Navegando por Autor "GALARZA TORO, Marco Antônio"

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Geocronologia e evolução crustal da área do depósito de Cu-Au Gameleira, Província Mineral de Carajás (Pará), Brasil
(2002-12) GALARZA TORO, Marco Antônio; MACAMBIRA, Moacir José Buenano
The Gameleira Cu-Au deposit is hosted by rocks of the Igarapé Pojuca Group, Itacaiúnas Supergroup, Carajás Mineral Province, southeastern Amazonian Craton. This group is represented mainly by mafic metavolcanic rocks (MVR), amphibolite, biotite schist, banded iron formation and/or hydrothermalite and cut by intrusive mafic rocks (IMR) as well as by deformed Itacaiúnas granites of Archean age (2.56 Ga) and Pojuca and Gameleira granites of Proterozoic age (1.87 and 1.58 Ga). Zircon crystals from a saprolite (2615 ± 10 Ma and 2683 ± 7 Ma) and from an IMR sample (2705 ± 2 Ma) are coeval with those from gabbros of the neighboring Águas Claras deposit. Pb-Pb dating of whole rock samples and chalcopyrite from the MVR indicated ages of 2245 ± 29 Ma and 2419 ± 12 Ma, respectively, while leached chalcopyrite yielded ages of 2217 ± 19 Ma and 2180 ± 84 Ma. These ages are interpreted as due to partial resetting provoked by the Proterozoic granitic intrusions or by tectonic reactivation along the Carajás and Cinzento strike slip systems or alternatively, as due to total resetting provoked by the last one. The TDM ages between 3.12 and 3.33 Ga for the MVR and IMR, and the initial Nd ε (t) values of –0.89 to –3.26 suggest continental contribution from older crustal material and possibly magma generation in a continental rift or active continental margin environment.
Acesso aberto (Open Access)
Geoquímica das águas do médio e baixo rio Madeira e seus principais tributários - Amazonas - Brasil
(Instituto Nacional de Pesquisas da Amazônia, 2013-12) HORBE, Adriana Maria Coimbra; QUEIROZ, Maria Mireide Andrade; MOURA, Candido Augusto Veloso; GALARZA TORO, Marco Antônio
The aim of this paper was study the water of the Madeira River and its tributaries, between the city of Humaitá and its confluence in the Amazon River. There were analyzed: pH, conductivity, turbidity, major ions, trace elements and strontium isotopes during the dry and wet seasons and also, in the transition from the wet to the dry season, throughout 2009 and 2010. The white waters from the Madeira River are bicarbonated, calcic, with pH between 5 and 6 and the ions concentrations are higher than those of the tributaries. The waters of the tributaries are black, are more acidic and are chemically heterogeneous; those from the left margin are chemically similar to the waters of Madeira River, while those from the right margin are enriched in dissolved SiO2. The concentrations of cations, Cl- and NO3- are higher during the wet season due to the contribution of soils, vegetation and the rainwater composition (Cl-), while HCO3-, SO42-, Al, Br e P are concentrated in the dry season, and their higher contents may be related to the bedrock. The higher concentrations of SiO2 and rare earth elements in both dry and wet season are related to vegetation, soil and rocks. The interaction of these factors causes the chemical heterogeneity of the water. However, the chemical similarities between the water tributaries of the left margin and the water of the Madeira River, are probably, consequence of the Andean rocks be the sources of the Cenozoic sedimentary rocks percolated by these tributaries while the chemistry water of the tributaries of the right margin are in accordance with the tectonic stability, the intense weathering and the low erosion rate of the Amazon craton.
Acesso aberto (Open Access)
Granitos pórfiros da região de vila Riozinho, província aurífera do Tapajós: petrografia e geocronologia
(2008-09) LAMARÃO, Cláudio Nery; SOUZA, Kleber Silva de; DALL'AGNOL, Roberto; GALARZA TORO, Marco Antônio
The Tapajós Gold Province (TGP) is located in the center of the Amazonian craton. It is dominated by Paleoproterozoic calc-alkaline and A-type granitoids and intermediate to felsic volcanic sequences. The Vila Riozinho region, situated in the central-eastern part of the TGP and constituted by the Vila Riozinho, Moraes Almeida and Jardim do Ouro villages, has the more important geologic units that characterize this province. The aim of this paper is to present new petrographic and geochronological data on the porphyry granites associated with the dominant monzogranitic rocks of the Older São Jorge granite and with ignimbrites and rhyolites of the Moraes Almeida Formation and leucogranitic rocks of the Maloquinha suite. The geochronological data revealed at least two distinct periods of generation of porphyry granites in the region. The first, associated with 1.98 Ga calc-alkaline magmatismo, and the second with 1.88 Ga alkaline rocks. Backscattered images and analyses of EDS (energy dispersive spectrometry) obtained with a SEM (scanning electron microscope) showed that is frequent the occurrences of gold particles in the porphyry granites filling cavities in quartz and plagioclase, or associated with epidote and alkali feldspar. These data suggest that the porphyry granites can have contributed to gold mineralization of the Vila Riozinho region, and shows that detailed studies are necessary to elucidate metallogenetic importance of these rocks in the gold mineralization of the region.
