Navegando por Orientadores "FERNANDES, Carlos Marcello Dias"

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Alterações hidrotermais associadas às rochas máfico-carbonatíticas do depósito de fosfato Serra da Capivara, região de Vila Mandi (PA), extremo sul do Cráton Amazônico.
(Universidade Federal do Pará, 2019-07-14) VIEIRA, Danilo Amaral Strauss; FERNANDES, Carlos Marcello Dias; http://lattes.cnpq.br/9442875601862372
Near the border of the states of Pará and Mato Grosso, in the Amazonian Craton, about 90 km west of the Vila Mandi district, Santana do Araguaia (PA) city, there is an unprecedented volcano–plutonism named Santana mafic-carbonatitic Complex. It is formed by a lower maficultramafic member with plutono–volcanic and other volcaniclastic lithofacies; besides an upper carbonatitic member with plutonic, effusive, and volcaniclastic lithofacies originated in a volcanic caldera environment with large areas of hydrothermal alterations and genetically related circular structures. The severe Amazon weathering partially affected this cluster, producing the Serra da Capivara Phosphate deposit supergenically. Although speculative, the Santana mafic-carbonatitic Complex is Paleoproterozoic in age, because it invades the Paleoproterozoic volcano-plutonic sequences Cinco Estrelas and Vila Mandi formations (1980–1880 Ma) and it is capped by sedimentary rocks from the same Era. The lower maficultramafic member has lithofacies with slabs of pyroxenite, and minor isolated metric blocks of ijolite and apatitite. They are medium-grained ceylonite-bearing (MgAl2O4) pyroxenites with augite (~ 90% vol.), magnesio-riebeckite, and olivine crystals replaced by clay minerals (saponite). The ijolite is composed of clinopyroxene and nepheline phenocrysts immersed in a fine-grained groundmass with nepheline, calcite, and interstitial magnetite. Apatitite blocks are composed of medium-grained apatite grains (~ 98% vol.) and calcite. The volcanic rocks of this lithofacies comprise isolated metric blocks of alkali basalt and rare associated outcrops of finegrained apatitite. This basalt rock presents plagioclase-rich groundmass and acicular augite phenocrysts as essential mineralogy. Aphyric samples have primary spherules filled with calcite and quartz, besides interstitial pyrite, iron oxides, apatite, barite, rutile, celestine, and monazite. This textural feature suggests silicate and carbonatitic melts immiscibility process. An explosive to autoclastic mafic volcaniclastic lithofacies encompasses poor sorting deposits of massive polymictic breccia, lapilli-tuff, crystal-rich tuff, and ash tuff. The autoclastic rocks reveal volcaniclastic texture comprising centimetric angular clasts sourced from autofragmentation of the mafic-plutonic plutono–volcanic lithofacies. Epiclastic sedimentary volcanogenic deposits usually cover all previous lithofacies. The upper carbonatitic member reveals coarse-grained carbonatite (sövite) lithofacies comprising reddish-yellow sövite (calcite carbonatite) composed of subhedral to euhedral calcite (85–90% vol.), with variations to magnesium-ferriferous calcite and dolomite. Primary accessories are magnetite, hematite, potassic feldspar, and pyrite. These lithotypes show hydrothermalized medium- to fine-grained carbonatite veins. Rare coarse-grained apatitite bodies occur associated with this lithofacies, which represents part of the proto-ore. An effusive carbonatite (alvikite) lithofacies reveals finegrained calcite-rich (80–85% vol.) to porphyritic alvikite, besides hematite, magnetite, potassic feldspar, and pyrite. Fragment-rich explosive carbonatitic volcaniclastic lithofacies encompassing poor sorting and texturally variable massive crystal-rich tuff, lapilli-tuff, and massive polymictic breccia formed by angular clasts sourced from host rocks and the complex. Syenitic stocks and dikes invade these rocks. The main hydrothermal magmatic alteration of the complex is represented by hydrothermalized carbonatitic rocks of reddish, brownish, and yellowish colors. The mineral paragenesis found was barite + fluorapatite + dolomite ± quartz ± rutile ± chalcopyrite ± pyrite ± monazite ± magnetite ± hematite. This alteration occurs in three distinctive ways; 1) in the deeper zones, where the minerals found were barite, fluorine apatite, and dolomite in pervasive to fracture-controlled alteration associated with deep fine carbonatites. 2) In the sövite, of weak interstitial form with mineralogy similar to the deep alterations. 3) in the alvikite with intense interstitial changes and formation of hydrothermal quartz associated with barite, fluorapatite, dolomite, monazite, celestine, and rutile. The mineral assemblage of the deeper alterations suggests initially sulphate-rich, magnesium, phosphorus, and CO2 fluids with possible transitional source between the late magmatic and the hydrothermal stages. In transition to more superficial phases of the volcanism, there was an assimilation of SiO2 from the country rocks evidenced by the formation of fine interstitial quartz crystals in alvikite. The interpreted environment of volcanic caldera occurs in the interception of regional NE-SW and NW-SE faults with up to 40 km of extension and that served as deep conduit of the precursor magma of the complex. The root of the system is represented by maficultramafic rocks and plutonic carbonatites. The pre-caldera phase involved intense degasification and hydrothermal activities as a function of magmatic evolution, and ascending by lithic faults and placing on the surface of large volume of carbonate lava (alvikites) that built the extinct volcanic building. The collapse of this structure and the topographic landslide coincided with explosive volcanism and formation of the volcanoclastic lithotypes, representing the intra-caldera filling. The late syenites may represent the post-caldera phase and sealing of these structures. The hydrothermal paragenesis identified in the Santana maficcarbonatitic Complex shows important metallogenetic potential for rare earth elements and phosphate and represents a prospective guide on Proterozoic terrains of the Amazonian Craton, like other areas of the planet.
