Formação ferrífera associada à sedimentação glaciogênica da Formação Puga (Marinoano) na Serra da Bodoquena, MS

Abstract

Iron formation associated with the glaciogenic deposits of the Puga Formation (Ma- rinoan) in the Serra da Bodoquena, Mato Grosso do Sul, Brazil. Iron formation associated with diam- ictite interpreted as belonging to the Puga Formation (Marinoan) is reported here in a different context from the already known deposits of the Jacadigo Group, at the Urucum´s Massif. The iron formation occurs as a bed about 2 m thick, oriented NS and dipping 45º to East, confined in a massive foliated diamictite with ferruginous matrix presenting low metamorphism. It’s composed of centimetric hematite and magnetite layers alternated with submilimetric layers of silica, sometimes stretched due to the tectonic deformation of the Paraguay Mo- bile Belt. Fe2 O3 vary from 75% in the borders, to 52% in the center of the body. The iron concentration in the borders is due to the remobilization of silica to the center of the body, probably because of the tectonic events. Chemical analyses show that Al2 O3 concentrations are high (2,89 – 3,45%), and the strong linear correlation with TiO2 and Zr indicate terrigenous contribution during chemical deposition. Isolated blocks of granite oc- cur within the BIF, but tectonic overprinting makes it difficult to have a clear observation of the relationship between the clasts and original lamination. Despite the Puga Formation has its origin related to glaciogenic events, there are no clear evidence to link this iron formation origin to the glacial processes.