Abstract The creation of tridimensional models that represent the quality and geomechanical characteristics of the rock mass to be excavated can be made by using spatial interpolation techniques. The aim of this research is to improve the safety in underground activities, as well as to spread and popularize the use of spatial interpolation methods to represent both the spatial continuity of the quality of the rock mass and the geomechanical variables through geostatistical methods. This article presents and demonstrates the viability of using Q-System block models estimated from the borehole data for previous classification of the rock mass surrounding the underground excavation and rock support design. The block model for the support design of galleries is justified because it allows to previously forecast the kind and quantity of support necessary for the stability of the excavation, as well as the costs with these devices, besides increasing the safety in the operations. Techniques of indicator kriging and ordinary kriging were used to build the Q-System index block model. The model was validated through the techniques of visual inspection and cross validation. The data used in this study were collected from the geotechnical description of 39 borehole core samples with a total measurement of 4,015 meters in Fazenda Brasileiro Mine, located in the town of Teofilândia, Bahia State, Brazil.

Abstract For the Brazilian iron ore mines, the presence of caves presents a challenge, since most of them are located within the ore deposit. The National Environment Commission (CONAMA 347 Resolution/2004) establishes that the speleological heritage, as well as its area of influence, cannot sustain irreversible environmental impacts. The physical integrity of caves adjacent to mining operations is an issue of pivotal importance to be scrutinised in studies towards the delimitation of the cave’s protection radius. This article presents the study of various models of correlation between the RMR and Q systems used for the stability assessment of natural iron ore caves. In order to study a correlation between the RMR and Q systems, the most popular rock mass classifications, and their application as a validation tool, a selection of measurements of Q and RMR, organized in a database from seven natural caves of ferruginous lithology, are submitted to a study and statistical analysis. An empirical equation was obtained from the data, using a simple linear regression. The result of the regression was compared with selected correlation equations and the best fit for the data was chosen. The best fit was the Rutledge & Pearson correlation equation, which presented the best combination of R² and S, after the equation created on basis of the real values for RMR, though the other equations have results similar to it. As the results were quite similar, the recommendation still is that correlations should be used with caution, and associated to other methods and field analysis.

Abstract Mining is very important to the economic, political and social development of the Minas Gerais State in Brazil ever since the time the country became a Portuguese colony in the early 1500s. However, few researches have been conducted to evaluate the environmental impacts associated with the mining activity at this time. There are many abandoned mines in Minas Gerais; these are mainly gold mines inherited from the colonial period, which have been considered to represent a considerable environmental liability. However, when a road was constructed in a rural area of the municipality of Descoberto, Minas Gerais, in 2002, a significant amount of mercury was detected in an abandoned gold mine. In 2014, the State Public Prosecutor's Office found both the State of Minas Gerais and the State Environmental Agency liable and responsible for this occurrence and ordered them to design an intervention project for the contaminated area that involved mine closure. This article provides information on how mercury contamination occurred and estimates the amount of mercury present in the contaminated area, with the aim of supporting proposals of alternative remediation, monitoring and management therein. This study includes a historical survey of mining operations in the region and a brief history of the use of mercury in amalgamation. Estimations are made of the amount of gold produced and the amount of mercury released into the environment between 1850 and 1892. Results show an estimated mass of 820 kg of mercury contained in soils and sediments within an area smaller than 1 hectare.

Abstract 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.

Abstract 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.

Abstract Mine closure is the set of all activities that follow the end of the productive phase of a mine, characterizing itself as the process of returning an area transformed by mining into a new condition of sustainability, considering the potential future and the best possible reclamation of the area impacted. However, such an understanding was not conceivable during the Colonial Period, a time when gold mining took place in the Ouro Preto Hill, among others, and nearly 200 years after the end of the gold rush, negative and positive impacts are revealed by the human interaction and the urban occupation on those mined areas. Through both geographic information data of eighteenth-century mining traces and a socioeconomic study involving six tourist gold mines, this article describes how overcoming paradigms involving underground mines have resulted in business opportunities, setting a success example of Mine Closure and future use of the area, showing an alternative way to handle the current abandoned mines.

