The Belterra Clay on the bauxite deposits of Rondon do Pará, Eastern Amazon

Abstract

Bauxite deposits in the Amazon region are commonly covered by yellowish clays which can reach up to 25m thick, known as Belterra Clay (BTC). In Rondon do Pará, Eastern Amazon, BTC is 13m thick and covers world-class bauxite reserves. Three pilot bauxite mines were investigated in Rondon do Pará for an initial characterization of the local BTC. In discordant contact with the lateritic profile, the BTC has reddish brown colors at its base to ocher tones towards the top. It has a massive structure with silt-clayey texture and nodular bauxitic fragments at its base. Rietveld mineral quantification of the material attests that it is dominated by kaolinite, with goethite, gibbsite, hematite, anatase and residual quartz. The thermal behavior of the material also confirms its mineralogical composition. Kaolinite is of low structural order, which was considered the main difficulty in the application of the Rietveld method. Goethite has up to 33 mol% of Al. As observed by scanning electron microscopy (SEM), the minerals represent pseudo-hexagonal crystals measuring from 150 to 700 nm. The BTC in the studied area is correlated to BTC on others bauxitic deposits of the Amazon region, suggesting this material experienced the same genesis and geological evolution, probably during the Pliocene.

Mineralogy, geochemistry and parent rock of Décio bauxite-bearing lateritic profile (Rondon do Pará, Eastern Amazon)

“…From the bottom to the top, these lateritic profiles are composed of clayey bauxite, massive bauxite, ferro-aluminous duricrust, fragmentary ferro-aluminous duricrust, spherulitic horizon and nodular bauxite horizon. Finally, a 12 to 15 m layer of the Belterra Clay unit covers the laterites (Pantoja 2015, Negrão et al 2018.…”

“…In addition to the weathering, polyphasic events such as erosion, transportation and deposition of lateritic materials also played an essential role in the structuration of the lateritic profiles, as demonstrated in the Paragominas and Açailândia deposits Kotschoubey 1981, Kotschoubey et al 1987). The post-lateritic events also include the formation of the covering material, e.g., the Belterra Clay unit, which comprises a friable yellow to red clay layer, with significant mineralogical and chemical affinity with the underlying bauxite-bearing laterites (Truckenbrodt and Kotschoubey 1981, Kotschoubey et al 2005, Cruz 2011, Negrão et al 2018.…”

Unraveling Parent Rock and Mineral Influences in Tropical Weathering Profiles: REE, Nd and Sr Isotopic Geochemistry

“…Evidence of truncation, previous dismantling, and a mixture of fragments are indicated by the breccia/fragmental and the pisolitic to nodular facies of the lateritic duricrust [58,67]. In lateritic regions, concentrations of gibbsite and kaolinite on the surfaces of lateritic profiles, forming soil, along with TiO 2 , HREE, Ga, Nb, Th, and Zr retention, mostly carried in residual minerals are common [59,60,[68][69][70]. A similar, although incipient process also occurs in profile 1, as evidenced by the rare yellowish and pinkish clayey matrix in the dismantled horizon and the very little thick soil covers.…”