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- Litoteca do LNEG Aljustrel, um espólio científico fundamental para a investigação da Faixa Piritosa Ibérica e da Zona de Ossa-MorenaPublication . Matos, João Xavier; Morais, Igor; Santos, Sara; Gonçalves, Pedro; Batista, Maria Joao; de Oliveira, Daniel Pipa Soares; Dias, Ruben PereiraSUMMARY: Since 2018 the LNEG’s Aljustrel drill core shed is dedicated to the southern Portugal collections distributed by Iberian Pyrite Belt (IPB) and Ossa-Morena Zone (OMZ). The archive includes exploration drill hole cores, soil, stream sediments and rock samples, technical reports, and a complete and detail map collection (1/5.000 and 1/25.000 scales), all organized in databases. Drill hole relog allow a better understanding of the subsurface being essential in stratigraphy, structural mapping, mineral exploration and metallogeny. Following the regional Smart Specialization Strategy defined by CCDR Alentejo to Geological Resources, the LNEG Aljustrel develops R&D programs dedicated to thematic mapping and mineral resources. Critical Raw Materials mineralizations are present at the archives like IPB VMS Cu-Zn-Pb(Au-Ag-Sn-Sb) and Fe-Mn deposits and OMZ sulphide-magnetite (Zn-Pb,Cu(Au)), magnetite and Cu(Au) veins. The preservation of the subsurface geological heritage is critical to the IPB and OMZ research and an institutional LNEG mission.
- Geological correlation of Neves-Corvo Mine and Pomarão Antiform sequences (Iberian Pyrite Belt, Portugal)Publication . Albardeiro, Luís; Matos, João Xavier; Mendes, Márcia; Solá, A. Rita; Pereira, Zélia; Morais, Igor; Salgueiro, Rute; Pacheco, Nelson; Araújo, Vítor; Oliveira, José TomásABSTRACT: A geological correlation between Neves-Corvo (NC) and Pomarão antiforms is attempted. These regional scale major sequences are easily correlated but, at local scale, facies and age differences stand out. Stratigraphy includes: i) the Phyllite-Quartzite Group with identical paleogeography setting and similar late Famennian ages for uppermost levels (LL to LN miospore biozones in Pomarão and NC respectively). ii) the Volcano-Sedimentary Complex shows some discrepancyconcerning the age distribution of the felsic volcanic rocks (ca. 356-330for Pomarão and ca. 365-346 Ma for all NC area) while sediments rangefrom mid-Famennian to late Visean age (VH to NM Miospore Biozonefor NC). iii); the Baixo Alentejo Flysch Group (late Visean NM MiosporeBiozone onwards in NC), covering the previous sequences and beingslightly older than the uppermost volcanic rocks of Pomarão. Thecorrelation between these two structures is supported by geology andisotopic/biozone ages and favours exploration scenarios in both regions.