Abstract 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, Quadrilátero Ferrífero. 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, dipole-dipole 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.

Abstract This article aims to review the issues to be considered in choosing primary access and transportation options for underground mines. The main accesses to underground orebodies are declines or vertical shafts. They serve both as a way to transport ore or waste, and move people, equipment or supplies. In underground mines, the ore transport option significantly affects the productivity and profitability of the company. Then, choice of access is a way to reduce costs and improve production. This study is primarily based on some case studies of Brazilian, South African, Australian and Turkish mines, among others. Literature review shows that the depth at which shaft hoisting becomes a more economically attractive alternative to decline truck haulage is changing from being previously 350 m to present 1000 m, depending on the mining country and cultural underground mine development. For some of them the depth of 1000 m would be the threshold for use of the access by decline. The main criteria in determining access are depth, rate of production and mine life. In South Africa, mines reach depths greater than 3000 m and shaft access is more common. In Australia there are mines that use a ramp (decline) to a depth greater than 1000 m. In Brazil, underground mines are still shallow (depth up to 800 m) and feature short mine life and, most of them have chosen access by decline. Results of this study corroborate the statement that decline is ideal for shallow mines and low production rates and that shaft is for deep mines, high production rate and long mine life.

Abstract Recently, the Brazilian media reported the withdrawal of the rate on profit from mining of coal and iron ore by the government of Australia. In Australia this rate was created in 2012 to finance social programs. However, due to the drop in the value of mineral commodities, the government has reversed this trend and seeks to quash the law that created such a rate, while keeping its social program financial support. One can observe the opposite in Brazil, where the states of Minas Gerais, Pará, Amapá and Mato Grosso do Sul, created the Rate for Controlling, Monitoring and Supervision of Exploration and Mining Activities of Mineral Resources (TFRM). These states' rates have been grounds for numerous political, economic, administrative and legal discussions. This paper presents an analysis of state laws that created the TFRM, examines the ways taken by mining companies to question the constitutionality of these laws and concludes that the levy of TFRM breaks the principle of equality, penalizes mining, violates the precept contained in article 152 the Federal Constitution of 1988 and helps reduce the competitiveness of Brazilian mining.

The legislation for the protection and conservation of caves is recent in Brazil. In 2008, the Decree 6.640 was enacted and in 2009, the Normative Instruction Nº 2 by the Brazilian Environment Ministry (MMA, Portuguese acronyms) was published. Mining operations cause a significant impact on the caves when they are present in or next to the mineral body. The impacts include the suppression of cavities and impacts on physical and bio-speleological stability of the caves. On the other hand, the actual legislation causes a significant impact on the mineable reserves when cavities are present. This article aims to assess the impact of the natural cavities on the feasibility of a mining project, based on the federal legislation, as well as to propose alternatives to combine mining activity with cave protection. For this research, three scenarios of open pit for a hypothetical ore body were considered for the assessments. This paper presents the results achieved for the three and comments on the necessity of researches to conciliate the conservation of the natural underground cavities with the mining activities.

Esse artigo avalia a eficácia da NRM-20 como uma diretriz e um instrumento de execução do fechamento de mina no Brasil. Avalia os critérios de análise e procedimentos de aprovação adotados pelo DNPM, para basear suas decisões sobre questões de fechamento de minas, e procura por falhas na NRM-20, em relação a questões técnicas, legais, ambientais e socioeconômicas. O estudo baseou-se em processos administrativos de mineração depositados no DNPM de Minas Gerais. Foram analisados 32 processos de mineração. O estudo mostra que o DNPM não tem critérios específicos para orientar a análise técnica dos planos de fechamento, o que torna o tema de análise uma interpretação pessoal. Esse estudo permite concluir que, após doze anos de sua publicação, a NRM-20 carece de protocolos de análises e de diretrizes que orientem o fechamento de minas no Brasil.

