Alexandra Guedes

A three stage fluid flow model for Variscan gold metallogenesis in northern Portugal

Mineralogical, fluid inclusion and geochemical studies were made on two intra-granitic gold deposits (Grovelas and Pene- dono), together with a deposit linked to sub-vertical structures in silicified metasediments at Tres-Minas, and several intra- metamorphic occurrences at Vila Pouca de Aguiar. They all possess similar mineral assemblages, deformational state, fluid flow characteristics, ore fluid composition and have comparable P-T conditions. Three successive crystallisation stages are recorded during the formation of gold-bearing structures independent of their location or host rocks (granites or metasedi- ments). They are: Stage 1 — the development of milky quartz veins that formed primarily after the emplacement of peraluminous two-mica granites (315-310 Ma) at P-T conditions reflecting high temperature and low pressure. They are similar to those from pluton induced metamorphismOPa 300-350 MPa and Ta 500-5508CU: No clear evidence was found for gold deposition during this stage. Stage 2 — during orogenic uplift and repeated tectonic reactivation a clear quartz was deposited in the early milky quartz veins (Stage 1) at P-T conditions between 100 and 300 MPa and 300 and 4508C. Local sulphide deposition (arsenopyrite II and pyrite II) occurred in clear quartz, but was never massive. The fluids percolating within the granite were mainly aqueous- carbonic and reflect equilibrium with the metamorphic host rocks. They are very similar to those found in metamorphic environments. No evidence for the involvement of magmatic fluids was found. Stage 3 — intense microfissuring of the earlier vein infillings occurred, associated with the main episode of gold deposition. The P-T conditions were ,100 MPa and ,3008C based on aqueous fluid inclusions. Native gold and electrum crystallised together with sulphides (galena, chalcopyrite and bismuthinite), native Bi and sulphosalts (Pb-Bi-Ag dominated). The fractures frequently contain chlorite (^ sericite) especially where they crosscut earlier sulphides (arsenopyrite). These processes and fluid types are similar in both the granites and metamorphic host rocks. Therefore, the gold ores appear to be the result of successive periods of fluid circulation, in this case related to the uplift of the Variscan basement in response to high heat flow and the intrusion of granites. Without exception, these fluids have been re-equilibrated with the metamorphic rocks. However magmatic fluids are absent; the granites thus act passively as heat engines for fluid circulation. q 2000 Elsevier Science B.V. All rights reserved.

Tailored design of CoxMn1−xFe2O4 nanoferrites: a new route for dual control of size and magnetic properties

This work reports the tailored design of novel mixed ferrite nanoparticles, CoxMn1−xFe2O4 (x = 0, 0.3, 0.7, and 1), through an optimized one-pot aqueous coprecipitation process. The influence of the substitution between Mn(II) and Co(II) and of the alkaline agent, isopropanolamine (MIPA) or NaOH, on the morphological, chemical and magnetic properties of the nanomaterials was investigated. The joint action between chemical substitution and type of alkaline agent allowed a precise tuning of the particle size, magnetic properties and inversion degree of the spinel structure. A wide range of particle dimensions (from 3 to 30 nm) and saturation magnetization (from 57 to 71 emu g−1) was achieved. The increase of Co(II) content from x = 0 to x = 1 led to a systematic decrease of the particle size, regardless of the base type, which could be modelled by an exponential decay function. For each Co:Mn composition, the use of MIPA instead of the traditional NaOH promoted a three times reduction of the particle size and simultaneously switched the magnetic state of the CoxMn1−xFe2O4 nanomaterials from ferromagnetic to superparamagnetic. These results constitute a step forward in the challenging quest for high-performance magnetic nanoprobes by an eco-friendly synthesis route.

