info:eu-repo/semantics/article
GEOCHEMISTRY, MINERALlZATIONS AND AGE OF TIN-BEARING GRANITES FROM PITINGA, NORTHWESTERN BRAZIL
GEOCHEMISTRY, MINERALlZATIONS AND AGE OF TIN-BEARING GRANITES FROM PITINGA, NORTHWESTERN BRAZIL
Autor
MACAMBIRA, MOACIR JOSE BUENANO
TEIXEIRA, JOSÉ THADEU
DAOUD, WALID EL KOURY
COSTI, HILTON TULIO
Institución
Resumen
One of the most important geological units of the Central Amazonian Province is formed by anorogenic granite plutons, some of them associated with important ore deposits. The largest ore deposits of Sn, Zr, Nb, Ta, and REE in this Province are associated with the Madeira (MD) and Água Boa (AB) plutons, Pitinga region, NW Brazil. These plutons crosscut the volcanic rocks from Iricoumé Group and sediments from Urupi formation, and follow the regional trend, suggesting magma ascension along deep faults. These plutons are composed by three granitic units, which are, in order of emplacement: granite with rapakivi tendency; fine-grained porphyritic granite; and biotite granite. There are metasomatic variations to greisen (in AB pluton) and apogranite (in MD pluton) associated genetically with ore deposits. Major and trace elements contents shown sub-alkalic to peraluminous characteristics, with an increasing of Si02, F, Sn, Rb, and Y, and a decreasing of A1203, FeO, Fe203, CaO, MgO, Ti02, Sr, Zr, and Nb toward the biotite granite. As a whole, AB pluton has the lowest Nb contents, while the MD pluton has the lowest Y and REE contents. The REE patterns of AB and MD are similar, showing high absolute contents, pronounced negative Eu anomalies, and a little fractionated patterns. The apogranite is depleted in LREE by albitization process. Rb-Sr whole-rock isochron constructed with nine samples from AB and MD plutons indicates an age of 1,691 ± 34 Ma with initial ratio of 0.7062 ± 0.0067. The geological and geochemical features of AB and MD plutons are similar with cratogenic bodies originated in tensional regions, as A-type granites. However, the classifications of these plutons in separated regional suites is not well established due to absence of more strong criteria to do so, up to now. A Província Amazônica Central cobre extensa área do noroeste do Brasil. O conhecimento da região foi rapidamente incrementado a partir dos anos 70 com a descoberta de Mineralizações importantes. Destacam-se nesta província granitos anorogênicos, que têm sido tentativamente agrupados em suítes, entretanto poucos plútons foram até agora bem estudados. Dois corpos graníticos situados entre os rios Pitinga e Alalaú-Madeira e Água Boa são enfocados no presente trabalho que objetiva melhor caracterizar esses corpos dando continuidade aos estudos já desenvolvidos sobre os granitos anorogênicos da Província Amazônia Central.