Summary:
Vale's Southern System consists of iron deposits located in the Quadrilatero Femfero (Iron Quadrangle), in the south central part of the State of Minas Gerais.
Ore reserves with high ratios of itabirite ore relative to hematite ore type. Itabirite ore has iron grade of 35-60%.
The Quadrilátero Ferrífero (QF) comprises an area of about 7000 km2 and hosts one of the largest concentrations of lateritic iron-ore deposits in the world. The QF is located in central Minas Gerais state, southeastern region of Brazil (Dorr, 1965). The QF has a quadrangular shape due to the dome and basin structures of the Minas Supergroup. Most of the iron ore in the QF are hosted in the oxidized, metamorphosed and heterogeneously deformed Banded Iron Formations (BIFs) of the Cauê Formation, the so-called itabirites. The BIFs are altered sedimentary deposits with laminated rocks formed by alternating layers of silica and hematite magnetite, as well as carbonates and iron silicates.
The Quadrilátero Ferrífero is located at the southeastern border of the São Francisco Craton, southeastern Brazil (Fig. 1). According to Alkmim and Marshak (1998) the most important lithostratigraphic units of the Quadrilátero Ferrífero are: (1) the Archean crystalline basement, (2) the Rio das Velhas Supergroup, (3) the Minas Supergroup, (4) the Post-Minas Intrusives and (5) the Itacolomi Group.
Basement crystalline rocks include a gneiss/migmatite complex and two generations of voluminous Late Archean plutons: calk-alkaline and anorogenic granites (Alkmim and Marshak, 1998). The Rio das Velhas Supergroup consists of greenstone (basalt and komatiite), rhyolitic lava and intercalated sedimentary rocks. Sedimentary units of the Rio das Velhas Supergroup include Algoma-type banded-iron formations (BIFs), carbonates and siliciclastics. The Minas Supergroup is a metasedimentary unit that unconformably overlies the Rio das Velhas Supergroup. According to Alkmim and Marshak (1998), the Minas Supergroup strata resist erosion, forming ridges that tower above the regions which are underlain by less resistant basement or greenstone rocks. These characteristics of the Minas Supergroup shaped the geomorphology of the southern Brazil highlands giving rise to high relief in this region. Alluvial conglomerate and sandstone made up the basal units of the Minas Supergroup. These units grade upward into shallow-water marine pelites of the Tamanduá and Caraça Groups. The Lake Superior-type Cauê banded-iron Formation lies on Caraça metasediments. The Cauê Formation is a carbonate sequence of the Gandarela Formation. Lying locally unconformably on the Gandarela Formation, the Piracicaba Group comprises a thick pile of shallow-water and deltaic strata. Separated from the Piracicaba Group by an unconformity, the Sabará Group is a thick sequence of turbidites, tuffs, volcaniclastics, conglomerates and diamictites derived from a source to the east–southeast. The PostMinas intrusives comprise thin, undated, pegmatite veins cutting Minas rock (Alkmim and Marshak, 1998; Herz, 1970). Finally, the Itacolomi Group is a unit consisting of alluvial sandstones, conglomerates and minor pelites (Dorr, 1969) deposited in intramontane grabens (Alkmim and Martins-Neto, 2012).
The main iron ore types in the Iron Quadrangle are:
Hematite: Hematite represents the high-grade ore type within the iron deposit. The iron content varies from 65 to 67 percent. It is either massive or foliated in nature. The hematite is classified according to its physical and chemical characteristics as Compact Hematite, Friable Hematite, and Goethitic / Argilitic Hematite. Its origin is related to hydrothermal or metasomatic processes.
Itabirite: Itabirite is a term widely used in Brazil to denote a metamorphosed iron formation composed of iron oxides (hematite, magnetite, and martite), abundant quartz, very rarely mica, and other accessory minerals. It may be foliated or compact. The un-enriched (poor) itabirites from the Quadrilatero Ferrffero tend to have little magnetite, and composed principally of quartz-hematite, quartz-hematite-carbonate and hematite-carbonate. Itabirite represents the majority of reserves and resources of the Iron Quadrangle deposits. According to Vale, it was originated by silica leaching and residual iron-oxide enrichment process during post-metamorphic weathering cycles. The iron content averages about 45 percent, and occasionally it may reach up to 60 percent. The Itabirite ore is classified according to its physical and chemical characteristics as Compact Itabirite, Friable Itabirite, Goethitic / Argilitic Itabirite or Ochre.
Canga: Canga ore consists of unconsolidated talus material formed by the weathering of the iron formation. The iron content ranges significantly, with generally high concentration of phosphorous and alumina.
Rolados: A second detrital mineralization type. Consists of a ferruginous or lateritic matrix with fragments and blocks of different materials such as hematite, itabirite, quartz; high Fe grade, with high contaminant levels, such as P and Al203.s.