Caracterização dos contaminantes do minério de ferro do depósito mineral da Serra do Sapo, Conceição do Mato Dentro, Minas Gerais

Os itabiritos do depósito mineral da Serra do Sapo estão localizados na região da Serra do Espinhaço Meridional e são descritos como parte da Formação Serra do Sapo, unidade superior do Grupo Serra da Serpentina, e estão sobrepostos aos xistos e aos filitos da Formação Meloso. Formações ferríferas com alto teor de Al e P ocorrem no contato com metassedimentos da unidade basal. Esses contatos são transicionais e geram uma rocha bandada, com níveis milimétricos a centimétricos contendo grande concentração de óxido de ferro. Essa litologia tem textura sedosa e ocorre sempre decomposta, sendo descrita como hematita-quartzo-mica xistos ou classificada como itabirito com alto teor de contaminantes (IFX). A classificação dos itabiritos é feita de acordo com o grau de decomposição intempérica da rocha. Formações ferríferas bandadas classificadas como itabiritos (IT), rocha sã, e que também apresentam altos teores de P como contaminante, são classificadas como itabirito com alto teor de fósforo (ITX). Estudos petrográficos identificaram muscovita, clorita e gibbsita como as principais fontes de Al para as amostras de IFX. Os altos teores de Al2O3 e P2O5 desses litotipos também são explicados pelo processo de formação supergênica, em que o espaço dos minerais lixiviados é preenchido por clorita e gibbsita. Para o ITX, os altos teores de P estão relacionados com minerais de apatita que ocorrem com maior frequência nesse litotipo. Dados geoquímicos de rocha total, quando normalizados ao Pos-Archean Australian Shale (PAAS), mostram que as amostras de IFX são enriquecidas em elementos terras raras leves (ETRL) se comparadas aos outros itabiritos. Essas amostras também são enriquecidas em elementos móveis como Ba e Sr. Isso indica que o enriquecimento The itabirites of Serra do Sapo ore deposit are located in the Serra do Espinhaço region and are described as part of the Serra do Sapo Formation, the upper unit of the Serra da Serpentina Group, superposed to the schists and phyllites of the Meloso Formation. Iron formations with a high content of aluminum and phosphorus occur in contact with the schists of the basal unit. These contacts are transitional and generate a rock with millimeter to centimeter levels containing high iron oxide concentration. This lithology has a silky texture and always occurs decomposed, being described as hematite-quartz-mica schists or classified as Itabirite with high content of contaminants (IFX). The classification of itabirites is made according to the degree of weathering of the rock. Banded iron formations classified as Itabirites (IT) that also present high levels of phosphorus as contaminants; are classified as Itabirite with high phosphorus content (ITX). Petrographic studies identified muscovite, chlorite and gibbsite as the main sources of aluminum for IFX samples. The high levels of Al2O3 and P2O5 in these lithotypes are also explained by the supergenic formation process, where the space of the leached minerals is filled by chlorite and gibbsite. For ITX the high levels of phosphorus are related to apatite minerals that occur more frequently in this lithotype. Geochemical data shows that IFX samples, when normalized to PAAS, are enriched in LREE compared to the other itabirites. These samples are also enriched in mobile elements such as Ba and Sr. This indicates that the enrichment is due to the mobility of the LREE in a weathered environment without HREE

Caracterização Tecnológica e Mineralógica dos Itabiritos Quartzo-Dolomítico e Dolomítico da Mina de Jangada, e Uso da Separação Magnética como Método de Concentração

Existe a necessidade crescente de aproveitamento de minérios de ferro com teores de ferro cada vez mais baixos. Para tal aproveitamento, são indispensáveis estudos de caracterização tecnológica e mineralógica do material. Neste trabalho, foram analisadas duas amostras de itabiritos carbonáticos com baixos teores de Fe para verificar a viabilidade da separação magnética como método de concentração. A amostra de itabirito quartzo-dolomítico apresenta em sua composição 28,68% de Fe, com grande quantidade de CaO (6,15%) e SiO2 (42,29%). A mineralogia é composta basicamente por magnetita, quartzo e dolomita. Os resultados da etapa rougher de separação magnética mostrou um aumento de teor de Fe para 56,43%, com uma recuperação de 88,24%, sendo necessária uma etapa cleaner para purificação do concentrado. A amostra de itabirito dolomítico apresenta em sua composição uma baixa quantidade de SiO2 (0,91%) e teor de Fe de 35,27%, com a presença majoritária de hematita. O resultado da etapa rougher da separação magnética apresentou um aumento do teor de Fe para 65,46%, já caracterizado como produto final. A etapa scavenger recuperou boa parte do Fe (72,63%) perdido na etapa rougher. No geral, a separação magnética se mostrou um método eficiente para a concentração de itabiritos dolomítico e quartzo-dolomítico

Provenance of the Buritirama Formation reveals the Paleoproterozoic assembly of the Bacaj? and Caraj?s blocks (Amazon Craton) and the chronocorrelation of Mn-deposits in the Transamazonian/Birimian system of northern Brazil/West Africa.

