Navegando por Assunto "CO2"

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Acesso aberto (Open Access)
Análise dos fluxos turbulentos de CO2 e energia entre o ecossistema aquático e atmosfera na Flona de Caxiuanã-PA
(Universidade Federal do Pará, 2019-02-26) SOUZA FILHO, José Danilo da Costa; CATTANIO, José Henrique; http://lattes.cnpq.br/1518769773387350
This research investigated turbulent fluxes of CO2 and energy at the interface of the Caxiuanã bay – atmosphere in the Caxiuanã National Forest (FLONA) located in the Eastern Amazon under influence of atmospheric variables, the bay dimension and the temperature gradient at the interface bay-atmosphere, during the years of 2013 and 2014. The data used in this study were obtained on average 7 meters above the water slide from a micrometeorological tower, installed in the Caxiuanã bay. Measures of fluxes of CO2 (FCO2), sensible heat (H) and latent heat (Le) were collected through a turbulent vortices system. Meteorological data were collected by an automatic weather station. It was verified that the precipitation registered in the studied years was superior to climatic standards. The average hourly water temperature of the bay was always higher than the air temperature over the months. The mean monthly vertical temperature gradient at the bay - atmosphere interface was always positive, reaching the highest and lowest values in the rainy and dry period, respectively. The results show a strong seasonal pattern in the partition of the energy balance to heat the atmosphere (H) and for the evaporation process (Le). In the FCO2 analysis we can verify a clear seasonal pattern with the rainy and dry period of the region, that is, the magnitudes of FCO2, both emission and sequestration by the bay, are higher in the rainy months when compared to the dry months.
Acesso aberto (Open Access)
Caracterização da alteração hidrotermal no alvo Coelho Central, depósito aurífero Pedra Branca, sequência Serra das Pipocas, maciço de Troia, com base em estudos isotópicos (O, H, S e C) e inclusões fluidas.
(Universidade Federal do Pará, 2019-05-08) LIMA, Rafael Guimarães Corrêa; KLEIN, Evandro Luiz; http://lattes.cnpq.br/0464969547546706
The gold mineralization of Pedra Branca deposit is associated with rhyacian metavolcanic rocks of Serra das Pipocas Greenstone Belt, at the Archean–Paleoproterozoic Troia Massif, in Borborema Province, NE of Brazil. The deposit comprises four mineralized targets, Mirador, Queimadas, Igrejinha and Coelho Central and has been classified as a hypozonal orogenic gold deposit based on the geological context, types of hydrothermal alterations and isotopic data obtained for Mirador and Queimadas targets. At Coelho Central target, the main gold host rocks are ilmenite- and garnet amphibolites (after mafic volcanic rocks). Some gold occurrences has been recognized in altered metadacites and metatonalites intrusive lenses. Hydrothermal and mineralized zones show mineral assemblages formed under amphibolite facies conditions. (i) calc-silicate veinlets (diopside, titanite, calcite, epidote and sulfides), (ii) hornblende, albite, biotite and garnet veinlets with pyrrhotite and gold, (iii) biotite-rich potassic alteration containing pyrrhotite, gold and tellurides and (iv) quartz veins are the main types of ore-related alterations. In addition, (v) epidote, titanite and calcite pockets, (vi) chloritization and (vii) pyrite-rich fissural carbonatization are the late and no ore-related alterations that marks a ductile-brittle deformation, probably under greenschist facies conditions. Gold occurs predominantly as inclusions in pyrrhotite, chalcopyrite, pentlandite and Co-pentlandite indicating their association with sulfur species and subordinately as free-milling microparticles in quartz veins. The metallic association of sulfidation zones also includes abundant Ag, Bi, Ni and Pb tellurides. Oxygen and hydrogen geothermometry for hydrothermal silicates yielded temperatures from 484 to 586 ºC for the gold-related alterations. The fluid isotopic composition in equilibrium with hydrothermal silicates (quartz, hornblende, biotite, tourmaline and titanite) shows values of δ18O (+6.8 to + 10.7 ‰) and δD (-58.4 to -35.5 ‰), as well as the values of δ34S in sulfides (-3.1 and +2.7 ‰) and δ13C for calcite (-11.1 to -5.8 ‰), indicative of deepseated magmatic-hydrothermal fluid, with possible interaction and mixing with fluids of the greenstone sequence. Fluid inclusions assemblages in quartz veins show the predominance of CO2 inclusions, with a density up to 1.15 g/cm3 and up to 15 mol% of CH4, coexisting with N2 inclusions, and also with low salinity (< 9.7 wt% NaCl equiv.) H2O-CO2-NaCl and H2O-NaCl-FeCl2±MgCl2 varieties. The petrographic and microthermometric criteria suggest the immiscibility of a CO2-H2O-NaCl-N2-CH4 fluid as responsible for the generation of the observed inclusions. Desestabilization of complexes such as Au(HS)-2 and precipitation of gold and associated metals occurred by immiscibility, fluid-rock interaction, and changes in redox conditions and fluid pH, between 2.2 and 5,5 kbar (6.3 to 16.0 km). A H2O-NaCl-CaCl2 latter fluid was the responsible for the calcite, with pyrite and sphalerite precipitation in fractures and faults. The characteristics presented above allow us to ratify the Coelho Central target and Pedra Branca deposit as a hypozonal gold mineralization formed under amphibolite facies conditions, from CO2-rich deep-seated magmatic fluids that interacted with the metamorphic sequence of Serra das Pipocas Greenstone Belt and precipitated gold and associated metals.
