Loading...
20 results
Search Results
Now showing 1 - 10 of 20
- Cartografia e caracterização de recursos minerais da região de Torres Vedras-Bombarral : Relatório final 2012Publication . Lisboa, Jose; Sardinha, Rui; Carvalho, Jorge; Oliveira, Álvaro
- Diferenças na intensidade de alteração química de sedimentos Pliocénicos a norte e sul do MondegoPublication . Oliveira, Álvaro; Dinis, Pedro A.; Rocha, FernandoProcede-se a uma análise comparativa de características mineralógicas e geoquímicas (elementos maiores), usadas na definição de intensidade de altyeração química, de sedimentos pliocénicos colhidos na margem Atlântica a norte e sul do rio Mondego. Ainda que se note alguma influência da granulometria dos sedimentos nas características composicionais, as unidades a norte do Mondego revelam sempre alteração química menos intensa que as unidades a sul do Mondego. Estas diferenças justificam-se por proveniência distinta e não devem ter qualquer significado climático.
- Estruturas negativas da Casa Romana do Castro de São Domingos (Lousada) : as fossas escavadas no saibroPublication . Nunes, Manuel; Lemos, Paulo; Leite, Joana; Novais, Hugo; Oliveira, Álvaro
- Posibles aplicaciones industriales de las arenas del Kalahari de Angola [Resumo]Publication . Lisboa, Jose; Oliveira, Álvaro; Rodrigues, José Feliciano; Fernández, J.; Manuel, JoséRESUMEN: Las arenas de color amarillo ocre con poca o ninguna matriz procedentes de la Formación Arenas Ocres (Mio-Plioceno) y las arenas lavadas de colores claros del Cuaternario (Oliveira y Sousa, 2021), presentes en la cuenca del Kalahari, se extienden sobre una vasta área en el SO de Angola, presentando una gran homogeneidad en todos los niveles a lo largo de esa cuenca. Sin embargo, muestran características morfológicas similares a las de las arenas del desierto y, como tales, no son adecuadas para usos más comunes en la obra civil, como el agregado de cemento. Son arenas de tamaño de grano generalmente < 1 mm, con predominio de fracción fina (125-250 μm), subangulares a subredondeadas, de tendencia bimodal, bien calibradas, con un contenido de matriz generalmente ≤ 7%. Están formados por granos de cuarzo, escasos minerales máficos u otros, dando como resultado una composición química con SiO2 > 98.5% y un reducido contenido en elementos penalizadores. Considerando la granulometría y el análisis químico, estas arenas tienen posibles usos en sectores de la industria cerámica y del vidrio, dependiendo, para aplicaciones menos exigentes, de métodos de beneficio sencillos, en particular para reducir el contenido de alúmina y especialmente de óxidos de hierro concentrados en los recubrimientos que a menudo afectan parcialmente a los granos. Estos pueden reducirse mediante lavados y tratamientos simples de fricción.
- Depth estimation of pre-Kalahari basement in Southern Angola using seismic noise measurements and drill-hole dataPublication . Carvalho, João; Alves, Daniela; Borges, José Fernando; Caldeira, Bento; Cordeiro, Domingos; Machadinho, Ana; Oliveira, Álvaro; Ramalho, Elsa; Rodrigues, José Feliciano; Llorente, J.; Ditutala, M.; Lobón, Jose Luis Garcia; Máximo, J.; Carvalho, Cristina Isabel Paulo; Labaredas, José; Ibarra, P.; Manuel, JoséABSTRACT: The remote Southern region of Angola is covered by siliciclastic Kalahari Cenozoic formations that host underground aquifers of great importance to local populations affected by water scarcity problems. These aquifers are well developed where Kalahari sands reach appropriate thicknesses. On the other hand, at the eastern end of this area, regional aeromagnetic data recently acquired suggested the possibility of the continuity of the geological structures of the Lufilian Arc, sited in the nearby Zambia and Congo, southwestwards into Angola under the Kalahari formations. Once the Lufilian Arc is associated with the presence of the so-called Central African Copperbelt, this possibility increased the interest in determining the depth to Pan-African rocks under the Kalahari basin. To estimate the thickness of Kalahari formations in this area of difficult access and poor logistics, an expedited and non-invasive geophysical method was needed. Seismic noise and the single-station Nakamura technique were chosen, but due to the large distance of the study area from the ocean, one of the major sources of seismic noise, a test survey was acquired in the Cuvelai region to assess the signal quality, where the data was calibrated using available drill-holes. >170 points of seismic ambient noise were later acquired and the horizontal/vertical (HVSR) amplitude versus frequency curves were 1D inverted for the best velocity/density model for each station. The results were compared with 1D inverted legacy vertical electrical soundings reprocessed and validated in this work, showing similar depth-to-basement, while interpreted velocities/densities of geological formations were sampled and confirmed with measurements. A depth-to-basement map was produced using seismic information, mechanical soundings, and geological information. Despite the relatively reduced geographical area covered, the map presents valuable information for hydrogeology and mineral exploration purposes and agrees with a previously available coarser map of Kalahari thickness and with observations from geological surveys simultaneously conducted at the time of the seismic surveys.
