Navegando por Assunto "Trace elements"

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Acesso aberto (Open Access)
Assinatura geoquímica do ouro na Província Mineral do Tapajós, Cráton Amazônico: o exemplo dos depósitos São Jorge e São Chico
(Universidade Federal do Pará, 2025-06-19) GOMES, Iolanda Clara do Carmo; LIMA, Rafael Guimarães Corrêa; http://lattes.cnpq.br/6751523860876497; LAMARÃO, Claudio Nery; http://lattes.cnpq.br/6973820663339281; https://orcid.org/0000-0002-0672-3977
Gold has a great economic importance, and the determination of its geochemical and isotopic signatures, exploited in Brazil’s main mineral provinces, has become a valuable tool not only for mineral exploration but also for tracing its origin and circulation. The aim of this study is to characterize and compare the chemical composition of gold from two different deposits using scanning electron microscopy paired with energy-dispersive spectrometry (SEM‑EDS), to evaluate the viability in differentiating provenance on local and regional scales, and to discuss the factors controlling element distribution in native gold. São Jorge and São Chico are gold deposits located in the eastern portion of Tapajos Mineral Province, aligned along the Tocantinzinho lineament (WNW‑ESE). The gold mineralization at São Jorge deposit consists of a paragenesis formed by gold + pyrite + chalcopyrite ± sphalerite and, rarely, galena, which host two generations of gold with distinct chemical compositions. These gold phases occur either in quartz veins and/or in sulfide disseminations in strongly hydrothermally altered host rocks. In this deposit, gold is mainly hosted by pyrite, occurring in the form of inclusions with high Au contents (84.27–91.02 wt%) and filling pyrite fractures with a composition richer in Ag (7.86–15.72 wt%). The geochemical and textural differences indicate at least two distinct mineralizing events. In contrast, the São Chico deposit shows a paragenesis formed by gold + pyrite + galena + sphalerite ± chalcopyrite, in which gold occurs as electrum within polymetallic sulfide‑bearing quartz vein systems. Here, gold is mainly hosted by galena, and textural relationships between these two minerals suggest simultaneous precipitation under low‑temperature conditions. Gold in this deposit also occurs with chalcopyrite and sphalerite, as reflected in its chemical composition, which shows higher average of Cu (0.44 wt%) and Zn (0.42wt%) contents, respectively. Principal component analysis (PCA) identified Ag, Fe, and Te as the elements with the greatest potential for gold discrimination between these two deposits. Gold microparticles from the São Jorge deposit exhibits a geochemical signature with higher contents of Au (73.82–91.02 wt%), Fe (0.54–6.21 wt%), and Te (0.37–3.61 wt%), compared to gold from the São Chico deposit, which displays higher concentrations of Ag (29.82–51.42 wt%).
Acesso aberto (Open Access)
Determinação dos elementos-traço (Zn, Co e Ni) em sedimentos da Plataforma Continental Amazônica sob influência da descarga do rio Amazonas
(Instituto Nacional de Pesquisas da Amazônia, 2006) SIQUEIRA, Gilmar Wanzeller; PEREIRA, Simone de Fátima Pinheiro; APRILE, Fábio Marques
Determination of trace elements (Zn, Co and Ni) in sediments at the Amazon Continental Shelf on influence of the Amazon River discharge This research was developed at Amazon Continental Shelf (ACS) between the Orange Cape (Amapá State) and the Maguari Cape (Pará State), to determine the levels of zinc, cobalt and nickel in the superficial sediments identifying its inputs and outputs. The rate of these metallic elements in the sediments decreases following Zn> Ni> Co. The concentrations of total metals in the surface sediments range from Zn = 52.8 159.5; Ni = 21.7 47.4 and Co = 14.3 48.8 (mg.kg-1). The levels of trace elements observed in the sediments at ACS are of natural occurrence. Pollution sources of metallic elements were not observed.
Acesso aberto (Open Access)
Geoquímica das águas do médio e baixo rio Madeira e seus principais tributários - Amazonas - Brasil
(Instituto Nacional de Pesquisas da Amazônia, 2013-12) HORBE, Adriana Maria Coimbra; QUEIROZ, Maria Mireide Andrade; MOURA, Candido Augusto Veloso; GALARZA TORO, Marco Antônio
The aim of this paper was study the water of the Madeira River and its tributaries, between the city of Humaitá and its confluence in the Amazon River. There were analyzed: pH, conductivity, turbidity, major ions, trace elements and strontium isotopes during the dry and wet seasons and also, in the transition from the wet to the dry season, throughout 2009 and 2010. The white waters from the Madeira River are bicarbonated, calcic, with pH between 5 and 6 and the ions concentrations are higher than those of the tributaries. The waters of the tributaries are black, are more acidic and are chemically heterogeneous; those from the left margin are chemically similar to the waters of Madeira River, while those from the right margin are enriched in dissolved SiO2. The concentrations of cations, Cl- and NO3- are higher during the wet season due to the contribution of soils, vegetation and the rainwater composition (Cl-), while HCO3-, SO42-, Al, Br e P are concentrated in the dry season, and their higher contents may be related to the bedrock. The higher concentrations of SiO2 and rare earth elements in both dry and wet season are related to vegetation, soil and rocks. The interaction of these factors causes the chemical heterogeneity of the water. However, the chemical similarities between the water tributaries of the left margin and the water of the Madeira River, are probably, consequence of the Andean rocks be the sources of the Cenozoic sedimentary rocks percolated by these tributaries while the chemistry water of the tributaries of the right margin are in accordance with the tectonic stability, the intense weathering and the low erosion rate of the Amazon craton.