Search

Neves Corvo is an underground high-grade Cu–(Sn)–Zn mine, located in the Portuguese part of the world-class Iberian Pyrite Belt (IPB), which is currently producing copper, zinc, and lead concentrates. The operation is owned by SOMINCOR, a subsidiary of Lundin Mining, with a maximum capacity of 2.6 Mtpy for the copper processing plant and 1.0 Mtpy for the zinc processing plant. From 2010 till end of 2019, the mine has accumulated 7.3 Mt of waste rock and 17 Mt of thickened tailings. These mining residues are stored in Cerro do Lobo Tailings Management Facility (Cerro do Lobo TMF), which completes a volume of 47 Mt since the beginning of the operation in 1989 (30 Mt are slurry tailings). The deposition method changed in 2010 from slurry subaquatic deposition to sub-aerial thickened tailings stack (vertical expansion) in co-deposition with potentially acid-generating (PAG) waste rock. X-ray fluorescence analysis have shown copper and zinc grades variation in the waste rock between 0.12 and 0.4%, and 0.1% and 0.3%, respectively, and concentrations up to 0.6% and 1.3% of copper and zinc, respectively, in the tailings. Mineralogically, the tailings consist mainly in pyrite, sphalerite, chalcopyrite, ± arsenopyrite, ± tetrahedrite-tennantite, and gangue minerals such as quartz, phyllosilicates, carbonates, and some oxides, and have a non-uniform particle size distribution ranging between 1 and 100 µm. The waste rock fraction is millimetric to centimetric in size and is formed by the local host rocks, mineralogically consisting in quartz, chlorite (clinochlore and chamosite), calcite, and variably abundant disseminated sulfides, largely dominated by pyrite. Both mining residues might be envisaged as materials with valorization potential both for base metal recovery (tailings) and/or as non-metallic raw materials for construction or other applications (waste rock).

Recent studies on historic mine waste (e.g. tailings, waste rock, metallurgical waste) indicate the recycling potential of the material for metal extraction. Historic mine wastes have been shown to be of more interest than modern mine wastes, due to the lower efficiency of ore processing in the past. Although the knowledge of processing has significantly improved, there are still some areas in the processing sector that could be improved. Most previous studies have focused on the bulk analysis of mine wastes, without a detailed analysis of important characteristics, such as mineral texture, associations, liberation and locking. Recent studies focus on detailed mineralogical analysis, in order to more accurately assess the availability of the metals within the potential material for metal extraction. The present study investigates the geochemical and mineralogical characteristics of different mine and metallurgical waste material from a tailings pond in Plombières (East Belgium). The tailings pond covers a minimum surface area of 8000 m2, comprising 4 main types of material. Ore microscopy, X-ray fluorescence (XRF), quantitative X-ray powder diffraction (XRD), scanning electron microscope (SEM) based Mineral Liberation Analysis (MLA) and electron microprobe (EPMA) were used to identify and characterise Pb and Zn phases within the material. XRF analysis shows that the mine wastes dominantly consist of SiO2, Al2O3 and Fe2O3, while the content of Zn and Pb varies from 51 ppm to 24 wt % and 10 ppm to 10.1 wt %, respectively. The mineralogy of the mine waste is characterised by quartz, amorphous phases and phyllosilicates, with minor amounts of Fe-oxide, Pb- and Zn-bearing minerals. Based on the processing of the ore, the amorphous phase is present as pyrometallurgical slag. Mineral- to element- conversion shows a lack of Pb and Zn content. MLA and EPMA analysis confirm that the missing Pb is distributed between Pb- droplets within the slags and in the amorphous structure of the slags. Additionally, the analyses reveal that zinc is also dominantly located within the slags.

