Navegando por Assunto "Geochemistry"

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Uma análise de cluster via CiteSpace a propósito da espectrometria WDXRF para geocientistas (2001-2021)
(Universidade Federal do Pará, 2023-08-17) CASTANHO, Rebeca Soares; PAZ, Simone Patrícia Aranha da; http://lattes.cnpq.br/5376678084716817
The present bibliometric analysis addresses the use of Wavelength Dispersive X-Ray Fluorescence (WDXRF) spectrometry in geochemical analysis to evaluate scientific trends over a twenty-year period, from 2001 to 2021, using the academic and free bibliometric tool, CiteSpace. For this purpose, 941 international scientific articles involving WDXRF were collected from the Web of Science (WoS) platform using the search terms "wdxrf" or "wavelength dispersive x-ray fluorescence". The data analysis was divided into two parts: the first part aimed to understand and interpret the quantitative aspects of the scientific production related to the technique, while the second part involved a co-occurrence analysis of keywords from the retrieved works. Despite fluctuations, there has been a constant increase in the number of articles related to this spectrometry technique, with 2020 being the year with the highest productivity in the historical series (105 publications). The United States of America leads the country rankings (110 articles); however, the relatively homogeneous distribution of these studies reveals that WDXRF is a widely disseminated technique worldwide. Brazil ranks among the top ten most influential countries in this field, occupying the eighth position with 59 publications. The journal X-Ray Spectrometry, with 82 articles, stands out as the primary venue for the dissemination of research on this analytical technique. In total, 569 keywords were found, connected by 2002 co-occurrence links. The term "trace element" denotes a solidified but always relevant interest in the use of WDXRF for this level of chemical analysis. On the other hand, "nanoparticle" is the keyword with the highest citation explosion over the past two decades, particularly between 2015 and 2021, highlighting a more recent trend in the elemental characterization of nanostructured compounds. The CiteSpace program identified 13 thematic groups, with five being the most notable in the application of this instrumentation: nanomaterial characterization (cluster #0), trace-level heavy metal analysis (cluster #1), chemical speciation (cluster #2), analysis of particulate matter on filters (cluster #5), and provenance of historical ceramics (cluster #6). In summary, it can be concluded that the chemistry of geological materials does not constitute a narrowly defined body of studies concerning WDXRF. Instead, it represents a scientific frontier that expands through interdisciplinary approaches, providing new and integrated methodological approaches to geoscientific research for those who delve into this technique.
Acesso aberto (Open Access)
Avaliação de risco ambiental por contaminação metálica e material orgânico em sedimentos da bacia do Rio Aurá, Região Metropolitana de Belém - PA
(Instituto Nacional de Pesquisas da Amazônia, 2013-03) SIQUEIRA, Gilmar Wanzeller; APRILE, Fábio Marques
The Aurá River basin is situated in the Belém Metropolitan region, between the municipalities of Belém and Ananindeua, where the rate of population growth has increased without any social and environmental control. The region is intensely exploited and the more frequent environmental problems are deforestation, erosion, flooding, water pollution and contamination, especially by heavy metals and organic compounds (OC). Geochemistry behavior (Al, Fe, Mn, Cr, Ni and Cu) and OC levels were determined in the 30 sampling sites between 2008 and 2010 in the bottom sediments of the river. There is an uncontrolled sanitary landfill situated at the north of the Aurá River responsible, in part, by the metallic contamination of the sediments. The environmental stress is classic in the region, and it has resulted from anthropic activities, which has transported unconsolidated material associated to metals to the Aurá. The variables studied were classified on the transport mechanisms and sources (allochthonous and/or autochthonous). The results showed that the main contribution of ions Al and Fe was the sanitary landfill; Mn and Ni was the adjacent soils; Cr was modified (III/VI) by the allobiochemistry, and Cu by bio-induced processes.