- Geophysical surveys in the Portuguese sector of the Iberian Pyrite Belt: a global overview focused on the massive sulphide exploration and geologic interpretationPublication . Matos, João Xavier; Carvalho, João; Represas, Patricia; Batista, Maria Joao; Sousa, P.; Ramalho, Elsa; Marques, Fábio; Morais, Igor; Albardeiro, Luís; Gonçalves, Pedro; Dias, P.ABSTRACT: The application of geophysical techniques to massive sulphide deposits exploration has proven to be a success in the Iberian Pyrite Belt (IPB) metallogenetic province, both in Portugal and in Spain. Several hidden deposits were discovered through the interpretation of geological models, supported by geophysical data collected in land and airborne surveys, as well as applied using down hole techniques in selected drill holes. This paper presents an overview of the methodologies applied in Portugal in the South Portuguese Zone (SPZ) geological domain, where the IPB is included, mostly by the LNEG and mining companies, with emphasis on the interpretation of the regional gravity, magnetometry and radiometry surveys, published in 1/400 000 scale by the EXPLORA/Alentejo2020 Project. In this regional mapping program, the large volume of data collected by LNEG and mining companies since the 1960’s was compiled and processed. The integrated interpretation and correlation between these methods will enable a better planning of new IPB exploration investments. IPB Volcano-Sedimentary Complex (VSC, Famennian to Late Visean age) lineaments are well defined in the gravity and magnetic fields along the IPB western region (e.g. Alcoutim/Neves-Corvo/Montinho/Sesmarias/Lousal/Caveira). Aeromagnetic data also reflect deep and large anomalies related with the SPZ basement. A rock density database is presented and used to interpret the gravity data. Radiometric map (Natural Radioactivity), based mostly in airborne radiometric surveys, show contrasts between rocks in Paleozoic, Mesozoic and Cenozoic formations and correlations with geological and hydrothermal mapping are highlighted. The use of geophysical techniques is particularly critical in areas where VSC is concealed by younger sediments (e.g. Baixo Alentejo Flysch Group and/or Cenozoic formations), allowing the selection of target areas. Case studies are discussed based on electromagnetic, seismic and magnetotelluric methods and on the high mineral potential of defined targets. Multilayered data correlation (geophysics including petrophysical data, geochemistry and stratigraphic high-resolution models) is a key prospecting methodology and is essential for the accurate modelling of ore horizons and geological structures. Considering the IPB potential for VMS deposits, including the possible discovery of new giant (> 200 Mt) deposits, an increase of investment in new geophysical methods can be predicted. LNEG development of R&D projects such as EXPLORA/Alentejo2020 and SmartExplorationTM/H2020 also contribute to a favourable setting in the province, both in near mining and green fields scenarios. Thus, new discoveries are expected, like others made in the recent times in the IPB Portuguese sector, such as Lagoa Salgada (SFM, 1992, SFM; Redcorp/EDM, 2011; Redcorp/Ascendant/EDM, 2017), Semblana (Somincor-AGC-Lundin Mining, 2010), Monte Branco (Somincor-Lundin Mining, 2012) and Sesmarias (Maepa/Avrupa, 2014). The importance of these data goes beyond the mineral exploration purpose. Since some of them use rock and mineral physical properties that can be related with environmental contamination (e.g. radiometry and magnetics) they can also be used in geochemical background studies, acid mine drainage and metal dispersion. Therefore, they can also promote a deeper knowledge in other areas of research related with environment preservation.
- Geochemistry of Iberian Pyrite Belt Portuguese sector massive sulfide deposits-related volcanic rocks. Considerations on hydrothermal alteration, petrology and tectonic evolutionPublication . Morais, Igor; Albardeiro, Luís; Batista, Maria Joao; Matos, João Xavier; Solá, A. Rita; de Oliveira, Daniel Pipa Soares; Salgueiro, Rute; Araújo, Vítor; Pacheco, NelsonABSTRACT: A geochemical compilation database of the main volcanic units of the Volcano-Sedimentary Complex (VSC) of the Iberian Pyrite Belt (IPB), one of the largest provinces of massive sulfides on a global scale, is presented and discussed. For this purpose, we used several mineral exploration rock geochemistry databases from six IPB areas, namely Cercal, Lagoa Salgada, Lousal, Aljustrel, Neves-Corvo and Chança, regarding unaltered/hydrothermaly altered felsic volcanic units interbedded in the Famennian-Late Visean volcano-sedimentary sequences of the