Neves Corvo is an underground high-grade Cu-(Sn)-Zn mine, currently producing copper, zinc and lead concentrates. Copper production started in 1989, followed by tin production, between 1990 and 2001, and zinc / lead production started in 2006. The operation is owned by SOMINCOR, a subsidiary of Lundin Mining, with a maximum capacity of 2.6Mtpy for the copper processing plant and 1.0Mtpy (ongoing expansion to 5.6Mtpy) for the zinc processing plant.The Neves Corvo VMS deposit is located in the Portuguese part of the world-class Iberian Pyrite Belt (IPB) and is composed of seven orebodies. The Neves, Corvo, Zambujal and Lombador orebodies are currently in production, whereas the Semblana and Monte Branco orebodies are relatively recent discoveries still under development and evaluation, and the Graça orebody has been already fully mined.From 2010 till end of 2019, the mine has accumulated 7.3Mt of waste rock and 17Mt of thickened tailings. These mining residues are stored in Cerro do Lobo Tailings Management Facility (Cerro do Lobo TMF), which completes a volume of 47Mt since the beginning of the operation in 1989 (30Mt are slurry tailings).The deposition method changed in 2010 from slurry subaquatic deposition to sub-aerial thickened tailings stack (vertical expansion) in co-deposition with potentially acid-generating (PAG) waste rock. The thickened tailings have an average of 63% solids. X-ray fluorescence analysis have shown copper and zinc grades variation in the waste rock between 0.3 and 0.9%, and 0.4% and 1.1%, respectively, and concentrations up to 0.3% and 0.4% of copper and zinc, respectively, in the tailings.Mineralogically, the tailings consist mainly in pyrite, sphalerite, chalcopyrite, +/- arsenopyrite, +/- tetrahedrite-tennantite, gangue minerals such as quartz, phyllosilicates, carbonates and some oxides, and have a non-uniform particle size distribution ranging between 1 and 100 µm. The waste rock fraction is millimetric to centimetric in size, and is formed by the local host rocks, which include acid volcanic rocks, schists and graywackes, all of them containing variably significant disseminated sulfides, largely dominated by pyrite.On-going research is being undertaken aiming to build a geometallurgical model for the Neves Corvo mine, ground on a huge database on the chemical and mineralogical composition, and particle size distribution of the mine tailings, coupled with (and calibrated by) new analytical and automated data acquired in a large set of carefully selected representative samples, in order to assess the potential recovery of base metals and their by-products out of these potentially valuable mine residues. The model construction and consequent resource estimation will be based on the daily monitoring of the tailings deposition at the disposal units, over the past 10 years (i.e., since the subaerial deposition has started at Neves Corvo), in terms of volume/tonnage, chemical and mineralogical compositions and physical characterization of the material.This study is part of the work package 1 (WP1) of ETN–SULTAN project (H2020) - European Training Network for the remediation and reprocessing of sulfidic mining waste sites. Publication supported by FCT- Project UID/GEO/50019/2019 - Instituto Dom Luiz.

Many by-product metals are classified as critical. However, they are only of marginal interest to many mining companies and are rarely part of detailed resource statements or geometallurgical assessments. As a result, there is a general lack of reliable quantitative data on the mineralogy and spatial distribution of these metals in ore deposits—hampering assessments of future availability. We propose here an innovative approach to integrate by-product metals into geometallurgical assessments. As an example, we use the distribution and deportment of indium at Neves-Corvo, a major European base-metal mine (Cu + Zn), and one of the largest and richest volcanic-hosted massive sulfide (VHMS) deposits in the world. Based on a combination of bulk-ore geochemistry and mineralogical and microanalytical data, this study is the first to develop a quantitative model of indium deportment in massive sulfide ores, demonstrating how regularities in indium partitioning between different minerals can be used to predict its mineralogical deportment in individual drill-core samples. Bulk-ore assays of As, Cu, Fe, Pb, S, Sb, Sn, Zn, and In are found to be sufficient for reasonably accurate predictions. The movement of indium through the ore processing plants is fully explained by its mineralogical deportment, allowing for specific mine and process planning. The novel methodologies implemented in this contribution for (1) the assessment of analytical uncertainties, (2) the prediction of complex mineralogical deportments from bulk geochemical data, and (3) the modeling of by-product recoveries from individual mining blocks, are of general applicability to the geometallurgical assessment of many other by-product metals in polymetallic sulfide ores, including Ga, Ge, Mo, Re, Se, Te, as well as the noble metals.