Acesso aberto (Open Access)
Distribuição geoquímica dos metais no material particulado em suspensão - MPS na margem direita da Baia de Marajó, Costa Amazônica, Brasil
(Universidade Federal do Pará, 2025-03-25) ANDRADE, Robinson da Cruz; KUTTER, Vinicius; http://lattes.cnpq.br/6652786694334612; https://orcid.org/0000-0001-7295-6800
The Marajó Bay, located in the Amazon region, is one of the largest estuarine systems in Brazil. It is influenced by the Amazon and Tocantins Rivers, with intense hydrodynamics and physico-chemical processes that affect metal distribution. This study aimed to analyze the concentrations and distribution of the elements Al, Fe, Mn, Mg, Zn, Cr, V, Ti, and Ca in suspended particulate matter (SPM) from the right margin of Marajó Bay, correlating the results with environmental factors such as salinity, pH, and local hydrodynamics. Samples were collected at three strategic points— Icoaraci (Point 1), Mosqueiro Island (Point 2), and Colares (Point 3) — during two campaigns carried out between April and May 2023. A Van Dorn bottle was used for surface and 20-meter depth sampling, covering the complete tidal cycle. The particulate material was filtered using cellulose acetate filters (0.45 μm) and analyzed by X-ray fluorescence spectrometry for quantitative determination of the elements. Physico-chemical data such as temperature, pH, salinity, and Eh were obtained using multiparameter probes, and current data using ADCP. Statistical analysis included Kruskal-Wallis tests, Pearson correlations, and boxplots. The results revealed significant variations in SPM concentrations among the sampling points. At Point 3 (Colares), the highest concentrations were observed at the surface (0.278 mg/L), indicating lower hydrodynamic energy and greater deposition of fine sediments, favored by saline intrusion and metal flocculation. Point 1 (Icoaraci) showed the lowest concentrations, suggesting higher sediment removal due to tidal dynamics and river discharge. The Kruskal-Wallis test indicated significant differences among surface samples, especially for Mg, Al, Ti, V, Cr, Fe, and Zn. At depth, only Mg and Zn showed significant variations. Pearson correlations revealed strong associations between Fe, Cr, Mn, and Zn at Point 3, suggesting co-transport of these metals, likely governed by adsorption onto iron and manganese oxides, particularly under low-energy conditions. The observed geochemical behavior highlights that hydrodynamics and saline intrusion are key factors controlling the spatial and vertical distribution of metals in Marajó Bay. It is concluded that Marajó Bay is a highly dynamic estuarine environment, where the deposition and transport of metals in SPM are controlled by both physical processes, such as hydrodynamic variation, and chemical processes, such as flocculation in saline environments. The findings contribute to the understanding of geochemical processes in the Amazon region and provide valuable insights for environmental management and the preservation of local ecosystems.
Acesso aberto (Open Access)
Efeitos das variações sazonais do clima tropical úmido sobre as águas e sedimentos de manguezais do estuário do rio Marapanim, costa nordeste do Estado do Pará
(Instituto Nacional de Pesquisas da Amazônia, 2008) SILVA, José Francisco Berrêdo Reis da; COSTA, Marcondes Lima da; VILHENA, Maria do Perpétuo Socorro Progene
To evaluate the short period climatic variations impact over Amazonic mangrove ecosystem, studies were carried out on the northeast coast of Para State. Sediments, surficial and interstitial waters were collected and examinated throughout salinity, pH and Eh (mV) measurements; mineralogical determination using X-ray diffraction and electronic microscopy. Chemical analysis of dissolved sulfides, sulfate and chloride, among others were made in samples collected seasonally, under spring and neap tides conditions. The seasonal chloride variations in the interstitial waters shows 20 g/l during the dry season and less of 10 g/l in the season; the concentration in surficial are higher at neap tides (rainy season) and spring tide (dry season). The dissolved sulfides were found only at 10 cm, indicating sediment exposure to the atmospheric oxygen advectives fluxes. The dissolved iron rates increases between 0-10 cm and the pH tends to neutrality. The saturation of interstitial waters at dry season is indicated by evaporitic minerals: gypsum and halite. The pluviometric variations are responsible by gradual changes in the nutrient and physical chemical properties of surficial and interstitial waters, into the saline equilibrium control at coastal waters, in the salinization and desalinization of sediments and the distribution of mangrove vegetation at the estuary. The prolonged exposure of sediments during the dry season and the morphological characteristics contribute to the total or partial oxidation of surficial sediments, modifying the mineralogy of sediments and the physical chemical characteristics of interstitial waters.
