The Iberian Pyrite Belt (IPB), in the southwestern Iberian Peninsula, is a large metallogenic province exploited since ancient times. As a result of historical and current mining activity, a vast volume of metallic mineral waste, mainly derived from the processing of pyrite, is still in situ and polluting the environment. A specific mine waste residuum locally known in the area as “morrongos”, which was produced during pyrite roasting mainly in the 19th century, is evaluated here in order to unravel untapped resources of high-tech metals commonly used in high-tech devices. Applying a combination of whole-rock geochemical (ICP-AES, ICPMS, FA-AAS) and single-grain mineralogical techniques (EPMA, LA-ICP-MS, FESEM, and FIB-HRTEM) on the “morrongos”, we unhide the still-present remarkable concentrations of Au, Ag, Pb, Zn, and Cu in them. The mineralogical expressions for these economic metals include oxides (hematite, magnetite, and hercynite), arsenates, sulfates of the jarosite group, native metals, and, to a lesser extent, relictic sulfides. This first-ever estimation of these economic metals in this type of residue allows their revalorization, highlighting them as suitable sources for the exploitation and recovery of metals necessary for the clean energy transition.

The Iberian Pyrite Belt (IPB) represents one of the largest districts of volcanogenic massive sulfide (VMS) deposits in the world, and is a critical source of base metals (Cu, Pb, and Zn) for Europe. Confirmed resources exceed 1700 Mt of massive sulfides with grades of around 1.2% Cu, 1% Pb, and 3% Zn as well as more than 300 Mt of stockwork-type copper mineralization. Significant resources of Sn, precious metals (Au and Ag), and critical metals (Co, Bi, Sb, In, and Se) have also been evaluated. The genesis of these deposits is related to a complex geological evolution during the late Devonian and Mississippian periods. The geological record of such evolution is represented by three main lithological units: Phyllite–Quartzite Group, the volcano–sedimentary Complex (VSC), and the so-called Culm Group. The sulfide deposits are located in the VSC, associated with felsic volcanic rocks or sedimentary rocks such as black shales. The massive sulfide deposits occur as tabular bodies and replacement masses associated with both volcanic and sedimentary rocks. Their mineralogical composition is relatively simple, dominated by pyrite, chalcopyrite, sphalerite, and galena. Their origin is related to three evolutionary stages at increasing temperatures, and a subsequent stage associated with the Variscan deformation. The present paper summarizes the latest developments in the IPB and revises research areas requiring further investigation.

Magnetite is a widespread ore mineral in skarn systems and usually hosts a wide variety of inclusions. Micro- to nano-sized solid inclusions in magnetite are unique tools to track the evolutionary processes of its host mineral and, subsequently, to constrain the timing of the mineralization event. In this study, we characterize micro- to nano-sized solid inclusions in magnetite from the La Víbora magnesian skarn (Málaga, Spain) using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). TEM energy-dispersive X-ray spectrometry (EDS) analyses and compositional mapping expose two types of nano-inclusions oriented along the (111) of magnetite: type 1 includes dolomite, spinel, and Mg–Fe–Al silicate, and type 2 is made up of Mg–Fe–Al silicates enveloping the Mg-bearing amorphous silica phase. High-resolution transmission electron microscopy (HRTEM), selected-area electron diffraction (SAED), and fast Fourier transform (FFT) patterns reveal that the majority of the solid inclusions display non-oriented matrices compared to the host magnetite, precluding the possibility of sub-solidus processes. Instead, these inclusions are thought to preserve skarn mineral assemblages that were entrapped during the growth of magnetite. However, the local supersaturation of fluids trapped in the boundary layer of crystallizing magnetite is evidenced by coherent lattice orientation of precipitated and host magnetite and by the occurrence of an Mg-bearing amorphous silica phase. Our findings reveal that skarn reactions observed at field and microscopic scales are also recorded in nano-sized inclusions within magnetite. These observations underscore the significance of micro- to nano-scale solid inclusions in magnetite to decipher overprinted skarn reactions as well as constraining the timing of Fe mineralization events in skarns.