Breccias composed of coarse monomictic porphyritic igneous clasts and fine-grained matrix are common in subaqueous volcanic successions. We use the descriptive name “sediment-matrix igneous breccia” for this facies and have recognized at least five different origins among examples in the Iberian Pyrite Belt: (1) peperite; (2) sediment-infill volcanic breccia; (3) mud-matrix resedimented hyaloclastite; (4) mud-rich water-settled fiamme breccia; and (5) apparent sediment-matrix igneous breccia. Because the components and textures are similar, discriminating among the different origins can be very difficult. Both peperite and sediment-infill volcanic breccia can occur along top contacts of thick intervals of felsic coherent and monomictic breccia facies. The presence of peperite indicates that the contact is intrusive, whereas the presence of sediment-infill volcanic breccia indicates that the contact is depositional. Hence, correct distinction between peperite and sediment-infill volcanic breccia is an important means of discriminating felsic intrusions from felsic lavas and domes. The distinction underpins the reconstruction of volcanic centers and facies architecture, and the ordering of volcanic, intrusive, sedimentary and mineralizing events in ancient submarine volcanic successions. In addition, in volcanic-hosted massive sulfide districts such as the Iberian Pyrite Belt, paleoseafloor positions are considered highly prospective for massive sulfide ore bodies. Correct interpretation of sediment-matrix igneous breccias is also important in this context, because sediment-infill volcanic breccia, mud-matrix resedimented hyaloclastite and mud-rich water-settled fiamme breccia all form or are deposited at the seafloor, and hence delineate paleoseafloor positions. In contrast, peperite and apparent sediment-matrix igneous breccias form subsurface and do not delineate paleoseafloor positions.

The Iberian Pyrite Belt (IPB) is a major metallogenic province with numerous volcanic-hosted massive sulfide (VMS) deposits. Albernoa, Serra Branca and Neves-Corvo represent three well-known felsic volcanic centers in the Portuguese portion of the IPB. Albernoa has no known VMS mineralization, whereas gossans are well known in Serra Branca. Neves-Corvo is a world-class VMS deposit with high grade and tonnage for massive Cu and Zn sulfide ores as well as for Sn (massive and stringer cassiterite ores; now exhausted). Magmatic-hydrothermal fluids may contribute to the metal budget in some VMS-forming systems. In the IPB, direct evidence for this has been lacking and the magmatic link was not yet fully established. This work presents the first quartz-hosted melt inclusion data of phyric felsic volcanic rocks from the Albernoa, Serra Branca and Neves-Corvo areas in the IPB. Melt inclusions of intermediate composition found in Albernoa felsic volcanics show evidence for early stages of crustal melt assimilation supporting previous petrogenetic models for the IPB. High Sn contents (up to 46 ppm) found in the melt inclusions from all volcanic centers are a primary magmatic feature on these IPB volcanic rocks and are above the background value for the IPB felsic volcanic rocks. Estimated temperature of formation of magmatic quartz, in excess of 800 °C, suggests that all three volcanic centers gathered favorable conditions for sustaining long-lived hydrothermal cells. Highest estimated temperatures (>892 °C) are attributed to one sample from Albernoa and one sample from Neves-Corvo. Their similar, pre-eruptive, Cu and Sn distribution supports the model for the Neves-Corvo deposit indicating that Sn and (at least part of the) Cu decoupled from a common magmatic source in the early stages of the ore-forming process. The occurrence of barren volcanic sequences originating from Sn-rich melts is evidence that a set of concurrent factors are additionally required to generate a high-grade VMS-deposit. Melt inclusion data can be used as a tool to assist future exploration of favorable volcanic centers in the IPB.

The South Portuguese Terrane encompasses three major pre-orogenic mega-sequences: the Phyllite-Quartzite Group and the Tercenas Fm., the Volcanic-sedimentary Complex, and the Carrapateira Group, all three overlain by the syn-orogenic Baixo Alentejo Flysch Group, dealt with in Chap. 11. During the Mid-Late Devonian all the three mega-sequences belonged to an epicontinental sea. From the late Devonian to late Visean major changes took place: the region that became the IPB Domain was the locus of important lithospheric extension that led to the emplacement of important volumes of igneous rocks associated to a Volcanic-Sedimentary Complex, to which the VHMS ore deposits are associated; in Southwest Portugal the Tercenas Fm. shallow water sediments changed to a mixed-siliciclastic-carbonate shelf succession (Carrapateira Group); during the late Visean the extensional regime changed to crustal compression that caused the onset of huge deposits of flysch sediments (Baixo Alentejo Flysch Group) in successive depocenters migrating southward until the late Moscovian.

