Navegando por Autor "SANTOS, Pabllo Henrique Costa dos"

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Evolução supergênica do depósito cuprífero Alvo 118 - Província Mineral de Carajás
(Universidade Federal do Pará, 2022-12-15) SANTOS, Pabllo Henrique Costa dos; COSTA, Marcondes Lima da; http://lattes.cnpq.br/1639498384851302; https://orcid.org/0000-0002-0134-0432
The Carajás Mineral Province is home to one of the most extensive cupriferous belts in the world, where hypogene mineralizations were partially transformed into gossans, later lateritized and/or truncated during landscape evolution. These covers represent an information source for mineral exploration and, in some cases, can be mined together with parental hypogene mineralizations. The plateaus of the South American Surface host complete and lateritized gossans, while the surrounding denuded areas, typical of the Velhas Surface, exhibit incomplete or immature gossans, with the Alvo 118 deposit as an example. In this orebody, the hypogene mineralization was converted into an immature gossan located at depth, while the host rocks were weathered near the surface, forming a mineralized saprolite. The gossan comprises an oxidation zone, which includes goethite, malachite, pseudomalachite, cuprite, tenorite, native copper, ramsbeckite, chrysocolla, and libethenite, with relics of a secondary sulfide zone, represented by chalcocite. These minerals are distributed in the goethite, malachite, cuprite, and libethenite zones, with their mineral successions reflecting the transition of mineralizing solutions from acidic to slightly alkaline conditions and an increase in oxidation potential. This environment was established from the interaction of acid solutions, derived from chalcopyrite dissolution, with the gangue minerals (calcite and apatite) and the host rocks, granodiorites and, secondarily, chloritites, which acted in buffering the system, favoring the formation of new copper-bearing minerals. The strong correlations of CuO with Ag, Te, Pb, Se, Bi, Au, In, Y, U, and Sn in the hypogene mineralization reflect the inclusions of petzite, altaite, galena, uraninite, cassiterite, and stannite in chalcopyrite. In the gossan, Ag, Te, Pb, Se, and Bi remained associated and were incorporated into neoformed copper minerals. On the other hand, Au, In, Y, U, and Sn exhibit greater affinity with iron oxyhydroxides, as well as Zn, As, Be, Ga, Mo and Ni. The δ65Cu values reinforce that the investigated gossan is immature and was not intensely affected by leaching processes. The main mineral phases identified in the saprolite are kaolinite (predominant), associated with chlorite, smectite, vermiculite, quartz, and iron oxyhydroxides. Iron oxyhydroxides are strongly correlated with Ga, Sc, Sn, V, Mn, Co, and Cr, partly derived from the weathering of parent rocks. Additionally, Mössbauer spectroscopy data point to the important role of ferrihydrite and goethite as copper-bearing phases. There is no evidence of copper incorporation by clay minerals. The δ56Fe values indicate a little contribution of primary mineralization to the Fe content of the saprolite, which is more influenced by chlorite weathering. The association Al2O3, Hf, Zr, Th, TiO2, Ce, La, Ba, and Sr represents the geochemical signature of the host rocks, which influence the chemical composition of the three types of mineralization. On the other hand, the association In, Y, Te, Pb, Bi, and Se comprise the main pathfinder elements of the hypogene mineralization. Detailed knowledge of the supergene mineral and geochemical fractionation makes the Alvo 118 deposit a reference guide for investigating immature gossans and mineralized saprolites in denuded areas of the Carajás Mineral Province or equivalent terrains.
Acesso aberto (Open Access)
Geologia, mineralogia e geoquímica do perfil lateritobauxítico da lavra piloto Décio (Rondon do Pará)
(Universidade Federal do Pará, 2017-03-24) SANTOS, Pabllo Henrique Costa dos; COSTA, Marcondes Lima da; http://lattes.cnpq.br/1639498384851302; https://orcid.org/0000-0002-0134-0432
During the Eocene-Oligocene, extensive lateritic coverings were formed in the Amazon. In this context, the sedimentary sequences of the Parnaíba and the Amazon Basins were lateritized and generated four world-class bauxite deposits: Juruti, Trombetas, Paragominas and Rondon do Pará. The latter is the new bauxite exploration frontier of the Amazon and the Décio pilot mine was developed in it, which presents a 3 m thick laterite-bauxite profile, which extends laterally through vast plateaus with about 350 m of altitude. This work sought to deepen the study of bauxite and its relationships with lateritic landscape in the Amazon region. In the field, five lithological profiles were described in the Décio pilot mine. Then, 42 samples were collected for laboratory analysis involving mineralogical characterization (X-ray diffraction); textural (Optical Microscopy and Scanning Electronics); and chemical (Optical Emission Spectrometry and Mass Spectrometry with Inductively Coupled Plasma). The most probable precursor rocks are the clay facies of the Itapecuru Formation. These would have evolved to a bauxitic clay horizon and then to massive microcrystalline and microporous red bauxite. Bauxite, on the other hand, converges to spherolytic iron-rich crust, rich in iron oxide and partially dismantled. This set is covered by a horizon of ferroaluminous spherolites and a nodular bauxite horizon. The whole set is covered by unconsolidated yellow to red clay, equivalent to the Belterra Clay. The minerals that resisted laterite weathering were zircon, tourmaline, rutile, kyanite and quartz. The neoformed were hematite, goethite, gibbsite, part of the kaolinite, besides the anatase. The main chemical constituents are Al2O3, Fe2O3, SiO2 and TiO2, which together make up more than 99.5% of the profile. Its distribution suggests that the lateritic evolution developed in situ occurred until the formation of the spherolithic horizon. The TiO2 content is much higher in the bauxitic clay horizon than in the other overlying horizons, which is not common in a lateritic evolution from a single, homogeneous parent rock. In addition, Zr and ETR decrease towards the top of the profile, which would also not be expected. Therefore, although the precursor rocks of the entire profile were sedimentary, there was a compositional contrast between those that generated the bauxitic clay horizon and those that generated the other horizons. In addition, the pattern distribution of trace elements shows that even starting from slightly differentiated parent rocks, almost the entire profile followed a similar pattern of evolution, with the exception of the nodular bauxite horizon that behaves as separate unit. These characteristics differ the lateritic profile of the Décio and Ciríaco pilot mine, located in the same bauxite region, but formed from more homogeneous parent rocks.