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  2. Pesquisar por Orientadores

Navegando por Orientadores "TORO, Marco Antonio Galarza"

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    Caracterização hidrogeoquímica e isotópica (87Sr/86Sr) dos sistemas aquíferos Barreiras e Pirabas Superior nos municípios de Castanhal e Santa Maria do Pará, Estado do Pará
    (Universidade Federal do Pará, 2015-09-30) SILVA, Igor Rafael Furtado da; TORO, Marco Antonio Galarza; http://lattes.cnpq.br/8979250766799749
    Geological surveys and remote sensing investigations in northeastern Pará State identified features and tectonic structures that characterized the neotectonic process in this region. Hydrogeological investigations in the Metropolitan Region of Belém and its surroundings were also held with the objective of characterizing the waters of the Barreiras and Pirabas (Lower Pirabas and Upper Pirabas) systems, and to evaluate the possibility of a mix between these aquifers through faults and fractures systems and the degree of their vulnerability in relation to anthropogenic inputs. Alongside the hydrogeochemical investigations, studies using isotopic signature of strontium (87Sr/86Sr) in groundwater have been performed in order to characterize the Sr sources for each aquifer system, their geochemical histories and the potential water mixture between them. Thus, studies were carried out in the isotopic composition of strontium (87Sr/86Sr) and hydrogeochemical analyzes in subareas from Castanhal and Santa Maria do Pará, aimed at the characterization of these aquifer systems, as well as detection of any possible case mixtures occur among them. The hydrogeochemical results revealed distinct features between aquifer systems studied, highlighting the parameters pH (3.52 to 5.97 in Barreiras System; 6.17 to 6.60 in Upper Pirabas System), Electrical Conductivity (45.50 to 193.90 S/cm in Barreiras; 133.80 to 194.70 S/cm in Upper Pirabas), HCO3– (up to 32.88 mg/L Barreiras; 89.10 to 117.15 mg/L in Upper Pirabas System), Cl– (3.87 to 40.50 mg/L Barreiras; 3.33 to 6.32 mg/L in Upper Pirabas), Na+ (1.00 to 18.55 mg/L in Barreiras System; 1.35 to 2.55 mg/L Pirabas Upper System), Mg2+ (up to 1.26 mg/L Barreiras, from 2.03 to 2.81 mg/L in Upper Pirabas), Ca2+ (up to 5, 14 mg/L in Barreiras, from 21.30 to 27.38 mg/L in Upper Pirabas) and Sr2+ (0.0065 to 0.0874 mg/L in Barreiras; 0.2129 to 0.2679 mg/L in Upper Pirabas). Statistical studies have shown good correlations between the aquifers (≥ 0.7), especially during the rainy season. According to the analyzes of Piper diagrams it was found that the Barreiras aquifer has predominantly Cl–-Na+ waters, which are influenced by the contribution of meteoric water and the anthropogenic action, with pH values acids around 4.7 and high vulnerability. The waters of the Upper Pirabas Aquifer System are mostly HCO3–-Ca2+, being this hydrochemical facies strongly influenced by the dissolution of carbonate, having a pH higher than 6 and less vulnerability to human action. Isotopic results showed that the Barreiras Aquifer samples are more radiogenic (0.712716 to 0.723881) that the sample of the Upper Pirabas Aquifer System (0.706080 to 0.709063) during the dry season. During the rainy season occurred the homogenization process of isotopic ratios of aquifer systems under study. Samples of the Barreiras Aquifer System there was significant decrease in values of isotopic the 87Sr/86Sr ratios from 0.712716 to 0.723881 for a range from 0.704239 to 0.709957, getting these values similar to those found in the waters of the Upper Pirabas Aquifer System. Composition diagrams of the major ions against chloride varied greatly, possibly indicating the presence of more than two end members in these waters mixing process. The multivariate statistical analysis (PCA), together with the diagram 1/Sr vs. 87Sr/86Sr showed a trend mixture between these aquifers and the meteoric waters during the rainy season. The hydrogeochemical modeling (Schoeller diagram) indicated that the degree of mixing between of the waters of the Upper Aquifer Pirabas and Barreiras is around 10% during the rainy season. Isotopic and hydrochemical studies together with on the existing neotectonic structure in the Metropolitan Region of Belém and its surroundings suggest mixing processes between Barreiras and Upper Pirabas aquifers systems, mainly in the rainy period. The lack of a planning and management system of the use of groundwater sources in the Castanhal and Santa Maria do Pará towns, as well as throughout the Metropolitan Region of Belém, alert to the risk of contamination of the Upper Pirabas Aquifer System by anthropogenic action, which represent the best alternative for public supply of the population of Belém and its surroundings with a excellent water quality with regard to portability for human consumption.
