Abstract
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 Para, Eastern Amazon, BTC is 13m thick and covers world-class bauxite reserves. Three pilot bauxite mines were investigated in Rondon do Para 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.
Highlights
Bauxites are covered by thick yellowish clay in the Amazon region, denominated Belterra Clay (BTC) (Truckenbrodt & Kotschoubey 1981, Bardossy & Aleva 1989, Truckenbrodt et al 1991, Horbe & Costa 1999)
A general description (Pantoja 2015) of this sequence, from the basis to the top, is: a clayey horizon composed of saprolitic material from rocks of the Itapecuru Formation followed by massive bauxite, massive iron-aluminous crust, a dismantled iron-aluminous crust, ferruginous spherulites, and a horizon with bauxite nodules within a clayey matrix
Gibbsite predominates in the bauxite, whereas the iron-rich horizons are ruled by hematite and Al-goethite
Summary
Bauxites are covered by thick yellowish clay in the Amazon region, denominated Belterra Clay (BTC) (Truckenbrodt & Kotschoubey 1981, Bardossy & Aleva 1989, Truckenbrodt et al 1991, Horbe & Costa 1999). The lack of sedimentary structures and apparent homogeneity of the BTC raised a range of discussions on its genesis, relating it to the strong weathered material of the upper part of the Barreiras Formation (Dennen & Norton, 1977); to mud flow or sheet flood deposits from the Plio-Pleistocene (Truckenbrodt & Kotschoubey, 1981); to the dealuminization of a previous bauxite crust (Bardossy & Aleva 1989, Tardy 1993); to in situ formation by weathering with termites’ contributions (Truckenbrodt et al 1991); and as result of geochemical differentiation of bauxites under intense tropical forest (Lucas, 1993). The genesis of the BTC is not yet completely understood, but it is well accepted that this material has a strong relation to the bauxites
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