Navegando por Assunto "Mineral chemistry"

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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)
Mineral chemistry and crystallization parameters of the A-type Paleoproterozoic Bannach Granite, Carajás Province, Pará, Brazil
(Sociedade Brasileira de Geologia, 2018-09) MESQUITA, Caio José Soares; ALMEIDA, José de Arimatéia Costa de; DALL'AGNOL, Roberto
The A-type Paleoproterozoic Bannach Granite belongs to the Jamon Suíte and cross-cut the Archean units of the Rio Maria Domain in the Carajás Province. It comprises eight facies with varied mafic content and texture: even-grained cumulate granite (CG), even coarse-grained biotite-amphibole monzogranite (cBAMz), even coarse-grained amphibole-biotite monzogranite (cABMz), porphyritic biotite monzogranite (pBMz), even coarse-grained leucomonzogranite (cLMz), early even medium-grained leucomonzogranite (EmLMz), late even medium-grained leucomonzogranite (LmLMz) and even fine-grained leucomonzogranite (fLMz). In the less evolved facies, the dominant amphibole is Fe-hornblende passing to Fe-edenite or hastingsite, with associated cummingtonite/grunerite originated from the destabilization of clinopyroxene. Biotite has ferroan composition and approaches annite in the late-emplaced leucomonzogranite. Plagioclase varies from andesine to oligoclase or from oligoclase to albite. Titanite, magnetite, and ilmenite are found in all granite facies showing magmatic origin. The near liquidus temperatures vary between 943ºC and 795ºC and the estimated emplacement pressure is 300 ± 50 MPa (~11.1 ± 1.9 km). Amphibole Fe/(Fe + Mg) ratios together with magmatic magnetite and titanite indicate that these granites crystallized at moderately oxidizing conditions, similar to those admitted for the Jamon granite and magnetite series granites of Laurentia. However, the composition of biotite suggests a more reduced character close to NNO to NNO -0.5. The late leucomonzogranite facies is an exception because it displays high Fe/(Fe + Mg) ratios in biotite and approaches to the reduced granites of Carajás, Laurentia and Fennoscandia in this regard. It derived from a more reduced source than the other facies of Bannach Granite
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)
Petrologia experimental e química mineral das suítes Neoarqueanas Vila Jussara e Planalto, Província Carajás, Amazônia, Brasil
(Universidade Federal do Pará, 2023-03-20) CUNHA, Ingrid Roberta Viana da; SCAILLET, Bruno; DALL'AGNOL, Roberto; http://lattes.cnpq.br/2158196443144675
In the Carajás Province (CP), during the late stages of the neoarchean (2.75-2.73), in the Sapucaia and Canãa dos Carajás domains granitoids represented by the Vila Jussara and Planalto suites were formed respectively. These suites are metaluminous and have a geochemical affinity with A-type granites and FeO/(FeO+MgO) whole rock ratios that vary from ferroan to magnesian. Chemical-mineralogical studies performed in these neoarchean granites, based on optical microscopy, scanning electronic microscopy, electron microprobe and experimental petrology revealed notable variation between the main mineral phases. Magmatic epidote is a common mineral phase in the reduced, oxidized and magnesian varieties of the Vila Jussara suite, with pistacite contents between 25 and 30% mol. In the Planalto Suite and others neoarchean granites of the CP magmatic epidote is absent. The study of the dissolution kinetics of Archean epidotes of the CP reveals that its formation and stability are directly linked to pressure, temperature and oxygen fugacity conditions, however, its stability is also conditioned by mechanisms of magma rise, emplacement and crystallization, which affected the dissolution intensity of the epidote crystals. Chemical-mineralogical performed on titanites of the Vila Jussara and Planalto Suites and the paleoproterozoic Jamon Suite revealed notable textural and compositional variations. The titanite’s Fe/Al ratios are quite variable in the studied granites, three major titanite groups were distinguished: 1) high Fe/Al ratio (Fe/Al>0.5); 2) moderate Fe/Al ratio (0.5≤Fe/Al≥0.25); and 3) low Fe/Al ratio (Fe/Al<0.25). Furthermore, in general, the obtained data support the major titanite tendency to stabilize under oxidizing conditions, near the nickel-nickel oxide buffer (NNO), however, the occurrence of magmatic titanite in the reduced varieties from the Planalto and Vila Jussara Suites ratifies that its crystallization is possible under conditions near the fayalite-magnetite-quartz buffer (FMQ). Moreover, experimental petrology studies performed on the same neoarchean suites, reveal that the sample MDP-02E, with tonalitic composition, which represents the magnesian oxidized magma from the Vila Jussara suite, exhibits SiO2 content around 60% in the whole rock composition and 61.05% in the experimental glass, while the sample with sienogranitic composition (AMR-116), from the strongly reduced variety of the Planalto Suite, shows SiO2 content of 74.13% in whole rock and 73.17% in glass, pointing out that the initially calibrated experimental conditions approach the natural magmatic conditions. To characterize the crystallization parameters of the tonalitic and sienogranitic magma, nine experiments were performed on the two samples, with the following conditions: pressure ~4 kbar, ƒO2 ~NNO-1.3 (1.3 log unit bellow the NNO buffer) and temperature varying from 850°C to 668°C and water content from 9% to 6% in weight. Experiments with ƒO2 ~NNO+2.4 and temperatures of 800°C to 700°C with similar pressures and water content variations of the reduced experiments were also performed. Subordinately, experiments with pressures of 8 to 2 kbar with variable redox conditions were performed. These experiments show that the tonalite from the Vila Jussara Suite was crystallized at ~4 kbar from a water-rich magma (>5% in weight) in ƒO2 oxidizing conditions, probably between NNO and NNO+1. On the other hand, the experiments performed on the sample with sienogranitic composition from the Planalto Suite show a main paragenesis of Cpx+Fa which substantially diverge from the natural minerals, suggesting that the experiments did not reach the natural conditions.
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.