Quantitative colour analysis of beach and dune sediments for forensic applications: A Portuguese example

In this study, the colour of 23 sediment samples collected in different Portuguese beaches in the North (Entre-Douro and Minho) and 33 in the South (Algarve) was tested. Spectral colour parameters (L*a*b*) were measured after several presentation/pre-treatment methods: drying at 40 degrees C, sieving (<150 and <63 microm) and ashing at 850 degrees C, using a Konica Minolta CM-2600d spectrophotometer. A descriptive statistical analysis with L*a*b* values for each presentation/pre-treatment method was performed to ascertain within-sample reproducibility followed by a hierarchical cluster analysis to obtain significant discrimination between samples using colour analysis. The samples analysed presented a colour closest to red and yellow continuums and a lightness close to the pale side of the L*a*b* system colour sphere with samples collected in the North presenting analysis on average darker L values than the samples collected in the South. The cluster analysis, dried, unsieved bulk samples L*a*b* values gave the best discrimination between samples. The clusters analysis dried, unsieved bulk samples-dried, sieved <150 microm fraction set allowed better discrimination between samples compared with the dried, sieved <63 microm fraction set or dried, unsieved bulk samples-ashed bulk, unsieved samples set and even with dried, unsieved bulk samples/dried, sieved <150 microm fraction/dried, sieved <63 microm fraction/ashed bulk, unsieved samples considered all together.

Variations in fly ash composition with sampling location: Case study from a portuguese power plant

Fly ash (FA) is a heterogeneous and complex material resulting from coal combustion in thermoelectric power plants (TPP). Therefore, different types of coals, worldwide, produce FAs with different compositions. However, the location of the FA sampling system, inside the TPP, is also important to the composition of the FA produced at each location. A case study of FA from a Portuguese TPP, using several coal and FA characterization techniques (particle size analysis, proximate and ultimate analyses, XRF, SEM/ESEM/EDS, Optical microscopy, XRD, inferred chemistry, and AAS), has shown that FA chemical classification, mineralogy and phase-mineral classification, and trace elements (Cr, Cu, Mn, Ni, Pb, and Zn) vary due to sampling location. This has implications for improved understanding of the combustion system, as well as in collecting ash products from TPPs for particular market applications. f 2009 The University of Kentucky Center for Applied Energy Research and the American Coal Ash Association All rights reserved. A R T I C L E I N F O Article history: Received 28 October 2009; Received in revised form 4 December 2009; Accepted 9 December 2009

Characterization of soils from the Algarve region (Portugal): A multidisciplinary approach for forensic applications

The Algarve is located at a very short distance from North Africa, in Southern Portugal, and as one of the most touristic regions of Portugal, it is accessible by air, land and sea. It is very susceptible to many illegal activities, such as illegal migration, drug trafficking, kidnapping, and murder, among others. Therefore, an Algarve soils database for forensic purposes is being conducted with the conjunction of geological and palynological methodologies on soils characterization, since this is of fundamental importance to assess reliable evidence on forensic investigations. In this study, the properties of soils from several proximate sites from the Algarve were investigated, namely: (i) colour determined by spectrophotometry; (ii) particle size distribution determined by laser granulometry; (iii) low-field magnetic susceptibility by a susceptibility meter; and (iv) pollen content using a light microscope. Finally, a hierarchical cluster analysis was applied to ascertain the capacity of the different soil properties for discrimination between samples. The study reveals the utility of geobotanical techniques for forensic discrimination of soils. Even though some similarities between some of the samples were found, each one presented a combination of colour, particle size distribution, magnetic susceptibility and pollen features that enable the determination of a fingerprint expected to reveal a specific site for future selection of coastal search areas in the Algarve region.

Blocking temperature in exchange coupled MnPt∕CoFe bilayers and synthetic antiferromagnets

Exchange coupled Mn51.5Pt48.5∕Co90Fe10 bottom-pinned bilayers and synthetic antiferromagnets (SAFs) were prepared by magnetron sputtering. Exchange bias, coercivity, and blocking temperature were determined as a function of the MnPt thickness. Interfacial exchange energy was found to be Jex=0.4erg∕cm2 for a Mn51.5Pt48.5(t⩾20nm)∕Co90Fe10 (5nm) bilayer. Thermal stability of the bilayers was analyzed by separation of the blocking temperature distribution in (a) width ΔTB and (b) center temperature TB,center of the distribution. For thick MnPt films ΔTB is constant but steadily increases for thin films. SAF structures show higher exchange coupling and higher blocking temperatures at thin layer thickness (tMnPt=8.5nm).Exchange coupled Mn51.5Pt48.5∕Co90Fe10 bottom-pinned bilayers and synthetic antiferromagnets (SAFs) were prepared by magnetron sputtering. Exchange bias, coercivity, and blocking temperature were determined as a function of the MnPt thickness. Interfacial exchange energy was found to be Jex=0.4erg∕cm2 for a Mn51.5Pt48.5(t⩾20nm)∕Co90Fe10 (5nm) bilayer. Thermal stability of the bilayers was analyzed by separation of the blocking temperature distribution in (a) width ΔTB and (b) center temperature TB,center of the distribution. For thick MnPt films ΔTB is constant but steadily increases for thin films. SAF structures show higher exchange coupling and higher blocking temperatures at thin layer thickness (tMnPt=8.5nm).