Acesso aberto (Open Access)
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.
Acesso aberto (Open Access)
Metalogênese do depósito aurífero Volta Grande, Domínio Bacajá (PA), Cráton Amazônico: aplicação de espectroscopia de infravermelho VNIR-SWIR.
(Universidade Federal do Pará, 2024-02-27) PARESQUI, Brenda Gomes Silva; FERNANDES, Carlos Marcello Dias; http://lattes.cnpq.br/0614680098407362; https://orcid.org/0000-0001-5799-2694
The world-class Volta Grande gold deposit contains measured reserves of ~6.0 Moz at 1.02 g/t, divided into north and south exploration blocks. It is inserted in the geological context of the Bacajá Domain and was affected by the Trans-Amazonian Cycle (2.26–1.95 Ga). Part of the mineralization is hosted in a group of gneisses and mylonitized granitoids in amphibolite facies of medium to high metamorphic grade of the Três Palmeiras Group (2.36 Ga). Recent research in the northern block has revealed the presence of late volcanics and plutonics, with isotropic texture and intermediate to felsic compositions, which host disseminated gold in different types and styles of hydrothermal alteration, as well as in quartz and carbonate (±sulfides) venules and veins. Thus, this Master's Thesis represents the continuity of research in the northern block of this repository with the application of the VNIR–SWIR (visible-near and short-wave infrared) infrared spectroscopy technique. This tool helps to explain in detail the configuration of the hydrothermal system, contributing to a better understanding of the genesis of the deposit. The mineralogy observed by spectroscopy in metamorphic rocks confirms the occurrence of potassic, propylitic, intermediate argillic, pervasive carbonate, and advanced argillic hydrothermal alterations types. The latter occurs associated with high levels of gold and alunite, a mineral indicative of epithermal systems with high-sulfidation. In turn, the isotropic volcanic and plutonic rocks present more developed, intense, and larger-volume hydrothermal alterations. They reveal greater diversification of hydrothermal minerals, where jarosite is the superior indicator of advanced clay alteration, which is also consistent with high-sulfidation epithermal mineralizations. In addition, the appearance of rhodochrosite, pyroxmangite, and galena, mainly related to volcanic rocks of andesitic and dacitic compositions, suggests an epithermal system of intermediate-sulfidation. The geological features present in the region and the hydrothermal alterations, especially the propylitic alteration in the rocks with allanite, clay minerals, montmorillonite, and zeolites, portray a typical epidote subzone of a low-temperature propylitic alteration that are genetically related to the medium-depth intrusions where they appear hydrated porphyry stocks. In this way, the Volta Grande gold deposit reveals characteristics compatible with rare and base metals porphyry and epithermal mineralizing systems, already identified in other regions of the Amazon Craton. The high-sulfidation conditions at the northwest portion of this repository and intermediate-sulfidation at the southeast region point to a transitional environment. The VNIR–SWIR spectroscopy method represents an important tool that identifies and characterizes hydrothermal minerals quickly and efficiently, as well as differentiating them from weathered ones. In general, it becomes a significant prospective guide when robustly analyzing minerals that are difficult to recognize by other methods such as conventional optical microscope or scanning electron microscope (SEM). The results presented here represent a remarkable contribution to the geological and metallogenetic knowledge of the Bacajá Domain, as well as the Amazonian Craton as a whole, pointing out the potential for identifying economically viable deposits of precious and base metals associated with volcanic and plutonic systems that occur in a vast area of this domain.