High concentrations of indium (In) and selenium (Se) have been reported in the Neves-Corvo volcanic-hosted massive sulfide deposit, Portugal. The distribution of these ore metals in the deposit is complex as a result of the combined effects of early ore-forming processes and late tectonometamorphic remobilization. The In and Se contents are higher in Cu-rich ore types, and lower in Zn-rich ore types. At the deposit scale, both In and Se correlate positively with Cu, whereas their correlations with Zn are close to zero. This argues for a genetic connection between Cu, In and Se in terms of metal sourcing and precipitation. However, re-distribution and re-concentration of In and Se associated with tectonometamorphic deformation are also processes of major importance for the actual distribution of these metals throughout the whole deposit. Although minor roquesite and other In-bearing phases were recognized, it is clear that most In within the deposit is found incorporated within sphalerite and chalcopyrite. When chalcopyrite and sphalerite coexist, the In content in sphalerite (avg. 1400 ppm) is, on average, 2–3 times higher than in chalcopyrite (avg. 660 ppm). The In content in stannite (avg. 1.3 wt.%) is even higher than in sphalerite, but the overall abundance of stannite is subordinate to either sphalerite or chalcopyrite. Selenium is dispersed widely between many different ore minerals, but galena is the main Se-carrier. On average, the Se content in galena is ~50 times greater than in either chalcopyrite (avg. 610 ppm) or sphalerite (avg. 590 ppm). The copper concentrate produced at Neves-Corvo contains very significant In (+Se) content, well above economic values if the copper smelters recovered it. Moreover, the high In content of sphalerite from some Cu-Zn ores, or associated with shear structures, could possibly justify, in the future, a selective exploitation strategy for the production of an In-rich zinc concentrate.

Assessment of geological, geochemical and isotopic data indicates that a significant subgroup of volcanic-hosted massive sulphide (VHMS) deposits has a major or dominant magmatic–hydrothermal source of ore fluids and metals. This group, which is typically characterised by high Cu and Au grades, includes deposits such as those in the Neoarchean Doyon-Bousquet-LaRonde and Cambrian Mount Lyell districts. These deposits are distinguished by aluminous advanced argillic alteration assemblages or metamorphosed equivalents intimately associated with ore zones. In many of these deposits, δ34Ssulphide is low, with a major population below −3‰; δ34Ssulphate differs from coexisting seawater and Δ34Ssulphate–sulphide ∼ 20–30‰. These characteristics are interpreted as the consequence of disproportionation of magmatic SO2 as magmatic–hydrothermal fluids ascended and cooled and as a definitive evidence for a significant magmatic–hydrothermal contribution. Other characteristics that we consider diagnostic of significant magmatic–hydrothermal input into VHMS ore fluids include uniformly high (>3 times modern seawater values) salinities or very 18O-enriched (δ18O > 5‰) ore fluids. We do not consider other criteria [e.g. variable salinity, moderately high δ18Ofluid (2–5‰), δ34Ssulphide near 0‰, metal assemblages or a spatial association with porphyry Cu or other clearly magmatic-hydrothermal deposits] that have been used previously to advocate significant magmatic–hydrothermal contributions to be diagnostic as they can be produced by non-magmatic processes known to occur in VHMS mineral systems. However, in general, a small magmatic–hydrothermal contribution cannot be excluded in most VHMS systems considered. Conclusive data that imply minimal magmatic–hydrothermal contributions are only available in the Paleoarchean Panorama district where coeval seawater-dominated and magmatic–hydrothermal systems appear to have been physically separated. This district, which is characterised by chloritic and sericitic alteration assemblages and lacks aluminous advanced argillic alteration assemblages, is typical of many VHMS deposits around the world, suggesting that for “garden variety” VHMS deposits, a significant magmatic–hydrothermal contribution is not required. Other than deposits associated with advanced argillic alteration assemblages, the only deposit for which we ascribe a major magmatic–hydrothermal contribution is the Devonian Neves Corvo deposit. This deposit differs from other deposits in the Iberian Pyrite Belt and around the world in being extremely Sn-rich, with the Sn closely associated with Cu and in having formed from high 18O-rich fluids (δ18Ofluid ∼8.5‰). We consider these characteristics, particularly the last, as diagnostic of a significant magmatic hydrothermal contribution. Our analysis indicates that two subgroups of VHMS deposits have a major magmatic–hydrothermal contribution: Cu/Au-rich deposits with aluminous alteration assemblages and reduced, very Sn-rich deposits in which Sn was introduced in a high-temperature ore assemblage. Comparison with “normal” VHMS deposits suggests that these subgroups of VHMS deposits may form in specialised tectonic environments. The Cu/Au-rich deposits appear to form adjacent to magmatic arcs, an environment conducive to the generation of hydrous, oxidised melts by melting metasomatised mantle in the wedge above the subducting slab. This contrasts with the back-arc setting of “normal” VHMS deposits in which relatively dry granites (In this contribution, we use the term granite sensu latto) formed by decompression melting drive seawater-dominated hydrothermal circulation. The tectonic setting of highly Sn-rich VHMS deposits such as Neves Corvo is less clear; however, thick continental crust below the ore-hosting basin may be critical, as it is in other Sn deposits.

