Navegando por Assunto "Amazonian Craton"

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Caracterização mineralógica com espectroscopia de reflectância por infravermelho (SWIR): exemplo do Complexo máficocarbonatítico Santana, sul do Cráton Amazônico
(Universidade Federal do Pará, 2021-09-21) COSTA, Jhoseph Ricardo Costa e; FERNANDES, Carlos Marcello Dias; http://lattes.cnpq.br/0614680098407362; https://orcid.org/0000-0001-5799-2694
On the border of the Pará and Mato Grosso states, in the Amazonian Craton, municipality of Santana do Araguaia (PA), there is a volcano-plutonism named Santana mafic-carbonatitic complex. This set houses the Serra da Capivara phosphate deposit. A lower mafic-ultramafic member reveals plutono-volcanic lithofacies with pyroxenite, ijolite, apatitite, and alkaline basalt. Autoclastic lithofacies contains poorly selected deposits of massive polymictic breccia, lapilli-tuff, crystal tuff, and ash tuff. Volcanogenic epiclastics rocks cover these lithofacies. The upper carbonatite member contains plutonic lithofacies with coarse calcite-carbonatite (sövite). Fine carbonatite veins with pervasive carbonatic and apatitic alterations crosscut this lithotype. Minor thick apatitite occcurs associated to this member and represents the protore of the deposit. Effusive volcanic lithofacies reveals fine calcite-carbonatite (alvikite) with porphyritic, equigranular, or aphanitic textures. A poorly sorted lithofacies of crystals tuff, lapilli-tuff, and massive polymictic breccia completes this member. Stocks and syenitic dykes invade these lithofacies. Detailed mapping suggests that the complex is a volcanic caldera in which large zones of hydrothermal alterations occur with reddish, brownish red, and yellowish carbonatitic rocks. Petrographic observations reveal paragenesis of barite + fluorapatite + calcite + dolomite ± quartz ± rutile ± chalcopyrite ± pyrite ± monazite ± magnetite ± hematite. The application of short wave infrared spectroscopy (SWIR) revealed the chemical characteristics and their importance in the crystallinity of most of these hydrothermal minerals, such as radicals (OH- and CO3), H2O molecule, and cation-OH bonds such as Al-OH, Mg-OH, and Fe-OH. The main mineral phases identified were dolomite, calcite, serpentine, chlorite, muscovite with low, medium, and high aluminum, montmorillonite (Ca and Na), illite, nontronite (Na0.3Fe2((Si,Al)4O10) (OH)2·nH2O), and epidote. The data suggest a control by temperature, fluids composition, and fluid/rock ratio during the evolution of the Santana mafic-carbonatitic complex. This low-cost exploratory technique, which is applied in hand-held samples or drill holes on a large scale, is promising in characterization of volcano-plutonic centers in regions subjected to severe weathering conditions, as well as helping to develop models for prospecting mineral deposits of Rare Earth Elements (e.g. Nd, La) associated with alkaline-carbonatitic complexes. We can even combine this tool with artificial intelligence algorithms for more robust and faster results.
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Geology and petrology of the Salto do Céu Suite: tectonic and stratigraphic implications on the SW Amazonian Craton
(Sociedade Brasileira de Geologia, 2018-09) MACAMBIRA, Moacir José Buenano; SOUSA, Maria Zélia Aguiar de; RUIZ, Amarildo Salina; BATATA, Maria Elisa Fróes; PIEROSAN, Ronaldo
The basic rocks of the Salto do Céu Suite outcrop as sills and flows in the southwestern Amazon Craton, Rondonian-San Ignacio Province, with an age of about 1.44 Ga. Sills are 2 to 30 m thick being hosted by pelites of the Aguapei Group. The flows are up to 5 m thick and cover this unit. Typical textures of magma mingling are observed near the contact with granites of Rio Branco Suite. The Rio Branco Intrusive Suite is composed of basic and acid rocks, as well as hybrid rocks that indicate mixing processes between basic and acids magmas. U-Pb (TIMS zircon) results indicate ages around 1.4 Ga for both terms. The Salto do Céu Suite rocks have tholeiites affinity classified as subalkaline and iron-rich tholeiitic basalts, with mg# values between 0.30 and 0.51. They can be separated into two groups, based on La N ; one is richer in ETR with La N greater than 100, while the other one has La N less than 100. Rocks of the Salto do Céu Suite and Rio Branco Suite are interpreted as a bimodal suites showing magma mingling features such as those developed in continental intraplate settings, extensional regime associated to the Columbia/Nuna breakup.