Acesso aberto (Open Access)
Estudo isotópico do depósito aurífero Volta Grande, domínio Bacajá, sudeste do cráton amazônico
(Universidade Federal do Pará, 2024-03-22) PIMENTEL, Helmut Sousa; VASQUEZ, Marcelo Lacerda; http://lattes.cnpq.br/4703483544858128; https://orcid.org/0000-0003-2729-9404; MACAMBIRA, Moacir José Buenano; http://lattes.cnpq.br/8489178778254136
The area of the Volta Grande of the Xingu River is crucial for the geological understanding of the Siderian and Riacian periods in the Bacajá Domain, Maroni-Itacaiúnas Province, Amazonian Craton, which hosts significant gold mineralizations. The Bacajá Domain is composed of tectonic associations with NW-SE orientation that contain reworked Archean and Siderian fragments, mainly during the Riacian, with significant crustal growth during the Transamazonian Cycle (2.26 to 2.06 Ga). The objective of this thesis is to investigate the tectonic environment and discuss the crustal evolution in accretionary and continental collision settings. The study relied on field surveys, geological-geophysical mapping, petrography, geochemistry, geochronology, and isotopic geochemistry, employing U-Pb and Lu-Hf methods in zircon via SHRIMP and LA-ICP-MS, U-Pb in titanite via LA-ICP-MS and Sm-Nd on whole rock via TIMS. The geological-geophysical integration reveals the NW-SE trending Bacajá Shear Zone with well-defined edges and foliated terrains of high magnetic susceptibilities, plastically deforming the lithotypes within. Petrographic analyses identified metavolcanosedimentary rocks of the Três Palmeiras sequence, the Intrusive Oca Suite (composed of granodiorite, quartz monzodiorite, quartz monzonite, monzodiorite, and diorite), as well as granodiorite, monzogranite, and sienogranite of the Bacajaí Complex and the Arapari Intrusive Suite. The zoned hydrothermal orogenic gold mineralization occurs at the contact between the Três Palmeiras Group and the Intrusive Oca Suite. The geochemistry of mafic volcanic rocks from the lower Itatá Formation of the Três Palmeiras Group indicates evolved tholeiitic character in a mid-oceanic ridge and juvenile island arc setting, while the volcanic rocks of the upper Bacajá Formation are related to calc-alkaline volcanic arcs in active compressional continental margins. Three groups of granitoids representing different phases of magmatic and tectonic evolution in the Bacajá Domain during the Riacian were distinguished, with ages spanning around 110 M.y.: granitoids from the Intrusive Oca Suite at 2.20-2.17 Ga, syenogranite with biotite from the Bacajaí Complex at 2.17 Ga, and biotite-bearing monzogranite from the Arapari Intrusive Suite at 2.09 Ga. The Intrusive Oca Suite comprises intermediate to acid, calcic to alkali-calcic, ultramafic to medium-mafic, metaluminous to peraluminous rocks formed in a cordilleran granitic setting related to volcanic arcs. The REE of Intrusive Oca Suite granitoids exhibit strong magmatic fractionation, reflected in high (La/Lu)N ratios, enrichment in Rb, Th, and K, and depletion in Ba, Nb, P, and Ti, sourced from mafic rocks with varying K contents. The Bacajaí Complex consists of calcic to alkali-calcic, medium-mafic, and peraluminous quartz monzonite, granite, and granodiorite, sourced from x mafic rocks with low-K and high-K components and some input from metasediments. The rocks of the Arapari Intrusive Suite are medium-mafic, calcium-alkali to alkali-calcic, and metaluminous, sourced from mafic rocks with high-K content. The syn- to late-collisional granitoids (Bacajaí Complex and Arapari Intrusive Suite) are enriched in LILE and LREE, exhibiting negative anomalies in Ni, P, and Ti, and depletion in HFSE, typical of orogenic granites in volcanic arcs. In terms of isotopes, the Três Palmeiras sequence has Nd-TDM values ranging from 2.35 to 2.58 Ga, with εNd(t) varying from -0.41 to +3.20. The Intrusive Oca Suite includes rocks with Nd-TDM between 2.24 and 3.06 Ga and εNd(t) ranging from -5.99 to +2.44. U-Pb zircon crystallization ages for this suite are 2203 ± 23 Ma, with Hf-TDM C values between 2.4 and 2.8 Ga and εHf(2.20Ga) ranging from -0.45 to +5.24 for the Ouro Verde body; 2173 ± 7 Ma with Hf-TDM C ranging between 2.3 and 2.6 Ga, and ɛHf(2.17Ga) between +2.04 and +7.65, added to a U-Pb age of 2171 ± 17 Ma in titanite, for the Central body, and 2171 ± 13 Ma, with Hf-TDM C values between 