The Volcanic Sedimentary Complex (VSC) of the Iberian Pyrite Belt (IPB) in southern Portugal and Spain, comprises an Upper Devonian to Lower Carboniferous submarine succession with a variety of felsic volcanic lithofacies. The architecture of the felsic volcanic centres includes felsic lavas/domes, pyroclastic units, intrusions and minor mafic units that define lava–cryptodome–pumice cone volcanoes. The diversity of volcanic lithofacies recognized in different areas of the IPB mainly reflects variations in proximity to source, but also differences in the eruption style. The IPB volcanoes are intrabasinal, range in length from 2 km to > 8 km and their thickest sections vary from 400 m to > 800 m. These volcanoes are dominated by felsic lavas/domes that occur at several stratigraphic positions within the volcanic centre, however the pyroclastic units are also abundant and are spatially related to the lavas/domes. The intrusions are minor, and define cryptodomes and partly-extrusive cryptodomes. The hydrothermal systems that formed the Neves Corvo and Lousal massive sulfide ore deposits are associated with effusive units of felsic volcanic centres. At Neves Corvo, the massive sulfide orebodies are associated to rhyolitic lavas that overlie relatively thick fiamme-rich pyroclastic unit. In several other locations within the belt, pyroclastic units contain sulfide clasts that may have been derived from yet to be discovered coeval massive sulfide deposits at or below the sea floor, which enhances the exploration potential of these pyroclastic units and demonstrates the need for volcanic facies analysis in exploration.

In the Iberian Pyrite Belt, volcanic rocks are relatively scarce, accounting for approximately only 25% of the geologic record, with the remaining 75% consisting of sedimentary units. This association is very clear in the host succession to the Neves Corvo massive sulfide deposit in Portugal. The Neves Corvo host succession comprises the products of explosive and effusive rhyolitic eruptions intercalated with mudstone that records a submarine below-wave-base environment and provides precise biostratigraphic age constraints. The first and second volcanic events involved eruptions at local intrabasinal vents. The first event generated thick beds of fiamme breccia that are late Famennian in age. The fiamme were originally pumice clasts produced by explosive eruptions and were subsequently compacted. The second event was the late Strunian (latest Famennian) effusion of rhyolitic lava that was pervasively quench-fragmented. The third and final event is younger than the massive sulfide deposits poorly represented in the mine area and minor compared with the two other events. The integration of biostratigraphic data with the volcanic facies architecture indicates that the Neves Corvo ore deposits are similar in age to the late Strunian rhyolitic lava. Although regionally the Iberian Pyrite Belt is essentially a sedimentary succession, ore formation at Neves Corvo can be closely linked to discrete volcanic events that produced a relatively narrow range of volcanic facies.