Acesso aberto (Open Access)
Mapeamento geoquímico da bacia do rio Itacaiúnas, Província Mineral de Carajás: Assinatura geoquímica dos blocos crustais e implicações para recursos minerais e meio ambiente
(Universidade Federal do Pará, 2020-10-26) SALOMÃO, Gabriel Negreiros; DALL'AGNOL, Roberto; http://lattes.cnpq.br/2158196443144675; ANGÉLICA, Rômulo Simões; http://lattes.cnpq.br/7501959623721607; https://orcid.org/0000-0002-3026-5523
Multielement geochemical surveys (MGS) when combined with advanced data processing techniques and robust statistical analysis, are important tools for understanding the environment. In the last decades, its application in mineral exploration is well established and, in the last decades, it has shown remarkable relevance for environmental studies linked to sustainable territorial management, particularly in the establishment of geochemical background concentration values. The definition of background values has been widely used to demonstrate the inconsistencies of laws and regulations, which establish concentration limits for potentially toxic elements in the environment, often without taking into account the complex spatio-temporal heterogeneity of each region. In Brazil, many MGS were, and continue to be carried out mostly by the Companhia de Pesquisa de Recursos Minerais (CPRM, Geological Survey of Brazil) in different parts of the national territory, although they are still scarce in the Amazon region. The present study is associated with a large geochemical mapping project called the Geochemical Background of the Itacaiúnas River Basin (GBI) carried out by the Instituto Tecnológico Vale (ITV). The Itacaiúnas River Watershed (IRW) is located in the largest mineral province of Brazil, the Carajás Mineral Province, and it is particularly relevant for geochemical studies, because the distribution of chemical elements in this region and the influence of the great geological domains on that distribution are not known. The purpose of this research is to investigate the influence of large geological domains in the chemical composition and geochemical signature of stream sediments of the IRW. In addition, it is intended to generate geochemical maps, identify the associations and geochemical processes in stream sediments, define geochemical compartments for the whole watershed, and determine background concentrations for the analyzed elements, taking into account the geochemical compartments and/or geological domains of the study area. In order to achieve these objectives, the stream sediment geochemical data from the GBI-ITV project obtained in the whole IRW in 2017, and those from two CPRM projects in the center-south portion of the BHRI with sampling in the years 2011-2012 were used. These projects were conceptualized at different scales and sample density; however, the sampling techniques and analytical procedures are similar. Stream sediment sample collections were carried out in active water stream, at surface levels from 0 to 10 cm deep, and preferably in the middle of the channel. Sample preparation included the following steps: drying, disaggregation, quartering and sieving. Approximately 50 g of the fraction <0.177 mm was sent to accredited laboratory for chemical analysis. In the laboratory, the samples were submitted to digestion with aqua regia, and then 51 elements were analyzed (Ag, Al, As, Au, B, Ba, Be, Bi, Ca, Cd, Ce, Co, Cr, Cs, Cu, Fe, Ga, Ge, Hf, Hg, In, K, La, Li, Mg, Mn, Mo, Na, Nb, Ni, P, Pb, Rb, Re, S, Sb, Sc, Se, Sn, Sr, Ta, Te, Th, Ti, Tl, U, V, W, Y, Zn and Zr) via Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) and Inductively Coupled Plasma Mass Spectrometry (ICP-MS). The geochemical data was submitted to descriptive statistical analysis and some non-parametric statistical tests. Several graphs (e.g., boxplots, histograms, probability and dispersion) were generated for the main chemical elements. Multivariate statistics (e.g., correlation matrices, cluster analysis and factor analysis) were used to investigate the main existing multi-element associations. To determine geochemical background values, modern methods widely used in the specialized literature were employed. Geospatial information was processed and managed in an environment of geographic information systems, in which different cartographic and geoprocessing techniques were used to generate geochemical distribution maps. In general, it was found