The Paragominas bauxite deposits are developed on a 10,000km2 plateau, situated 50 m to 150 m above the drainage-incised valley floors. The average altitude does not exceed 150 m in the plateaus.
The Miltônia 3 (M3) and Miltônia 5 (M5) gibbsitic bauxite deposits have formed by deep tropical weathering of the Ipixuna Formation. The bauxite layer forms a nearly continuous tabular body, less than 5 m thick, but extending 20km north–south, and as much as 8km east–west, beneath the plateau surface.
Prolonged weathering and oxidation of aluminum-rich sediments allowed the formation of gibbsite, an aluminum hydroxide, which can occur in a microcrystalline, porcelain-like form (amorphous bauxite), or as fine-grained euhedral crystals that occasionally reach 1 mm in size. Minerals within the deposit display either ‘detrital’ or ‘secondary’ character. Minerals that are ‘detrital’ were originally deposited as part of the host water-borne sediment (e.g., quartz and anastase); those that are ‘secondary’ are weathering products of kaolinite and feldspar.
The geological profile of the Miltônia deposit has eight horizons, with lateral variation in thickness to characterize the following lenticular horizons: Clay Overburden (CAP), Nodular Bauxite (BN), Crystallized Nodular Bauxite (BNC), Ferruginous Laterite (LF), Crystallized Bauxite (BC), Crystallized/Amorphous Bauxite (BCBA), Amorphous Bauxite (BA), and Variegated Clay rocks of the District pertain to th ........