- Home
- Conferences
- Conference Proceedings
- Conferences
10th International Congress of the Brazilian Geophysical Society
- Conference date: 19 Nov 2007 - 23 Nov 2007
- Location: Rio de Janeiro, Brazil
- Published: 19 November 2007
401 - 420 of 484 results
-
-
Descoberta de Novos Alvos de Cu no Noroeste do Arco Magmático de Mara Rosa Utilizando Dados Aerogeofísicos de Alta Densidade de Amostragem
The Goiás Magmatic Arc hosts several gold and copper-gold deposits. Recently this region was investigated by Mutunópolis Project, where airborne geophysical and geological data mapped new Cu occurrences. The processing and interpretation of the aerogeophysical data from the first part of Goiás airborne geophysical (2004) lead the generation of themes than can be used as a tool to support mineral exploration. The magnetic images of anomalous field, first vertical derivative and analytical signal amplitude maps were used to delineate shear zones, in this region represent a main metalogenetic control. The RGB ternary image (K:Th:U) was used to delineate the gamma-spectrometric domains and anomalies. The anomalous potassium and uranium were correlated with zones of hydrothermal alteration that suggest targets for future prospects of cupper and gold.
-
-
-
Caracterização dos distritos diamantíferos da região de São João da Chapada e Datas MG
This paper focused on identifying and describing geological-geophysical signatures of Sopa Brumadinho Formation, the host of diamond occurrences mapped in the southern Espinhaço region, State of Minas Gerais, Brazil. The work aimed at combining and analyzing digital spatial data to predict and select host rock mineralization. Aerogeophysical and multispectral orbital data, in addition to geological and diamond occurrence maps, were employed both separately and in an integrated approach. The digital processing steps involved several enhancements techniques, which were here employed in 1D and 2D analysis aiming to map the physical contrast of the main host rock in the study area. The results yielded by the processing, integration and interpretation steps proved methods to be effective in the understanding of the known mineralization. Some of these mineralization areas show an extension in depth and occurs under the Galho do Miguel Formation.
Key-words: Airborne geophysics; diamond districts; Sopa Brumadinho Formation.
-
-
-
Aplicação de técnicas de classificação espectral a dados magnetométricos e gamaespectrométricos para mapeamento de áreas favoráveis à mineralização de EGP na região de Serra Leste, Província Mineral de Carajás (Pará)
More LessDigital classification of airborne geophysical data was performed for mapping potential areas for PGE mineralization in the eastern portion of the Carajás Mineral Province, northern Brazil. The classification techniques applied were Principal Component Analysis, Spectral Angle Mapper and Mixture Tuned Matched Filtering. Control classes were obtained from composed magnetic and gammaspectrometric signatures of two particular mineral deposits with
known PGE occurrences, namely Serra Pelada (Au-(Pd-Pt)) and Luanga (PGE-chromite). The classified maps show that areas with mafic and ultramafic rocks have similar geophysical signatures to that of the Luanga deposit. In the case of the Serra Pelada deposit, only the surrounding areas show similar classes; this is explained by the peculiar geological characteristics of this type of deposit in the Carajás Mineral Province.
-
-
-
Algoritmos Spectral Angle Mapper e Mixture Tuned Matched Filtering aplicados à aerogeofísica para estudo da favorabilidade de mineralizações auríferas primárias no contexto da Província Mineral do Tapajós, Pará
More LessTechniques originally developed for the classification of hyperspectral remote sensing data (Spectral Angle Mapper and Mixture Tuned Matched Filtering) were here adapted to airborne geophysical data processing. Using the signature of known gold occurrences as endmembers, the results yielded through these methods proved successful to produce mineral potential maps, indicating targets potentially mineralized in gold within the terrains of the Tapajos Mineral Province (Pará State, Brazil).
-
-
-
Análise e Interpretação de Dados Aerogeofísicos Aplicados ao Mapeamento Geológico no Arco Magmático de Mara Rosa, Goiás, Brasil Central
The Mara Rosa Magmatic Arc is characterized by limited outcrops, deep weathering and thick regolith cover and
lack of systematic mapping. This area is covered by highdensity aeromagnetic and aerogamaespectrometric data.
The geophysical images provide an overview of the geological units. In this paper, these geophysical data were successfully used to highlight the relationships between the principal main lithologies, as well as their internal structural framework and boundaries. Enhancement of gamma-ray spectrometry data showed their usefulness in mapple subtle compositional variations in the area, which concur with and complement available geological data.
