fe, Cu and S stable isotopes applied to giant Iberian Pyrite Belt (IPB). • Detailed study of isotopic compositions of different minerals and pyrite textures. • Fe in pyrite from the IPB is inherited from hydrothermal fluids and microbial reduced iron. • Superimposed hydrothermal refining partially overprints δ 56 Fe, δ 65 Cu, and δ 34 S signatures.

Accurate estimation of water acidity is essential for characterizing acid mine drainage (AMD) and designing effective remediation strategies. However, conventional approaches, including titration and empirical estimation methods based on iron speciation, often fail to account for site-specific geochemical complexity. This study introduces a high-accuracy, site-specific empirical model for predicting acidity in AMD-impacted waters, developed from field data collected at the Trimpancho mining complex in the Iberian Pyrite Belt (Spain). Using multiple linear regression (MLR), a robust predictive relationship was established based on Cu, Al, Mn, Zn, and pH, achieving a coefficient of determination (R²) of 99.2%. The model significantly outperforms the standard Hedin method, with a lower mean absolute percentage error (13% vs. 29%). Results also reveal strong spatial and seasonal hydrochemical variability, underscoring the limitations of generalized acidity models in such environments. This work demonstrates the applicability of site-calibrated multivariate models as practical tools for enhancing acidity prediction in complex AMD systems.

Radiological assessment of wastes from copper mining in Iberian Pyrite Belt

Estuaries are excellent containers for the prehistorical and historical pollution that develops in their river basins. This paper studies the Au contents obtained by inductively coupled plasma spectrometry of two cores extracted from the Doñana National Park (Guadalquivir Estuary, SW Spain). Concentrations of this precious metal have been associated with the different prehistoric and historical stages of exploitation of the Iberian Pyritic Belt. The three detected peaks correspond to the first mining operations in the area around the park, the first systematic Tartessian mining and strong exploitation during the Roman period. Consequently, Au is an appropriate marker of the contamination phases prior to its current extraordinary biological diversity.

Acid mine drainage, a consequence of exposure of sulfide mining waste to weathering processes, results in significant water, sediment, and soil contamination. This contamination results in acidophilic ecosystems, with low pH values and elevated concentrations of sulfate and potentially toxic elements. The São Domingos mine, an abandoned site in the Iberian Pyrite Belt, lacks remediation measures and has numerous waste dumps, which are a major source of contamination to local water systems. Therefore, this study examines sediment accumulation in five mine dams along the São Domingos stream that traverses the entire mine complex. Decades of sediment and waste transport since mine closure have resulted in dam-clogging processes. The geochemical, mineralogical, and magnetic properties of the sediments were analyzed to evaluate the mineralogical controls on the mobilization of potentially toxic elements. The sediments are dominated by iron oxides, oxyhydroxides, and hydroxysulfates, with jarosite playing a key role in binding high concentrations of iron and toxic elements. However, no considerable correlation was found between potentially toxic elements and magnetic parameters, highlighting the complex behavior of these contaminants in acid mine drainage-affected systems.

To address energy challenges linked to decarbonization, geosciences are focusing more on advancing mineral resource exploration and exploitation. This study uses the Iberian Pyrite Belt, one of the world's largest metallogenic provinces, as a test site to: (a) develop predictive models of physical properties of rock (PPR) and (b) classify lithological units based on these PPR. Over 1,000 surface rock samples and six boreholes from the Riotinto mine were analyzed, providing a comprehensive dataset. A robust quality control process, aided by Machine Learning models (ML), refined the PPR data, ensuring accuracy and reliability. Both traditional statistical models and cuttingedge ML models were used for PPR prediction and lithofacies classification. Our study revealed that geological evolution can lead to significant overlaps in PPR across different lithologies, making traditional models insufficient for accurate predictions. However, ML models, such as Random Forest, XGBoost, k-Nearest Neighbors, and Support Vector Regression, demonstrated over 80% accuracy in predicting PPR and classifying lithofacies. This approach redefines how lithofacies are identified and establishes an innovative methodology for subsurface lithological characterization. Results highlight the potential of ML models in mining and geology, paving the way for more accurate 3D characterization of lithological units through integrating geophysical data and direct measurements.

Preliminary study of the suitability of an abandoned mining area for harvesting efflorescent sulfate salts in the Iberian pyrite Belt, Nerva (Spain)

The Iberian Pyrite Belt (IPB) contains the world’s largest massive sulfide deposit, and, due to extensive mining developed during the last 200 years, large amounts of mining waste have been abandoned in this area, with roasted pyrite ash being the focus of this study. Polymetallic mining is also classified as a NORM (naturally occurring radioactive material) activity, thus the main objective of this work was to develop a radiological and physicochemical characterization of this waste (mineral phases, elemental and radionuclide concentrations) in order to perform a valorization diagnosis of this material. The composition of this waste strongly depends on its origin (mine), and is mainly formed by iron oxides (hematite, Fe₂O₃) and heavy metals and metalloids such as As, Pb, Zn, and Cu, in levels 2–4 orders of magnitude higher than those of undisturbed soils, depending on each particular element. However, the average natural radionuclide levels are similar to those of unperturbed soils (around 30 Bqkg−1 of 238U-series, 50 Bqkg−1 of 232Th, and 70 Bqkg−1 for 40K), thus they are below the limits established by European Union regulations to require radiological control during their future valorization. As the main potential applications of roasted pyrite ash, the valorization diagnosis indicates that it can be used as a source of Fe (FeCl₃ or FeSO₄), or an additive in the manufacturing of cements, pigments, etc.