Prospecção geofísica de detalhe em área potencialmente mineralizada em ouro em São Sepé (RS)
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Data
2019-09-20
Autores
Lima, Antônio Elton da Silva
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Universidade Estadual Paulista (Unesp)
Resumo
O potencial geológico do Brasil para mineralizações auríferas é mundialmente reconhecido, quer seja pelo seu passado histórico, como por conta do expressivo número de ocorrências, depósitos, minas e as centenas de áreas ativas e inativas distribuídas por todo o país. Na região em que presente estudo foi realizado, já foram detalhados uma série de jazimentos desta natureza, caracterizadas por associações de filões de quartzo e pequenas proporções de óxidos de ferro, pirita e calcopirita. Este trabalho apresenta, portanto, os resultados de um estudo de prospecção geofísica de detalhe realizado a partir da aplicação conjunta dos métodos da Eletrorresistividade e da Polarização Induzida, integrados a análise estrutural. O local estudado consiste numa área potencialmente mineralizada em ouro no Complexo Bossoroca, localizada na zona rural do município de São Sepé (RS). Para obtenção dos dados geofísicos foram realizadas cinco linhas de 400m de comprimento e 10m de espaçamento entre eletrodos, através da técnica de tomografia elétrica em arranjo Schlumberger. O levantamento estrutural, por sua vez, considerou medidas de lineamentos, extraídas a partir de imagem SRTM da área, assim como dados de acamamentos e de fraturas de litotipos pertencente ao Complexo Bossoroca, obtidos a partir de levantamento estrutural sistemático. Os resultados de resistividade não permitiram a definição de zonas mineralizadas, possivelmente devido ao pequeno contraste existente entre a rocha encaixante e a zona mineralizada. Os dados de cargabilidade indicaram três zonas com altos valores (≥ 4,4 mV/V) localizadas a leste, sudoeste e sul da área investigada e interpretadas como possíveis zonas mineralizadas. Destas zonas, as encontradas a sudoeste e sul da área possuem forma de cone alongado segundo as direções NW-SE e NE-SW e apresentam continuidade lateral e em profundidade. A análise estrutural dos lineamentos e das fraturas revelou duas famílias principais com trends segundo as direções NE-SW e NW-SE. O conjunto de estruturas possivelmente serviu como condutos de fluxo de fluidos mineralizantes até os locais de resfriamento e retenção, reconhecidos nas regiões de altos valores de cargabilidade.
Brazil’s geological potential for auriferous mineralization is recognized worldwide for its historic past, as well as for the number of occurrences, deposits, mines and hundreds of active and inactive areas distributed throughout the country. In the region where the present study was carried out, series of such deposits have already been described, characterized by associations of quartz lodes and small proportions of iron oxides, pyrite and chalcopyrite. This work presents the results of a geophysical prospecting study obtained through the joint application of the DC resistivity and induced polarization methods, integrated to the structural analysis. The studied areas consists of a potentially gold mineralized area in the Bossoroca Complex located in the county of São Sepé (RS). In order to obtain the geophysical data, five lines with 400m in length and 10m of spacing between electrodes were made through the electrical tomography technique in a Schlumberger arrangement. The structural data collecting considered measures of lineaments, extracted from the SRTM image of the area, as well as data of bedding and fractures of lithotypes belonging to the Bossoroca Complex, obtained from a systematic structural data collecting. The results of resistivity did not allow the definition of mineralized zones, possibly due to the small contrast between the rock and the mineralized zone. The chargeability data indicated three zones with high values of load (≥ 4,4 mV / V) located to the east, southwest and south of the investigated area and interpreted as possible mineralized zones. These zones are elongated in NE-SW and NW-SE directions and have lateral and depth continuity. Structural analysis of lineaments and fractures revealed two main families with trends in the NE-SW and NW-SE directions. The set of structures possibly served as a flow conduit of mineralizing fluids to the cooling and retention sites, recognized in regions of high chargeability values.
Brazil’s geological potential for auriferous mineralization is recognized worldwide for its historic past, as well as for the number of occurrences, deposits, mines and hundreds of active and inactive areas distributed throughout the country. In the region where the present study was carried out, series of such deposits have already been described, characterized by associations of quartz lodes and small proportions of iron oxides, pyrite and chalcopyrite. This work presents the results of a geophysical prospecting study obtained through the joint application of the DC resistivity and induced polarization methods, integrated to the structural analysis. The studied areas consists of a potentially gold mineralized area in the Bossoroca Complex located in the county of São Sepé (RS). In order to obtain the geophysical data, five lines with 400m in length and 10m of spacing between electrodes were made through the electrical tomography technique in a Schlumberger arrangement. The structural data collecting considered measures of lineaments, extracted from the SRTM image of the area, as well as data of bedding and fractures of lithotypes belonging to the Bossoroca Complex, obtained from a systematic structural data collecting. The results of resistivity did not allow the definition of mineralized zones, possibly due to the small contrast between the rock and the mineralized zone. The chargeability data indicated three zones with high values of load (≥ 4,4 mV / V) located to the east, southwest and south of the investigated area and interpreted as possible mineralized zones. These zones are elongated in NE-SW and NW-SE directions and have lateral and depth continuity. Structural analysis of lineaments and fractures revealed two main families with trends in the NE-SW and NW-SE directions. The set of structures possibly served as a flow conduit of mineralizing fluids to the cooling and retention sites, recognized in regions of high chargeability values.
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Palavras-chave
Geofísica, Eletrorresistividade, Polarização induzida, Ouro, Sulfetos, Pesquisa mineral, Resistividade, Cargabilidade, Modelagem 3D, Mineral exploration, Gold, Sulfides, Resistivity, Chargeability, 3D modeling