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| Pierosan,Ronaldo; Lima,Evandro F.; Nardi,Lauro V.S.; Campos,Cristina P. de; Bastos Neto,Artur C.; Ferron,José M.T.M.; Prado,Maurício. |
| The Iricoumé Group correspond to the most expressive Paleoproterozoic volcanism in the Guyana Shield, Amazonian craton. The volcanics are coeval with Mapuera granitoids, and belong to the Uatumã magmatism. They have U-Pb ages around 1880 Ma, and geochemical signatures of α-type magmas. Iricoumé volcanics consist of porphyritic trachyte to rhyolite, associated to crystal-rich ignimbrites and co-ignimbritic fall tuffs and surges. The amount and morphology of phenocrysts can be useful to distinguish lava (flow and dome) from hypabyssal units. The morphology of ignimbrite crystals allows the distinction between effusive units and ignimbrite, when pyroclasts are obliterated. Co-ignimbritic tuffs are massive, and some show stratifications that suggest deposition... |
| Tipo: Info:eu-repo/semantics/article |
Palavras-chave: Amazonian Craton; Caldera complex; Ignimbrite; Iricoumé volcanism; Surge deposits; Uatumã magmatism. |
| Ano: 2011 |
URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0001-37652011000300012 |
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| Minuzzi,Orlando R.R.; Bastos Neto,Artur C.; Formoso,Milton L.L.; Andrade,Sandra; Janasi,Valcir A.; Flores,Juan A.. |
| This work aims at the geochemical study of Pitinga cryolite mineralization through REE and Y analyses in disseminated and massive cryolite ore deposits, as well as in fluorite occurrences. REE signatures in fluorite and cryolite are similar to those in the Madeira albite granite. The highest ΣREE values are found in magmatic cryolite (677 to 1345 ppm); ΣREE is lower in massive cryolite. Average values for the different cryolite types are 10.3 ppm, 6.66 ppm and 8.38 ppm (for nucleated, caramel and white types, respectively). Disseminated fluorite displays higher ΣREE values (1708 and 1526ppm) than fluorite in late veins(34.81ppm). Yttrium concentration is higher in disseminated fluorite and in magmatic cryolite. The evolution of several parameters... |
| Tipo: Info:eu-repo/semantics/article |
Palavras-chave: Cryolite; REE; Y; Pitinga; Amazonia. |
| Ano: 2008 |
URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0001-37652008000400012 |
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