Alexandre Lima

Chemical variations and significance of phosphates from the Fregeneda-Almendra pegmatite field, Central Iberian Zone (Spain and Portugal)

Abstract Field, textural, paragenetic, and chemical data for micas from pegmatites of the Fregeneda-Almendra pegmatitic field (Central-Iberian Zone) are used to characterize and evaluate their petrogenesis. These pegmatites show a zonal distribution from barren to evolved, with an increase in degree of evolution with increasing distance from the Mêda-Penedono-Lumbrales leucogranite. Five types of evolved pegmatites have been recognized: (1) petalite-rich, (2) spodumene-rich, (3) Li-mica + spodumenerich, (4) Li-mica-rich, and (5) cassiterite-rich pegmatites, plus six types of barren and intermediate pegmatites. Representative micas from the different pegmatite types and from the leucogranite were analyzed for major and trace elements. All micas belong to the muscovite-lepidolite series. Lithium is incorporated into Li-micas via the Li3Al-1□-2 and Si2LiAl-3 substitutions, where □ represents vacancies. The Al4Si-3□-1 and Al2□1R2+-3 substitutions, where R2+ = (Fe + Mg + Mn), account for the compositional variability of micas from the Li-mica-free pegmatites. The Li, Rb, Cs, Be, Ta, and Nb contents of micas increase in the order: leucogranites and barren pegmatites < intermediate pegmatites < spodumene-bearing and petalite-bearing dikes < Li-mica-bearing pegmatites. The Ba content decreases in the same order, and Sn and Zn are relatively abundant in the intermediate pegmatites. These variations are consistent with rare-element enrichment via fractionation processes combined with partitioning of rare elements from the pegmatite melt into the minerals and volatile phases. However, some pegmatite types occurring in this area, such as the cassiterite-rich dikes, do not seem to form part of the same evolutionary trend.

Field trip activity in an ancient gold mine: scientific literacy in informal education

Considering informal education and field trips as important didactical elements that promote science and scientific literacy (to know, to understand, to apply science), this article presents the work carried out in the gold mines of Castromil (city of Paredes, Portugal), a region with an unquestionable richness in terms of geological heritage. The field trip involved 166 students, ranging from 10 to 21 years of age, and was organized according to Orion’s model. The evaluation of the field trip was observed in three aspects: i) the construction of scientific knowledge; ii) the quality of the activities performed; and iii) the promotion of environmental education. The results were obtained through a questionnaire applied to the participants, and interviews of the two monitors responsible for the field trip. The results allow us to conclude that Orion’s model was successfully applied in an informal field trip activity promoting scientific literacy.

Geology and mineralogy of Li mineralization in the Central Iberian Zone (Spain and Portugal)

Abstract Lithium mineralization is common in the Central Iberian Zone and, to a lesser extent, in the Galizia-Trás-Os-Montes Zone of Spain and Portugal, occurring along a ~500 km-long NNW-SSE striking belt. There are different styles of Li mineralization along this belt; they are mainly associated with aplite-pegmatite bodies and, to a much lesser extent, with veins of quartz and phosphate. Lithium mineralization in the Central Iberian Zone may be classified into four types: aplite-pegmatite dykes occurring in pegmatitic fields, Li mineralization associated with leucogranitic cupolas, beryl-phosphate pegmatites and quartz-montebrasite veins. The main Li minerals of these bodies include Li-mica, spodumene and/or petalite in the pegmatitic fields and leucogranitic cupolas; triphylite-lithiophilite in the beryl-phosphate pegmatites, and amblygonite-montebrasite in the quartz-montebrasite veins. The origin of these different styles of mineralization is considered to be related to differentiation of peraluminous melts, which were generated by partial melting of metasedimentary rocks during the Variscan orogeny. On the basis of paragenesis and chemical composition, the pegmatitic fields and Li mineralization associated with granitic cupolas record the highest fractionation levels, whereas the beryl-phosphate pegmatites and quartz-montebrasite veins show lower degrees of fractionation. There are a number of textural and mineralogical indicators for Li exploration in the Central Iberian Zone and in the Galizia-Trás-Os-Montes Zone, with the highest economic potential for Li being in the pegmatite fields.

Ferronigerite with dominant substitution TiSn −1 in muscovite+chlorite aggregate from massive quartz nodule associated with a petalite-rich aplite-pegmatite of the Barroso-Alvão pegmatite field, Northern Portugal

Strange ferronigerite with dominant substitution TiSn-1 in muscovite+chlorite aggregate from massive quartz nodule associated with a petalite-rich aplite-pegmatite of the Barroso-Alvao pegmatite field, Northern Portugal was examined including associated minerals. Such extensive substitution is not typical.

