Assessment of the effects of vegetational cover on the long-term stabilityof a waste rock dump.

Waste rock dump reclamation includes re-grading the banks to flatten the overall slope followed by re-vegetation. These measures are required to reduce surface erosion, provide physical stability, and meet future use goals. In some cases, the presence of trees can cause localized shear zones in a waste rock dump by the load of the tree mass and the action of wind, the presence of roots in the soil and the death of some species. In geotechnical assessment, however, the influence of trees on slope stability of waste rock dumps is only qualitative. This article assesses the effects of trees on slope stability of a reclaimed waste rock dump of an iron ore mine. Historic data of construction, laboratory tests, and stability analysis were evaluated. Slope stability assessments were performed after an extensive geotechnical and forest campaign, considering two scenarios - the final waste rock dump without the vegetational cover and the final waste rock with vegetational cover. Tree vegetation in slopes produces both positive and negative effects on slope stability. For scenario 1, the lowest factor of safety occurs for a potential failure surface near the bottom of the waste dump, passing by a layer 6 m depth from the surface. In scenario 2 the factor of safety is increased by 10%. For deeper failure surface, the smallest factor of safety occurs 30 m deep. However, very tall trees at the top of the waste dump are subject to wind action, which has a negative impact on slope stability

Aspectos legais e ambientais sobre fechamento de mina, com ?nfase no estado de Minas Gerais.

Este artigo descreve sobre o estado atual dos aspectos legais e ambientais que regulamentam a atividade de fechamento e descomissionamento de empreendimentos miner?rios no Brasil, e no Estado de Minas Gerais. Este ?ltimo det?m a lideran?a na produ??o mineral do pa?s. A explora??o das jazidas minerais produz elevado potencial de riscos ambientais e, quando abandonadas ou encerradas, passivos ambientais s?o gerados. No Brasil, o fechamento de mina foi considerado a partir do advento da Lei n? 6.938/81, da Constitui??o Federal de 1988 quando ganharam import?ncia o Estudo e Relat?rio de Impacto Ambiental - EIA/RIMA. A legisla??o do setor mineral encontra-se dispersa, pois ? vinculada a dois minist?rios: Minas e Energia e Meio Ambiente. Em Minas Gerais, dentre outras normas, a DN COPAM N? 127, de 2008, estabelece diretrizes para avalia??o ambiental da fase de fechamento de mina. Empresas de grande porte v?m apresentando planos de fechamento e de descomissionamento, entretanto, as pequenas empresas aliada ? falta de fiscaliza??o, t?m sido as principais respons?veis pela gera??o de passivos ambientais.This article describes the current status of legal and environmental factors that regulate the closure and decommissioning of mining activities in Brazil and in Minas Gerais State. The latter has the lead in mineral production in the country. The exploitation of mineral deposits produces a high potential for environmental hazards and, when abandoned or closed, environmental liabilities are generated. In Brazil, the mine closure has been considered from the enactment of Law No. 6.938/81, of the Constitution of 1988 with the Study and Environmental Impact Report - EIA / RIMA. The law of the mineral sector is dispersed because it is linked to two ministries: Mines and Energy and the Environment. In Minas Gerais, among other provisions, the DN COPAM No. 127, 2008, establishes guidelines for environmental assessment phase of a mine closure. Large companies have presented plans for closure and decommissioning, however, small businesses coupled with the lack of supervision have been mainly responsible for the generation of environmental liabilities

Remediation alternatives for an abandoned gold mine contaminated with mercury in Brazil / Alternativas para descontaminação de mina de ouro abandonada contaminada com mercúrio no Brasil

