Caracterização mineralógica e determinação do grau de liberação dos itabiritos da Mina Córrego da Onça, Barão de Cocais, Minas Gerais, Brasil

Abstract

A mineral deposit reflects the geological, physical-chemical and structural factors of its genesis and evolution in space and geological time. Understanding the potential of a deposit not only facilitates the selection of the most appropriate techniques to concentrate the metals of interest but also helps to ensure the efficiency of the process, reducing operating costs and environmental impacts. This work provides technical guidance for the GSM Mineração ore treatment plant expansion project, which research investigated the chemical composition and mineral associations present in itabirites from Córrego da Onça Mine, located in Barão de Cocais, Minas Gerais, focusing on the concentration of iron ore. For this purpose, an exploratory analysis of the geological drill core database was performed to map targets of interest for laboratory tests. Hierarchical clusters classified according to numerical multivariate analysis helped preparing three samples of quartz itabirites and other three of amphibolitic ones, which are representative of the mineral resource. The samples were composed by combining selected intervals of sixteen drill cores and were subjected to granulometry, geochemistry and reflected-light optical microscopy tests. For both lithotypes FeT contents are typical of poor itabirites from the Iron Quadrangle (Quadrilátero Ferrífero), with Si, Al, P and Mn as the main contaminants. The major iron minerals identified are hematite, martite, magnetite and goethite, which occur in different forms, habits and proportions. The degree of alteration and porosity are considered high, and the particle size is quite varied. The predominant gangue mineral in all samples is quartz, which occurs both freely and/or in aggregates with other silicates and iron and aluminium oxides and hydroxides. Mineral associations suggest that the origin of the deposit may be attributed to intercalations of iron formations of the silicate, oxide-silicate and amphibole facies. The amphibolitic itabirites indicated the majority presence of earthy goethite with low potential for iron recovery. However, the quartz itabirites presented a significant percentage of magnetite, indicating a positive sign for magnetic separation processes. Flotation can also be evaluated, since the typologies showed no restrictions regarding deleterious elements such as Ca, Mg and K. In summary, the results consolidate the prospect of generating commercial products and will serve as a basis for guiding bench and pilot plant tests. Since the facies coexist intrinsically in the deposit, the most pragmatic economic scenario aimed at optimizing the mineral reserve and increasing the useful life of the project is joint open-pit mining, with blending of the two types to compose the feed for the concentration plant in appropriate proportions, so that the performance of the quartz itabirite route is not compromised.