The role of biological agents in the microstructural and mineralogical transformations in aluminium lateritic deposit in Central Brazil

- The biota caused transformations in Barro Alto bauxite.
- The bioturbation by termites formed micro-aggregate and granular structures.
- The degradation caused by roots formed porphyric and fine monic structures.
- The activity of termites transformed gibbsite into boehmite.

Petrological studies using X-ray diffraction (XRD) and micromorphological analyses (Optical Microscopy and SEM), were done to understand the role of biological activity in the evolution of Barro Alto bauxite. The results indicated that this influence came through structural (or microstructural) and mineralogical transformations, namely: I - the bioturbation caused by termites and II - the mechanical degradation and geochemical transformation promoted by roots. In the bioturbation caused by termites were formed: I - a intergrain micro-aggregate structure, characterised by gibbsite crystals from isalteritic bauxite fragmentation on the bottom of the profile and II - a granular structure characterised by a termitic microaggregates with fragments of gibbsite immersed in a kaolinite-gibbsite-goethite-boehmite micromass, formed by bioturbation of the degradation clay with nodules of gibbsite, whose origin is the geochemistry degradation of isalteritic bauxite. The processes associated with geochemical and mechanical degradation caused by roots were responsible for the genesis of: I - a porphyric texture with bauxite fragments surrounded by nonaggregate material and II - fine monic structure where the gibbsite neoformation has the mould cavities left by old roots, generating riziform features.