- Cartografia e caraterização composicional cerâmica de argilas comuns da região de Torres Vedras - BombarralPublication . Lisboa, Jose; Sardinha, Rui; Oliveira, Álvaro; Carvalho, J. F.
- Preliminary study of quartz gravel and veins occurring in the Equimina region, Benguela (Angola): potential uses in industryPublication . Lisboa, Jose; Pereira, L. F.; Osório, A.; Rodrigues, José Feliciano; Fernández, J.; Oliveira, Álvaro; Manuel, JoséABSTRACT: Vast occurrences of quartz in veins and extensive gravel beds in the coastal area of Equimina, approximately 100 km south of Benguela, constitute the object of this study, aiming for its industrial use. These occurrences are related to Paleoproterozoic gneisses and migmatites on which they outcrop. The veins are quite dismantled on the surface, and show a pronounced strike scattering, but the NE-SW orientation prevails. Some veins are pegmatitic (feldspar, quartz, and mica), others, if not the majority to the East in the study area, have a strong predominance of milky quartz with low content of other minerals. Except for a superficial and removable patina of iron oxides that often coats the quartz, it is free of visible impurities. Chemical analysis confirms high purity (SiO2 > 99.5%) and very low content of penalizing oxides. Although the composition of quartz is suitable for use in the ceramic and glass industry, due to the ways it occurs, the main potential of this abundant resource in the studied area is for the refractory and metallurgy industry. Besides the chemical composition, the size of the gravel mostly meets the dimensional requirements for silicon metal production, needing minimal beneficiation.
- Contribuição para o conhecimento das argilas da Bobonaro Scaly Clay e suas potencialidades na região de Venilale, Timor LestePublication . Lisboa, Jose; Carvalho, Jorge; Oliveira, Álvaro; Carvalho, C.; Grade, JoséEfectuou-se o levantamento geológico de uma área de afloramento da formação Bobonaro Scaly Clay (Miocénico médio) em Venilale. A mineralogia das amostras revelou argilas constituídas por ilite, caulinite, quartzo e esmectite, por ordem decrescente de teores; em percentagem acessória ocorrem feldspato potássico, plagioclase, gesso e hematite. Não existem variações significativas na composição mineralógica das amostras. A natureza essencialmente es,ectítica destas argilas, referida noutros trabalhos, não se confirmou. A possibilidade de aplicação destas argilas em cerâmica estrutural è condicionada pela adição de areia, devido ao excessivo teor de esmectites. Considerando correcções várias ao cálculo de recursos, admite-se que estes deverão rondar os 9.000.000 m3, na área cartografada.
- Typological classification of clayey raw materials for ceramics manufacture, in the Tábua region (central Portugal)Publication . Lisboa, Jose; Carvalho, Jorge; Cunha, Pedro Proença e; Oliveira, ÁlvaroMapping of clay resources in the Cenozoic deposits of the Tábua region (central Portugal) has been carried out, together with the chemical, mineralogical and technological characterization of seventeen clay samples. The study was undertaken to relate the lithostratigraphic units and the typology of raw materials with regard to the manufacture of ceramics. The sedimentary succession comprises two units with different suitability for the manufacture of ceramics: an upper unit, with clays that present technological restrictions; and a lower unit with a much greater potential. A small set of parameters has been identified which differentiate the typological units. These parameters allow a realistic estimation to be made of the ceramic properties of any clay layer sampled in the study area. It is anticipated that with minor field work and sampling, the typological column can also be used in adjacent areas.
- Argilas de Timor Leste : contribuição para o seu conhecimentoPublication . Oliveira, Álvaro; Lisboa, Jose; Carvalho, C.; Grade, José; Carvalho, Jorge