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    Geocronologia U-Pb LA-ICP-MS em zircão das rochas do Grupo Jacareacanga, Domínio Tapajós, Cráton Amazônico, Brasil
    (Universidade Federal do Pará, 2022-02-02) ORTEGA CARDOZO, Jenny Alexandra; VASQUEZ, Marcelo Lacerda; http://lattes.cnpq.br/4703483544858128; https://orcid.org/0000-0003-2729-9404; TORO, Marco Antonio Galarza; http://lattes.cnpq.br/8979250766799749; https://orcid.org/0000-0002-7271-4737
    The Jacareacanga Group is divided into the Sai Cinza and Cadiriri formations, which are composed of mica schists, chlorite schists, actnolite schists and talc schists, metacherts, quartzites with pelitic paragneisses and amphibolites. It comprises a volcanic-sedimentary sequence formed by siliciclastic and chemical sedimentation and mafic-ultramafic volcanism that correspond to a turbidite sedimentation with intercalated oceanic bottom basalts of a backarc basin or trench basin related to the earliest magmatic arc (Cuiú-Cuiú Arc) of the Tapajós Domain of the Tapajós-Parima Province from the Amazon Craton. The field data of mapping programs of the Geological Survey of Brazil – CPRM and the petrography and scanning eletron microscope analysis of this study supported the selection of samples for a new geochronological analysis of the Jacareacanga Group. The U-Pb LA-ICP-MS in zircon crystals dated a mica schist, an amphibolite and two pelitic paragneisses of this unit and gave 207Pb/206Pb ages close to previously dating obtained for this unit. However, these previous dating applied few appropriate geochronological methods (U-Pb TIMS in zircon and Pb-evaporation in zircon) and analyzed not enough amounts of zircon crystals to constrain the age of formation of metasedimentary rocks. The present study gets robust geochronological data obtained by an in situ dating method appropriated to analyze large amounts of zircon and identify the ages of detrital sources and constrained ages for the sedimentation of metasedimentary rocks of the Jacareacanga Group, distinguishing them from the ages of later events. A cutoff of ages < 2000 Ma was applied in order to distinguish the later events are related to the granitic intrusions that cut this unit. The pelitic paragneisses have given 207Pb/206Pb ages between 2008 and 2042 Ma and the mica schist ages of ca. 2056 Ma for the sedimentation age of low and high metamorphic grade metasedimentary rocks of the Jacareacanga Group. Furthermore, these rocks have detrital zircon populations of Rhyacian ages and subordinated of Archean ages that indicate detrital sources original from adjacent cratonic areas. The amphibolite did not furnish good geochronological data to constrain the age of basaltic volcanism associated to the sediments of the Jacareacanga basin. The geochronological data of this study show that the Jacarecanga basin was formed during the early Orosirian, and the oldest detrital sources support that was a basin of a continental margin magmatic arc of a Rhyacian to Archean crust continent.
