Ocorrências manganesíferas da região de Júlio Borges, sul do Estado do Piauí: contexto tectônico, rochas encaixantes e mineralogia do minério.

Abstract

In the region of Julio Borges, in the south of Piauí State, there are a lot of manganese occurrences that are associated with the rocks of the Crístalândia Piauí Complex (Archean / Paleoproterozoic) and of the Orogen Rio Preto, structured in the Neoproterozoic. The main aim of this work corresponds to a geological mapping in the scale 1:25.000, carried out in order to establish the configuration of the enclosing geological framework and to identify the main manganese occurrences in the Julio Borges region. Map produced shows the rocks of the Crístalândia of Piauí Complex occur at the longitudinal edges of the area, bordering the thin occurrence strip of the metasedimentary rocks of the named Rio Preto Group, and the Cenozoic sedimentary rocks that cover all of these previous lithologie. The manganese occurrences occur either as gondite such as spessartine type garnet associated with the rocks of the Rio Preto Group, rhodonite in the portion dose to the contact between the rocks of the Crístalândia of Piauí Complex and those of the Rio Preto Group, and Mn-rich and oxidized concretions present in the colluviums overlying the manganese ore is formed of oxidized phases pirolusita and críptomelano but the manganese silicates are also prevalent and are crosscutted by quartz veins. Concerning their genesis, the Manganese occurrences appear to have been resulted oflatelly enrichment processes in relation to the metamorphic events that affected the region.