Mineração Usiminas (MUSA) is a joint venture between Usinas Siderurgicas De Minas Gerais S.A. (Usiminas), which holds 70% of the company and Japanese group Sumitomo Corporation, holding the remaining 30%.
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Summary:
The Mineração Usiminas mineral claims are located along the western segment of Curral ridge, locally referred to as the Serra Azul (literally Blue Ridge). The Serra Azul, extending for ca 30 km in the NE-SW, is underlain by a continuous outcrop belt of the Cauê Formation, which hosts several iron ore deposits (Simmons, 1968; Romano, 1989; Romano et al, 1991; Alkmim, 2009), including the Western, Central and Eastern mines, as well as the Camargos and Pau de Vinho deposits of the Mineração Usiminas. As part of the Curral ridge, the Serra Azul is the morphologic expression of an overturned, SE-dipping homocline that involves Rio das Velhas and Minas strata (Dorr, 1969). Along the Serra Azul, the basal units of the Minas supergroup are very thin and Gandarela Dolomite is absent for over almost its whole length (Simmons, 1968; Alkmim, 2009).
The Serra Azul overturned homocline can be subdivided into three structural domains (Alkmim 2009). Along the structural domain I, which encompasses the Western Mine and the major part of the Central Mine, the thickness of the overturned Cauê Iron Formation increases from west to east, varying from around 50 m, at the western end of the ridge, to 250 m at the Central Mine. The dips also increase from west to east, being 20o at Ponta da Serra and reaching 45o at Central Mine. Standard itabirites and their weathering products are the more abundant ore types in this domain. The amount of fresh magnetitic itabirite is negligible. However, its weathering product, a magnetiterich, ochreous itabirite occurs as a continuous layer on top (stratigraphic base) of the iron formation, especially in the Western Mine. A small lens of hard haematite was identified near to the base (stratigraphic top) of the Cauê Formation in the Western Mine.
The ca 15 km long domain II encompasses the central portion of Serra Azul, including the Camargos deposit. Minas Supergroup strata strike ENE-WSW and dip 40o to 80o to SSE. NW-verging folds and faults give rise to local structural complexities. Magnetitic itabirites occur in form of layers or lenses intercalated with siliceous itabirite, which in turn grades laterally into dolomites. A clay-rich, deeply weathered itabirite (called by the miners AIF, for ‘argillaceous iron formation’) is quite frequent close to the contact with the Cercadinho Formation, the basal unit of the Piracicaba Group.
Along the structural domain III, which hosts the Pau de Vinho deposit, layers of the Minas Supergroup describe a large curve with the concave side facing north. On the easternmost sector of the curve, the strata dip NW, a change probably caused by the uplift of the adjacent the Bação Dome. NW-trending sinistral to reverse-sinistral shear zones cut the homocline along its whole length. One of the largest sinistral faults runs along the border of a large dyke (~300 m wide) of gabbro that divided the domain (as well as the Pau de Vinho deposit) in two sectors. To the southwest of the dyke, layers of NW-striking fresh itabirites predominate along the ca 500 m thick Cauê Formation. To southeast of the dyke, the Cauê Formation consists of a sequence of magnetitic itabirite, dolomite, friable ore and argillaceous iron formation (AIF).