Estudo integrado de geofísica e geologia estrutural na identificação de drenagem ácida em mina de urânio
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Data
2021-10-22
Autores
Camarero, Pedro Lemos
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Universidade Estadual Paulista (Unesp)
Resumo
Localizado na região sul do Estado de Minas Gerais (Brasil), o Maciço Alcalino de Poços de Caldas apresenta diversas ocorrências de minerais de urânio e tório. A mais importante está localizada na Mina Osamu Utsumi, um complexo mineiro industrial pertencente as Indústrias Nucleares do Brasil (INB). Durante seus 13 anos de operação não contínua, iniciada em 1982, a Mina Osamu Utsumi gerou graves impactos ambientais, especialmente aqueles relacionados a grandes quantidades de resíduos de processamento químico, resíduos rochosos e poluição da água - Drenagem Ácida de Mina (DAM). Atualmente, este complexo mineiro está em fase de descomissionamento e enfrenta um grande desafio na resolução de passivos ambientais. O entendimento e diagnóstico das zonas preferenciais de geração e fluxo de DAM são fundamentais para estabelecer medidas de mitigação para sustentabilidade ambiental de longo prazo, em qualquer empreendimento mineiro em fase de descomissionamento. Assim, esse estudo fornece uma análise dos principais mecanismos de geração de drenagem ácida e onde eles ocorrem na região da antiga cava da Mina Osamu Utsumi, área afetada pelo passivo. Uma investigação geofísica foi realizada ao longo de cada frente da mina com o emprego da técnica de tomografia elétrica, a partir dos arranjos Dipolo-dipolo e Schlumberger. O espaçamento entre eletrodos adotado foi de 10m. Para uma melhor compreensão do sistema de aquífero fraturado local, um mapeamento estrutural da área a céu aberto foi necessário. Foram utilizados, também dados hidroquímicos de poços de monitoramento ao longo da cava para agregar na interpretação dos dados geofísicos. A compilação de resultados de campo e dados geoquímicos de poços de monitoramento proporcionou condições para distinguir áreas onde a água flui por fraturas no maciço e áreas com maior contribuição de águas ácidas, com valores de resistividade elétrica inferiores a 15 Ohm.m. Foram identificadas contribuições de drenagem ácida em todas as frentes de exploração da cava, associada a zonas mineralizadas remanescentes. O método geofísico da Eletrorresistividade se mostrou adequado a proposta do estudo. A partir desses resultados, são citadas propostas medidas de mitigação do passivo como tratamento de maciço rochoso.
Located in the southern region of Minas Gerais State (Brazil), the Poços de Caldas alkaline massif presents several occurrences of uranium and thorium minerals. The most important one is placed at the Osamu Utsumi Mine, an industrial mining complex owned by Nuclear Industries of Brazil (INB-Indústrias Nucleares do Brasil). During its 13 years of non continuous operation, started in 1982, the Osamu Utsumi Mine has generated serious environmental impacts, specially those related to arge amounts of chemical processing waste, rocky waste and water pollution – Acid Mine Drainage (AMD). Nowaday, this mining complex is in the decommissioning phase and faces a major challenge in solving environmental liabilities. The understanding and diagnosis of preferential zones of generation and flow of AMD are fundamental to establish mitigatation measures for long-term environmental sustainability in any mining undertaking in the stage of decommissioning. Thus, this study provides an analysis of the main mechanisms of acid drainage generation and where they occur in the region of the old pit of the Osamu Utsumi Mine, an area affected by the liability. A geophysical investigation was carried out along each from of the mine pit using electrical resistivity tomography (ERT), using dipole-dipole and Schlumberger arrays. The spacing between electrodes adopted was 10m. For a better understanding of the local fractured aquifer system, a structural mapping of the open-pit area was necessary Hydrochemical data from monitoring wells along the pit were also used to add to the interpretation of geophysical data. The compilation of field results and geochemical data from monitoring wells provided conditions to distinguish areas where water flows through fractures in the massif and areas with a greater contribution of acid water, with electrical resistivity values below 15 Ohm.m. Contributions of acid drainage were identified in all exploration fronts of the pit, associated with remaining mineralized zones. The geophysical method of Electroresistivity proved to be adequate for the purpose of the study. From these results, proposed mitigation measures are cited as rock mass support.
Located in the southern region of Minas Gerais State (Brazil), the Poços de Caldas alkaline massif presents several occurrences of uranium and thorium minerals. The most important one is placed at the Osamu Utsumi Mine, an industrial mining complex owned by Nuclear Industries of Brazil (INB-Indústrias Nucleares do Brasil). During its 13 years of non continuous operation, started in 1982, the Osamu Utsumi Mine has generated serious environmental impacts, specially those related to arge amounts of chemical processing waste, rocky waste and water pollution – Acid Mine Drainage (AMD). Nowaday, this mining complex is in the decommissioning phase and faces a major challenge in solving environmental liabilities. The understanding and diagnosis of preferential zones of generation and flow of AMD are fundamental to establish mitigatation measures for long-term environmental sustainability in any mining undertaking in the stage of decommissioning. Thus, this study provides an analysis of the main mechanisms of acid drainage generation and where they occur in the region of the old pit of the Osamu Utsumi Mine, an area affected by the liability. A geophysical investigation was carried out along each from of the mine pit using electrical resistivity tomography (ERT), using dipole-dipole and Schlumberger arrays. The spacing between electrodes adopted was 10m. For a better understanding of the local fractured aquifer system, a structural mapping of the open-pit area was necessary Hydrochemical data from monitoring wells along the pit were also used to add to the interpretation of geophysical data. The compilation of field results and geochemical data from monitoring wells provided conditions to distinguish areas where water flows through fractures in the massif and areas with a greater contribution of acid water, with electrical resistivity values below 15 Ohm.m. Contributions of acid drainage were identified in all exploration fronts of the pit, associated with remaining mineralized zones. The geophysical method of Electroresistivity proved to be adequate for the purpose of the study. From these results, proposed mitigation measures are cited as rock mass support.
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Palavras-chave
Eletrorresistividade, Tomografia elétrica, Passivo ambiental, Hidroquímica, Poços de Caldas, Resistivity, Electrical resistivity tomography, Environmental liabilities, Hydrochemical