Navegando por Autor "SILVA, Joseanna dos Santos"

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Acesso aberto (Open Access)
Granito Porquinho, Domínio Tapajós: exemplo de magmatismo alcalino-peralcalino e considerações metalogenéticas preliminares
(Universidade Federal do Pará, 2018-08-27) SILVA, Joseanna dos Santos; LAMARÃO, Claudio Nery; http://lattes.cnpq.br/6973820663339281
Porquinho Granite (PG) is a subcircular batholith located at the Tapajós Domain, Amazonian Craton, petrographically composed of isotropic hypersolvus alkali feldspar granites, grouped In: Biotite alkali feldspar granite (BAFG), Amphibole alkali feldspar granite (AAFG) and greisenized rocks. Biotites are classified as annite, while amphiboles vary in composition, from calcic (hastingsite, ferro-edenite, ferro-actinolite and ferro-ferri-hornblende) to sodic-calcic (ferro-ferri-winchite, ferro-ferri-katophorite, ferro-richterite, potassic-ferro-ferri-katophorite and ferro-katophorite) to sodic (riebeckite). Geochemically, PG is metaluminous to peraluminous, locally peralkaline, shows K 2 O/ Na 2 O ratios between 1 and 2, and FeO t /(FeO t + MgO) very close to 1, which led it to be classified as a ferroan granite. It is a reduced granite, with geochemical characteristics of A-type granites of the A 2 -subtype and is similar to the Phanerozoic intraplate granites. AAFG rocks are slightly more enriched in REE than BAFG, but they all present similar comportment, and strong negative Eu anomaly, forming the typical gullwing-shaped pattern of the A-type and the Sn-Ta-Nb mineralized granites. BAFG also shows similar behavior with Europa Granite (EG, Madeira Intrusive Suite; Pitinga) and Velho Guilherme Intrusive Suite (VGIS; Xingu), both mineralized in Sn-Ta-Nb, while AAFG approaches, geochemically, more to Maloquinha Intrusive Suite (MIS; Tapajós), non-mineralized. In this work, PG presented a geochronological age of 1,889 ± 2 Ma, interpreted as the age of crystallization, which is about 100 Ma older than the former one (1,786 ± 14 Ma). The older geochronological age fits better with geological context in which Porquinho Granite is inserted, but also means more detailed investigations need to be done in this area in order to eliminate possible doubts about its crystallization age and find out if PG has a more complex history of evolution.
Acesso aberto (Open Access)
Morphological and compositional variations of zircon and their metallogenetic implications: the example of the Jamon, Serra dos Carajás and Velho Guilherme suites, Amazonian Craton
(2014-03) LAMARÃO, Cláudio Nery; SILVA, Joseanna dos Santos; BORGES, Régis Munhoz Krás; DALL'AGNOL, Roberto
Zircon from granites of the Jamon suite (JS), Serra dos Carajás suite (SCS) and Velho Guilherme suite (VGS) were studied by scanning electron microscope (SEM) through backscattered electron and cathodoluminescence images and energy dispersive spectroscopy (EDS) analyses. Granites and greisens of the VGS have predominantly anhedral zircons that are altered and intensely corroded, are enriched in Hf and have the lowest Zr/Hf ratios of the studied suites. In the granites, these ratios decrease towards the more evolved varieties. Zircons of the JS are euhedral to subhedral, zoned and slightly altered; they are also comparatively depleted in Hf and display the highest Zr/Hf ratios, indicating limited potential for tin-associated mineralization. Zircons from granites of the SCS are subhedral to anhedral, altered and corroded, and show Hf contents and Zr/Hf ratios intermediate to those of the JS and VGS. The granites of the VGS with Sn-, Ta- and W-associated mineralization contain zircons with Zr/Hf ratios varying from 7 to 22. It is concluded that ratios of similar magnitude can be used as a prospecting guide for specialized granites. Zircons from the greisens associated with the Cigano granite of the SCS have average Zr/Hf ratios of approximately 23, but no cassiterite was found in these rocks, indicating that the zircons preserved their magmatic geochemical signature. This study distinguished the three granitic suites in terms of zircon composition and demonstrated the importance of their geochemical signature, especially in terms of their Zr/Hf ratio, in the identification of specialized granites. EDS-SEM analysis can thus be used in a preliminary assessment of the metallogenic potential of tin granites.