2.4 and 3.4 Ga and εHf(2.17Ga) ranging from -10.32 to +4.34 for the Buma body, indicating distinct crustal generations between the Mesoarchean and Siderian/Riacian. The Bacajaí Complex has a crystallization age of 2165 ± 10 Ma, Hf-TDM C values between 2.5 and 2.8 Ga, and εHf(2.16Ga) ranging from -0.35 to +3.04, with mantelic sources from the Neoarchean. The Arapari Intrusive Suite has a crystallization age of 2094 ± 13 Ma, Nd-TDM at 2.38 Ga, εNd(2.09Ga) at -1.15, Hf-TDM C values between 2.6 and 2.8 Ga, and εHf(2.09Ga) varying from -2.77 to +1.59, indicating a mixture of mantle and crustal sources generated from the Neoarchean to the Siderian. The geological evolution of the study region is marked by various events. In the Siderian, volcanic-sedimentary sequences with tholeiitic basalts and island arc andesites were followed by the emplacement of diorites to granites around 2.20 to 2.09 Ga and collision, originating continental arcs. The most advanced and late stage of the Transamazonian orogeny in the Volta Grande region is represented by the emplacement of peraluminous granitoids from the Arapari Intrusive Suite, closing the complex geological bevolution of the region. The analyses in this study highlight the proposed similarity based on petrographic, geochronological, and isotopic similarities between the Volta Grande region and the Lourenço and Carecuru domains, located in the state of Amapá, in the northeastern portion of the Maroni-Itacaiúnas Province.
Acesso aberto (Open Access)
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)
Hidrodinâmica, transporte e proveniência sedimentar no baixo rio xingu e sua importância como “Tidal River” amazônico
(Universidade Federal do Pará, 2022-07-14) MEDEIROS FILHO, Lucio Cardoso de; LAFON, Jean Michel; http://lattes.cnpq.br/4507815620234645; ASP NETO, Nils Edvin; http://lattes.cnpq.br/7113886150130994
This research is based on the investigation of the processes (geological and hydrodynamic) that govern the recent evolution of a large tributary of the lower Amazon, the Xingu River. The aim was to investigate its aspects of sedimentary evolution and hydrological flows, from already consolidated data on the filling of its ria and how its patterns of transport and sediment trapping, its seasonal and tidal effects have been established, in addition to understanding the role of the Amazon River as a regulator in the dynamics of its tributary. Hydrodynamic measurements of flow, velocity and water level along with bottom sediment and MPS samples were collected at 3 annual seasons (February, June and November). The results provided support for the investigation of the Xingu-Amazonas interaction and the evolution of the bottom morphology of the lower Xingu. The results suggest a filling of the ria both by the Xingu River, forming a prominent headwater delta, and the Amazon River, where tidal variations transport sediments upstream in the Xingu River. On the other hand, large areas in the central part of the ria indicate muddy sedimentation. Elementar geochemistry allowed us to trace part of the history of sediments and source rocks, together with the analysis of immobile elements (Al, Ti, Zr, Hf, Th) and rare earth elements (REE) because they are poorly fractionated during weathering processes. and they are concentrated in the bottom sediments to the detriment of the dissolved fraction of the rivers. The deposits preserved in the lower Xingu River, despite draining cratonic regions in higher areas, confirm that the bottom material is derived from heterogeneous sources with predominantly intermediate igneous compositions and that they underwent important recycling during fluvial transport. The hydrodynamic modeling allowed to indicate the fluvial discharge as the most relevant forcing for the muddy deposition dynamics in the Xingu estuary. From a numerical model, it was possible to extrapolate the flow and transport dynamics beyond the open boundaries, that is, the central portion of the ria, elucidating the interaction mechanism between river and tidal discharge and the associated sedimentary dynamics. The determination of the amplitudes and phases of the tidal components, whether of purely astronomical origin or resulting from shallow waters, as well as the average level and the hourly discharge proved to be fundamental for the understanding of the governing processes.
