Browsing by Author "Yvon, Jacques"

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    Ages and possible provenance of the sediments of the Capim River kaolin, Northern Brazil.
    (2007) Sousa, Daniel José Lima de; Varajão, Angélica Fortes Drummond Chicarino; Yvon, Jacques; Scheller, Thomas; Moura, Candido Augusto Veloso
    Provenance studies carried out on the soft and flint facies of the Capim River kaolin (northern Brazil) trace the possible sources of sediments that host the ore. Pb–Pb evaporation geochronology was applied to four predominant morphologic classes of detrital zircons, and the ages obtained were compared to the main age intervals of the rocks surrounding the Capim kaolin district (CKD). Four major plateau ages (2.15, 2.02, 1.87, and 1.51 Ga) were defined for both soft and flint facies, indicating a common source for the kaolin and provenance from NE and SW. The 2.15 and 2.02 Ga ages correlate with the granitic bodies of the Gurupi region, located NE of the study area. The 1.87 and 1.51 Ga ages show provenance from the Amazon Craton, the former from the southern portion, in the Caraja´s region, and the latter from the southwestern portion. Although less abundant, Archean (3.18, 2.79, and 2.55 Ga) and Neoproterozoic ages (0.8 and 0.51 Ga) also correlate with the SW and NE provenances, respectively. The first corresponds to the oldest rocks of the Caraja´s region and the second to the rocks of the Gurupi region, corresponding to the Brasiliano orogeny.
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    Genesis of clayey bodies in Quadrilátero Ferrífero, Minas Gerais, Brazil.
    (2004) Santos, Marcelo Cabral; Varajão, Angélica Fortes Drummond Chicarino; Yvon, Jacques
    This work deals with macromorphological, mineralogical, micromorphological and geochemical studies in clayey bodies from Quadrilátero Ferrı́fero in order to define their genesis and formation conditions in this geologic province from Minas Gerais State. Methodologies, based on the description of outcrops and drill cores, using X-ray diffraction (XRD), differential and gravimetric thermal analyses (DTA-TG), scanning electron microscopy (SEM), optical analysis of thin sections and chemical analyses allowed for the definition of two different genetic types of clayey bodies. One type, SET 1, occurs upon saprolitic material from Paleoproterozoic rocks in unconformity contact. It is constituted, from the base to the top, by four facies: nodular, ferruginous kaolinitic, mottled kaolinitic, and massive kaolinitic. The origin of this set is related to the deposition of lateritic materials by gravitational process. The faciological differentiation of this set is related to the syn-depositional process and postdepositional mechanisms of ferruginization and deferruginization. The second type, SET 2, is composed by an ilmenitic–kaolinitic tabular facies in discordant relationships with the saprolite material from Paleoproterozoic rocks. The origin of this second set is related to “in situ” alteration of intrusive rocks of acidic composition.
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    Geochemical evolution of the capim river kaolin, northern Brazil.
    (2006) Sousa, Daniel José Lima de; Varajão, Angélica Fortes Drummond Chicarino; Yvon, Jacques
    The Capim River kaolin, located in the eastern Brazilian Amazon, constitutes one of the most important kaolin deposits in the world. Known for its high whiteness, its noble application is in the paper industry. Studies were carried out on samples from the six facies of the deposit (sand kaolin, soft kaolin, lower transition facies, ferruginous crust, upper transition facies and flint kaolin) in order to trace its geochemical evolution. The kaolin developed at the expense of Cretaceous sandy–clayey sediments of the Ipixuna Formation. Intense lateritic processes characterized by ferruginization and deferruginization mechanisms led to the distinction of the different facies.
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    Geochemistry of a sedimentary lateritic kaolin deposit in Quadrilátero Ferrífero, Brazil.
    (2006) Santos, Maria do Carmo; Varajão, Angélica Fortes Drummond Chicarino; Yvon, Jacques
    The present study deals with the mineralogy and geochemistry of the clayey facies of the Água Limpa kaolin deposit, situated in the Moeda Syncline, Quadrilátero Ferrífero, Minas Gerais, Brazil. Kaolinite, quartz, oxides and iron hydroxides (hematite and goethite) represent the mineral assembly of the five facies of the deposit. White mica, rutile, anatase and gibbsite are heterogeneously distributed along the profile. Despite the variable behavior of the chemical elements along the profile, the geochemical patterns for major and rare earth elements enable to define the filiations generated by the laterization process that affected the sediments.
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    The Cenozoic deposits of the ancient landscapes of Quadrilátero Ferrífero highlands, Southeastern Brazil : sedimentation, pedogenesis and landscape evolution.
    (2020) Varajão, Angélica Fortes Drummond Chicarino; Mateus, Ana Carolina Campos; Santos, Maria do Carmo; Varajão, César Augusto Chicarino; Oliveira, Fabio Soares; Yvon, Jacques
    The Quadrilátero Ferrífero (QF), Southeastern Brazil, is a very important tropical highland region in the world’s geological context for its large and diverse Archean and Proterozoic rocks with great reserves of gold, iron, manganese, aluminum and industrial rocks, on a apparently stable geological structure. There, Cenozoic deposits perched on highland valleys show unclear genetic relationships with the underlying bedrock, with no apparent regional correlation. We studied five representative Cenozoic deposits (BR356, Água Limpa, Padre Domingos, Pau Branco and Casa de Pedra) on the highlands of the Serra da Moeda syncline, Western QF, to answer the question of their sedimentological origin, and investigate their pedological evolution. Field sampling was complemented by macromorphological, mineralogical and micromorphological analysis supported by X-ray diffraction (XRD), differential thermal analysis (DTA), infrared analysis (IR), scanning electron microscopy (SEM), micropobre and transmission electron microscopy (TEM). The evolution of these isolated highland de- posits comprises a deep-weathered source area, a tectonic activity, besides sedimentological and pedological processes, during and after the deposition. The deposits overlie deep saprolites of Precambrian rocks (Piracicaba and Itabira Groups), representing unconformable contact. The onset of the deposition was marked by torrential, coarse colluvial and large blocks landslides into the small basins generated by reactivating tectonic events during the Oligocene, producing local grabens. These tectonic basins were filled by cohesive debris and mudflow from the adjacent and previously laterized cover, developed under the hot and humid climate in the Eocene. The cover reveals an upside-down lateritic profile where morphology and kaolinite crystal properties (values of size of coherent scattering thickness ranging from 135 Å to 162 Å) in the bottom is related to the pedolith horizons of the former lateritic cover. Later, due to climate changes (during and after the Miocene), renewed weathering on these pre-weathered sediments occurred, characterized by alternating ferruginization and Fe-losses, with the superimposed generation of new pedogenic features such as nodules, ferruginous duricrusts and mottling (redox features). In addition to demonstrating that the Brazilian platform was not stable during the Cenozoic, these deposits reveal the role of polygenetic tropical pedological processes in their formation and transformation.