Acesso aberto (Open Access)
Estudo das alterações petrofísicas e mineralógicas em amostras de calcita e dolomita decorrentes da interação com água carbonatada e CO2 supercrítico
(Universidade Federal do Pará, 2023-05-29) SOUZA, Felipe Pereira de; LUCAS, Cláudio Regis dos Santos; http://lattes.cnpq.br/1695226159975283; HTTPS://ORCID.ORG/0000-0001-5443-462X; AUM, Pedro Tupã Pandava; http://lattes.cnpq.br/7515419219571335; https://orcid.org/0000-0002-2339-9865
CO2 capture, utilization, and storage techniques, known by the acronym CCUS (Carbon capture, utilization, and storage), have been studied as primary tools for achieving the decarbonization targets, stipulated to slow down the rise in temperature earth average. In this context, geological storage consists of injecting CO2 into the rock formation, so that it is trapped in saline aquifers, coal deposits or oil reservoirs. CO2 injection is already carried out, for example, in the Brazilian pre-salt fields, where the oil produced has a high concentration of CO2 in its composition. It is expected that other geological structures can be used for geological carbon storage. However, the geological sites must be carefully selected, one of the key points being the geochemical stability due to the contact of CO2 with the rock formation. Thus, this project aimed to study the process of interaction of CO2 with formations of carbonate rocks, to increase the fundamental knowledge regarding the processes of rock-fluid interaction in the geological storage of CO2. The methodology included the analysis of the petrophysical properties of commercial carbonate rocks (Indiana Limestone and Silurian Dolomite) and of the dolomitic carbonate sample from the Itaituba Formation, before and after exposure to CO2 in the form of carbonated water and in the supercritical form. We also used X-ray microtomography to study the porous structure of samples at different scales. The results showed that the Indiana rock samples present distributed porosity, being essentially formed by structures predominantly composed of pallets, skeletal grains, ooids and shell fragments. The samples of Silurian Dolomite presented a structure formed by less pores, however larger and more concentrated. The rock samples from the Itaituba formation showed very low porosity and permeability. The petrophysical properties evolved after contact with CO2. Rock-fluid interaction studies will show changes in rock matrices resulting from the dissolution/or expansion process. The microtomography technique of x-ray was used in the imaging of the samples to visualize the change in the morphology of the rocks, the technique allowed the comparison of before and after CO2 attack. The DRX and FRX analyzes showed positive results regarding the mineral composition of the samples used. The results of this work will contribute to the reduction of uncertainties related to the processes and mechanisms of the geological storage of CO2.
Acesso aberto (Open Access)
The mineralizing fluid in the Piaba gold deposit, São Luís cratonic fragment (NW-Maranhão, Brazil) based on fluid inclusion studies in quartz veins
(2013-03) FREITAS, Saney Cecílio Ferreira de; KLEIN, Evandro Luiz
Piaba is the first gold mine to operate in the São Luís cratonic fragment, NW-Maranhão, northern Brazil. The geological setting comprises chiefly metavolcano-sedimentary sequences (Aurizona Group) and subduction-related granitoids (Tromaí Intrusive Suite), formed in island arc between 2240 and 2150 Ma. Gold mineralization is hosted in a fine-grained granophyric granodiorite (Piaba Granophyre) and in a subvolcanic andesite of the Aurizona Group. The mineralized zone is confined within the limits of the Piaba fault (ENE-WSW-trending brittle-ductile shear zone) and consists of quartz veins and veinlets and accompanying hydrothermal haloes (chlorite + muscovite + carbonate + pyrite + chalcopyrite + gold) disposed in stockwork geometry. Petrographic, microthermometric and microRaman spectroscopic studies of quartz have defined two- and three-phase aqueous-carbonic fluid inclusions produced by heterogeneous trapping during phase separation, in addition to late aqueous fluids. The mineralizing solution is an aqueous-carbonic fluid composed of CO2 (5 - 24 mol%), H2O (74 - 93 mol%), N2 (< 1 mol%) and CH4 (< 1mol%). It presents low salinity (5.5 wt.% NaCl equivalent) and density of 0.96 - 0.99 g/cm3). Ore deposition occurred at 267 - 302ºC and 1.25 - 2.08 kbars, corresponding to 4 - 7 km in depth, in agreement with the structural information. The P-T-X and reduced characteristics (log ƒO2 -31.3 to -34.3) of the fluid, combined with host rock sulfidation, altogether indicate that gold has been transported as a sulfur complex and that ore deposition occurred in response to phase separation and lowering of the sulfur activity and ƒO2 during fluid-rock interaction.