Augusto César Bittencourt Pires

Integração e análise de dados aerogeofísicos por meio da aplicação de técnicas de processamento digital de imagens e classificação não supervisionada: o exemplo do Greenstone Belt Rio das Velhas, quadrilátero ferrífero, MG

Poor outcrop and deep weathering characterize the Rio das Velhas Greenstone Belt in the southeastern from Brazil. This paper summarizes the use of high-density airborne survey for mineral exploration studies based on interpretation enhancements of magnetic, radiometric and frequency domain electromagnetic data using image-processed methods and an unsupervised classification. The generated products provide new insights and an excellent tool for mapping and trace individual lithological units, improving the information content of the single geophysical channels. The geophysical images were processed using different combinations. The best product was the analytical signal amplitude and inclination integrated by IHS transformation. Information extracted from this image maps the geology and lineament patterns at both regional and local scales. The K-means technique using ten classes was also applied to the geophysical data. These results enhance the lithologies mapped by the field geologists at the 1:100.000. Also shows important host rocks and different gold mineralized geological domains. Such domains host the known gold mineralization, illustrating the utility of these techniques to improve the geological knowledge in the study area.

Radiação gama e resistividade elétrica em solo com aplicação de carbonatito e fertilizantes agrícolas no Distrito Federal

EMBRAPA (Empresa Brasileira de Pesquisa Agropecuaria) and Brasilia University developed a research project about the viability of carbonatite rock as agricultural fertilizer. As an initial experiment, several mixtures of carbonatite, limestone, phosphorous and potassium compounds were added as fertilizers in an oxisol area (red-latosol, according with Brazilian System of Soil Classification), in Distrito Federal, central Brazil. The experiment area was divided in 56 plots (4 × 7m) and each plot received a fertilizer mixture. The purpose of this work was to verify if the addition of fertilizer mixture to the soil modified its radiometric and resistivity properties and if it is possible to identify this change. Gamma-ray and electrical resistivity measurements were obtained in an experimental area and in a natural savannah type vegetation area. The results showed that the fertilizer addition modified soil natural properties causing a small increase in K, U, Th levels and decreasing ten times electrical resistivity. A low contrast of radiation was observed between plots, and then it was not possible to differentiate the several treatments in base of gamma-ray measurements. Electrical resistivity was efficient to identify three groups of plots related to mixtures characteristics, respectively with phosphorous, potassium and limestone / carbonatite predominance.

PHOSPHORITE PROSPECTION USING GROUND GAMMA SPECTROMETRY IN NORTHEAST GOIÁS STATE, BRAZIL

ABSTRACT. The Bambui Group, where the study area is located, is a favorable environment for phosphate rock formation, and hence, is an area of economic interest. The use of gamma ray spectrometry aims at selecting targets for ore exploration, since apatite, a phosphatemineral, generally has a high content of uranium. To this end, approximately 10 linear kilometers (527 stations) of ground gamma ray spectrometry data were acquired, along five profiles, pre-selected based on geophysical data,as well as public domain geochemical and geological information. The analysis of uranium, thorium and potassium and their ratios indicates that the enrichment of Urelative to K is well mapped by the eU/eTh and eU/K ratios, as it was confirmed in the field. Keywords: ground gamma ray prospection, phosphorites targets, Bambu´i Group, uranium. RESUMO . O Grupo Bambui, onde se encontra inserida a area de trabalho, possui um ambiente favoravel a formacao de rochas fosfaticas, apresentando-se assim como uma regiao de interesse economico. A utilizacao do metodo gamaespectrometrico tem como finalidade a selecao de alvos para prospeccao do minerio, uma vezque a apatita, mineral fosfatico, geralmente apresenta um teor elevado de U. Para este fim foi realizada a aquisicao de, aproximadamente, 10 km lineares, totalizando 527 estacoes de dados gamaespectrometricos terrestres ao longo de cinco perfis pre-selecionados com base em dados aerogeofisicos, informacoes geoquimicas e de geologia de dominio publico. A analise dos dados dos radioelementos obtidos e de suas razoes indica que o enriquecimento de U em relacao ao K, e bem mapeadopelas razoes eU/eTh e eU/K, o que foi confirmado em campo. Palavras-chave: prospeccao gamaespectrometria terrestre, alvos de fosforitos, Grupo Bambui, urânio.

Interpretação de dados gamaespectrométricos do Projeto Rio do Sangue, Mato Grosso

This paper presents the results of an extensive processing, interpretation and geological integration of airborne gamma-ray spectrometric data. It comprised data from 30.360 linear kilometers of profiles, spaced 2000 m apart, covering an area of 54.000 km 2 in northwest Mato Grosso State (Rio do Sangue Project, DNPM/DGM/CPRM). Individual and composite images of K, Th, U and TC data channels (RGB and CMY), allowed the interpretation of radiometric units. The integration of geophysical and geological information leads to a better picture of the lithological units present in the project area. Introducao

Estudo da compactação do solo por meio de ensaios geotécnicos e de métodos geofísicos

The main objective of this work is to investigate the effect of sand-gravel compaction piles on the behavior of loose sand deposits. Reduced model tests were carried out on an artificial sand deposit filling a trench 1.5 m wide, 3.0 m long and 2.5 m deep, excavated in a clay rich soil. In situ geotechnical tests and DC electrical resistivity measurements were carried out before and after the construction of compaction piles, in order to characterize the changes in the sand deposit. Conductivity anomalies were observed in the position of the compaction piles with better performance. These anomalies are caused by the