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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

10.25249/0375-7536.2010404506515

ISSN

2177-4382

Autores

Mario Luiz de Sá Carneiro Chaves, Paulo Roberto Gomes Brandão, Bernhard Bühn,

Tópico(s)

Geological and Geochemical Analysis

Resumo

Due to the discovery of monazite occurrences in an uncommon geologic setting, in quartz veins cutting rocks of the Southern Espinhaço Range, a study was carried out on the geology and mineral chemistry of these deposits in three localities (Buenópolis, Olhos d’Água and Diamantina), as well as to make U-Pb laser ablasion MC-ICP-MS geochronological determinations in the Diamantina and Olhos d’Água samples. In Buenópolis, monazite specimens are common as twin crystals, occurring in colluvial gravel deposits in a contact zone between the Espinhaço Supergroup with the Macaúbas Group. The Olhos d’Água occurrence is in metric oval-shaped pockets hosted in metapelitic rocks of the Macaúbas Group, where large crystals have been discovered. In Diamantina, millimeter-size crystals were studied as broken grains recovered in a colluvial deposit near the Caeté-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’Água 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 a geotectonic view, such ages can signify the last events related to the Brasiliano Cycle in the region.

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