VSC. Volcanic rocks within the Phyllite-Quartzite Formation (Givetian-Famennian) IPB basement were also considered. From this, Neves-Corvo sector rhyolites (Rhyolite type 1 and 2) present the most intense hydrothermal alteration, directly related with the age of mineralization and coeval with hosted VSC sedimentary formations. Similar cases were also observed in the volcanic units hosting Lagoa Salgada, Chança and Aljustrel Volcanic-hosted massive sulfide (VHMS) deposits. The variety of felsic and intermediate volcanic rocks in the IPB (and within each sector) reflect different petrogenetic processes and/or distinct crustal sources. Application of Zr vs TiO2 binary diagrams allows to define three main trends of andesitic (Lagoa Salgada and Chança sectors), dacitic-rhyodacitic (Aljustrel sector) and rhyolitic (Cercal, Neves-Corvo, Aljustrel and Lousal sectors) composition. Cercal rhyolites are the most evolved felsic rocks (Zr/TiO2 ≈ 1562), followed by Neves-Corvo rhyolites (Zr/TiO2 ≈ 936), Lousal (Zr/TiO2 ≈ 845) and Aljustrel (Zr/TiO2 ≈ 840). In addition, four distinct compositional clusters can be distinguished based on Al2O3/TiO2 vs Zr/TiO2 and Al2O3/Zr vs TiO2/Zr ratios according to its nature as, rhyolitic, rhyodacitic/dacitic and andesitic, probably reflecting differential partial melting rates. Ybn vs La/Yb(n) diagram ratio indicates that Neves-Corvo (mainly 2 types of rhyolites), Aljustrel (Tufo da Mina rhyolitic unit), as well as Lagoa Salgada sector rhyolites are projected along FIIIa and FIIIb rhyolite fields considered of higher metalliferous potential in the IPB, once their petrogenetic processes are considered ideal to trigger, sustain and host hydrothermal systems and consequently VHMS deposits. Future work, combining geochemical characterization of each volcanic unit with their stratigraphic positioning, is essential in order to achieve a correct correlation between the different sectors and, is therefore, a useful tool in IPB mineral exploration and drill-hole data correlation.
- Geophysical characterization of the Cercal Paleozoic structure, Iberian Pyrite Belt, from a mineral exploration perspectivePublication . Feitoza, L. M.; Carvalho, João; Represas, Patricia; Ramalho, Elsa; Sousa, Pedro; Matos, João Xavier; Albardeiro, Luís; Morais, Igor; Santos, Telmo M. Bento DosABSTRACT: The Cercal Volcano-Sedimentary Complex (Cercal VSC) structure is the westernmost sector of the Iberian Pyrite Belt (IPB) giant metallogenic province and was explored since Roman times for volcanogenic massive sulphides (VMS) and Fe–Mn (Ba) deposits. However, presently only a single deposit is known, the Salgadinho Cu-Ag-Au stockwork/disseminated deposit. Nevertheless, according to several mining companies that operated in the area during the last two decades, the Cercal area keeps a high potential for the discovery of new massive and stockwork mineralization deposits hosted in VSC felsic volcanic rocks. The lack of seismic data and deep drill holes (> 800 m), has been limiting the discovery of possible deep seated massive/stockwork deposits. The goal of this work is to provide new insights into the Cercal deep and near surface structure through the integrated interpretation of geophysical and geological data and contribute to the discovery of new stockwork or massive sulphide deposits. For this purpose, we reprocessed ground gravity, airborne magnetic/radiometric and electrical resistivity/induced polarization data which was interpreted and integrated with geological data. Data interpretation included 2.5D forward gravimetric modeling constrained by i) a new rock density database (from outcrops and drill-holes) built under the scope of this work, ii) the scarce available drill-holes and iii) geological information. A small magnetic susceptibility/conductivity database based on drill-hole core samples was also built to assist the magnetic and electrical/chargeability data interpretation. The integrated interpretation agrees with some of the expected geological scenarios predicted by surface mapping and exploration drill-hole logs in the IPB and provides further details on the deep structure of the Cercal Anticline, a NNW-SSE oriented VSC unrooted structure, controlled by variscan SW verging thrust faults and discordant strike-slip Late-Variscan faults. This geological scenario favors the possibility of new findings at relatively shallow depths (200–900 m), and a few sites for further exploration are indicated based on the integrated interpretation. Therefore, this work contributes to the understanding of the Cercal deep structure from a mineral exploration perspective and confirms the proposed structural models for the IPB’s westernmost region.