Acesso aberto (Open Access)
Holocene history of a lake filling and vegetation dynamics of the Serra Sul dos Carajás, southeast Amazonia
(Academia Brasileira de Ciências, 2017-08-24) GUIMARÃES, José Tasso Felix; SAHOO, Prafulla Kumar; SOUZA FILHO, Pedro Walfir Martins e; FIGUEIREDO, Mariana Maha Jana Costa de; REIS, Luiza Santos; RODRIGUES, Tarcísio Magevski; SILVA, Marcio da Silva
Down-core changes in sedimentary facies, elemental geochemistry, pollen, spore, δ13C, δ15N and radiocarbon records from a filled lake, named R4, of the Serra Sul dos Carajás were used to study the relationship between the paleomorphological and paleoecological processes and their significance for Holocene paleoclimatology of the southeast Amazonia. The sediment deposition of the R4 lake started around 9500 cal yr BP. Increase of detrital components from 9500 to 7000 cal yr BP suggests high weathering of surrounding catchment rocks and soils, and deposition into the lake basin under mudflows. At that time, montane savanna and forest formation were already established suggesting predominance of wet climate. However, from 7000 to 3000 cal yr BP, a decline of detrital input occurred. Also, forest formation and pteridophytes were declined, while palms and macrophytes were remained relatively stable, indicating that water levels of the lake is likely dropped allowing the development of plants adapted to subaerial condition under drier climate conditions. After 3000 cal yr BP, eutrophication and low accommodation space lead to high lake productivity and the final stage of the lake filling respectively, and forest formation may has acquired its current structure, which suggests return of wetter climate conditions.
Acesso aberto (Open Access)
Mineralogia e Geoquímica de U, Th, ETR e outros elementos-traço em bauxitas da região de Paragominas, NE do Pará
(Universidade Federal do Pará, 2022-08-17) PARAENSE, Breno Marcelo Ribeiro; ANGÉLICA, Rômulo Simões; http://lattes.cnpq.br/7501959623721607; https://orcid.org/0000-0002-3026-5523
The state of Pará has the largest deposits of metallurgical bauxite in Brazil, with emphasis on the western regions (municipalities of Oriximiná and Juruti, with two mines in operation) and Northeast regions of the state (municipalities of Paragominas – one mine in operation – and Rondon do Pará). The lateritic/bauxitic cover of the bauxite province of Paragominas is a product of extreme weathering of siliciclastic sedimentary rocks and is composed of minerals resulting from the highest degree of alteration, that is, kaolinite (Al2Si2O5 (OH)4), gibbsite (Al(OH) )3 , goethite (FeOOH), hematite (Fe2O3) and anatase (TiO2), to which are added traces of relict quartz, traces of heavily degraded mica and heavy minerals of greater resistance in humid tropical conditions such as rutile (TiO2), tourmaline and zircon (ZrSiO4). In addition to the extraction of bauxite, its mineral transformation, which takes place in the industrial district of Barcarena, near Belém, with the Hydro-Alunorte Alumina refinery, and the production of metallic aluminum by Albras. Due to recent events related to the disposal of waste in decantation basins (DRS) used by the mining company, a climate of