This paper assesses the effectiveness of the NRM-20 as a guideline and a enforcement tool to mine closure in Brazil; assesses the analysis criteria and approval procedures adopted by DNPM to base their decisions on mine closure issues, and looks for gaps in the NRM-20 regarding technical, legal, environmental and socio-economic issues. The study was based on administrative mining proceedings deposed DNPM of Minas Gerais. Were assessed 32 mining proceedings. The study shows clear evidence that DNPM does not have specific criteria to guide the technical analysis of the closure plans required for, which makes the analysis subject to a personal interpretation. This study supports the conclusion that after twelve years of its publication, the NRM-20 lacks in proper regulating and guiding mine closure in Brazil.

A utilização do ANFO (ammonium nitrate fuel oil) implica um reduzido custo de desmonte. Tais custos podem ser mais baixos ao se substituir o óleo diesel por combustíveis alternativos como biomassa (biodiesel, palha de arroz, sabugo de milho, bagaço de cana-de-açúcar) e resíduo de pneu. Esse artigo investiga o emprego de novos combustíveis, em substituição ao óleo diesel presente no ANFO via medição da velocidade de detonação e verificação do efeito desses combustíveis na mistura explosiva. Com exceção do biodiesel, todos os ensaios provenientes da mistura entre o nitrato de amônio e os combustíveis alternativos apresentaram desempenho insatisfatório comparado ao ANFO. Os percentuais obtidos de velocidade de detonação das misturas em relação à do ANFO foram de 55,4% (NA + Casca de arroz), 64,9% (NA + Sabugo de milho), 70,1% (NA + bagaço de cana), 74,4% (NA + resíduo de pneu) e 93,7% (NA + Biodiesel). Ainda, a metodologia adotada pode ser aplicada como referência para determinação e elaboração de misturas explosivas (agentes oxidantes e combustíveis), uma vez que, nos ensaios realizados, ocorreu a detonação das cargas.

The use of ammonium nitrate and fuel oil (ANFO) results in low cost blasting. Such costs may be further reduced by replacing fuel oil with alternative fuels such as biomass (biodiesel, rice straw, corn cob, sugar cane bagasse) and tires residue. This paper investigates the use of other fuels instead of fuel oil by measuring the detonation velocity (VOD) and verifying the importance of these fuels in an explosive mixture. Except for biodiesel, all the tests conducted for the mixture of ammonium nitrate and alternative fuels showed poor performance when compared with ANFO. The achieved percentage of detonation velocity (VOD) of the mixtures in relation to the ANFO were 55.4% for ammonium nitrate + rice straw, 64.9% for ammonium nitrate + corn cob, 70.1% for ammonium nitrate + sugar cane bagasse, 74.4% for ammonium nitrate + tires residue and 93.7% for ammonium nitrate + biodiesel. This study indicates that the methodology proposed can be applied as a reference for determination and preparation of explosive mixtures of fuel and oxidizing agents since in all the tests conducted the detonation of the charges occurred.