Pegmatite spectral behavior considering ASTER and Landsat 8 OLI data in Naipa and Muiane mines (Alto Ligonha, Mozambique)

The Naipa and Muiane mines are located on the Nampula complex, a stratigraphic tectonic subdivision of the Mozambique Belt, in the Alto Ligonha region. The pegmatites are of the Li-Cs-Ta type, intrude a chlorite phyllite and gneisses with amphibole and biotite. The mines are still active. The main objective of this work was to analyze the pegmatite’s spectral behavior considering ASTER and Landsat 8 OLI data. An ASTER image from 27/05/2005, and an image Landsat OLI image from 02/02/2018 were considered. The data were radiometric calibrated and after atmospheric corrected considered the Dark Object Subtraction algorithm available in the Semi-Automatic Classification Plugin accessible in QGIS software. In the field, samples were collected from lepidolite waste pile in Naipa and Muaine mines. A spectroadiometer was used in order to analyze the spectral behavior of several pegmatite’s samples collected in the field in Alto Ligonha (Naipa and Muiane mines). In addition, QGIS software was also used for the spectral mapping of the hypothetical hydrothermal alterations associated with occurrences of basic metals, beryl gemstones, tourmalines, columbite-tantalites, and lithium minerals. A supervised classification algorithm was employed - Spectral Angle Mapper for the data processing, and the overall accuracy achieved was 80%. The integration of ASTER and Landsat 8 OLI data have proved very useful for pegmatite’s mapping. From the results obtained, we can conclude that: (i) the combination of ASTER and Landsat 8 OLI data allows us to obtain more information about mineral composition than just one sensor, i.e., these two sensors are complementary; (ii) the alteration spots identified in the mines area are composed of clay minerals. In the future, more data and others image processing algorithms can be applied in order to identify the different Lithium minerals, as spodumene, petalite, amblygonite and lepidolite.

Potential of Sentinel-2 data in the detection of lithium (Li)-bearing pegmatites: a study case

Only recently remotely sensed data and image processing techniques have been used in the detection of lithium (Li)- bearing pegmatites because of the current growing importance and demand of Li for the construction of Li-ion batteries for electric cars. The study area of this work was the Fregeneda (Spain)-Almendra (Portugal) region, where different known types of Li-pegmatites have been mapped. The objective of this study is to develop a methodology considering remotely sensed data, capable of identifying Li-pegmatites based on the recognition of the associated alteration halos. For that, Level 1-C cloud free Sentinel-2 images with low vegetation coverage were used. The normalized difference vegetation index (NDVI) was computed and a threshold was considered (NDVI<0.2). This study also aims exploiting the potential of Sentinel-2 data for this purpose. Minerals have important absorption features in the visible and infrared regions. Based on these features and with the aim of determining the most accurate methodology, Sentinel-2 reflectance data was used to compute RGB combinations, band ratios, principal component analysis (PCA) and image classification (supervised). These methodologies allow to predict the occurrence of iron oxides and clay minerals, and to discriminate between non-altered and hydrothermally altered zones. Band ratio 3/8 also predicts the occurrence of Li-bearing minerals. The results of the application of remote sensing data, in particular, Sentinel-2 images and image processing techniques to Li-mineralizations is of great interest to mining companies since they could lead to an increased efficiency and sustainability of mineral exploration.

Evaluation of remote sensing data potential in the geological exploration of Freixeda area (Mirandela, Portugal): a preliminary study

The value of remote sensing data to geological exploration has increased as technology has improved. The advent of multispectral and hyperspectral imaging has allowed surface mapping to be performed remotely, thereby enabling vast areas to be mapped in a short time at a fraction of the cost of traditional geologic mapping. Different scanning spectrums enabled researchers to begin cataloguing various reflection and adsorption properties of soils, rock, and vegetation. These spectra could be used to interpret actual surface lithologies from remote sensing images. The study area focused in this work was the Freixeda stretch, district of Mirandela, Portugal. In this work, an ASTER image (March 2011) from the study area was used. ASTER VNIR and SWIR reflectance data have been used to produce colour composite images that seek to maximize the lithological information in the area; ratio images have been used to highlight ferric iron; and relative band depth images of the SWIR bands have been used to predict the occurrence of Alunite/Pyrophyllite, Kaolinite, Illite and Prophylitic group minerals. The VNIR bands were used to define vegetation and also ferric iron (defined by the ratio of band 2/band 1).The vegetation ratio is defined by the ratio of band 3/band 2. The SWIR data consists of 6 bands. Band 4 is located where most cover types have maximum reflectivity. Bands 5-9 cover an area of the SWIR where many-OH bearing minerals and carbonate minerals have absorption features. The presence of Au and Ag mineralization confirm the richness of this area.