-
-
-
Contribuições à caracterização geológica e à exploração mineral em terrenos equatoriais úmidos a partir de processamento de dados magnetométricos e gamaespectrométricos: estudo de caso em Serra Leste, Província Mineral de Carajás
More LessThe Amazon region is characterized by dense equatorial forest, thick soil cover and rainy weather. This makes airborne geophysics a key tool for lithologic and structural mapping and improvement of preexisting geological maps. This paper presents an application study of airborne magnetic and gammaray data in the Serra Leste region, Carajás Mineral Province, providing discussions about the geophysical signatures of specific lithologies and
strategies to constrain favorable targets for exploration of Au–Pd–Pt, Cr-PGE, Cu–Au and Fe deposits.
-
-
-
Integração de dados aerogeofísicos e dados geoquímicos da área de Lagartixa, sul do Arco Magmático de Goiás
This work shows the integrated interpretation of airbone geophysical data with stream sediment geochemistry.
Gamma-ray spectrometric and magnetic data obtained with profile lines spaced 500m from Levantamento
Aerogeofísico de Goiás, Área 2, were interpreted and integrated with PGBC geochemistry results. Interpreted gamma-ray and magnetic data led to the definition domains and structures associated to each field. Domains and structures can be correlated with mapped geology. Higher contents of elements such as Pb, Zn and Cu, in
geochemistry samples, are concentrated to the southwestern portion of the area. There magnetic field shows lower values. The associated gamma-ray domains have low potassium. High contents of elements like Y, La and Zr are present in the northwestern portion of the region. The area is characterized by domains with high potassium concentration, associated to granitic intrusions. Magnetic field intensities in the area are intermediate to high. Results suggest possible potassium hydrothermal alteration in position of the northern region of the study area. Higher contents of metal in the northwestern portions associated with low potassium could be more indicative sericitic or propilytic alteration.
-
-
-
Integration of geophysical and geological data from central region of Borborema Province, Northeast of Brazil
This work shows the integration of geophysical data - gamma-ray spectrometric and magnetometric data
(Carmelo et al. 2007; Fianco et al. 2007) - of the airborne geophysical survey Cariris Velho (CPRM 2007) and
geologic data. The analysis and interpretation of the geophysics products generated a geophysical model to
the area which was correlated it with known geology. The selected area for this study comprises primary gold
deposits, inserted in the complex structural system of the Borborema Province, consisting of transcurrents shear
zones with dextral and sinistral kinematics (Bizzi et al. 2003). The main purpose of this study was to improve the geological knowledge of the area through the integration of geology, magnetometry, and gamma-ray spectrometry. Results from the present study showed good agreement, when compared with known geology. With the geological/geophysical integration, we show a concise and direct approach supporting evaluation at the scale of 1:1.000.000.
-
-
-
Interpretation of gamma-ray spectrometric data from central region of Borborema Province, Northeast of Brazil
This work shows gamma-ray spectrometric interpretation of the airborne geophysical survey Cariris Velho (CPRM
2007). The analysis and interpretation of the geophysics processing products generated a geophysical model to
the area. The study area is inserted in the complex structural system of the Borborema Province, consisting
of transcurrents shear zones, which present dextral and sinistral kinematics (Bizzi et al. 2003). The main purpose was to improve the geological knowledge of the area through the integration of geology and gamma-ray spectrometric data. Results from the present study when compared with known geology showed good agreement. With the geological/ geophysical integration, we show a concise and direct approach supporting evaluation at the scale os 1:1.000.000.
-
-
-
Aplicação Técnicas de Sensores Remotos Multi-espectrais e Hiperespectrais em Dados Aerogeofísicos Visando a Seleção de Alvos para Prospecção de Minério de Ferro na Serra do Espinhaço Meridional, MG.
More LessThis paper focused on identifying and describing geological-geophysical signatures of iron ore occurrences
associated southern Espinhaço in the State of Minas Gerais, Brazil. The work aimed at combining and
analyzing digital spatial data to predict and select iron mineralization. Aerogeophysical and multispectral orbital
data, in addition to geological and iron occurrence maps, were employed both separately and in an integrated
approach. The digital processing steps involved several enhancements techniques – conventional (pseudocolor
compositions and principal component analysis), as well as techniques originally developed for the classification of
hyperspectral remote sensing data (Spectral Angle Mapper and Mixture Tuned Matched Filtering), which were here adapted to aerogeophysical data processing. The results yielded by the processing, integration and interpretation steps proved the classification methods to be effective in the selection of targets potentially mineralized in iron. Sites with known occurrences of iron ore, associated to Serra do Sapo Ridge were successfully mapped. Additionally, other key areas, where no iron ore occurrences are known, were also individualized and great part were ground thruted in the field.
