(U-Th)/He Ages from the Fuorite Mineralization of the Tanguá Alkaline Intrusion Idades

Abstract

The Tanguá Alkaline Suite formed as a result of Mesozoic to Cenozoic magmatic events that affected the part of the South American Platform in Brazil's southeast. The alkaline intrusion is composed of alkali-feldspar syenite with nepheline (pulaskites and umptekites), syenite (with or without the presence of pseudo-leucite), varied nepheline syenites (foyaites, micro-foyaites etc.) and alkaline magmatic breccias. The intrusion contains important fluorite mineralization, in the form of NE-SW oriented veins, which were economically extracted in recent decades at the Emitang Mine. This paper focuses on the analysis of these centimetric crystals of fluorite which vary in color from (yellow, to white and purple.) associated with mineralization of Tanguá Body. Geochronological dating by (U-Th)/He of fluorite mineralization showed a wide range of ages, with the oldest age of 74 ± 3 Ma (Late Cretaceous) and the youngest of 0.11 ± 0.02 Ma (Late Pleistocene). Most ages are concentrated between 25 and 8 Ma (Miocene). The oldest age (74.0 ± 3 Ma) is associated with hydrothermal fluids percolating at the time of intrusion of the Tanguá Body. The other ages represent episodes of percolation of hydrothermal fluids and consequent growth of fluorite crystals. Of note is a set of Miocene ages that can be associated with regional tectonic events. This phase of flurite growth may be associated with the reactivation of basement faults and structures in the Tanguá region and the circulation of hydrothermal fluids associated with intrusion of younger dikes. The youngest ages may be associated with neotectonic reactivation of faults during neotectonic events. Keywords: Tanguá Alkaline Intrusion; fluorite mineralization; (U-Th)/He Ages; Mesozoic to Cenozoic magmatism Resumo A Suíte Alcalina de Tanguá é representante das manifestações magmáticas meso-cenozoicas que ocorreram na Plataforma Sul-Americana na região sudeste brasileira. O corpo alcalino é constituído de álcali-feldspato sienitos com nefelina (pulaskitos e umptekitos), sienitos (com ou sem presença de pseudo-leucita), nefelina sienitos variados (foiaitos, micro-foiaitos etc) e brechas magmáticas alcalinas. Destacam-se ao longo da intrusão importantes mineralizações filoneanas de fluorita de orientação NE-SW exploradas economicamente nas últimas décadas na Mina Ermitang. As datações geocronológicas pelo método (U-Th)/He das fluoritas associadas a estas mineralizações apresentaram uma grande variação de idades, sendo a idade mais antiga de 74 ± 3 Ma (Cretáceo Superior) e a mais jovem de 0,11 ± 0,02 Ma (Pleistoceno Superior). A idade mais antiga (74,0 ± 3 Ma) é associada aos fluidos hidrotermais percolantes no momento da intrusão do Corpo de Tanguá. Porém a maior parte das idades concentram-se principalmente no intervalo 25 a 8 Ma (Mioceno), e, , provavelmente representam o principal estágio de mineralização da fluorita. Este estágio pode estar associado a reativações de antigas falhas/lineamentos presentes na região do Corpo Alcalino de Tanguá e eventuais percolações de f...

Geochemistry and Geochronology (U-Pb and Lu-Hf) of the Soarinho Alkaline Massif (Brazil): Implications on Mantle versus Crustal Signature of Syenitic Magma

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Water and Geological Assessment in the Micro-Watersheds of the Alkaline Rocks of Tanguá and Soarinho in Rio de Janeiro State

“…According to Biondi (2003), alkaline rocks are of interest to companies in the mineral sector, as they are a source of economically important minerals. In the case of the Tanguá Alkaline Complex, the fluorite veins stand out (Da Silva et al 2018).…”