Brazil's main bauxite deposits are concentrated in the Amazon region, specifically in the state of Pará. The three main mines are located in Trombetas, Paragominas and Juruti, and they’re responsible for 85% of Brazil's bauxite production. Even with the favorable mineral scenario in Brazil and especially in the state of Pará, there are already companies that are currently competitive in the current market, they are seeking to develop studies of the characterization and use of nodular bauxite in this type of deposit. The ore, so far, is considered as marginal, it means low-grade ore in the mineral industry. In this context, this work sought to evaluate Trombetas deposits’ nodular bauxite from their texture, mineralogical and chemical
characteristics as a possible aluminum ore. In the field, seven lithographic profiles were described on the mining fronts of Bela Cruz and Monte Branco mines belonging to ‘Mineração Rio do Norte’. Then, 19 samples were collected, which were described, photographed and prepared for mineralogical and chemical analyzes. The mineralogical phases were identified by X-ray Diffraction (XRD) and Scanning Electron Microscopy coupled to the Dispersive Energy System (SEM/EDS). The textural aspects involved optical microscopy and Scanning Electron Microscopy coupled to the Dispersive Energy System (SEM/EDS). The chemical analyzes were performed by Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES), Inductively Coupled Plasma Mass Spectrometer (ICP-MS), X-ray Fluorescence (XRF), titulometry and gravimetry. The profiles investigated comprise from the base to the top the
bauxite horizon (HBX) which is represented by gibbsite concretions surrounded by a clay matrix. The overlapped bauxite nodular horizon subdivided into HBNB, HBNI and HBNT, is formed by gibbsitic nodules, of fine texture, that impresses solid and porcelanate aspect and they are surrounded by a clayey matrix. The clay cover (CAR) at the top is formed by a yellow clay, corresponding to Belterra Clay. In the profiles, the fragments > 0.500 and ~0.500 mm of the HBX and HBNB, HBNI and HBNT are essentially composed of gibbsite associated with kaolinite, hematite and anatase. The dominance of gibbsite in the fragments > 0.500 and ~ 0.500 mm of the HBNB, HBNI and HBNT, presents a potential of nodular bauxite as a possible
aluminum ore. However the fragments < 0.500 mm, clayey matrix of HBX and HBNB, HBNI, HBNT and CAR are mainly composed of kaolinite associated with gibbsite, hematite, quartz and anatase. The kaolinite domain in the HBNB, HBNI, HBNT fragments < 0.500 mm, makes it difficult to consider them as possible aluminum ore. As for the heavy minerals (zircon, rutile and tourmaline), no contrast was found between the horizons and the clayey cover. The chemical composition consists essentially of SiO2, Al2O3, Fe2O3 and TiO2, which reinforce the main minerals identified and as these the contents differ according to the horizons. The concentrations of the trace elements are variable, V, Cr, Ga, Se, Zr, Nb, Mo, Sn, Hf, Ta, W, Hg, Bi, Th and U are above the crustal average in all fragments, clayey matrix of HBX, HBNB, HBNT and CAR. Trace elements such as V, Cr, Ga, Mo, Hg and Bi correlate positively with Fe2O3 (hematite and goethite). While Nb, Sn, Hf, Ta, Th, U, correlate positively with zirconium (zircon) and titanium (anatase). When normalized to the chondrites, the distribution curves present parallelism between the various fragments, clayey matrix of HBX, HBNB, HBNT and CAR, with curves that exhibit Eu anomaly, as well as an enrichment of the heavy rare earth elements (HREE) in front of the light rare earths elements (LREE). The data obtained in the investigated profiles of Bela Cruz and Monte Branco mines demonstrate broad similarity to Belterra clay-type nodular lateritic-bauxite profiles found in Amazon, where the clayey matrix of the nodules resembles textural, chemical (larger elements and traces) and mineralogical (including heavy minerals) with this covering clay.
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