-
-
-
Aerogeofísica e SAR (R99-B/SIPAM) como ferramentas de auxílio ao mapeamento de áreas com potencial mineral na Região de Anapu-Tuerê (PA)
This paper presents an integrated approach to select potential areas for mineral exploration in the Anapu-Tuerê region, southeastern portion of the Amazonian Craton, by the use of high-resolution airborne geophysical data with radar remote sensing data (SAR-R99-B/SIPAM) and geological information. Innovation in data processing allowed the production of different types of integrated images, which were interpreted for evaluating tectonic domains,
geological units and structural elements. The integrated images, that display simultaneously geophysical and geomorphological signatures of the lithological types, showed high potential to highlight geological contacts and tectonic structures. The integration of airborne geophysical data, remotely sensed images and geological data demonstrated to be fundamental for geological mapping, producing maps with more detailed geological and structural information compared to the available maps, minimizing difficulties which usually hampers geological mapping in the Amazon. Key words: geological mapping, high-resolution airborne geophysical data, data integration, Amazon Craton.
-
-
-
Aplicação do método da polarização induzida nos arranjos gradiente e dipolo-dipolo como ferramenta de suporte à identificação de extensões da mineralização aurífera no depósito Amapari
The Amapari gold mine is located in central Amapá State of Brazil and was discovered in 1994 by Anglo American.
The mineralization is hosted by clastic chemical sediments of the Vila Nova Group (Lima et al. 1974), which is a Paleoproterozoic greenstone belt sequence. Airborne geophysics, stream sediment and soil geochemistry were the main methods used for that discovery. Among the several defined targets, the Taperebá set (Taperebá AB, Taperebá C and Taperebá D) and Urucum orebodies are the exploitable ones, nowadays, in Amapari Mine. Between Taperebá C and Urucum planned open pits, a gap in drilling investigation was observed. A dispersed soil geochemistry gold anomaly suggests the continuity of the mineralization in between those pits. IP survey in gradient and dipole-dipole arrays indicated the mineralized trend continuity. Auger and diamond drilling confirmed the mineralization extension, with about 5.000 ounces of gold in the colluviums and saprolite - sulphide resources under estimation.
-
-
-
Aplicação de Dados Aerogeofísicos e de Sensores Remotos no Refinamento da Cartografia Geológica da Região de São João Chapada-Datas, MG.
This paper presents an integrated approach to geological mapping in the Southern Espinhaço, Chapadas and Datas region, by the use of high-resolution airborne geophysical data with remote sensing data (SRTM and ETM+/Landsat 7) and geological information in 1:100.000 scale. The airborne magnetic and the remote sensing data were used to investigate the regional structural setting of the area and better define lithological boundaries. The results highlight three structural systems: NW-SE and, in minor scale, NE-SW; NE-SW in the central part and the E-W type. Combined gamaspectrometric-magnetic images portrayed the lateral continuity and the internal structure of several unities. The best interpretations of the southern part of the Espinhaço were achieved from visual analysis of the ternary radioelement map, the thorium channel map and the analytical signal amplitude map. These maps highlighted key areas and their unique inter-relationships.
-
-
-
Coronal mass ejection geometry using single coronagraph observations
Authors A. Dal Lago, W.D. Gonzalez and R. SchwennIn this work it is presented a study of the geometrical shape of CMEs derived from single coronagraph observations. The relationship between CME radial and expansion speeds is revisited and extended in order to test its validity using a larger range of CME speeds, from 200 to 3600 km/s. A high correlation between these two speeds has been found, indicating that this relation is valid for this range of speeds. Vrad-Vexp ratio from 3 self-similar expanding CME geometrical models are calculated and compared with the empirical results from LASCO observations. The general conclusion was that CMEs with angular sizes bellow 80 degrees are on average best fitted by a self-similar expanding cone with a spherical front of radius equal to the distance between the solar surface and the front of the CME, while CMEs with angular sizes above 80 degrees are on average best fitted by a self-similar expanding structure formed by a cone connected to the half of a sphere of radius equal to the major radius of the cone. These results suggest that on average the shape of CMEs changes with increasing angular size. The results presented in this work will be revisited when stereoscopic observations from STEREO are available.
-
-
-
Intense and super intense magnetic storms compared by using interplanetary parameters and geomagnetic indices
Authors A. de Lucas, E. Echer, W.D. Gonzalez, L.F. Guarnieri, A. Dal Lago, M.R. da Silva, L.E. Vieira and N.J. SchuchGeomagnetic storms are great disturbances on the Earth’s magnetic field, which are conventionally measured by the Dst geomagnetic index. Of great importance to space weather environment is the development of intense (-250 < Dst < -100 nT) and very intense magnetic storms (Dst < -250 nT). One point of current research is the study of the interplanetary causes and consequent magnetospheric response during these two classes of storm. For each storm class, it have been determined the interplanetary parameters such as Ey, Bz, and the solar wind ram pressure, PSW, and geomagnetic indices, Dst/Sym, Asy, AE, and Kp. The main goal of this study is to distinguish the interplanetary causes and the magnetospheric responses of intense and very intense magnetic storms. Besides, a criterion which characterizes the space weather phenomena during different disturbed levels is suggested.