The most recent submarine eruption observed offshore the Azores archipelago occurred between 1998 and 2001 along the submarine Serreta ridge (SSR), ~ 4–5 nautical miles WNW of Terceira Island. This submarine eruption delivered abundant basaltic lava balloons floating at the sea surface and significantly changed the bathymetry around the eruption area. Our work combines bathymetry, volcanic facies cartography, petrography, rock magnetism and geochemistry in order to (1) track the possible vent source at seabed, (2) better constrain the Azores magma source(s) sampled through the Serreta submarine volcanic event, and (3) interpret the data within the small-scale mantle source heterogeneity framework that has been demonstrated for the Azores archipelago. Lava balloons sampled at sea surface display a radiogenic signature, which is also correlated with relatively primitive (low) 4He/3He isotopic ratios. Conversely, SSR lavas are characterized by significantly lower radiogenic 87Sr/86Sr, 206Pb/204Pb and 208Pb/204Pb ratios than the lava balloons and the onshore lavas from the Terceira Island. SSR lavas are primitive, but incompatible trace-enriched. Apparent decoupling between the enriched incompatible trace element abundances and depleted radiogenic isotope ratios is best explained by binary mixing of a depleted MORB source and a HIMU­type component into magma batches that evolved by similar shallower processes in their travel to the surface. The collected data suggest that the freshest samples collected in the SSR may correspond to volcanic products of an unnoticed and more recent eruption than the 1998–2001 episode.

The oxygen, hydrogen, and carbon isotope compositions of hydrothermally altered rocks and minerals from massive and stockwork ores of the Neves-Corvo volcanic-hosted massive sulfide deposit have been used to infer its thermal history and the origins of the hydrothermal fluids. Quartz and cassiterite separated from the stringer and massive cassiterite ores of the Corvo orebody (“tin corridor”) have δ18O values of 12.5 to 13.6 and −1.4 to −0.4 per mil, respectively. Quartz-cassiterite oxygen isotope fractionation indicates temperatures of 174° to 207°C (avg 191°C) for precipitation of this mineral pair. The calculated oxygen isotope composition of the fluid (δ18OH2O = −0.4 to +0.7‰; avg 0.1‰) suggests that cassiterite precipitation resulted from extensive mixing of a tin-bearing fluid with seawater at sea-floor hydrothermal vents. The whole-rock oxygen isotope composition of the hydrothermally altered, felsic volcanic rocks hosting the sulfide stockwork of the Corvo orebody varies from the central stockwork (chloritic alteration zone I, δ18O = 8.7–9.6‰), to the peripheral zones (sericitic and paragonitic alteration zones IIa, δ18O = 11.6–13.1‰, and IIb, δ18O = 11.0–14.1‰). The δ18O values of quartz also increase from alteration zone I (avg 13.9‰) to alteration zone IIa (avg 14.4‰) to alteration zone IIb (avg 15.0‰). Quartz from the hanging-wall jasper unit yielded higher δ18O values of 15.5 to 17.9 per mil. Chlorite from alteration zone I has δ18O values of 6.1 to 8.4 per mil (avg 7.4‰). Sericite has δ18O and δD values that vary slightly from δ18O = 9.3 to 10.1 per mil (avg 9.9‰) and δD = −59 to −47 per mil (avg −53‰) in alteration zone I, to δ18O = 9.8 to 11.4 per mil (avg 10.5‰) and δD = −50 per mil in alteration zone IIa, to δ18O = 9.4 to 11.7 per mil (avg 10.6‰) and δD = −61 to −36 per mil (avg −45‰) in alteration zone IIb. Siderite associated with waning hydrothermal activity has low δ13C values (−11.1 to −5.8‰), suggesting the incorporation of oxidized, organic carbon from the footwall sequence and/or the addition of magmatic carbon. In alteration zone I, quartz-chlorite fractionation indicates temperatures of 249° to 402°C (avg 335°C) and δ18OH2O values of 6.1 to 10.2 per mil (avg 8.3‰). Quartz-sericite pairs gave isotopic equilibrium temperatures of 250° to 289°C (avg 269°C) and δ18OH2O values of 5.8 to 7.0 per mil (avg 6.4‰) in alteration zone IIa, and 170° to 318°C (avg 223°C) and δ18OH2O = 1.4 to 8.3 per mil (avg 4.5‰) in alteration zone IIb. The oxygen isotope data show that in the core of the feeder system (alteration zone I), the temperature and the δ18OH2O values were very high. The δD values calculated for the ore fluids (δD = −37 to −11‰) are also significantly lower than seawater. Outward from the central stockwork (alteration zones IIa and IIb) the ore fluid was depleted in 18O and the temperatures were lower. The oxygen, hydrogen, and carbon isotope signatures of the Neves-Corvo ore fluids are best explained by incorporation of magmatic and/or metamorphic fluids into a seawater-dominated hydrothermal system. Magmatic fluids, in particular, were a likely source for the tin and much of the copper in the Neves-Corvo ores.

