Alteration of pyrophanite: transition in chemical composition to a manganese analogue of pseudorutile - evidence from the Quadrilatero Ferrifero of Minas Gerais, Brazil
Cabral, Alexandre Raphael; Sattler, Carl-Diedrich
published: Mar 5, 2004
Alteration of Fe-bearing pyrophanite from a manganese oxide deposit (Conta História) in the Quadrilátero Ferrífero of Minas Gerais, Brazil, was investigated by electron-microprobe analysis. The microanalyses suggest that the alteration products range in composition from Mn-deficient pyrophanite to a hypothetical Mn-rich pseudorutile-like mineral. In the sample material analysed, crystals of Fe-bearing pyrophanite cut by gibbsite-filled veinlets and vugs are altered, whereas Mn-rich ilmenite from gibbsite pseudomorphs after garnet remains unaltered.