No abstract

decreasing ore grades and decline of mass recovery, which led to significant negative impacts on the production of phosphate concentrate. The operations at Araxá have a growing need to process ores from the base of weathering profile in order to extend the life of mine. This type of ore has characteristics strongly dependent on the fresh-rock protoliths (proto-ores). This geological study started with the recognition of protoliths. There is a close association between bebedourite, phoscorite and carbonatite rocks, which were classified into macrogroups according to the main associations observed in the field and in drill core. The study of the mineralogical evolution was carried out on each protolith macrogroups at different horizons within the base of the weathering profile. The altered rock has a complex assembly of primary minerals, and no significant quantities of supergene minerals. The lower micaceous ore is characteristically free of carbonates and has greater amounts of supergene minerals such as anatase, goethite, quartz and interstratified phyllosilicates. In the upper micaceous ore, diopside and phlogopite were completely eliminated and the assembly of supergene minerals becomes more expressive. The geometallurgical behavior of the studied ores is heavily dependent on their protoliths and weathering horizons. Multivariate statistical analyses of principal components and linear regression were used to elaborate geometallurgical models. The geometallurgical behavior, once considered in mine planning, subsidizes the process engineering in the quest for improvements or operational and ore-processing adjustments for achieving better mass and P 2 O 5 recoveries. The geometallurgical models were applied in a three dimensional block model, so that the geometallurgical variables and their variations become spatially defined and can be used in mining engineering, for results best suited to phosphate concentrates and fertilizers production plans. x Figura 2.10: Características texturais e mineralógicas microscópicas dos dolomita carbonatitos. A) Amostra SC06 52 m: carbonato euédrico e apatita grossa, ambos dispersos na rocha, polarizadores cruzados; B) Amostra SC06 52 m: detalhe de um cristal cumulus de tetraferriflogopita associado à magnetita intercumulus, polarizadores paralelos; C) Amostra SC06 52 m: cristais de apatita com núcleos diferentes das bordas, e magnetita cumulus, polarizadores cruzados; D) Amostra SC06 52 m: magnetita cumulus e pirocloro zonado, polarizadores paralelos; E) Amostra CMA-BAR-DH151 65. (Ribeiro, 2008;Cordeiro, 2011b;Barbosa, 2012b;Palmieri, 2011) e o campo dos cumulados nelsoníticos de Serra Negra em roxo (Grasso, 2010 Figura 3.4: Imagens eletrônicas por elétrons retroespalhados dos minerais e suas texturas em amostras de testemunhos de sondagem do macrogrupo de protolito BEB/DC. A) Associação textural entre anatásio e estroncianita -amostra MB59 71.40 a 84.40 m, rocha alterada; B) gorceixita e apatita com textura fina e porosa -amostra MB59 62.5 a 71.40 m, rocha alterada; C) Prová...