The Mn-bearing Buritirama Formation along the homonymous ridge consists of a 40?km long by ca. 3?km wide NW-SE trending unit that limits the northern border of the Archean Caraj?s domain with the Paleoproterozoic Bacaj? domain in the southeastern Amazon Craton. The Buritirama Formation type section is arranged in four imbricated thrusts that individualize three main stratigraphic units: Lower Unit, Intermediate Unit and Upper Unit. Detrital U-Pb zircons ages from the Lower Unit and Upper Unit record the prevalence of Neoarchean populations, suggesting the Caraj?s block as the main sedimentary source for the Buritirama basin. However, minor Paleoproterozoic populations attributed to the Bacaj? block are also recognized, defining a maximum depositional age at ca. 2186 Ma. The anorogenic Buritirama metagranite occurs at the local basement, represents a probable precursor stage of the Buritirama rift and yielded a Concordia age of 2549???5.9?Ma (U-Pb). Supported by these new geochronological data, a framework model for the evolution of the Buritirama basin is proposed. Contrary to previous interpretations, the basin was active until at least the Rhyacian, representing a platformal setting fringing the northern margin of the Caraj?s block. A regional metamorphic event (ca. 2.06?Ga) records the closure of the basin during the Transamazonian Orogeny and the amalgamation of the Bacaj? and Caraj?s blocks. The depositional age bracketed in between 2.3 and 2.1?Ga links the Buritirama Mn deposit (southeastern Amazon Craton) with those of Serra do Navio (Amap? Block, northeastern Amazon Craton) and Nsuta (West African Craton), suggesting: (i) widespread chronocorrelation of Mn-bearing sequences in the continental-scale Rhyacian Transamazonian/Birimian orogenic system, and (ii) formation of the primary carbonate ores under the influence of a major global manganese deposition episode

Metaturbidite-hosted gold deposits, Córrego do Sítio lineament, Quadrilátero Ferrífero, Brazil

A study of geology and rocks paragenesis has been conducted at the Córrego do Sítio auriferous lineament, containing the Cachorro Bravo, Laranjeiras and Carvoaria metaturbidite-hosted lode-gold deposits located in the Quadrilátero Ferrífero Region, Minas Gerais, Brazil. These representative deposits are described to illustrate the essentially similar general character of all the deposits of lineament as well as the wide compositional and mineralogical differences in the ore of the different deposits, where, for the Cachorro Bravo deposit, a geological mapping included two underground mine galleries. The Córrego do Sítio unit is a metamorphosed turbidite in an alternating sequence of metagraywackes and phyllites, with parallel to discordant metamafic dikes and sills. The ore zone is predominantly hosted at the stratigraphic break between metasedimentary and metamafic rocks. Four deformation events affected the mine sequence. Mineralized veins and veinlets are considered to have formed within a brittle-ductile shear-zone environment and occurred in multiple episodes. Different vein types are recognized, but the most important volumetrically is a S1-concordant type characterized by smoky and milky quartz-carbonate-sulfide ± sulfosalts veins. Veins are dominated by quartz, but locally they are characterized by carbonate and a large variety of sulfide and sulfosalt minerals. Pyrite is the commonest associated sulfide mineral, followed by arsenopyrite and pyrrhotite. An extensive mineralogical study of polished sections has confirmed different generations of sulfide minerals. The sulfides and sulfosalt minerals are interrelated in the veins and disseminated on wall rocks. The data are consistent with a genetic models related to other Archean lode-gold deposits

Metaturbidite-hosted gold deposits, Córrego do Sítio lineament, Quadrilátero Ferrífero, Brazil

A study of geology and rocks paragenesis has been conducted at the Córrego do Sítio auriferous lineament, containing the Cachorro Bravo, Laranjeiras and Carvoaria metaturbidite-hosted lode-gold deposits located in the Quadrilátero Ferrífero Region, Minas Gerais, Brazil. These representative deposits are described to illustrate the essentially similar general character of all the deposits of lineament as well as the wide compositional and mineralogical differences in the ore of the different deposits, where, for the Cachorro Bravo deposit, a geological mapping included two underground mine galleries. The Córrego do Sítio unit is a metamorphosed turbidite in an alternating sequence of metagraywackes and phyllites, with parallel to discordant metamafic dikes and sills. The ore zone is predominantly hosted at the stratigraphic break between metasedimentary and metamafic rocks. Four deformation events affected the mine sequence. Mineralized veins and veinlets are considered to have formed within a brittle-ductile shear-zone environment and occurred in multiple episodes. Different vein types are recognized, but the most important volumetrically is a S1-concordant type characterized by smoky and milky quartz-carbonate-sulfide ± sulfosalts veins. Veins are dominated by quartz, but locally they are characterized by carbonate and a large variety of sulfide and sulfosalt minerals. Pyrite is the commonest associated sulfide mineral, followed by arsenopyrite and pyrrhotite. An extensive mineralogical study of polished sections has confirmed different generations of sulfide minerals. The sulfides and sulfosalt minerals are interrelated in the veins and disseminated on wall rocks. The data are consistent with a genetic models related to other Archean lode-gold deposits