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- Constraints on the structure of Maio Island (Cape Verde) by a three-dimensional gravity model : imaging partially exhumed magma chambersPublication . Represas, Patricia; Catalão, João; Montesinos, Fuensanta G.; Madeira, José; Mata, João; Antunes, Carlos; Moreira, Mário
- New approach on the gravity data of the Lagoa Salgada structure, Iberian Pyrite Belt, PortugalPublication . Represas, Patricia; Matos, João Xavier
- 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.
- 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.
- Modelling of the Neves Corvo AreaPublication . Inverno, Carlos; Rosa, C.; Matos, João Xavier; Carvalho, João; Castelo-Branco, José Mário; Batista, Maria Joao; Granado, Isabel; Oliveira, José Tomás; Araújo, Vítor; Pereira, Zélia; Represas, Patricia; Solá, A. Rita; Sousa, Pedro
- Modelización magnética del Complejo de Cunene (SW Angola) [Resumo]Publication . Mochales, Tania; Merino-Martínez, E.; Rey-Moral, Carmen; Machadinho, Ana; Carvalho, João; Represas, Patricia; García-Lobón, J. L.; Feria, María Carmen; Martín-Banda, Raquel; López-Bahut, T.; Alves, Daniela; Ramalho, Elsa; Manuel, José; Cordeiro, DomingosRESUMEN: El Complejo de Cunene (CC) representa un extenso macizo ígneo mesoproterozoico compuesto por rocas anortosíticas, gabroicas y ácidas contemporáneas, que aflora 18.000 km2 en dirección NNE-SSW desde el SW de Angola al NW de Namibia. Se han interpretado y modelizado en 2,5/3D los datos aerogeofísicos obtenidos en el proyecto PLANAGEO para investigar los límites no expuestos del CC, reconstruyendo la estructura de la corteza superficial bajo la cobertera del Kalahari. Gracias a la modelización se descifra una geometría lobular cuya extensión es casi tres veces la superficie aflorante y superior a la estimada mediante gravimetría (45.000 km2; Rey-Moral et al., 2022). Las anomalías magnéticas identificadas definen cuerpos individuales que conforman diversos pulsos magmáticos coalescentes durante el Mesoproterozoico. Las lineaciones magnéticas indican grandes sistemas de cizallamiento desarrollados en varias fases intrusivas en un contexto colisional de arco. Los lineamientos magnéticos al E sugieren un emplazamiento asociado a etapas transtensivas. Al W, con los pulsos más jóvenes, se detectan lineamientos en un régimen contraccional complejo. Estructuras tardías NNW-SSE extensionales, involucran magmas mantélicos y cuencas mesoproterozoicas tardías (<1,33 Ga).
- New evidence of Late Cretaceous magmatism on the offshore central West Iberian Margin (Estremadura Spur) from potential field dataPublication . Escada, Cláudia; Represas, Patricia; Santos, Fernando Monteiro; Pereira, Ricardo; Mata, João; Rosas, Filipe M.ABSTRACT: The West Iberian Margin (WIM) is a key example of a magma-poor passive margin, punctuated by several postrift magmatic manifestations that are part of the Late Cretaceous Atlantic Alkaline Province. In this work, potential field (gravity and magnetics) data, constrained by 3D multichannel seismic reflection data, are used to describe and characterise the geometry and nature of magmatic features located offshore the central segment of the margin, the Estremadura Spur. The estimated geometry and nature of the magmatic features was achieved through the integration of 3D gravity and magnetic inversion and 2D magnetic forward modelling. The results provide an insightful 3D subsurface model revealing that: 1) the Estremadura Spur Intrusion represents a 28 x 15 km wide laccolith with an overall granitic nature and an estimated density of 2490-2640 kg/m3 and 0.01-0.05 SI magnetic susceptibility, 2) the 26 x 17 km Fontanelas buried volcano is dominantly basaltic, with density values of 2500-2821 kg/m3 and magnetic susceptibility of 0.01 to 0.0875 SI, and 3) multiple sill complexes intruded the region, thus producing a higher magnetic background on otherwise inconspicuous anomalies The models allowed achieving a confident fit suggesting that both the ESI and the Fontanelas volcano are coeval with the outcropping magmatic features from this same magmatic event. Additionally, the results support that Late Cretaceous alkaline magmatism on the West Iberian Margin is more significant than anticipated and provide further evidence to clarify unclear geometrical aspects of similar intrusions observed onshore. Acknowledging the geometry and nature of these magmatic entities allows to better understand the role of postrift intra-plate magmatism on continental hyper-extended rifted margins by clarifying how shallow plumbing systems evolve in these settings.
- Introduction and geological setting of the Iberian Pyrite BeltPublication . Inverno, Carlos; Díez-Montes, Alejandro; Rosa, C.; García-Crespo, J.; Matos, João Xavier; García-Lobón, J. L.; Carvalho, João; Bellido Mulas, Félix; Castelo-Branco, José Mário; Ayala, C.; Batista, Maria Joao; Rubio, F.; Granado, Isabel; Tornos, F.; Oliveira, José Tomás; Rey, C.; Araújo, Vítor; Sánchez-García, Teresa; Pereira, Zélia; Represas, Patricia; Solá, A. Rita; Sousa, Pedro
- Massive sulfide exploration models of the Iberian Pyrite Belt Neves Corvo mine region, based in a 3D geological, geophysical and geochemical ProMine studyPublication . Inverno, Carlos; Matos, João Xavier; Rosa, Carlos J. P.; Castelo-Branco, José Mário; Granado, Isabel; Carvalho, João; Batista, Maria Joao; Represas, Patricia; Pereira, Zélia; Oliveira, José Tomás; Araújo, Vítor
- Metallogenetic potencial of the Paleoproterozoic mafic-ultramafic Hamutenha intrusion (SW Angola). New data from PLANAGEO project [Abstract]Publication . Morais, Igor; Batista, Maria Joao; Represas, Patricia; Albardeiro, Luís; Prazeres, Cátia; Plastov, José Manuel; Sousa, João Carlo; Bravo, Paulo; Sousa, Pedro; Carvalho, João; Rodrigues, José Feliciano; de Oliveira, Daniel Pipa Soares; Cordeiro, DomingosABSTRACT: In the SW sector of the Angolan shield occur the Kunene Anorthositic Complex (KAC), one of the most remarkable magmatic anorthositic suites worldwide. The KAC is considered a long-lived magmatic system that operated in the area intermittently during the Mesoproterozoic (1450 ± 2 Ma to 1371 ± 2.5 Ma). Smaller mafic-ultramafic intrusive bodies ranging in composition from dunite to harzbugite, pyroxenite, troctolite and gabbro are located in the KAC periphery (e.g. Epupa, Ombuku, Hamutenha, Oncócua). The Hamutenha body is a 3 km long oriented NW-SE, banded intrusion with internal zonation hosted in the Paleoproterozoic granitic rocks (1970 ± 2 Ma). The internal zone is composed by rocks with ultramafic nature, mostly harzburgites and dunites with diorites in the external zone.
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