Heavy metal contamination of soils has generated two major problems, namely, loss of land value and health risk for people near contaminated sites. Studies on soil remediation are typically conducted on a pilot scale under very controlled conditions. This is a misleading approach, once the complexity of the actual biogeochemical soil conditions may causes inefficiency in full scale real-world application. In addition, environmental impacts of remediation practices themselves are often ignored, which may make them unfeasible. In 2002, an occurrence of mercury in an abandoned old gold mine was detected in a rural area of Descoberto, Brazil. In 2014, the State Public Prosecutor required from the responsible State Environment Agency, a remediation project to the area. This study compares alternatives for remediation of the contaminated area. Also a historical approach on mercury amalgamation in gold mining in the region, in order to estimate the amount of mercury remaining in the site. The geochemical characterization of the contaminated area was performed to describe the contamination process.  The results were compared with the remediation proposal advocated by the Brazilian Ministry Public, and some alternatives for decontamination of the area were studied. The electrokinetic method has displayed the lowest overall unit cost, between US$120.00/t and US$ 260.00/t. The residual Hg concentration after four cycles of the electrokinetic technique was estimated at 1.28 mg (Hg)/kg (soil), slightly higher than the intervention value for agricultural soil, which is 1.20 mg (Hg)/kg (soil)

Long-term evolution of heap surface of paste tailings under erosion / Evolução a longo prazo de pilha da pasta de rejeitos sujeita a erosão

Many mines are moving from conventional tailings storage facilities to filtered tailings disposal systems. The benefits of these systems include increased water recovery, reduced size of containment landfills, improved facility safety, and reduced environmental impact. In geotechnical terms, the challenges are to find the correct way of waste disposal: whether in piles of dry sandy tailings or co-disposal waste rock. The long-term evolution of the surface of fine and sandy tailings stockpiles is a matter of concern. The goal of this study was to quantitatively evaluate the temporal evolution of a paste tailings pile, using a computational model of landscape evolution. For this, SIBERIA, a simulator of the evolution of landscapes under the action of runoff and erosion, was used. The effect of erosion on a trunk-pyramidal tailings pile with about 21% of slope after long periods of decommissioning (100 and 250 years) was studied. The SIBERIA modelling data considered the surface roughness and the average diameter of the sediment particles and the typical properties of iron ore tailings. The results indicate that for a lower Manning roughness coefficient and larger average apparent diameter of the sediment particles (or clods), the lower the sediment transport will be and, therefore, in the long term, the greater will be the integrity of the tailings pile

Geophysical analysis of natural caves in iron lithotypes in the region of Mariana, Southeastern Quadril?tero Ferr?fero, Brazil.

In Brazil, natural caves in iron lithotypes have increasingly been discovered in iron mining areas and its surroundings. Mining companies attempt to study them according to the Federal Decree 6640/2008 and the Normative Instruction 2/2009 of the Ministry of the Environment, which is concerned with the preservation of the Brazilian Speleological Heritage. This research is within one of those studies in which a geophysical campaign methodology is established for an attempted prospection of caves, in an area located on the north flank of Mariana's Anticlinal, Quadril?tero Ferr?fero. The flank, which is sustained by iron formations from the Itabira Group and covered by the product of alteration and sedimentary redistribution, experienced extensive and compressive tectonics, generating, respectively, the main structuration in the NW-SE direction and schist thrust slices from the Nova Lima Group. Caves are mainly developed in the lithological contacts and in fault zones. In the regional stage, the methodology uses aeromagnetometric (identification of iron lithotypes, structural and statistical analysis of magnetic lineaments) and aeroradiometric (structural-geological mapping and setting of lithological contacts) methods. Results have shown some caves in lateral contact zones between lithologies, and the structural control imposed by a shear zone in the area. At the local stage, the electrical resistivity method - EL was used, dipoledipole array, data mathematical inversion, presentation of pseudo-depth sections and tridimensional modeling. The results, in accordance with the topographic data, show the possible limits of the geometric contour and the tendency for cave deepening. However, studies of the moisture, of similar caves with different spacings, and the use of Ground Penetration Radar ? GPR are suggested

Divulgação do acervo arqueológico de mineração no período colonial em Ouro Preto e Mariana

