Evaluating geoscan AMSS MK-II for gold exploration in the Fazenda Maria Preta District, Rio Itapicuru greenstone belt, Bahia State, Brazil

The Rio Itapicuru Greenstone Belt (RIGB), located in north-eastern Brazil, is an important gold producing region. It hosts two important mining districts, the Fazenda Brasileiro and the Fazenda Maria Preta, owned by Companhia Vale do Rio Doce (CVRD), plus a number of gold occurrences, all associated with hydrothermal alteration along shear zones. In 1992, Geoscan multispectral scanner data were acquired for mineral exploration purposes over more than 7,500 km² in this greenstone belt. Geoscan AMSS is a 24-band airborne scanner, with 5 meter spatial resolution. Standard image processing techniques, applied immediately after data acquisition, defined some spectral anomalies, particularly due to silicification and oxidation, which could be due either to hydrothermal alteration or to weathering processes. We have reprocessed the Geoscan data over a portion of the RIGB in order to define possible anomalies due to hydrothermal alteration minerals, using the feature-oriented principal component selection (FPCS) technique, modified for use with Geoscan data. Laboratory reflectance spectra of residual soils were acquired to establish superficial expression of hydrothermal minerals that occur in sub-surface and to guide image processing and interpretation. This led to the production of "mineral component" images, in which the spatial distribution of some minerals are shown. Results of the spectral analysis of soil samples showed that goethite may be used as a surface indicator of hydrothermal alteration and that it is not possible to differentiate the alteration zones from surrounding rocks based on the hydroxyl or carbonate spectral features.O Greenstone Belt do Rio Itapicuru (RIGB), localizado no nordeste do Brasil, é uma importante região produtora de ouro no país. Ele contém dois importantes distritos mineiros, o da Fazenda Brasileiro e Fazenda Maria Preta, pertencentes à Companhia Vale do Rio Doce (CVRD), além de diversas outras ocorrências auríferas, todas elas associadas a processo de alteração hidrotermal ao longo de zonas de cisalhamento. Em 1992, imagens do sensor multiespectral Geoscan foram obtidas em mais de 7.500 km² do greenstone. O Geoscan AMSS Mk-II é um sensor aeroportado que cobre 24 bandas espectrais, com 5 metros de resolução espacial no caso deste levantamento. Técnicas padrão de processamento de imagens, aplicadas imediatamente após o levantamento, definiram uma série de anomalias espectrais, relacionadas a processos de silicifícação e oxidação, que podem tanto ser devidos a processos de alteração hidrotermal quanto intempéricos. Esses dados foram reprocessados para uma porção do RIGB na tentativa de se definir possíveis anomalias espectrais devidas a minerais de alteração hidrotermal, utilizando a técnica denominada feature-ohentated principal component selection (FPCS), modificada para uso com os dados Geoscan. Análises espectrais de laboratório foram realizadas em amostras de solos residuais e em rochas, no sentido de estabelecer a expressão superficial dos minerais de alteração hidrotermal que ocorrem em sub-superfície e orientar o processamento e a interpretação das imagens. Isso resultou na produção de imagens "componentes minerais", nas quais a distribuição espacial de alguns minerais de alteração é mostrada. Resultados da análise espectral de solos residuais mostraram que a goetita pode ser utilizada como um indicador superficial da presença de alteração hidrotermal e que não é possível diferenciar as zonas de alteração das rochas que as contém com base em feições espectrais de minerais contendo o ânion hidroxila ou carbonato

Semiclassical structure of chaotic resonance eigenfunctions

We study the resonance (or Gamow) eigenstates of open chaotic systems in the semiclassical limit, distinguishing between left and right eigenstates of the non-unitary quantum propagator, and also between short-lived and long-lived states. The long-lived left (right) eigenstates are shown to concentrate as $\hbar\to 0$ on the forward (backward) trapped set of the classical dynamics. The limit of a sequence of eigenstates $\{\psi(\hbar)\}_{\hbar\to 0}$ is found to exhibit a remarkably rich structure in phase space that depends on the corresponding limiting decay rate. These results are illustrated for the open baker map, for which the probability density in position space is observed to have self-similarity properties.Comment: 4 pages, 4 figures; some minor corrections, some changes in presentatio

Sarcophagidae (Diptera) atraídos a cadáveres de cochinillo, con nuevas citas para la fauna portuguesa

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Orbital Magnetism in Ensembles of Parabolic Potentials

We study the magnetic susceptibility of an ensemble of non-interacting electrons confined by parabolic potentials and subjected to a perpendicular magnetic field at finite temperatures. We show that the behavior of the average susceptibility is qualitatively different from that of billiards. When averaged over the Fermi energy the susceptibility exhibits a large paramagnetic response only at certain special field values, corresponding to comensurate classical frequencies, being negligible elsewhere. We derive approximate analytical formulae for the susceptibility and compare the results with numerical calculations.Comment: 4 pages, 4 figures, REVTE

Short-range interactions in a two-electron system: energy levels and magnetic properties

The problem of two electrons in a square billiard interacting via a finite-range repulsive Yukawa potential and subjected to a constant magnetic field is considered. We compute the energy spectrum for both singlet and triplet states, and for all symmetry classes, as a function of the strength and range of the interaction and of the magnetic field. We show that the short-range nature of the potential suppresses the formation of ``Wigner molecule'' states for the ground state, even in the strong interaction limit. The magnetic susceptibility $\chi(B)$ shows low-temperature paramagnetic peaks due to exchange induced singlet-triplet oscillations. The position, number and intensity of these peaks depend on the range and strength of the interaction. The contribution of the interaction to the susceptibility displays paramagnetic and diamagnetic phases as a function of $T$.Comment: 12 pages,6 figures; to appear in Phys. Rev.

Chemical composition of corn and sorghum grains cultivated in Oxisol with different application methods and doses of zinc.

In general, tropical soils present low concentrations of zinc (Zn), and the deficiency of Zn is recognized as a world nutritional problem for cereal production and human beings. Therefore, the main goal of this study was to assess the effects of different methods of Zn application on the quality of corn and sorghum grains grown in Oxisol. Two experiments were set up in the experimental area of UNESP (campus of Jaboticabal, Brazil). The following nine treatments were applied:three doses of Zn by banded application (seed furrows), three doses of Zn by incorporation into soil (0-20 cm depth), foliar application, seed application, and control (no Zn applied). The treatments were arranged in randomized blocks with four replicates. The contents of Zn, carbohydrates and proteins were determined for corn and sorghum grains. Regardless of the method, Zn application promoted higher contents of this micronutrient in corn and sorghum grains. The banded application method of Zn in soil promoted greater contents of total carbohydrates, starch and protein in both cultures. The incorporation of Zn into the soil method provided higher contents of soluble carbohydrates in both corn and sorghum grains