Raman Microspectroscopy of Genuine and Fake Euro Banknotes

ABSTRACT To evaluate the effectiveness of Raman microspectroscopy in euro banknotes’ recognition, several genuine and fake 10 and 20 euro banknotes were analyzed. Raman microspectroscopy revealed itself to be very useful in the detection of differences in the inks used to provide the color on the banknotes. However, the study revealed that the Raman analysis results are not decisive to guarantee the authenticity of a specific banknote since similar Raman spectra were obtained for genuine and fake banknotes. Even the Raman microspectroscopy analysis obtained for the same color on different areas of fake banknotes revealed similar spectra, and this can help law enforcement agencies to identify counterfeit tracking routes.

Pla a_1 aeroallergen immunodetection related to the airborne Platanus pollen content

Platanus hispanica pollen is considered an important source of aeroallergens in many Southern European cities. This tree is frequently used in urban green spaces as ornamental specie. The flowering period is greatly influenced by the meteorological conditions, which directly affect its allergenic load in the atmosphere. The purpose of this study is to develop equations to predict the Platanus allergy risk periods as a function of the airborne pollen, the allergen concentration and the main meteorological parameters. The study was conducted by means two volumetric pollen samplers; a Lanzoni VPPS 2000 for the Platanus pollen sampling and a Burkard multivial Cyclone Sampler to collect the aeroallergen particles (Pla a_1). In addiction the Dot-Blot and the Raman spectroscopy methods were used to corroborate the results. The Pla a_1 protein is recorded in the atmosphere after the presence of the Platanus pollen, which extend the Platanus pollen allergy risk periods. The Platanus pollen and the Pla a 1 allergens concentration are associated with statistical significant variations of some meteorological variables: in a positive way with the mean and maximum temperature whereas the sign of the correlation coefficient is negative with the relative humidity. The lineal regression equation elaborated in order to forecast the Platanus pollen content in the air explain the 64.5% of variance of the pollen presence in the environment, whereas the lineal regression equation elaborated in order to forecast the aeroallergen a 54.1% of the Pla a_1 presence variance. The combination of pollen count and the allergen quantification must be assessed in the epidemiologic study of allergic respiratory diseases to prevent the allergy risk periods.

Quantitative Determination of Gaseous Phase Compositions in Fluid Inclusions by Raman Microspectrometry

ABSTRACT Raman microspectrometry has been revealed as a powerful technique for performing qualitative analysis and estimation of relative molar fractions of the gaseous species present in minerals fluid inclusions. In this work, the methodology and calibration procedures used for the quantification of the different species in fluid inclusions are described, paying special attention to the estimation of the CO2 molar fraction. A discussion about the Fermi resonance of CO2 vibrations (ν1-2ν2; 1285–1388 cm−1) is also included.

Pollen Raman spectra database: application to the identification of airborne pollen.

Raman microspectroscopy allows a non-destructive identification of airborne particles. However, the identification of particles such as pollen is hindered by the absence of a spectral library. Although reference spectra of pollen have been published before, they have always been limited to a certain number of species. In this work, Raman spectra of 34 pollen types are presented and were used to build a pollen spectra primary library. Afterward, the applicability of this database for detecting and identifying pollen in airborne samples was tested. Airborne pollen samples collected during April, May and August were compared with blank pollen spectra by means of Hit Quality Index. Although a much larger library would be required, our results showed that all first hits correspond to the same blank pollen species of the questioned sample from the air. This possibility is an innovative idea and a promising line of investigation for future RAMAN technology development in the area of aerobiology.