ITABIRITOS E MINÉRIOS DE FERRO DE ALTO TEOR DO QUADRILÁTERO FERRÍFERO – UMA VISÃO GERAL E DISCUSSÃO

Résumé

Itabirites are Palaeoproterozoic metamorphic banded iron formations from the Itabira Group, MinasSupergroup, that crop out in the Quadrilátero Ferrífero District, Minas Gerais, Brazil. The followingcompositional types occur: quartz itabirite, being metamorphic jaspilites, dolomitic itabirite, beingdolomitized banded iron formations, and amphibolitic itabirite modified by the presence of pelitic sediments.These rocks are also associated to pyritic phyllites and hematitic phyllites. A multiple metamorphic –deformational history during two main tectonic events, the Palaeoproterozoic Transamazonian and theNeoproterozoic Brasiliano Event, produced a variety of mineralogical assemblages in the more impurefacies and hydrothermal alteration was responsible for carbonatization, intensive oxidation and mineralization.Hypogenic iron mineralization developed in two main phases resulting in thick massive bodies with norelationship to tectonic structures, denominated non-tectonic ores; and schistose ore associated to shearzone, denominated syn-tectonic ores. The mineralizing fluids might be of metamorphic origin, but theimportance of hypogenic fluids of magmatic origin is emphasized. Supergene processes on quartz andspecially dolomitic itabirites are also of utmost importance in the development of giant ore bodies.