As cidades de Ouro Preto e Mariana foram palco de intensas atividades de mineração do ouro no período colonial (Século XVIII), que deixaram remanescentes e vestígios até os dias atuais. O esvaziamento das atividades mineiras e, consequentemente das cidades, fez com que este acervo fosse preservado até a década de 1970, quando iniciou-se o processo de ocupação urbana destas áreas, muitas vezes com a degradação do patrimônio, pela depredação dos resquícios da antiga mineração, quase sempre pelo desconhecimento da importância destes locais. Na década de 1990 iniciaram-se estudos nestas áreas com a abordagem da preservação patrimonial, com o cadastramento e mapeamento de ruínas, estruturas de mineração e galerias subterrâneas, sendo que hoje tem-se um bom conhecimento do acervo existente. Neste contexto, há uma grande demanda pela divulgação da existência e importância deste acervo e dos estudos que até o momento foram realizados sobre o tema junto ás comunidades que habitam estas áreas. Assim, o projeto de extensão aqui relatado foi desenvolvido para tentar preencher esta lacuna e fomentar uma maior participação da população na preservação deste patrimônio arqueológico, buscando criar um elo entre o conhecimento acadêmico hoje existente e as comunidades que residem nos locais onde houve a extração de ouro no século XVIII. O projeto focou cinco comunidades, porém em duas destas, fatores externos impediram a continuidade dos trabalhos. As principais atividades desenvolvidas foram o inventário e coleta de dados e informações acerca dos locais, realização de reuniões e palestras junto às comunidades abordando o patrimônio e a história da mineração do ouro no Século XVIII, caminhadas pelos sítios arqueológicos e debates sobre o tema. Também constou como parte do projeto o mapeamento e avaliação da estabilidade de algumas minas subterrâneas que são atualmente exploradas turisticamente por moradores de uma das comunidades alvo das atividades do projeto.</span

Physical stability of iron ore caves : geomechanical studies of a shallow underground cave in SE Brazil.

Caves hosted in iron formations are attracting considerable interest due to their scientific and environmental value. Some of these caves are located in or near iron ore mine sites, which represent an important source of income to Brazil. However, the Brazilian legislation requires speleological studies that currently have an impact upon ore reserves and environmental licensing processes. The aim of this study was to apply conventional geotechnical empirical approaches to a cave located within the grounds of an iron ore mine in the Iron Quadrangle and validate it with numerical modelling, to ensure the method's applicability to natural caves under mining activity influence. These studies comprised the mapping of structural, geotechnical and geomechanical features of rocks hosting and surrounding the cave and to propose geotechnical domains. Field data collection covered the geotechnical parameters necessary to calculate the characteristic Mining Rock Mass Rating (MRMR) for each geotechnical domain, and to evaluate the stability conditions using the stability index or hydraulic radius of the cave. These geotechnical parameters were then used to calculate the physical parameters used in two-dimensional numerical simulations to verify the good stability conditions of the cave, corroborating the adequacy of Laubscher's diagram. The results of this study, although comprising only one cave, suggest that Laubscher's diagram is applicable for assessing the geotechnical behavior of iron ore caves

Aplicação do Sistema de Monitoramento de Dinâmica de Rocha (SMDR) para Controle Geotécnico Contínuo de Cavidade Natural Subterrânea no Quadrilátero Ferrífero (MG)

Nos últimos anos uma série de estudos tem sido conduzida sobre cavidades naturais subterrâneas em formações ferríferas. Esses estudos decorrem da necessidade de se preservar as cavidades naturais e, ao mesmo tempo, viabilizar de forma sustentável, a operação de uma mina de minério de ferro. Isso ocorre pelo fato da legislação ambiental do Brasil estipular, empiricamente, um raio de proteção de 250 m, de forma a evitar dano ambiental irreversível às cavernas, que por sua vez, bloqueia a lavra de considerável fração de minério de ferro. Dessa forma, com o intuito de verificar a influência do desmonte com uso de explosivos na estabilidade física da cavidade BRU_0034, nas proximidades da Mina de Brucutu da empresa Vale S.A., foram propostos, por intermédio desse estudo,monitoramentos sismográficos e de deslocamento através do uso do Sistema de Monitoramento de Dinâmica de Rocha (SMDR). No que se refere aos resultados obtidos com o SMDR, foi possível verificar por meio dos dados sismográficos e de deslocamento que não houve uma grande movimentação aparente nos sensores durante o monitoramento de desmontes de rochas por explosivos realizados em distâncias inferiores a 250 m