SW Iberia is interpreted as an accretionary magmatic belt resulting from the collision between the South Portuguese Zone and the autochthonous Iberian terrane in Variscan times (350 to 330 Ma). In the South Portuguese Zone, pull-apart basins were filled with a thick sequence of siliciclastic sediments and bimodal volcanic rocks that host the giant massive sulphides of the Iberian Pyrite Belt. Massive sulphides precipitated in highly efficient geochemical traps where metal-rich but sulphur-depleted fluids of dominant basinal derivation mixed with sulphide-rich modified seawater. Massive sulphides formed either in porous/ reactive volcanic rocks by sub-seafloor replacement, or in dark shale by replacement of mud or by exhalation within confined basins with high biogenic activity. Crustal thinning and magma intrusion were responsible for thermal maturation and dehydration of sedimentary rocks, while magmatic fluids probably had a minor influence on the observed geochemical signatures. The Ossa Morena Zone was a coeval calc-alkaline magmatic arc. It was the site for unusual mineralization, particularly magmatic Ni–(Cu) and hydrothermal Fe-oxide–Cu–Au ores (IOCG). Most magmatism and mineralization took place at local extensional zones along first-order strike-slip faults and thrusts. The source of magmas and IOCG and Ni–(Cu) deposits probably lay in a large mafic–ultramafic layered complex intruded along a detachment at the boundary between the upper and lower crust. Here, juvenile melts extensively interacted with low-grade metamorphic rocks, inducing widespread anatexis, magma contamination and further exsolution of hydrothermal fluids. Hypersaline fluids (d18OfluidN5.4x to 12x) were focused upward into thrusts and faults, leading to early magnetite mineralization associated with a high-temperature (N500 8C) albite– actinolite–salite alteration and subsequent copper–gold-bearing vein mineralization at somewhat lower temperatures. Assimilation of sediments by magmas led in turn to the formation of immiscible sulphide and silicate melts that accumulated in the footwall of the layered igneous complex. Further injection of both basic and sulphide-rich magmas into the upper crust led to the formation of Ni–(Cu)-rich breccia pipes.

Portugal holds jurisdiction, and exclusive economic rights, over a very large area of the seabed. One of the main national objectives, at the present time, is to increase the rather limited knowledge that exists on the resources that may be contained herein.

Gold mineralization in the Neves Corvo copper stockworks occurs in two geochemical associations: (1) Au+Co+Bi(±Te) and (2) Au+Cu+Ag(±Hg). Type 1 gold occurs in the deeper parts of the feeder zones. Its associated mineralogical assemblage is consistent with low sulfur activity of the fluid and high temperature (360°–400°C) conditions. The second type of gold geochemical association reflects pH increase and/or temperature decrease as the fluid moves upwards in the stockwork and reaches the base of the massive sulfide Neves Corvo is accompanied by high sulfidation parageneses. These might have resulted either from the long-lived maturation of the ore-forming system, which would have led to extreme zone refining effects, and/or from the late input of an external fluid component (possibly magmatic?) in the Neves Corvo hydrothermal system. In the PACMANUS hydrothermal field, native gold also occurs in both high and low sulfidation mineral associations. Gold occurs at the seafloor level either associated with: (1) chalcopyrite+sphalerite +tennatite, or (2) chalcopyrite+bornite ± covellite. At depth, instead, gold occurs in sphalerite as small native gold inclusions (silver-poor). Following the process of copper enrichment by zone-refining, gold frequently concentrates in the borders of the sphalerite grains.