that, on the scale of geochemical surveys conducted by ITV and CPRM, there is no conclusive evidence of contamination related to human activity, but very strong evidence of a marked geological contribution in the geochemistry of the stream sediments of the IRW. A consistent and replicable methodology was used to identify the main multi-element associations and to define IRW’s surface geochemical compartments. The geochemical associations identified are controlled by the geological domains, by specific lithologies in restricted areas and/or by biogeochemical factors acting in the study area. The delimitation of geochemical compartments revealed a strong similarity with the simplified geological domains of the basin. Geochemical background concentrations were determined for the IRW and its geological domains. Among the methods suggested for determining the background, the Median ± 2*Median Absolute Deviation showed the most consistent and realistic results. In addition, it is considered essential to define reference values based on geochemical compartments, or even a simple geological setting. The assumption of a single uniform reference value for a wide area is inappropriate. The background values proposed in this research may assist environmental impact studies by monitoring anomalous concentrations of potentially toxic elements, which exceed background concentrations. In addition to its scientific interest, the results presented here can be useful to assist local surveys of geochemical prospecting and in the formulation of environmental policies in the Brazilian territory.
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.
Acesso aberto (Open Access)
Petrografia, alterações hidrotermais e eventos mineralizantes do Bloco Norte do depósito aurífero Volta Grande, Domínio Bacajá (PA), Cráton Amazônico
(Universidade Federal do Pará, 2021-09-22) SOUZA, Hugo Paiva Tavares de; VASQUEZ, Marcelo Lacerda; http://lattes.cnpq.br/4703483544858128; https://orcid.org/0000-0003-2729-9404; FERNANDES, Carlos Marcello Dias; http://lattes.cnpq.br/0614680098407362; https://orcid.org/0000-0001-5799-2694
The southeastern region of the Amazonian Craton has been the target of several mineral survey programs over the past few years, which have recently led to the identification of the world-class Volta Grande gold deposit, with reserves of ~3.8 Moz at 1.02 g/t, which provides an expectation of 17 years of operation. The deposit is in the municipality of Senador José Porfírio in Pará and is housed in Rhyacian granitoids (2.15 Ga) that occur associated with the volcano-sedimentary Siderian sequence (2.45 Ga) of the Três Palmeiras Group. These units are in the Bacajá Domain, which is formed by belts of high-grade para- and orthoderived rocks and greenstone belt of Archean to Siderian protoliths, reworked during the orogenesis of the Transamazonian Cycle (2.26–2.06 Ga). Granitoids and charnockites sectioned this set in Rhyacian. Part of the mineralization at the Volta Grande is housed in granitoids metamorphosed under medium to high-grade conditions. Local kinematic indicators suggest dip-slip movement in which the greenstone moves up relative to the intrusive rocks. Petrographic descriptions carried out in this work revealed: 1) gray to greenish mylonitic granodiorite, with intense deformation of the main minerals that make up them, such as quartz, biotite, and feldspars. The texture in this lithotype is mainly porphyroclastic. Main metamorphic foliation (S1) is defined by biotite and amphibole, as well as reveals concordant quartz veins and venules. The highest gold contents are distributed in upper amphibolite facies zones. In these, the ore occurs mainly as isolated grains in cm-sized quartz veins and venules associated with pervasive carbonatic alteration that was synchronous to dynamic metamorphism, as well as in a fracture-controlled style. Part of the gold is also associated with a low sulfides content disseminated in the veins and host rock; 2) The metamafic rocks comprise foliated fine- to medium-grained amphibolite and andesite with a dark grayish-green color and nematoblastic texture. Chlorite, calcite, sericite, and opaque minerals are the main secondary phases. These relationships are compatible with lode-type gold systems, usually developed in the transition between greenschist to amphibolite metamorphic facies. Lava flows and dykes of isotropic rhyodacite, rhyolite, and plutonic rocks