Gibbsite as low-temperature hydrothermal overprint on lateritised Cenozoic sediments, Quadrilátero Ferrífero of Minas Gerais, Brazil

ABSTRACT

Gibbsite, typically a clay-sized mineral in lateritic profiles, occurs as crystals between 50 and 150 µm across in druse-like cavities that characterise veins hosted in lateritised Cenozoic sediments, exposed along a road cut in the Quadrilátero Ferrífero of Minas Gerais, Brazil. Both the veins and the host rock, a red diamictite, contain gibbsite, but the drusy gibbsite in the former is remarkably larger than the matrix gibbsite in the latter. It is suggested that the coarser gibbsite is a low-temperature hydrothermal mineral. The coarse grain size of gibbsite and its occurrence in veins comprise important criteria to recognise hydrothermal overprint of low temperature on lateritic profiles.

KEYWORDS:

• Gibbsite
• hydrothermal overprint
• Cenozoic sediments
• Quadrilátero Ferrífero
• Minas Gerais

Acknowledgements

This contribution derives from fieldwork performed by two of us, MLSO and TKM, as a requisite for obtaining a BSc degree in Geology at the Universidade Federal de Minas Gerais (UFMG). We thank Dr Carlos Alberto Rosière for his assistance in the field and supervisorship. We gratefully acknowledge Dr Cristiane Paula de Castro Gonçalves for providing access to a scanning electron microscope (SEM), housed at the Department of Geology, Universidade Federal de Ouro Preto. The SEM was kindly operated by Débora Vasconcelos de Oliveira. We also thank Igor Vasconcellos Santana for carrying out X-ray diffraction at the Centro de Pesquisa Manoel Teixeira da Costa, UFMG. Our manuscript benefited from thoughtful comments by two anonymous reviewers. Dr Simon Jowitt is thanked for his diligent editorial handling. Production work by Mr Irudayaraj Edward and his team is indeed appreciated.

Disclosure statement

No potential conflict of interest was reported by the authors.