Navegando por Assunto "Hematite"

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Mineralogia e geoquímica do perfil laterítico do depósito de ferro da Serra Leste, Carajás-PA
(Universidade Federal do Pará, 2020-07-17) SILVA, Rayara do Socorro Souza da; COSTA, Marcondes Lima da; http://lattes.cnpq.br/1639498384851302
The Carajás Province hosts one of the largest high-grade iron ore deposits in the world, distributed in the districts Serra Norte, Serra Sul and Serra Leste. The process of Fe mineralization in the region is still a stage of discussion, due to the textural complexity typical of the ore, which induces different interpretations regarding its genetic model. In this context, in order to better understand its origin, the present work evaluates the contribution of lateritic weathering to the formation of the iron deposit of Serra Leste. In the field, a profile of weathering and its substrate were described, through two drill holes provided by the company VALE S.A, followed by sampling. After that, about 20 samples were described, photographed and prepared for mineralogical and chemical analysis. The mineralogical phases were identified by X-Ray Diffraction (XRD) and the micromorphological images obtained by Scanning Electron Microscopy (SEM), accompanied by semi-quantitative analyzes by Energy-Disperse Spectroscopy (EDS). The textural aspects also involved optical microscopy by reflected and transmitted light. Analysis by Mössbauer spectroscopy were used in order to identify the oxidation states of Fe ions present in the samples, complementing the information obtained by the other techniques. Chemical analyzes were performed by Inductively Coupled Plasma Atomic Emission Spectrometer (ICP-AES), and Inductively Coupled Plasma Mass Spectrometer (ICP-MS). The investigated profile comprises two successions of lateritic alteration, one derived from jaspilites and the other derived from mafic composition rocks. The profile comprises jaspilites and chloritites at the base, followed by saprolitic horizons (thick saprolite and fine saprolite) and ferroaluminous crusts. The chemical composition shows that the SiO2 contents (chert/quartz) decreased drastically during the formation of the horizons from the base of the profile, with an increase in the levels of Fe2O3 (mainly hematite and goethite) and its substantial concentration in the saprolitic horizon (mineralized zone). From the top of the fine saprolite there is an increase in the contents of Al2O3, TiO2 and P2O5, related to the presence of gibbsite, aluminous goethite and anatase, in the same way trace elements (Ga, V, Cr, Ta, Nb, W, Zr, ETR and others) present in the structure of newly formed minerals. The data obtained in the investigated profile, therefore, shows a lateritic evolution, and are similar to the mature lateritic profiles of the Amazon.
Acesso aberto (Open Access)
Mineralogia e geoquímica do perfil laterito bauxítico na serra Sul, Província Mineral de Carajás
(Universidade Federal do Pará, 2020-11-03) RODRIGUES, Paulo Ronny Soares; COSTA, Marcondes Lima da; http://lattes.cnpq.br/1639498384851302
The Amazon holds the largest reserves of bauxites in Brazil, located in Trombetas, Juruti, Paragominas and Rondon do Pará. The Carajás region, with large lateritic deposits, especially of iron, is also emerging with potential for bauxite deposits, with emphasis on those of Serra Norte. In Serras Sul, smaller occurrences were identified, which were investigated in this work. In this context, field activities were carried out with sample collection and textural, mineralogical and chemical analyzes and then a genetic discussion was presented. In four alteration profiles on a side road near the Serra Sul, after geological cartography, 23 samples were collected, which were described, photographed and prepared for mineralogical analysis (X-ray diffraction), textural (optical and scanning electron microscopy) and chemical (mass and optical emission spectrometry, with inductively coupled plasma). The bauxite laterite profile comprises from the base to the top of: 1) Kaolin Horizon (HC); 2) Mottled clay Horizon (HAM); 3) Nodular Bauxite Horizon (HBN); 4) Clayey Bauxite Horizon (HBA) and 5) Ferruginous crust Horizon (HF); and finally to the top 6) Dismantled crust ferruginous horizon (HFD. The chemical composition is essentially dominated by Al2O3, Fe2O3, SiO2 and TiO2, which compose the main minerals, kaolinite, gibbsite, hematite, goethite and anatase. The trace elements V, Cr, Cu, Ga, As, Zr, Cd, Hf, Bi and Th, whose concentrations are generally higher than those of the Upper Crust of the Earth, are more concentrated in the ferruginous horizons, related to Fe oxy-hydroxides (hematite and goethite) and also to zircon. On the other hand, the elements Co, Zn, Se, Rb, Sr, (Nb), Ag, (Sn), Cs, Ba and Pb are at lower levels than theUpper Continental Crust, and their concentrations are lower in ferruginous horizons, suggesting affinity with clay minerals.ETR at levels lower than UCC, are enriched in ETRP and present strong positive and negative C and positive Eu anomaly, and suggest distribution in zircon, oxy-hydroxides of Fe and other mineral phases. and mass clearly demonstrate a complete lateritic evolution, only partially modified in its upper portion. The bauxite zone, however, does not have local potential for ore, due to the low content of usable alumina and high in reactive silica. However, its occurrence opens an opportunity for further research in view of the geological and paleoenvironmental potential of the Mineral Province of Carajás.