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    Geologia, controle estrutural e geocronologia das rochas hospedeiras e do minério: implicações para o modelo genético do depósito aurífero do Palito, Província Tapajós, Itaituba-PA
    (Universidade Federal do Pará, 2016-09-24) SERRA, Vitor Felipe Hage; TORO, Marco Antonio Galarza; http://lattes.cnpq.br/8979250766799749
    The Palito gold deposit, located at east portion of the Tapajós Gold Province, southwestern Pará State, comprises a nearly vertical mineralized quartz vein system, hosted by the Palito and Rio Novo Paleoprooterozoic granites and controlled by a sinistral strike-slip brittle-ductile shear zone, trending to NW-SE direction, which belongs to the regional Tocantinzinho lineament. The host granites are two oxidized calc-alkaline monzogranite stocks of Orosirian age and magmatic arc affiliation, correlated to the Parauari Intrisive Suite. The thicker lodes of the veining system are hosted by the major shear, along the N40-50W direction, whereas the thinner veins are housed by faults and fractures of second order and oblique to the main shear direction, both at low angle (around 20), moderate angle (nearby 50) and high angle (around 80). Such a structural situation is compatible with the Riedel system, with the major lodes parallel to the main shear direction (D), associated with low-angle veins (in R and P faults), moderate-angle gash veins (in extension T fractures) and high-angle veins (in R’ an X faults). Stockwork veinlets also occur as a minor ore type. The veins are always involved by a well-developed, normally brecciated, hydrothermal alteration halo. Phyllic alteration (quartz + phengite + pyrite) and chloritization are the two main hydrothermal alteration types, associated to minor potassic alteration (K- feldspar), carbonatization (calcite + sericite + quartz) and sufidation (pyrite + chalcopyrite + sphalerite). Three generations of hydrothermal veining quartz are well characterized in the Palito gold deposit. The youngest low-angle veins (R and P) are made up by quartz1, whereas the later thicker lodes (D) are composed by quartz1 and 2. Tension gash quartz veins may occur at any time of the hydrothermal system evolution and are made up by both quartz1 (youngest gash veins) and quartz2 and 3 (later gash veins). Gash veinlets of quartz3 correspond to final stages of the Palito hydrothermal process. The gold ore, hosted chiefly by quartz1 and 2 veins, is always associated to iron and copper sulfides (pyrite and chalcopyrite), besides sphalerite. Pyrrhotite, bismuthinite, galena, native bismuth and gold are minor metallic phases. Three generations of pyrite and chalcopyrite and one generation of sphalerite were recognized. Chalcopyrite1 replaces pyrite1 and it is replaced by sphalerite, which, in turn, is replaced by chalcopyrite2. Pirite2, coeval to sphalerite, occurs in mineralized veins as anhedral masses replacing tiny remnant grains (islands) of chalcopyrite1, showing concave or corroded edges. Gold is always associated or included in chalcopyrite1 and 2 and pyrite2, bismuthinite and native bismuth crystals. Veinlets of pyrite3 and chalcopyrite3, crosscutting sulfide masses in transtension zones of tiny sinistral faults, are the latest sulfide generations. Two generations of phengite and chlorite were identified in the gangue minerals, being veinlets of phengite2, chlorite2 and carbonate the last one. Fluorite, rutile, zircon and ilmenite still occur as minor gangue phases. The Pb-Pb age of 179417 Ma, obtained for the Palito ore, was interpreted as rejuvenation of the Pb-Pb system caused by Sthaterian alkaline granitic magmatism (Porquinho Intrusive Suite) related to the third extensional deformation phase. The geological features of the Palito gold deposit, as structural controlled veining style of ore bodies and hydrothermal alteration halos, predominating sericitization and cloritization and metallic association (Au-Cu-Bi-Zn) of the ore, all favor classification of the Palito deposit as intrusion-related vein gold deposits. It is a non-porphyritic intrusion-related deposit type, possible related to alkaline granites of the Maloquinha Intrusive Suite, which occur around the Palito deposit. The granitic magma should has provided the ore fluids and metals and the shearing should has controlled the fluid circulation and ore deposition of the Palito deposit.