Acesso aberto (Open Access)
Petrography, magnetic susceptibility and geochemistry of the Rio Branco Granite, Carajás Province, southeast of Pará, Brazil
(2013-03) SANTOS, Patrick Araujo dos; FEIO, Gilmara Regina Lima; DALL'AGNOL, Roberto; COSTI, Hilton Túlio; LAMARÃO, Cláudio Nery; GALARZA TORO, Marco Antônio
The Paleoproterozoic Rio Branco stock intrudes the Archean Cruzadão biotite monzogranite. It occurs west of the Canaã dos Carajás city, close to the Sossego copper mine in the Carajás Province. It is constituted by undeformed and isotropic, hololeucocratic syenogranites, showing equigranular texture. The granite is formed essentially by perthitic alkali feldspar, quartz, and plagioclase, with additional variable amounts of chloritized biotite. Fluorite, allanite, and zircon are common accessory minerals, whereas pyrite and chalcopyrite are scarces. Albitization and subordinate greisenization are the main alteration processes that affected the granite. The secondary mineralogy is represented by albite, fluorite, topaz, chlorite, muscovite, siderophyllite, and iron oxides. Magnetic susceptibility values are systematically low and vary between 1.3 x 10-5 a 6.9 x 10-4 (SI). The Rio Branco Granite is metaluminous to peraluminous and shows high FeOt/(FeOt + MgO). It has geochemical affinities with ferroan, reduced A2-subtype granites. The rare earth element (REE) patterns are flat with little heavy REE fractionation and show accentuated negative Eu anomalies (Eu/Eu* = 0.08 - 0.13). These characteristics are typical of evolved granites, derived from volatile-enriched liquids responsible by the intense subsolidus hydrothermal alteration. The dating of the Rio Branco granite did not give conclusive results, but the obtained data, associated with geological evidence, suggest that it is of Paleoproterozoic age. The comparison between the Rio Branco granite and Paleoproterozoic A-type suites of the Carajás Province suggests that the Rio Branco granite has more affinity with the Velho Guilherme suite and, in lesser degree, with the Serra dos Carajás suite. On the other hand, is clearly different from oxidized A-type granites of the Jamon suite. Despite its similarities with tin-specialized granites, the Rio Branco Granite is not associated with tin mineralizations.
Acesso aberto (Open Access)
Rhyacian evolution of the eastern são luís craton: petrography, geochemistry and geochronology of the rosário suite
(Sociedade Brasileira de Geologia, 2017-06) NOGUEIRA, Bruna Karine Correa; GORAYEB, Paulo Sérgio de Sousa; DANTAS, Elton Luiz; LEAL, Rafael Estumano; GALARZA TORO, Marco Antônio
The São Luís Cráton comprises an area between northeast Pará state and northwest Maranhão that exposes Paleoproterozoic granitic suites and meta-volcanosedimentary sequences. In the east of this geotectonic unit, about 70 km south of São Luís, there is a portion of the São Luís Craton, represented by the intrusive Rosario Suite (RS). This work is focused on rocks of this suite, including petrographic, lithochemical and geochronological studies to understand the crustal evolution of these granitoid rocks. The rock spectrum varies from tonalitic to granodioritic, quartz dioritic and granitic compositions, and there are partial structural and mineralogical changes related to deformation along transcurrent shear zones. The geochemical studies show granitic metaluminous compositions of the calc-alkaline series with I-type affinity typical of magmatic arc. Rare earth elements show marked fractionation and slight Eu positive or negative anomalies (Eu/Eu* = 0.82 to 1.1). Zircon U-Pb data provided consistent ages of 2165 ± 7 Ma, 2170 ± 7 Ma, 2170 ± 7 Ma, 2161 ± 4 Ma and 2175 ± 8 Ma, dating emplacement of these granitoids as Paleoproterozoic (Rhyacian). Sm-Nd isotopic data provided model ages (TDM) of 2.21 to 2.31 Ga with positive values of εNd +1.9 to +3.2 (t = 2.17 Ga), indicating predominantly Rhyacian crustal sources for the parental magmas, similar to those ones found in other areas of the São Luís Craton. The data, integrated with published geological and geochronological information, indicate the occurrence of an important continental crust formation event in this area. The Paleoproterozoic evolution between 2.17 and 2.15 Ga is related to the Transamazonian orogeny. The granitoids of the Rosario Suite represent the main phase of continental arc magmatism that has continuity in other parts of the São Luís Craton and can be correlated with Rhyacian accretionary magmatism in the northwestern portion of the Amazonian Craton that amalgamated Archean terrains during the Transamazonian orogeny