Ore mining fundamentally depends on the definition of its tenor and volume, something extremely complex in disseminated mineralization, as in the case of certain types of deposits of gold and sulfites. This article proposes the use of electrical tomography for definition of a geophysical signature in terms of electrical resistivity and chargeability, in an outcrop of mineralized quartz lode at the end of an inactive gold mine. One of the targets was to analyze the continuity of the mineralized body, the occurrence of new outcrops and the applicability of the method as an auxiliary tool in mineral extraction. Three parallel lines of electrical tomography in a dipole-dipole arrangement, being orthogonal to the orientation of the gold lode, were installed in an area outside the mine. The results allowed the geophysical characterization of the mineralized zone by high resistivity (above 1000Ω.m) and high chargeability (above 30mV/V). The results of the 2D inversion models were interpolated in 3D visualization models, which allowed definition of the contour surfaces for the physical parameters measured, and the morphological pattern modeling of the mineralization. The data reveal the existence of a new lode in subsurface, localized 30m to the south of the lode outcrop. The versatility of the acquisition and data processing indicate the application potential of electrical tomography as a criterion for sampling and tenor definition in ore extraction activities, since it is objective and low cost.
The Parnaíba Basin, like other Brazilian Paleozoic intracratonic basins, contains intrusive igneous bodies in its sedimentary section in the form of dykes and, mainly, thick sills. The identification of the geometry and the emplacement mechanism are important for the determination of the traps controlling gas and/or oil accumulations. A variety of models available in the literature suggests a complex relationship between the magma and the host rock. Several factors, such as the density and pressure of the magma injection, steam generation, regional and local stress fields, and the rheology of the host rock, work together controlling emplacement, expansion and the final geometry of intrusions in the sedimentary column. Well logs show a conspicuous signature (e.g. gamma-ray curve with paunchy feature) for the igneous bodies (sills). Many sills occur parallel to the bedding, generally intruding thick sections of shales along the contact of the lithostratigraphic units of the Longá-Poti, Pimenteiras-Cabeças and Tianguá-Jaicós formations. Seismic sections reveal a variety of geometries, including layer parallel, saucer-shaped, planar transgressive and fault block. By far the most common sill geometry is the layer parallel, which is able to reach up to hundreds of kilometres in extent, and has minimal thickness ranging between 2 and 5 m, and with a maximum of around 250 m.
The discovery of new mineral resources involves various research techniques through direct and indirect studies. The geophysical methods are important tools in the detection of deep deposits because they use the contrast between the physical properties of the hosting rocks and the mineralized zone. In this sense, electrical geophysical methods are widely used in the prospecting of sulfide deposits. This work presents and discusses the results of the application of the Induced Polarization geophysical method in the investigation of a tin mineral occurrence associated with greisen, located on the western border of São Sepé Granite. The study area is located in the central portion of the Rio Grande do Sul State, in the municipality of São Sepé (RS), housed in the metavolcano-sedimentary rocks of the Vacacaí Metamorphic Complex. Six lines of electrical tomography were parallel arranged in the N30W direction. The 2D inversion models allowed to identify areas of high chargeability (above 5.0 mV/V), possibly attributed to areas with sulfide accumulation. The areas with low values (below 1.9 mV/V) area associated with soil and rocks absent of mineralization. Through the 3D visualization models, it was possible to identify that the mineralized zone apparently has continuity for more than 36 m. These models also allowed identifying the morphology and the lateral continuity of the sulfide zone. Thus, the results of this work demonstrate the possibility of using Induced Polarization in the research of cassiterite deposits with associated sulfides due to the contrast of physical properties obtained from the high polarizability of the sulfides.