Esse trabalho apresenta uma ferramenta para gerenciamento de minas inoperantes sob a responsabilidade da Gerência de Fechamento de Mina e Projetos de Ferrosos/Departamento de Planejamento e Desenvolvimento de Ferrosos - Vale SA, Brasil. Minas inoperantes são definidas como minas nas quais as operações de lavra estão, temporariamente, suspensas e não há nenhuma estratégia definitiva de encerramento. Os principais desafios de gestão são: (i) atuar em uma variedade de ambientes e condições com base nas prioridades de ação, (ii) identificar riscos à imagem da empresa, (iii) planejar atividades de manutenção e monitoramento, (iv) cuidar das condições ambientais dos locais e seguir as recomendações de auditoria, (v) coordenar as operações de campo e de reabilitação local, (vi) reavaliar o desempenho de reabilitação do sítio ao longo do tempo, (vii) apoiar a equipe local de fechamento de mina. A ferramenta é baseada na consolidação das informações de campo através de análises qualitativas e quantitativas dos riscos ambientais e da qualidade de cada mina e suas diversas estruturas, por exemplo, cava, barragens de rejeitos e pilhas de estéril. Essas análises apoiam o processo de tomada de decisão e priorização de ações. A ferramenta fornece uma avaliação de desempenho das diversas estruturas, permitindo a avaliação, ao longo do tempo, das ações de manutenção e reabilitação realizadas. A ferramenta é alimentada por dados primários e secundários (geotécnicos e ambientais) coletados durante os trabalhos de campo, para posterior tratamento em planilhas. Nessas planilhas, são atribuídos valores de prioridades com base em dois temas principais: risco e qualidade ambiental. Cada um desses temas inclui grupos específicos como vegetação, influência humana e aspectos geotécnicos, entre outros - e cada grupo é subdividido em itens com classificação específica. A planilha de priorização gera mapas temáticos que apresentam a classificação das áreas das minas, bem como as prioridades de ação. Resulta dessa ferramenta um plano de ação que orienta a gestão, considerando-se todas as estruturas de cada local sob sua responsabilidade. O desenvolvimento e utilização da ferramenta têm tornado possível a criação de planos de ação mais pormenorizados e eficazes, proporcionando uma maior precisão no tratamento de irregularidades, possibilitando uma avaliação do desempenho de cada área, minimizando o risco de exposição da empresa e fornecendo uma base de dados confiável, para a concepção, a implementação e o monitoramento de planos de fechamento.

This paper presents a tool for managing inoperative mines under the responsibility of the Mine Closure and Projects Management/Ferrous Planning and Development Department - Vale S.A., Brazil. Inoperative mines are defined as mines where mining operations are temporarily suspended and there is no definitive strategy regarding their closure. The main management challenges are to: (i) act in a variety of environments and conditions based on action priorities; (ii) identify the main company's image risks; (iii) plan for maintenance and monitoring; (iv) take care of environmental conditions of the sites and follow up audit recommendations; (v) coordinate the field operations and site rehabilitation; (vi) re-evaluate the rehabilitation performance of the site over time, (vii) support the mine closure team. The tool is based on the consolidation of field information through qualitative and quantitative analyses of the environmental risks and quality of each mine. These analyses support the decision-making process and the prioritisation of action to be taken. The tool provides a performance evaluation of the sites, allowing evaluation over time of the maintenance and rehabilitation actions carried out. The input for the tool consists of primary and secondary data (geotechnical and environmental) collected during fieldwork, which is then processed in spreadsheets. These assign prioritisation values based on two main themes: environmental risk and quality. Each of these themes has specific groups of subjects. The prioritization spreadsheet generates thematic maps that present the classification of the mine areas and the action priorities. The tool output is an action plan that guides management, considering all the structures of each site under its responsibility.

Taludes vegetados são mais resistentes contra movimentos de massa e erosão pela água. A vegetação contribui para a estabilidade do solo, principalmente pelo aumento da resistência ao cisalhamento por meio do reforço oferecido pelas raízes. As espécies vegetais que mais têm sido eficientes na estabilização de taludes instáveis são as gramíneas, pertencentes à família Poaceae. Um exemplar dessa família, capim vetiver (Chrysopogonzizanioides (L.) Roberty), tem se revelado muito eficaz nessa estabilização. Com o objetivo de avaliar a melhoria dos parâmetros de resistência ao cisalhamento oferecida ao solo pelas raízes do capim vetiver com o tempo de plantio, realizaram-se experimentos de cisalhamento direto por meio de amostras indeformadas de solo sem vegetação e cultivadas com capim vetiver na idade de um, dois, três e quatro anos de plantio. Também foram realizados experimentos de cisalhamento direto em talude do mesmo solo sem vegetação e com cobertura desse capim. Os resultados do ensaio de cisalhamento direto das amostras de talude de solo foram avaliados por três métodos de equilíbrio limite para verificação de um fator de segurança médio nos taludes. A partir dos ensaios de cisalhamento direto, determinaram-se os parâmetros de resistência ao cisalhamento (intercepto de coesão e ângulo de atrito interno), verificando que o capim vetiver proporcionou incremento de coesão aparente ao solo, sendo esse destacado após três anos de plantio do capim. Esse capim promoveu melhoria nos parâmetros de resistência com consequente elevação do fator de segurança de taludes e aumento da resistência ao cisalhamento de solos, o que auxiliou na estabilização de taludes em planos superficiais de ruptura.

