Produção Nacional
Monazita em veios de quartzo da Serra do Espinhaço Meridional(MG): mineralogia, idades LA-ICP-MS e implicações geológicas
2010; Sociedade Brasileira de Geologia; Volume: 40; Issue: 4 Linguagem: Inglês
10.5327/rbg.v40i3.1537
ISSN2317-4889
AutoresMario Luiz de Sá Carneiro Chaves, Paulo Roberto Gomes Brandão, Bernhard Bühn,
Tópico(s)Geochemistry and Geologic Mapping
ResumoDue to the discovery of monazite occurrences in an uncommon geologic setting, in quartz veins cutting rocks of the Southern Espinhaco Range, a study was carried out on the geology and mineral chemistry of these deposits in three localities ( Buenopolis, Olhos d’Agua and Diamantina) , as well as to make U-Pb laser ablasion MC-ICP-MS geochronological determinations in the Diamantina and Olhos d ’A gua samples. In Buenopolis, monazite specimens are common as twin crystals, occurring in colluvial gravel deposits in a contact zone between the Espinhaco Supergroup with the Macaubas Group. The Olhos d’Agua occurrence is in metric oval-shaped pockets within metapelitic rocks of the Macaubas Group, where large crystals have been discovered. In Diamantina, millimeter-size monazites were studied as broken grains recovered in a colluvial deposit near the Caete-Mirim river. Certainly in the first and in the third cases, such grains came from the abundant regional quartz veins. Electron microprobe analyses showed similar oxide values for the three deposits, but with some chemical specific aspects. The samples have been identified as monazites-(Ce), locally Nd-rich; the Diamantina and Olhos d’Agua deposits seem to have some chemical similarities, although in general there are no absolute resemblance between the two deposits. The U-Pb results showed an older age of ~491 My that probably indicates the crystallization age of the mineral, and a complete extension between 490-440 My that could mean a later reheating periods. In geological terms, such ages can signify the last events related to the Brasiliano Cycle in the region.
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