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    Petrografia, geoquímica e assinatura isotópica de PB de formações ferríferas associadas à gênese das cavernas da Serra Sul, Carajás – PA
    (Universidade Federal do Pará, 2016-06-17) CABRAL, Erica da Solidade; MACAMBIA, Joel Buenano; http://lattes.cnpq.br/4842128592488825; TORO, Marco Antonio Galarza; http://lattes.cnpq.br/8979250766799749
    Geospeleological studies in hosted caves in banded iron formation (banded iron formation - BIF's), type jaspilite, which is the iron protore the S11D body, Serra Sul, showed that these rocks are at different stages of weathering, allowing classifies them into three groups: 1) non-altered jaspilite, 2) altered jaspilite and 3) Iron Ore. Samples BIF’s were collected both in caves and in correlated drillholes stratigraphically to S11D-0035 cave. This stratigraphic correlation was established from the construction of geological section, which allowed us to determine the likely initial lithological setting of the cave and its stratigraphic level. It was concluded that the cave is in the lower portion of the Carajás formation near the contact with the Parauapebas Formation. Petrographic observations showed that jaspilite is characterized by alternating centimetric bands of opaque mineral composed of hematite-1, magnetite and maghemite and subordinate siliceous bands formed by chert and granular quartz. While the non-altered jaspilite consists predominantly of hematite-2 and subordinately hematite-1 and magnetite, banding is absent because the band of silica minerals, which is more soluble, it was almost in its entirety leached, which led to the generating dissolution cavities. In addition, they also observed neo-formed mineral phases, goethite and hematite-3. The chemical analysis of rocks of different groups corroborate the petrographic evidence. Samples of non-altered jaspilite SiO2 content ranges from 40.0 to 44.5% and Fe2O3T content from 53.9 to 58.3%, and the other oxides present, Al2O3, MnO, P2O5, TiO2, CaO, MgO, Na2O, K2O, have very low levels, as well as in other types. In contrast, the rocks are classified as altered jaspilite higher concentration of iron (from 87.9 to 97.1%) and lower SiO2 content (0.3 to 1.1%). The iron ore classified as representing the most advanced stage change, has a high content of Fe2O3T, ranging from 96.2 to 98.3% and low amounts of SiO2 from 0.4 to 1,0%. In all three groups of rock a low content of ETR was observed and, from bottom to top of the weathering profile is observed an increase in the amount of these elements, from 6 to 18 ppm. The ratio La/Eu ranges from 1.3 to 2.2 ppm non-altered jaspilite, from 0.2 to 1.6 ppm altered Jaspilite and 0,1 to 0,8 ppm Iron Ore. This decrease in iron ore may be due to less mobile behavior of HREE relative to LREE in the advanced stages of weathering. The positive anomaly Eu (Eu/Eu* > 1), typical of the BIF's was observed in all samples from different groups change. The Pb-Pb isotopic analyzes in non-altered jaspilite indicate 206Pb/204Pb ratios ranging from 15.247 to 26.111, the ratio 207Pb/204Pb ranges from 15.292 to 16.300, and the ratio 208Pb/204Pb ranges from 34.596 to 37.614. The figures suggest that these rocks are less radiogenic and have isotopic signature similar to the upper crustal rocks. In jaspilite Changed the isotopic ratios 206Pb/204Pb ranging from 16.827 to 23.244, the 207Pb/204Pb from 15.635 to 16.279, and 208Pb/204Pb from 34.715 to 38.811. In Iron Ore the 206Pb/204Pb ratios ranging from 15.702 to 22.845, 207Pb/204Pb from 15,369 to 16,221, and 208Pb/204Pb from 35,169 to 38,467. Therefore, changes were observed in the isotopic signature over change profile suggesting that there were no metamorphic events, tectonic reactivations, percolation of hydrothermal fluids or any other event that upset the Pb-Pb geochronometer and would add materials (Pb) come from other sources. The genesis and evolution of the caves, in addition to chemical processes, relief plays an important role, acting at two different times. First, facilitating the infiltration and percolation of rainwater and channel them to underground portions of the plateau, causing the dissolution of the siliceous layer and the formation of iron ore, loss of rock volume, reduction of layers and concomitant formation of caves. In a second step these caves are exposed by relief denudation processes that favor the retreat of the slopes. Therefore, the analysis of chemical processes with the help of petrography and geochemistry showed that the dissolution and leaching processes are the primary processes in the formation of caves linked to erosive processes provide its evolution. The analysis of chemical processes indicates common origin (weathering) for both the caves and for iron ore, probably contemporary.
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