distrust on the part of public opinion regarding the safety of the mining populations that live in the vicinity of the company, especially regarding the issue of human health, since the constitution of residues from the mineral transformation of the ore is not completely known. The objective of this research is to determine the presence and study the geochemical behavior of trace elements such as U, Th and ETR, in addition to other heavy metals, such as Hg, Cd and Pb, in bauxites and lateritic covers from the Miltônia mine, in Paragominas, and residues (red muds) from Barcarena, the relationship with the accessory mineralogy of these materials and establishment of reference or background values for environmental assessment. The present work was carried out with samples from 1 bauxite profile (section HIJ-231), located in the Miltônia 3 mine, collected through drilling holes and/or from the mine front, process samples were also collected from the SAG mill of the plant I, separated into different granulometric fractions, supplied by Norsk Hydro. The XRD and XRF analytical processes were carried out at the Mineral Characterization Laboratory (LCM) from UFPA, while the Scanning Electronic Microscopy stage was carried out at the Microanalysis Laboratory of same Unit/Institution. The results of chemical and mineralogical analyzes of samples from the Miltônia 3 mine, both raw bauxite and its granulometric fractions, after autogenous milling, showed a relationship between the high values of ZrO2 and TiO2 verified and the accessory minerals - zircon, rutile and anatase.
Acesso aberto (Open Access)
Mineralogia e química dos sedimentos de fundo do médio e baixo Madeira e de seus principais tributários: Amazonas - Brasil
(Instituto Nacional de Pesquisas da Amazônia, 2011) QUEIROZ, Maria Mireide Andrade; HORBE, Adriana Maria Coimbra; MOURA, Candido Augusto Veloso
This study reports the granulometric, mineralogic and chemical analyses, including Pb isotope, carried out on the bottom sediments of the Madeira River, whose headwaters are in the Andes Mountain, and its tributaries that come from the cratonic region, in order to investigate the compositional variation of the sediments transported by the major rivers of the Amazon. The analytical data show that the bottom sediments of the Madeira River have higher amounts of sand and quartz, and lower contents of Al2O3, Fe2O3, K2O, MgO, Na2O, PF, TiO2O, P2O5, MnO and trace elements, and the maturity increases toward downstream. Among the tributaries, the bottom sediments from Machado and, secondarily, Marmelos rivers are those that more closely match the composition of the sediments of Madeira River. The sediments of Jamari River, with higher proportion of Ti2O, Zr, Y, Nb, Ga, Hf, U, Ta and REE, are quite distinct. In spite of the intense weathering and erosion, in humid tropical conditions, that the rocks drained by the Madeira river basin have been submitted, the Th/Co, Th/Pb, Th/Yb, Al/Pb, Zr/Co ratios and Pb isotope data indicate that different sources contributed to the bottom sediments. It is suggested that mafic rocks are the main source of the sediments of the Madeira River, while felsic rocks are the source of the tributaries.