Palavras-chave: Aquiclude. Salinidade. Tomografia elétrica. Permeabilidade. ResumoO Brasil é um país privilegiado em relação aos seus recursos naturais, mas enfrenta problemas de diagnóstico da situação das águas superficiais e subterrâneas, devido à qualidade e a quantidade deste recurso. Questões quanto aos parâmetros físico-químicos como elevada salinidade ou baixa condutividade hidráulica podem prejudicar o uso deste recurso hídrico subterrâneo. O estudo de procedimentos para diagnóstico direto e indireto de salinidade em aquíferos pode auxiliar na seleção de locais adequados para que ocorra a captação da água. Neste sentido, este estudo descreve uma análise comparativa entre dados geoquímicos e ensaios geofísicos em um aquífero livre, com salinidade elevada, numa tentativa de estabelecimento de correlações entre dados diretos e indiretos, além de possibilitar uma análise das limitações de uso do método geofísico da eletrorresistividade como ferramenta indicadora de graus de salinidade. O contexto geológico local é representado por solos argilosos assentados sobre siltitos e argilitos da Formação Corumbataí, unidade geológica pertencente à Bacia Sedimentar do Paraná. Esta unidade representa um aquiclude regional, com o nível aquífero livre no contato solo/rocha, caracterizado por salinidade variável e bastante utilizado como fonte de abastecimento em propriedades rurais. Os parâmetros físico-químicos medidos em amostras coletadas em poços foram: sólidos totais dissolvidos (STD), condutividade elétrica (CE), além de medidas de condutividade hidráulica (k). Os dados de STD e CE foram amplamente variáveis, mas resultaram numa correlação direta satisfatória. A comparação entre dados de resistividade elétrica com STD e com k não resultaram em correlações com resposta tão satisfatória, devido à complexidade geológica e salinidade amplamente variável, fatores que controlam a resistividade elétrica no ambiente geológico. AbstractBrazil is a privileged country in relation to their mineral resources, but have problems in diagnosis the situation about the surface water and groundwater, because the quality and the quantity of water. Questions about physico-chemical parameters as high as salinity or low hydraulic conductivity can affect the use of this underground water resource. The study of procedures for diagnostic directly or indirectly in salinity in groundwater can assist the selection of sites for acquisition. In this direction, this study describes a comparative analysis between geochemical analyzes and tests on geophysical study of saline free aquifer, in an attempt to establish correlations between data, whether direct or indirect, in addition to providing an analysis of the limitations of the DC Resistivity geophysical method as indicator tool of degrees of salinity in an indirect way. The geological site consist in clay soils settled on siltstone and argillites of the Corumbataí Formation, of the Basin of Paraná Sedimentary Basin in Brazil. This unit represents an aquiclude regional, the occurrence of level f...
Sulfide prospecting with the geophysical methods, such as electrical resistivity and induced polarization, are promising due to the contrast of electrical resistivity and chargeability, where deposits with disseminated sulfides or filoneans are characterized by low resistivity and high polarizability. This work carried out a study of geophysical prospecting by means of tomographic acquisition in mineral copper occurrence, in the region of Caçapava do Sul. Three acquisition lines were performed by means of electrical tomography technique using a Dipole-dipole arrangement, with a length of 400 m and a spacing of 5 m between the electrodes, arranged in perpendicular layout to the structure of the area, represented by a large synclinal where research galleries with carbonates and copper sulfides were recognized in the ridge. The 2D inversion models and 3D multilevel maps indicate central and lateral regions with high resistivity and chargeability with indication of probable presence of copper sulfide, possibly housed in quartz veins. Peripheral zones with moderate resistivity and chargeability infer possible areas with presence of argilization, zones with high chargeability and low resistivity are likely to be zones of sulfation and possible silicification zones with high resistivity and low chargeability, observed in the vicinity of the probable mineralized zones.Keywords: Chargeability, Mineral Research, Resistivity, Sulfide, 3D Multilevel modeling.RESUMO A prospecção de sulfetos por meio de métodos geofísicos de eletrorresistividade e polarização induzida são altamente efetivos devido ao contraste de resistividade elétrica e cargabilidade, uma vez que os depósitos com sulfetos disseminados ou filoneanos são cvaracterizados por baixa resistividade e alta polarizabilidade. Esse trabalho realizou aquisição de tomografia elétricas em ocorrência mineral de cobre, na região de Caçapava do Sul (RS). Foram realizadas 3 linhas de tomografia elétrica em arranjo dipolo-dipolo, com 400 m de comprimento e 5 m de espaçamento entre eletrodos, dispostas de forma perpendicular à crista de um anticlinal, onde no passado foram reconhenhecidos carbonatos e sulfetos de cobre, em galerias de exploração mineral. Os modelos de inversão 2D e mapas de multiníveis 3D indicam regiões centrais e laterais com alta resistividade e alta cargabilidade com provável zona de sulfetos alojados em veios de quartzo. Zonas periféricas com moderada resistividade e cargabilidade sugerem a presença de argilização; zonas com alta cargabilidade e baixa resistividade são prováveis zonas de sulfetação e altos valores de resistividade e baixos de cargabilidade indicam zonas de silicificação.Palavras-chave: Cargabilidade, Pesquisa Mineral, Resistividade Elétrica, Sulfeto, Modelamento Multinível 3D.
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