De Campos_et_al._Bauxite_Espinhaço

Abstract: Bauxites evolved from unusual parent rocks in quartzite-dominated landscapes have not been previously reported. At the Southern Espinhaço Range, Minas Gerais, Brazil, bauxitic weathering profiles are found in a unique geomorphological-lithological-climatic setting. Resistant quartzites acted as a barrier against erosion and facilitated deep weathering of hematite-phyllite units. The long-term exposure of the hematite-phyllites under alternating wet and dry tropical climates favored widespread bauxitization. Here we investigate the geochemical, mineralogical, geochronological and micromorphological signatures of scaffolded bauxites in order to reconstruct their evolutionary history. Our data suggests that recurrent aluminum and iron mobilization within the profiles were mainly driven by mineral dissolution-reprecipitation mediated by bioturbation and the influx of vegetation-derived organic species. (U–Th)/He geochronology of Al-goethite reveals bauxitization started at least since the Lower Miocene, with important intensification of weathering in the Upper Miocene and Lower Pleistocene. The adjacent resilient quartzites acted as scaffolds for bauxitization and supported the preservation of ancient landscape features. The evolutionary history of Southern Espinhaço Range bauxites suggests a new model of bauxitization in ancient landsurfaces.

Table 2: Geochemistry of profiles
Table 3: Mineral quantification obtained by Rietveld refinement
Table 4: (U-Th)/He geochronology
Supplementary Data 1: Chemical Analysis of hematitic-phyllite
Supplementary Data 2: Electron Microprobe Thin Sections
Supplementary Data 3: Electron Microprobe Goethites