Vegetated slopes are more resistant to mass movement and erosion by water. The vegetation contributes to the soil stability, especially by increasing the shear strength provided by roots. Plant species that have been most effective in stabilizing unstable slopes are the grasses, belonging to the family Gramineae. One specimen of this family, vetiver (Chrysopogon zizanioides (L.) Roberty), has proved very effective in slope stabilization. With the objective of evaluating the improvement of soil shear strength parameters at different times after vetiver planting, direct shear tests were carried out on soil without vegetation and soil with vetiver grass one, two, three and four years after planting. Direct shear tests were also carried out on the same slope soil without vegetation and covered with vetiver grass. The results of direct shear tests with soil slope samples were evaluated by three limit equilibrium methods to determine an average safety factor for the slopes. From the direct shear tests, the parameters cohesion and angle of internal friction were determined, which showed that vetiver grass increased apparent soil cohesion, which became significant three years after planting vetiver. The vetiver grass induced an improvement in resistance parameters with a consequent increase in the safety factor of slopes and increase in soil shear strength, contributing to slope stabilization of shallow ruptures.

Uma estrada de mina foi dimensionada com materiais típicos ocorrentes em mineração de minério de ferro no Brasil, utilizando-se os métodos empíricos CBR e DNER. Através do programa de dimensionamento estrutural mecanístico-empírico ELSYM5, compararam-se os resultados obtidos pelos métodos anteriores e propôs-se a otimização do dimensionamento feito pelo método DNER. Os resultados mostram que a espessura total do pavimento calculada pelos dois métodos é, basicamente, a mesma, sendo que a espessura da camada de base pelo método DNER é superior à obtida pelo CBR, enquanto o oposto ocorre com a sub-base. Ambos os dimensionamentos mostram, através da aplicação do software ELSYM5, que não são os mais apropriados, visto que a deformação de algumas camadas, principalmente no caso CBR, está acima do limite aceitável de 2000 µε. Através da variação da espessura das camadas, obteve-se um dimensionamento adequado, que levou à redução da espessura da camada total do pavimento de 1,97 m para 1,40 m. A redução da deformação das camadas, em que se variou o módulo de elasticidade, demonstra a importância da realização de ensaios de caracterização física dos materiais.

An unpaved mine haul road, based on CBR and DNER empirical methods, was designed using materials which are typical in current Brazilian iron ore mining. By means of the mechanistic-empirical structural ELSYM5 software, the results obtained by previous methods were compared and an optimization of the DNER design was proposed. The results demonstrate that the total thickness of the pavement calculated by the two methods is basically the same and that the base layer thickness calculated by the DNER method is superior to the one obtained by the CBR method, whereas the opposite occurs in relation to the sub-base. Both designs show through the application of ELSYM5 software that they are not the most appropriate, since the strain of some layers, especially in the CBR case, is above the acceptable limit of 2000 µε. Analyzing the variation of the layer's thickness, it was possible to obtain an adequate design, which led to the reduction of the total pavement layer thickness from 1.97 m to 1.40 m. The reduction of the layer's strain in which the elastic modulus was submitted to variation, demonstrates the importance of performing tests for the physical characterization of materials.