- Um novo método de prospeção geoquímica para a identificação de depósitos profundos do tipo VMS. Aplicação ao depósito de Cu-Zn de Neves-Corvo, Faixa Piritosa IbéricaPublication . Morais, Igor; Rosado, L.; Albardeiro, Luís; Mirao, Jose; Batista, Maria Joao; Matos, João XavierSUMMARY: The fast energetic transition in the world needs large amounts of mineral resources that are currently scarce. For the suppression of these needs, new mineral deposits must be found, demanding the development of new exploration techniques. Currently, in several metalogenetic provinces, surface deposits are rare. In the Iberian Pyrite Belt, geophysical techniques, namely gravimetry and electromagnetics, have been used over the last years leading to the discovery of several hiden Volcanogenic Massive Sulphide deposits (VMS). Therefore, it is proposed a new geochemical technique that, through the chemical analysis of rock coatings, can lead to the identification of mineral deposits located at greath depth. The method is represented by the European Patent EXPLORA – LNEG/Évora University-Hércules Laboratory.
- Late Famennian (latest Strunian) palynomorph assemblages and their role in the Neves Formation depositional environment -The Neves-Corvo mine case study (Iberian Pyrite Belt, Portugal)Publication . Mendes, Márcia; Pereira, Zélia; Matos, João Xavier; Albardeiro, Luis; Morais, Igor; Araújo, VitorABSTRACT: This research examines palynomorph assemblages preserved in sediments of the Iberian Pyrite Belt (IPB) that host the Neves-Corvo massive sulfide deposit and its importance for mineral exploration. The sediments belong to the Neves Formation, characterized by black shales and minor occurrences of siltstones and cherts, indicative of reduced environmental conditions, favorable to sulfide deposition in a hydrothermal context dominated by submarine felsic volcanism and graben structures. Analysis was performed in barren drill holes (e.g., Monte Novo), as opposed to productive sectors with massive sulfide mineralization and/or stockwork vein networks (e.g., Lombador, Corvo and Semblana deposits) and favorable sectors like Algar & eacute;. The recovered palynological assemblages are assigned to the LN Miospore Biozone, indicating a Late Famennian (latest Strunian) age. Several characteristic species of this age are identified, such as Retispora lepidophyta and Verrucosisporites nitidus in close association with Densosporites spitbergensis, Dictyotriletes fimbriatus, Retusotriletes cf. incohatus, Retusotriletes crassus, Vallatisporites spp. (including V. pusillites, and V. verrucosus). ) . Despite some palynomorphs showing signs of breakage, folding, and indistinctness, no significant preservation or diversity differences were noted between barren and mineralized areas. The high abundance of marine phytoplankton in all studied black shales indicates ecologically stressed setting, dominated by dysoxic to anoxic conditions in a distal marine setting with active felsic volcanism and hydrothermal mineralizing events during Late Famennian time. This geologic context correlates with other IPB deposits and the global latest Devonian anoxic Hangenberg event.