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)
Vetorização geoquímica, caracterização e modelamento 3D de alterações hidrotermais em sistemas cupro-auríferos: exemplo do Complexo Sossego (PA), Província Mineral de Carajás
(Universidade Federal do Pará, 2023-04-18) SANTOS, Antônio Fabrício Franco dos; FERNANDES, Carlos Marcello Dias; http://lattes.cnpq.br/0614680098407362; https://orcid.org/0000-0001-5799-2694
The copper-gold Sossego Complex, Pista, Sequeirinho/Baiano, and Curral/Sossego sectors, is in the southern portion of the Carajás Mineral Province, along with a WNW-ESSE regional shear zone. The main host lithologies that take place at the Complex are granitoids, felsic metavolcanic rocks, and mafic to ultramafic intrusive rocks. This work involved the application of multivariate statistical techniques to define geochemical units and vectors to help with geological interpretation, exploratory guides, and geometallurgy of the Complex concerning the mineralization. Overall, the use of those techniques revealed a good correlation between elemental data and the geochemical units proposed, which allowed coherently defining of the units, major elements, and probable hydrothermal mineralogical paragenesis for the deposits. Individual analyses and elemental correlation of chosen elements in probability diagrams, histograms, binary, ternary, and boxplots were carried out and aimed at identifying the geochemical features and their relation to the mineralogical association. At the Pista sector, at least five geochemical units occur (sodic, sodic-silica, potassic-chloritic, magnesian, and potassic feldspathic), where are highlighted the units with a higher concentration of sodium and silica for zones closer to the orebody. Geochemical vectors that predominate over this sector and that can be considered as trackers or contaminants about the ore zones are As, Al, Ag, Hf, Sr, Te, Zr, Mo, Na, Pb, S, La, W, and U, directly associated with sodic-silica and sodic geochemical units. Ternary diagrams have shown an indicator of paragenesis, which comprises a vector from an initial phase of sodic evolving to potassic. At Sequeirinho/Baiano sector, occur nine geochemical units (sodic, sodic-silica, sodic-ferric, sodic-calcic, calcic-ferric, ferric, magnesian, potassic-chloritic, and potassic feldspathic) in which the paragenesis is observed from the distal to the proximal zones concerning the orebody. Over distal zones, higher sodium concentration is observed, evolving to medium concentration of sodium and calcium, achieving high iron, calcium, and magnesium content nearby the mineralization, showing that the geochemical units related to the copper mineralization of high-grade are calcic-ferric and ferric. Elements such as Ag, As, Bi, Cd, Co, Fe, Ga, Ge, In, Ni, P, Pb, S, Se, Te, and V (secondary Ca, Mg, Mn, Re, Sb, Sn, Th, and U) were the main vectors directly associated with mineralization and calcic-ferric to ferric units. Ternary diagrams of this sector suggest two probable paragenesis vectors, both from initial stages of the sodic unit, although, one of them showed an evolution towards sodic-ferric and the other to a sodic-calcic stage and evolving to calcic-ferric unit afterward. In the Sossego/Curral sector occur seven geochemical units (sodic, sodic-silica, sodic-potassic, potassic, chloritic, ferric, and calcic). This sector has revealed a complex correlation between hydrothermal zoning and geochemical units because of its geological features (breccias, veins, veinlets, and late dissemination). The graphics show that geochemical units that display an affinity with mineralized zones are chloritic, calcic, and ferric (breccia and vein zones). Over the chloritic unit, the highlighted elemental vectors are Ag, Be, Bi, Ca, Ce, Cu, La, Mn, Mo, Ni, P, and S (secondary K, Al, Mg, and Fe). Ferric geochemical unit happens mainly associated with chloritic and calcic zones, although it is not similar due to high iron concentration (>15% Fe), and the main geochemical vectors are As, Cd, Ce, Co, Fe, Ga, Ge, In, La, Re, S, Sb, Se, Sn, Te, U, and Y (secondary Ag, Be, Ca, Cs, Li, Mg, Mn, Mo, and V). The calcic unit corresponds to calcite, actinolite, and epidote-rich intervals in breccias and veinlets that cut chloritic rocks. Its main geochemical vectors are Al, Ca, Cr, Mn, Sc, Sr, V, and Zn (secondary Ag, As, Cd, Co, Fe, Ga, In, S, Se, and Sr). The probable paragenesis vector points to an initial sodic stage, evolving to a potassic stage followed by chloritic. Spatial materialization of the units and geochemical vector was made by 3D modeling obtained by statistical results that were developed, displaying a better visual geological understanding of hydrothermal flow, probable chemical/mineralogical paragenesis, and correlation with mineralization. This work will contribute in the future to the understanding of lithology, structural, and geochemistry of the Sossego Complex, besides provisioning geometallurgical data. This work can benefit open pit operations with direct or indirect reduction of cost, safety increment, and better operational performance of the ore processing.