Acesso aberto (Open Access)
Petrogênese da Suíte Igarapé Gelado: implicações para o magmatismo neoarqueano da Província Carajás, Cráton Amazônico
(Universidade Federal do Pará, 2025-04-30) MESQUITA, Caio José Soares; DALL’ AGNOL, Roberto; http://lattes.cnpq.br/2158196443144675
The Igarapé Gelado suite (IGS) is located near the northern border of the Carajás Province, almost at its boundary with the Bacajá Domain, along the Cinzento lineament, and is intrusive in metavolcanic mafic rocks and banded iron formations. The central-eastern portion of the IGS comprises four rock varieties: tonalite to granodiorite with varying contents of biotite and amphibole, (1) with associated clinopyroxene and/or orthopyroxene (PBHTnGd) or (2) devoid of pyroxenes (BHTnGd); and monzogranites that exhibit variable biotite and amphibole content and can be (3) moderately (BHMzG) or (4) strongly (RBHMzG) reduced. The PBHTnGd shows ferrosilite and/or augite with subordinate hedenbergite. The amphiboles are K-hastingsite and, subordinately, Fe-Tschermakite in monzogranites. Biotites are ferroan, and in reduced granites show #Fe > 0.90. These micas are similar to those of alkaline to subalkaline rocks and compositionally akin of primary magmatic biotites. Plagioclase is oligoclase. The integration of thermineral chemistry;mobarometry results and thermodynamic modeling and their comparison with the paragenesis present in natural rocks improved the estimation of crystallization parameters (T, P, ƒO2, H2O), and allowed a better interpretation of magmatic evolution. The IGS granites crystallized at pressures of 550 ± 100 MPa, higher than those attributed to other Neoarchean granites in Carajás provinve. The estimated liquidus temperature for the IGS pyroxene variety is ~1000±50°C. BHTnGd and BHMzG formed within a similar temperature range to PBHTnGd, while RBHMzG had lower liquidus temperatures (≤900°C). Solidus temperatures of around ~660 °C were estimated for the four IGS varieties. The BHMzG magma evolved under conditions of low ƒO2, slightly above or below the FMQ buffer (FMQ±0.5), like those of the Planalto suite and the reduced granites of the Vila Jussara and Vila União suites of Carajás province. In the magmas of the PBHTnGd and BHTnGd varieties the oxygen fugacity attained FMQ+0.5. The RBHMzG crystallized under strongly reduced conditions equivalent to FMQ-0.5 to FMQ-1. The magmas of the monzogranitic varieties evolved with a H2O content of ≥4 wt%, attaining 7 wt% in the case of the reduced monzogranites. This is comparable to, or slightly exceeding, the levels typically attributed to the Neoarchean granites of Carajás province (≥ 4% wt%). In contrast, the variety with pyroxene has a water content (~4 wt%) like that of Café enderbite and Rio Seco charnockite from Carajás province, and Matok Pluton from Limpopo belt. Based on the chemical composition, the rocks from IGS are ferroan, reduced to oxidized A-type-like granites, akin to other Neoarchean granite suites from the Carajás province. The IGS are younger than the 2.76-2.73 Ga Neoarchean granites from the Carajás province. A crystallization concordia age of ~2.68 Ga was obtained by U-Pb SHRIMP in zircon for the RBHMzG variety, and similar upper intercept ages were furnished by the other IGS varieties, except for ages of ~2.5 Ga that resemble the ages of the IOCG Salobo deposits associated with reactivation of the Cinzento Lineament. Tmineral chemistry;he deformation of the IGS rocks was influenced by shear zones linked to that lineament, forming elongated bodies with varied foliation. These zones facilitated the migration and deformation of magmas from the final crystallization stages until their complete cooling, characterizing a syntectonic process. This syntectonicity is associated with the inversion of the Carajás Basin, and the younger crystallization age of these rocks indicates that the inversion occurred up to 2.68 Ga, extending the previously estimated interval (2.76– 2.73 Ga). The IGS displays negative to slightly positive values of εNd(t)(-2.86 to 0.18) and εHf(t)(-3.3 to 0.1), and Paleoarchean to Mesoarchean TDM ages [Nd-TDM(2.98-2.84) and Hf-TDM C (3.27-3.12)]. The positive values of εNd(t) and εHf(t) for the RBHMzG variety, suggest possible juvenile contribution or contamination in the source of its magma. The IGS rocks come from the melting of 19% (PBHTnGd) or 14% (BHTnGd) of contaminated mafic granulite, - and from melting of 9% (BHMzG) and 7% (RBHMzG) of a tholeiitic mafic granulite. The area of occurrence of the IGS is marked by hydrothermalism and mineralizations that locally modified the composition of rocks and minerals, allowing the leaching of REE and Y that changed the composition of some samples of BHMzG approaching them of (false) A1- subtype granites. In addition, these processes were responsible for zircon alteration, which resulted in grains showing enrichment of U, Th, and LREE, and massive textures, that furnished upper intercept U-Pb ages, contrarily to the zircon crystals of the RBHMzG variety that preserved primary characteristics and presented Concordia ages.