such as quartz monzonite, granodiorite, monzodiorite, and minor microgranite cut the mineralizing event previously described. Plutonic rocks are medium- to coarse-grained, have a gray color with reddish and greenish portions throughout the profiles, inequigranular texture with quartz, feldspar, biotite, and amphibole. Apatite, zircon, calcite, epidote, and opaque minerals are primary accessories. In turn, volcanics have light gray, black or dark red colors, porphyritic to aphyric texture, and microlithic or felsophyric groundmass. They reveal phenocrysts of plagioclase, amphibole, potassic feldspar, and quartz. This volcano-plutonic system contains potassic, propylitic, intermediate argillic, and/or carbonate hydrothermal alterations in selective, pervasive, or fracture-controlled styles. In hydrothermalized zones, gold occurs as isolated grains disseminated or associated with sulfides, as well as in cm-sized quartz veins in a stockwork arrangement. These characteristics are like those of shallow intermediate- to lowsulfidation epithermal systems already identified in the Amazonian Craton. The Volta Grande data suggest a second overprinted mineralizing event, common in high-tonnage productive gold deposits in China, Finland, and other areas of the planet and represents a new exploration guide for the Bacajá Domain. Several mineralizing events are critical to the economic feasibility and longevity of world-class gold deposits. Thus, new geochemical, geochronological, microthermometric, and stable isotope data will be obtained to better define the genetic modeling of the Volta Grande gold deposit.
Acesso aberto (Open Access)
A relação entre o domínio bacajá e o domínio carajás, sudeste do cratón amazônico, com base em geologia isotópica e química mineral
(Universidade Federal do Pará, 2020-01-30) ALVES, João Paulo Silva; MACAMBIRA, Moacir José Buenano; http://lattes.cnpq.br/8489178778254136
The Amazonian Craton represents a large continental plate, composed of several crustal provinces of Archean to Mesoproterozoic ages, with boundaries between provinces based on geological and, mainly, geochronological data. Although these boundaries are well established, doubts about how this might have happened are raised, such as the contact between the Carajás Domain (Central Amazonian Province) and the Bacajá Domain (Maroni- Itacaiúnas Province), southeastern of the craton. The study region is located in this boundary and is characterized by the occurrence of several lithotypes, among them amphibolites, granulites, granites, gneisses and charnockites. Mineral chemistry analyses on amphiboles of the amphibolites showed magnesium-hornblende and ferropargasite composition, with medium to high amphibolite facies metamorphism and temperature between 676 to 730º C, with pressure 3,7 to 8,8 kbar. Amphiboles from charnockites were classified as magnesiumhornblende and magnesium-hastingsite, biotite as annita, plagioclase with andesine composition and pyroxenes as augite and ferrosilite. The magmatic temperature for the charnockites ranges from 853 to 910 ºC, with pressure from 3,3 to 6,6 kbar. The generation environment is proposed as a magmatic arc, since it presented a metaluminous and magnesian composition. Biotite from granulites was classified as phlogopite, plagioclase has an andesine composition and pyroxenes classified as augite and ferrosilite. The temperature of 650º C indicates a low granulite facies, recording the minimum temperature imposed on the rock. The Igarapé Gelado granite-related metagranite was 2854 ± 11 Ma old, weakening the idea of a relationship between them. Two crystallization ages were found for orthognaisses protoliths, one of 2848 ±8 Ma and other of 2882 ± 25 Ma; and two ages that indicates a metamorphic event, 2763 ± 16 Ma and 2748 ± 47 Ma. For the model-ages a range between 3,12 and 3,48 Ga was determined, with εHf (t) -3,68 to 2,12. The other model-age ranges from 3,00 to 3,16 Ga, εHf (t) from 1,99 to 4,45. Three distinct events were described for the study area: (1) a magmatic event during the Mesoarchean, around 2.8 Ga, with possible contribution of magmatic arc environment, generating metamonzogranite and monzogranitic orthognaisses protoliths; (2) subsequently a dynamic metamorphic event acting in the study area, recorded in Carajás Domain lithotypes; (3) the union between the Bacajá Domain and the Carajás Domain, at the end of the Transamazonic Cycle.