Summary:
Santa Cruz (Corumba deposit)
Corumba ore reserves are comprised of hematite ore type, which generates operations lump ore predominantly.
The manganese and iron deposits of the Morro do Uruclun are located about 25 kilometers south of the city of Corumba, Mato Grosso, Brazil.
The deposits of both manganese and iron occur in the Jacadigo series, of unknown but probably late pre-Cambrian or early Paleozoic age. This has been subdivided into the Urucum, the Corrego das Pedras, and the Band' Alta formations. The Urucum formation, between 400 and 500-meters thick, consists of continental deposits of arkose and conglomerate. It grades upward into the Corrego das Pedras formation, about 95 meters thick, in which ferruginous arkose at the base grades upward into ferruginous sandstone and ferruginous jasper. Above the Corrego daa Pedras formation is the Band' Alta formation, at least 300 meters in thickness, which contains the deposits of manganese and iron. At the base of the Band' Alta is a widespread bed of the manganese oxide cryptomelane. This is overlain by banded siliceous hematite, which makes up the greater part of the formation but is interbedded, about 40 meters or more above the base, with other lenticular beds or cryptomelnns, and, higher in the section, with lenticular beds of clastic rocks, including siltstone, sandstone, and, rarely, conglomerate. The formation is cut off at the top by an erosion surface.
The Corumba formation consists of calcareous shales and argillites, sandy shales, black, well-bedded limestone, gray limestone and dolomite, andwhlte dolomite. It extends at least 200 kilometers westward from Corumba into Bolivia, 100 kilometers to the south, more than 100 kilometers to the north, and an unknown distance to the east.
In many localities the Corumba formation has been marmorized. Although this recrystallization has been attributed to metamorphic effects of the intrusive granite which crops out near Fazenda do Urucum, it is more probably the result of dynamic stresses induced during the complex deformation of the area. There is no known evidence to prove or even strongly indicate that the granite is intrusive into the Corumba formation.
Urucum deposit
The Urucum deposits are associated with banded iron formations (BIF), locally known as jaspelites. The iron and manganese deposits are found in the plateaus which rise from the plains of the Paraguay River and near Mutum Mountain.
The sediments of the Urucúm Basin constitute an epicontinental marine sequence beginning with the basal Jacadigo Group that comprises clastic sediments with carbonatic matrix, overlain by iron-rich arkoses and Jaspilites with manganese layers (Band'Alta Formation), followed by the Corumba Group with limestones, dolomites slates and siltites (Cerradinho Formation) overlain by dark dolomites and limestone breccia of the Araras Formation. This sequence developed in a slow sinking basin with upward gradation from clastic to chemical sedimentation without volcanic contribution. Deposition of widespread iron and manganese rich sediments is due to sharp variation in the Eh conditions most probably under the influence of marine currents in a restricted basin partially protected from atmosphere by large ice caps.
The jaspilites of the Band'Alta Formation present a primary banding defined by planar layers and lenses of quartz and hematite, with variable thickness, from mm to cm. (Fig. 4d). Quartz is usually cryptocrystalline (chert) and hematite appears, similar to the Carajás jaspilites, as microcrystalline aggregates or as very fine platy crystals. Recrystallization of both hematite and quartz results in xenoblastic aggregates that occur discontinuously. Near to the contact with manganese layers hematite may also appear intergrown with cryptomelane (Schneider 1984). Martite is also present in form of hypidiomorphic to idiomorphic crystals as individuals and aggregates. Fine clastic components are common at the base of the sequence but are also present as layers and lenses in the upper levels. Erratic blocks of glacial origin are quite frequent. The most puzzling feature is the presence of small hematitechert ellipsoidal concretions with variable diameter (few mm to several cm), displaying a concentric structure similar to oolites. They are always aligned on the banding and own their shape to differential compaction. Thicker levels of primary high-grade ores occur in the whole sequence. In these layers, banding is less conspicuous, defined by slight variation in the proportions of quartz (chert) and hematite. Superficial leaching of the quartz leads to the development of a very high grade ore especially suitable to direct reduction plants.