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Geosciences Center
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3D Magnetic Inversion in Angola
Publication . Machadinho, Ana; Represas, Patricia; Alves, Daniela; Cordeiro, Domingos; Carvalho, João; Lopes, Rui; Caessa, Paulo; Pereira, Luis; Osório, André; GeoBioTec - Geobiociências, Geoengenharias e Geotecnologias; IGME - Instituto Geológico y Minero de España
Demanding and speculative economies make it imperative to search for new areas of mineral exploration. Angola’s geological diversity presents an enormous potential for mineral resources. This potential can be assessed by applying different methods, such as geophysical prospecting, to discover new potential targets of areas to explore. For many years, the magnetic method has been successfully used in mineral exploration. In this work we apply a 3D magnetic inversion technique to aeromagnetic data in two different study areas. The Serra da Neve alkaline complex (SNAC) represents a potential source for rare earth elements (REE) and the Jamba itabirites provides metallic mineral deposits with iron and gold mineralizations. In both case studies, whether concerning alkaline intrusions or itabirites deposits, their magnetic properties are characterized by strong magnetic anomalies clearly delineated on magnetic anomaly maps. The high magnetic susceptibility (k) contrast between these target structures and the host rocks allowed us to obtain a coherent three-dimensional geometry for the SNAC structures and the itabirites deposits. The magnetic inversion technique also provided magnetic vector inversion (MVI) susceptibility values estimation for constituent lithologies, as well as the shape and size of the studied structures and deposits. The results demonstrate the effectiveness of the magnetic method for the detection and characterization of target areas, offering an innovative technique to identify potential areas in mineral resources exploration.
Detailed in-depth mapping of the world largest anorthositic complex
Publication . Mochales, T.; Merino-Martínez, E.; Rey-Moral, C.; Machadinho, A.; Carvalho, J.; Represas, P.; García-Lobón, J. L.; Feria, M. C.; Martín-Banda, R.; López-Bahut, M. T.; Alves, D.; Ramalho, E.; Manuel, J.; Cordeiro, D.; GeoBioTec - Geobiociências, Geoengenharias e Geotecnologias; Elsevier BV
The Kunene Complex (KC) represents a very large Mesoproterozoic igneous body, mainly composed of anorthosites and gabbroic rocks that extends from SW Angola to NW Namibia (outcropping 18,000 km2, NE-SW trend, and ca. 350 km long and up to 50 km wide). Little is known about its structure at depth. Here, we use recently acquired aerogeophysical data to accurately determine its hidden extent and to unravel its morphology at depth. These data have been interpreted and modelled to investigate the unexposed KC boundaries, reconstructing the upper crustal structure (between 0 and 15 km depth) overlain by the thin sedimentary cover of the Kalahari Basin. The modelling reveals that the KC was emplaced in the upper crust and extends in depth up to ca. 5 km, showing a lobular geometry and following a large NE-SW to NNE-SSW linear trend, presumably inherited from older Paleoproterozoic structures. The lateral continuation of the KC to the east (between 50 and 125 km) beneath the Kalahari Cenozoic sediments suggests an overall size three times the outcropping dimension (about 53,500 km2). This affirmation clearly reinforces the economic potential of this massif, related to the prospecting of raw materials and certain types of economic mineralization (Fe-Ti oxides, metallic sulphides or platinum group minerals). Up to 11 lobes have been isolated with dimensions ranging from 135.5 to 37.3 km in length and 81.9 to 20.7 km in width according to remanent bodies revealed by TMI mapping. A total volume of 65,184 km3 was calculated only for the magnetically remanent bodies of the KC. A long-lasting complex contractional regime, where large strike-slip fault systems were involved, occurred in three kinematic pulses potentially related to a change of velocity or convergence angle acting on previous Paleoproterozoic inherited sutures. The coalescent magmatic pulses can be recognized by means of magnetic anomalies, age of the bodies as well as the lineations inferred in this work: (i) Emplacement of the eastern mafic bodies and granites in a stage of significant lateral extension in a transtensional context between 1500 Ma and 1420 Ma; (ii) Migration of the mantle derived magmas westwards with deformation in a complex contractional setting with shearing structures involving western KC bodies and basement from 1415 Ma to 1340 Ma; (iii) NNW-SSE extensional structures are relocated westwards, involving mantle magmas, negative flower structures and depression that led to the formation of late Mesoproterozoic basins from 1325 Ma to 1170 Ma. Additionally, we detect several first and second order structures to place the structuring of the KC in a craton-scale context in relation to the crustal structures detected in NW Namibia.
Mural Paintings Characterisation Using X-ray Fluorescence and Raman Spectroscopy-A Case Study
Publication . Freire-Lista, David M.; Vázquez, Ezequiel; Castro, Pablo Barreiro; Salavessa, Eunice; Costa, Maria do Rosário; Moreira, Rafael de Faria Domingues; López , Ana J.; CHAM - Centro de Humanidades; MDPI - Multidisciplinary Digital Publishing Institute
Sixteenth-century mural paintings of Nossa Senhora das Neves in Vilar de Perdizes (Galicia—North Portugal Euroregion) were analysed. An iconographic study has allowed us to understand the meaning of the seven scenes that constitute the mural painting. X-ray fluorescence (XRF) and Raman spectroscopies determined the compounds used in this mural painting, both in the original and in later repaintings. The black paint was bone black. Hydroxyapatite characteristic bands and those of the associated phosphates have been identified. White lime was used as white paint. Lepidocrocite and goethite were used to make yellows, and hematite was used to make red shades. Cinnabar has been used for a later red repaint. Carbon-based compounds and rutile were used to create different tonalities by darkening or lightening colours. It is of great significance to obtain accurate and reliable mural painting information through scientific means, since preservation, restoration, and repainting without detailed information can be harmful to mural paintings.
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Entidade financiadora
Fundação para a Ciência e a Tecnologia
Programa de financiamento
6817 - DCRRNI ID
Número da atribuição
UIDB/00073/2020