-
-
-
The Lowering of the EEJ Backscattering Region Based on Coherent Radar Soundings in the Brazilian Sector
In the present paper we present a new feature of the equatorial electrojet observed in the Brazilian sector based on the RESCO coherent radar observations. The center height of the scattering region of the equatorial electrojet is observed to systematically decrease in altitude along the years. It has been observed through VHF radar soundings at São Luís (2.3º S, 44.2º W). This feature is discussed in terms of the displacement of the dip equator from the radar site due to the long term variations in the Earth magnetic field, which can be detected by measurements using ground magnetometers at the radar site. The math tolls used to infer the center height is presented and all different aspects of the equatorial electrojet are present and discussed in terms of established concepts and theories.
-
-
-
Variação Intersazonal da Mesopausa sobre o Cariri (7.4º S, 36.5º O), Brasil a partir de Dados de Satélite
Authors J. Fechine, C.M. Wrasse, H. Takahashi, M.G. Mlynczak and J.M. RussellAn inter seasonal variation study of mesopause structure over Cariri (7.4º S, 36.5º W) in 2005 was realized using
daily mean temperature profiles from TIMED/SABER satellite. The results show a cooler mesopause (10 K) than predicted by CIRA-86 model. It also was verified the occurrence of double mesopause structure between March and April, and September and October not predicted by model, and a mesospheric inversion layer in 83 km twice more strong than the predicted amplitude.
-
-
-
Estudo sobre a Presença de Camadas Ionosféricas Esporádicas em Períodos Calmos e Perturbados em São Luís (MA): Um Caso Estudado
Authors L.C.A. Resende, C.M. Denardini, P.S.C. Almeida and H.C. AveiroIn the present paper we show some new results related to the study on the presence of sporadic ionospheric layers at São Luís (2º31´ S, 44º16´ W), on the equatorial region, during quiet and disturbed periods before, during and after the magnetic storm that occurred in October 2003. Ionospheric profiles obtained from digital sounders were used in order to verify comparatively the height of reflection and typical frequencies related to the E and Es layers. It was made with the intention to identify in the ionospheric parameters possible evidences of the reaction of the Magnetosphere-Ionosphere system to the strong magnetic storm. To characterize the level of magnetic disturbances the Dst index has been chosen. The achieved results evidenced that the ERegion can behave in a particular way that shows the influence of the magnetic storm depending upon the magnetic activity level and its latitudinal location.
-
-
-
Variance Analysis of Incoherent Integration Applied to Simulated Equatorial Electrojet Irregularities Radar Power Spectra
Authors H.C. Aveiro, C.M. Denardini, M.A. Abdu, N.J. Schuch, L.C.A. Resende and P.D.S.C. AlmeidaThe spectral analysis of the received echoes from equatorial electrojet irregularities may show the signatures of two different plasma irregularities: Type 1 and Type 2. Each Type is related to a distinct process of plasma instabilities. Each irregularity presents itself as one gaussian-like shape in the frequency domain and the characteristics of the curve may be extracted using nonlinear curve fitting methods. Some techniques are applied to the irregularities spectra before the curve fitting so that the variance between the data and the fitting is minimum. One of these techniques is called incoherent integration and consists of averaging subsequent spectra. We simulated equatorial electrojet radar power spectra of Type 1 irregularities to elucidate the effects. The advantages and disadvantages of applying such technique are analyzed in terms of the variance between the radar spectra and the fitted curve.
-
-
-
Ultra Fast Kelvin waves in the equatorial upper atmosphere
Meteor radar wind measurement at Cariri (7.4°S, 36.5°W) and Ionosonde measurements at Fortaleza(3.9°S, 38.4°W) have been carried out in 2005. 3 to 5 days period oscillations in the mesospheric zonal wind and ionospheric F-layer bottom height (h’F) and the maximum frequency (foF2) were observed during a period from March 01 to 11, 2005. Atmospheric temperatures observed by the SABER/TIMED satellite also showed a similar
periodic oscillations. From the characteristics of the downward phase propagation, longitudinal and latitudinal extension, we conclude that this oscillation must be a 3.5–day Ultra Fast Kelvin (UFK) wave. The observed amplitude of oscillation of the F-layer height caused by the UFK waves, 20–30 km, are significant, and worthwhile to investigate in terms of the day to day variability of the Spread F occurrence.
-