Well-preserved primary textural features were recognized in cherts and jaspers that form one of the manganese ore-hosting units of the Soloviejo Mn deposit, in the Iberian Pyrite Belt. These include (i) spherulitic, (ii) banded and (iii) brecciated. The spherulites (0.04—0.3 mm) consits of a central core of minute grains of hematite or quartz, rimmed by chalcedony or microcrystalline quartz. Banded jaspers show no spherulitic textures. Banded textures are made up by alterations of micro- to meso-bands of silica and hematite. They often show soft-sediment deformation features, such as microslumps, pinch-and-swell, and load cast. Diagenetic brecciation overprints these pristine textures. Breccias consist of jasper fragments (mm to cm), affected by total or partial recrystalization, cemented by different proportions of microcrystalline quartz. Primary textures in siliceous hydrothermal precipitates reflect different stages of formation and diagenetic maturation of its silica gel precursor. Their interpretation helps in constraining the initial conditions assisting the hydrothermal activity at the Soloviejo deposit, and its early evolving stages.

The combination of biostra-tigraphic data with the facies architecture of the Neves Corvo massive sulfide deposit allows dating of the two major volcanic events identified in the mine stratigraphy. Both volcanic episodes are represented by submarine and proximal to source vent deposits, with intrabasinal origin and rhyolitic composition. Thick pyroclastic pumice-rich facies of the late Famennian and youngerlavas of the late Strunian (latest Famennian) constitute the host sequence of the massive sulfides. The hydrothermal mineralizing event occurred after the emplacement of the rhyolitic lavas.

New Re and Os analyses of pyrites from Aljustrel, Lagoa Salgada and Neves-Corvo deposits yield concentrations that are similar to those previously reported for the Rio Tinto and Tharsis deposits, all at the Iberian Pyrite Belt. Osmium contents in IPB pyrites increase from the deeper stockwork zones towards the upper massive sulphides. Pyrite samples from IPB sulphide orebodies plot on a major 187Re/188Os-187Os/188O linear array, yielding an age of 359±26 Ma and an initial 187Os/188O ratio of ca. 0.57. Five samples from Neves-Corvo sulphide-rich stockwork ores yield an age of 358 ±29 Ma and an initial 187Os/188O ratio of 0.49 ±0.07, in accord with palynological and isotopic age constraints for ore formation at the IPB. Pyrites from Neves-Corvo copper-tin ores have Re/Os ratios and osmium concentrations that are similar to those in pyrites from sulphide-rich stockwork ores; however, their highly radiogenic initial 187Os/188O ratios (4.89–7.85, if preserving original isotope system-atics) preclude derivation from the same sources as the remaining IPB sulphides. The overall Re-Os geochemical data conform to previous Sr, Nd and Pb isotopic studies supporting multiple sources for IPB metallogenesis.

Lead, Rb–Sr, and Sm–Nd isotopes have been used to constrain the sources and the timing of mineralisation at the Neves Corvo VHMS deposit of the Iberian Pyrite Belt (IPB). Sulfide- and cassiterite-rich ores, together with a mineralised felsic volcanic rock, yield a Rb–Sr errorchron age of 347±25 Ma with an initial 87Sr/86Sr=0.71031±65. The Rb–Sr results agree with palynological age constraints for ore formation at Neves Corvo, and are indistinguishable from several other mineralisation ages, indicating that major orebodies in the IPB formed coevally at ~350 Ma. In contrast, wide variations in initial 143Nd/144Nd indicate limited rare-earth-element redistribution during ore deposition. Initial eNd (350 Ma) values range from –0.2 to –9.7 for copper ores, –8.9 to –9.4 for copper-tin ores, and –6.9 (cassiterite) to –9.5 for tin ores, implying that neither the IPB volcanic host rocks [eNd (350 Ma) >–2.1; 87Sr/86Sr0

This work constitutes the first contribution for the systematisation of geological heritage knowledge in Portugal, following the international recommendations for the characterisation of geological heritage (IUGS, ProGEO). The application of the ProGEO methodology has resulted in the creation of fourteen frameworks with international relevance, established by consensus among the Portuguese geological community. The description of each category in this paper is not exhaustive and only the most relevant scientific settings are presented. The following are the three key outcomes of this work: i) At a national level, the most important geosites are identified, indicating where geoconservation efforts should be prioritised based on scientific justification; ii) At a regional level, conditions have been developed to foster dialogue with Spanish colleagues in order to create Iberian frameworks; iii) At an international level, it is now possible to integrate Portuguese geosites in to the global inventories promoted by IUGS, UNESCO, and ProGEO.