The Leite target is located in Carajás Mineral Province and has a magnetic anomaly with 140 nT of amplitude, elongated in the northwest-southeast direction. Four exploratory drillholes were performed to test the magnetic anomaly. The test showed that the source of the anomaly is a narrow magnetite hydrothermal alteration zone bearing copper mineralization up to 2%. In addition, geologic and geochemical data, magnetic susceptibility (MS) measurements were collected to identify the lithotypes with ferromagnetic minerals. We use three different techniques to estimate the depth and geometry of the magnetic source: standard Euler deconvolution, total field magnetic anomaly modeling, and magnetic amplitude inversion. When visualized in 3D, the depth of solutions from Euler deconvolution crossed the real magnetic layer with less inclination. The modeling, using the solutions from Euler deconvolution, was performed, and the magnetic anomaly produced by the body modelled achieved a low misfit. The body used in the forward modeling is geometrically similar to the geologic magnetic layer. The magnetic amplitude inversion successfully recovered the MS distribution. Finally, we carried out a borehole magnetic survey in two drillholes to validate the obtained models and investigate the magnetic source. This survey confirmed that the models were intercepted and the magnetic anomaly was associated, a hydrothermal alteration zone, with magnetite intercepted by drillholes. In this study, we demonstrated that the use of those techniques was effective in Greenfield exploration programs
Há mais de meio século a utilização de dados geofísicos representa importante ferramenta auxiliar nas pesquisas em geociências. Dentre outras características, tais produtos facilitam a discriminação de feições estruturais, ajudam a caracterização de corpos geológicos em subsuperfície e permitem a delimitação de domínios geofísicos com correspondentes geológicos. O Graben de Água Bonita, localizado nos estados de Goiás e Tocantins, foi definido na metade da década de 60 do século XX como uma estrutura de 80 km por 7 km, com bordas paralelas e retilíneas de direção N35-40◦E. O conhecimento desta estrutura restringe-se ao mapeamento geológico, inexistindo dados em profundidade. O presente trabalho trata da interpretação de dados aerogeofísicos do Levantamento Geofísico Brasil-Canadá (PGBC); aquisição e interpretação de dados gravimétricos terrestres visando contribuir ao conhecimento geológico-estrutural do Graben de Água Bonita, situado no contexto do Lineamento Transbrasiliano. A interpretação qualitativa e quantitativa dos dados geofísicos e geológicos originada de modelagem 2D, sugere que o Graben de Água Bonita inclina-se para oeste, devido às baixas anomalias e ao mergulho das sequências sedimentares detríticas. Esta inclinação evidencia que o depocentro da Formação Água Bonita localiza-se a aproximadamente 4 km de profundidade a oeste do limite superficial desta Formação. ABSTRACT: For over half a century geophysical data is an important auxiliary tool used in geosciences research. Among other features, these products facilit at ethe discrimination of structural features, aid the characterization of subsurface geological bodies and allow the delimitation of areas with corresponding geophysica land geological data. The Água Bonita Graben (GAB), which straddles the border of Goiás and Tocantins states, was defined in the mid-60s as an 80-km long by 7-km wide structure, with parallel, straight borders towards N35-40◦E. This paper presents an interpretation of the geophysical data obtained by the the Geophysical Survey Brazil-Canada (Programa de Levantamentos Geofísicos Brasil-Canadá, PGBC), as well as acquisition and interpretation of ground gravity data aiming at improving the geological knowledge of the Água Bonita Graben, situated in the Transbrasilian Lineament. The PGBC geophysical data allowed the extraction of lineaments and geophysical delineation of the GAB limits. The 2D model suggests that the Água Bonita Graben leans to the west, due to the observed low gravity anomaly values and inclined detrital sedimentary sequences dipping 8◦-12◦, in the direction 300◦ to 330◦, suggesting that the depocenter of the Água Bonita Formation is near by the western edge of the graben.Keywords: ground gravity, Água Bonita Graben, Transbrasilian Lineament.
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