Methods of Mechanical Mining of Compact-Rock—A Comparison of Efficiency and Energy Consumption

This paper compares the methods of mechanical mining of rock in terms of their efficiency, energy consumption, and the durability of the tools they involve. It presents the advantages of mechanical heading-driving methods. In the first part, we described the methods used to assess rock workability, and the influence of rock types and parameters on mining efficiency. Furthermore, we discussed the compact-rock mining process in terms of the energy it consumes. We provided the description of the most common mechanical methods, such as milling, static crumpling and undercutting, including the tools involved, and the requirements and limitations for the use of these methods. The paper presents unique machinery solutions designed to reduce the energy consumed by mining processes. In the final part of the paper, we propose a solution to select the mechanical method of rock mining as a function of rock type and parameters.

ELECTRICAL RESISTIVITY APPLIED TO OPTIMIZATION OF BLASTING DESIGN AT PRODUCTION BENCHES: A CASE STUDY AT ABÓBORAS MINE, QUADRILÁTERO FERRÍFERO, MINAS GERAIS – BRAZIL

ABSTRACT. Quadrilátero Ferrífero is one of the main regions of iron ore production in the world. The action of the weathering processes promotes the conformation of compact rock immersed in friable material. The usual model of blasting applied in production benches, with blast drillholes distributed homogeneously, produces boulders of compact rock, which are impracticable to extract and grind, causing impacts on daily production of iron ore. Therefore, this work proposes a methodology capable of overcoming this problem caused by weathering, using the electrical resistivity method. The application of it was carried out at the Abóboras mine (VALE S.A.), and was able to differentiate two types of materials, interpreted as compact and friable itabirite. With the use of the electrical data, it was possible to generate a geophysical model that allowed to determine the position of the compact itabirite boulders. From this model, it was possible to optimize the blasting design, with higher concentration of detonation drillholes where the model indicated the compact rock. With the appropriate tests, it was observed a 75% decrease in the amount of boulders present in the fragmented material as compared to the usual model. Consequently, there was a significant increase in ore loading effectiveness, thus optimizing iron ore production.Keywords: Applied geophysics, iron ore, mining. RESUMO. Quadrilátero Ferrífero é uma das principais regiões de produção de minério de ferro no mundo. A ação dos processos intempéricos promovem a conformação de rochas compactas imersas em material friável. O modelo usual de detonação e desmonte aplicado em frentes de lavra, com furos de detonação distribuídos de modo homogêneo, gera matacões de rocha compacta, o que inviabiliza sua extração e moagem e impacta na produção diária de minério de ferro. Desse modo, este trabalho propõe uma metodologia capaz de suplantar esse problema causado pelo intemperismo, através da utilização do método de eletrorresistividade. A aplicação do método foi realizada nas dependências da mina de Abóboras (VALE S.A.), e foi capaz de diferenciar dois tipos de materiais, interpretados como itabirito compacto e friável. Com o uso dos dados elétricos, foi possível gerar um modelo geofísico que possibilitou determinar a posição dos blocos de itabirito compacto. A partir desse modelo, houve uma otimização da malha de desmonte, com maior concentração de furos de detonação onde o modelo indicou rocha compacta. Com os devidos testes de detonação, foi observado diminuição dos matacões em 75% em relação à malha de desmonte usual. Como resultado, houve significativo aumento da efetividade do carregamento de minério, e consequente otimização da produção de minério de ferro.Palavras-chave: Geofísica aplicada, minério de ferro, mineração.

The mechanism of replacement as illustrated by metasomatism of the Whin Sill

Where the solutions which carried the lead vein minerals pass along joint planes through the Whin Sill, the dolerite is altered to a white, compact rock for a distance of several feet. The original texture is well preserved in the altered dolerite; the ferromagnesium minerals are replaced by calcium, magnesium and iron carbonate, the feldspars by a minutely crystalline mixture of kaolin and muscovite and the ilmenite by small rutile crystals. The former areas of interstitial quartz are increased and apatite remains completely unchanged. The microscopic evidence that there is neither gain nor loss of alumina during the metasomatism, taken in conjunction with analyses of altered and unaltered rock, may be used to prove that there was a contraction of about 14% during metasomatism. This result is corroborated by the occurrence of cracks which are formed by shrinkage during metasomatism and which are now filled with carbonates.