A ORIGEM DOS FILITOS HEMATÍTICOS DA SERRA DO ESPINHAÇO MERIDIONAL, MINAS GERAIS

Abstract

This work present stratigraphic, mineralogical and geochemistry dates about  the “hematitic phyllites” of the Espinhaço Range, specially in its meridional portion. For these rocks, composed essencially by sericite/muscovite and hematite and very poor in quartz, many investigators have suggested an origin from a low grade metamorphism of some unique igneous rocks.

Typical of the “Guinda Group”, basal portion of the Espinhaço Supergroup, with Paleo/Mesoproterozoic age (1.7 – 1.75 G.y.), the hematitic phyllites presents an interesting chemistry composition, characterized by 35,4% SiO₂, 5,4% TiO₂, 23,2% Al₂O₃; 25,3% FeO, 0,1% MnO, 1,5% MgO, 0,5% CaO, 0,3% Na₂O; 7,9% K₂O and 0,4% P₂O₅. These numbers shows, clearly, alteration processes.

The evolutive aspects of the Espinhaço Supergroup put constraints that indicate one of the follow processes: modification from fluid percolation in shear zones or superficial alteration processes in atmosphere- lithosphere boundary. The present studies show that the last alternative (superficial processes) is more feasible to explain the characteristics of the hematitic phyllites.

Thus, we believe that these rocks are paleoregolith/paleosols ( from Paleo/Mesoproterozoic) specially origined from the basalts of the “Espinhaço Basin” opening. Associated rocks with so much chloritoid (90.0%) are, probably, paleobauxities with variable iron content.