Spatial Distribution of Weathering Using Seismic Refraction – Further Results in the Vicinity of Canelas, NW Portugal

In the recent years the ever growing concern of policy makers with respect to natural hazards has led researchers and practitioners to seek more reliable, precise and time efficient techniques map zones prone to hazards. Mass movement is a hazard common to many mountainous areas around the world which can pose a serious threat to the population living within the area as well as to the structures, property, environment and crops. Several geophysical methods assume a relevant role in monitoring and surveying unstable slopes. Our aim was to show that seismic refraction can meet the demands of a time efficient and cost effective method to map this vulnerability. We performed a series if profiles with the aim of determining distribution of rock weathering thickness and velocity distribution within the vicinity of Canelas (NW Portugal). The results of each profile were analysed to give thickness of geotechnical soil as well as average values for both near surface and deeper part of each profile. The results were georeferenced in GIS and thus the estimation of the spatial distribution of the parameters allowed a means of observing some correlation with the previously mapped features of the area, namely the geology and topography.

Granitic pegmatites: the State of the Art. Preface.

The PEG2007 symposium was held on May 6–12, 2007 in Porto, Portugal. The conference was organised by the Department of Geology of Porto University, the Department of Mineralogy and Petrology of the University of the Basque Country, Bilbao, Spain, the Laboratory of Mineralogy of the University of Liège, Belgium, and the Laboratory of Mineralogy of Paul Sabatier University, Toulouse, France. The aim of this symposium was two-fold. On the one hand, specialists from all over the world had the opportunity to meet, discuss and learn about current research ideas and findings on granitic pegmatites. On the other hand, the tradition of gathering members from the scientific community every two years to advance our understanding on pegmatites was maintained, following on the “LERM” conference in the Czech Republic in 2003 and the “Crystallization processes in granitic pegmatites” conference on Elba Island (Italy) in 2005. Research on granitic pegmatites will continue to expand and, in 2009, the PEG2009 meeting will take place in Recife (Brazil). Information on the PEG2009 meeting is already available on the webpage at http://www.ufpe.br/geologia/peg2009brazil/. The PEG2007 conference was attended by 74 participants, representing 16 countries. There were 24 oral presentations and 19 poster presentations, abstracts of which are available at http://www.fc.up.pt/peg2007/. A selection of six papers presented at PEG2007 constitutes this thematic issue of the European Journal of Mineralogy. The topics of the papers presented in this issue encompass several aspects of modern pegmatite research, from regional (Neiva et al.) to detailed mineralogical studies (Novák et al., Uher et al.) through crystal-growth (Sánchez-Muñoz et al.) and trace-element (Müller et al.) aspects, as well as a review on the latest discoveries and theories on pegmatites by Simmons & Webber. We would like to thank Chief Editor Fernando Nieto and special issues coordinator Walter Maresch who helped us with the manuscripts. We are also in debt to the referees who helped us in the reviewing process of the manuscripts. A thank you also to Tania Martins and Romeu Vieira for helping in the PEG2007 organization. Although 2007 was a good year for “pegmatologists”, thanks to this meeting, it was also a sad year, because of the loss of two well-known researchers who contributed to the development of studies on granitic pegmatites. We take this opportunity to dedicate these contributions to the memory of François Fontan and Bernard Charoy.

Seismic Refraction Applied to Weathering Thickness Characterization and Slope Stability in NW Portugal

In the past decades urban areas have suffered large demographic pressures, forcing people and their housing compounds to migrate to peripheral regions were they often build without land planning concerns, and where many times they are subject to adverse natural conditions and exposed to natural hazards being landslides one of the main threats. Nowadays, geophysical methods assume a relevant role monitoring and surveying unstable slopes. We performed thirty seismic profiles with the aim of determine distribution of rock weathering through seismic refraction techniques, in Canelas, a small village in NW Portugal. Each profile was summarized with average values of velocity for each depth. Despite having a low density coverage for the area involved, the results seem to show that seismic refraction is an important tool to rapidly characterize weathering thicknesses, a very important factor to be taken into account in problems of slope stability.