- Biostratigraphic and structural research of the Guedelhinha-Lançadoiras- Algaré sector of the Neves-Corvo mine region, Iberian Pyrite BeltPublication . Pereira, Zélia; Matos, João Xavier; Mendes, Márcia; Solá, A. Rita; Albardeiro, Luís; Morais, Igor; Araújo, Vítor; Pacheco, Nelson; Oliveira, José TomásABSTRACT: Based on drill hole sampling and sedimentary rock dating by palynology, the present research focuses on the palynostratigraphic events established in the key geological section of Guedelhinha-Lancadoiras-A lgare located in the Portuguese Neves-Corvo mine region, Iberian Pyrite Belt. The age data allow detailing the lithostratigraphic sequence and further understanding the complex structural setting, representing an important contribution to the geological knowledge of this sector located to the immediate WNW of the Neves-Corvo VMS deposit. The combination of the studied events allows the reconstruction of the Devonian-Carboniferous sedimentation and paleoenvironments along the Iberian Pyrite Belt. Several stratigraphic hiatuses identified in the Neves-Corvo region by the palynological record are con-firmed, mainly occurring from the mid Frasnian to mid Famennian, from the early and mid Strunian, and from the early to late Tournaisian, which were mainly coincident with the worldwide extinction events, in particular during Frasnian-Famennian and Late Devonian times. Extensional tectonics and related gravitational faults, local uplift mechanisms and intense volcanic activity could also explain the lack of palynological data and sedimentary hiatus. In this research, the importance of the late Strunian times in the Iberian Pyrite Belt (Miospore Biozone LN of the Neves Formation) is highlighted, confirming the contemporaneity of felsic volcanism, hydrothermalism, sulphide mineralization precipitation and black shale anoxic sedimentation.
- 3D Constrained Gravity Inversion and TEM, Seismic Reflection and Drill-Hole Analysis for New Target Generation in the Neves-Corvo VMS Mine Region, Iberian Pyrite BeltPublication . Marques, Fábio; Dias, Pedro; Carvalho, João; Represas, Patricia; Spicer, Bill; Araújo, Vítor; Matos, João Xavier; Morais, Igor; Albardeiro, Luís; Sousa, Pedro; Pacheco, Nelson; Gonçalves, Pedro; Barbosa, DiegoABSTRACT: Located in the Iberian pyrite belt, the Neves-Corvo mine is a world-class massive sulfide deposit and the largest operating mine in Portugal with underground mining down to 1000 m depth focused on massive and stockwork Cu, Zn, Pb rich ores. Gravimetric data have had a leading role in the discovery of the seven known deposits, together with time-domain electromagnetic (TEM) ground data. In this work, we present the results of a 3D constrained gravity inversion carried out with legacy ground gravity data. The 3D gravity inversions were carried out using an updated density database containing approximately 142,000 measurements. A recently constructed 3D geological model based on reprocessed 2D seismic reflection, 3D seismic, TEM and updated geology from detailed surface mapping and drill-hole data, was used to constrain the inversions. The results show multiple high-density anomalies that may indicate the presence of mineralization at depth. These anomalies were therefore cross-checked with holes previously drilled. Approximately 97% of more than 1000 available surface drill-holes located on or at a distance of less than 200 m from the high-density anomalies intersected mineralization. However, gravity anomalies have been drilled in the past and particularly dense black shales or rhyolitic/gabbroic rocks have been intersected. To increase the success of future drilling, gravimetric anomalies have been correlated spatially with high-conductivity TEM zones and strong-amplitude seismic reflections, because igneous rocks usually present weak-to-moderate conductivity and a massive column of black shales presents a seismic signature quite different from that of mineralization. We concluded that some of these locations represent high-quality targets to consider following up with drilling and further exploration.
- O magmatismo mais antigo da Faixa Piritosa Ibérica: dados geocronológicos UPb da Jazida do Salgadinho, CercalPublication . Feitoza, L. M.; Santos, Telmo M. Bento Dos; Amaral, Joao Lains; Solá, A. Rita; Tassinari, Colombo C. G.; Basei, M.A.S.; Matos, João Xavier; Albardeiro, Luís; Morais, IgorSUMMARY: New U-Pb geochronological data (SHRIMP/LA-ICP-MS) is presented for zircons of volcanic rocks and dark shales of the Salgadinho deposit, located in Cercal, Iberian Pyrite Belt. Results show that the main magmatic event was placed between 387-392 Ma, indicating the oldest volcanism in the Iberian Pyrite Belt so far. Inherited and detrital zircon ages suggest affinity to Laurussian and Avalonia (s.l.) peri-Gondwanan sources, which provides additional constraints on the paleogeographic positioning of the Iberian Pyrite Belt during the Variscan Cycle.