The Triassic sedimentary rocks of the external zone of the Betic Cordillera in southern Spain host abundant igneous basic rocks (“ophites”) metamorphosed in the greenschist facies. Investigation based on high-resolution transmission electron microscopy (HRTEM) reveals magmatic sulfides intimately intergrown with primary silicates (pyroxene, plagioclase and olivine), consisting of pyrrhotite (FeS to Fe₇S₈; monoclinic C2/c polytype 4C) and pentlandite ((FeNi)₉S₈; cubic Fm3m), bounded by tetragonal I$\stackrel{\mathrm{‾}}{\mathrm{4}}$ 2d chalcopyrite (CuFeS₂). Whole-rock and clinopyroxene geochemical data suggest that Fe–Ni–Cu sulfides crystallized from melt droplets segregated by immiscibility from transitional-alkaline magmas, after their fractional crystallization and volatile oversaturation within crustal conduits developed during intraplate rifting. In contrast, hydrothermal sulfides are pyrite (FeS₂) and/or chalcopyrite associated with secondary silicates (chlorite, epidote, saussurite, prehnite, sericite and quartz). Porous pyrite (cubic Pa3) hosts nanodomains of pyrrhotite (monoclinic C2/c polytype 4C and orthorhombic Cmca polytype 11C) and orthorhombic Pnnm marcasite (FeS₂), evidencing disulfide formation via coupled Fe loss and S addition in pyrrhotite due to reaction with high-fS₂ and high-fO₂ fluids at < 300 °C. Tetragonal I$\stackrel{\mathrm{‾}}{\mathrm{4}}$ 2d chalcopyrite replacing pyrite also preserves nanodomains of pyrrhotite as well as of pyrite $/$ marcasite, suggesting reaction of pre-existing Fe sulfides with Cu transported by low-temperature (∼ 200–100 °C) acidic-to-neutral fluids. Additionally, inclusions of sphalerite (ZnS), galena (PbS) and vaesite (NiS₂) in pyrite and chalcopyrite spotlight metal remobilization during hydrothermal alteration, which is further confirmed by the crystallization of cobaltite coronas (CoAsS) around pyrite. Our new results contribute to the current debate of the full sequence of processes operating in ore-forming mafic systems.

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.

The Ronda ultramafic massif constitutes the Earth’s largest outcrop of peridotites (~ 300 km2) of the subcontinental lithospheric mantle (SCLM). This massif is located in the westernmost part of the Málaga province in SW Spain, and mainly consists of peridotites (lherzolites and harzburgites with lesser amounts of dunites) and mafic pyroxenite layers (usually <10 %). These rocks are arranged in a petrologic and geochemical zoning consisting, from the top to the bottom of the mantle section, of the following domains: (1) spinel (±garnet) tectonite corresponding to the exhumed SCLM roots, (2) granular peridotite formed by thermal erosion of pre-existing spinel (±garnet) tectonite due to upwelling of the asthenosphere during unroofing, and (3) plagioclase tectonite corresponding to shear zones originated shortly before or contemporaneously to the crustal emplacement. The rocks forming these three domains exhibit contrasting degrees of fertility in a wide suite of elements, offering an unequal opportunity to evaluate the impact that different bedrocks have for the distribution of High-Tech Critical Metals in soils.We performed bulk-rock analyses of around 70 samples from 10 soil profiles above peridotites from the three aforementioned petrological domains. Regardless of the original bedrock, all the analyzed soils show a common trend of progressive enrichment of Fe2O3 and Al2O3 and depletion of MgO from bedrock to the atop of the profile. Minor elements such as MnO, TiO2, Na2O and K2O overall increase from bottom to top, whereas SiO2 remains generally unchanged. Interestingly, there is positive correlations between Fe2O3 and MnO as well as other transition metals such as Cr (up to ~9000 pm),  Co (up to 310 ppm), V (up to 181 ppm), Zn (up to 136 ppm) and Sc (up to 38 ppm). A general increasing of total REE (up to ~20 ppm) is also observed in most profiles with a significant enrichment of LREE over HREE.