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On the Morphology and Geochemistry of Hydrothermal Crypto- and Microcrystalline Zircon Aggregates in a Peralkaline Granite

Department of Mineralogy and Geotectonics, Institute of Geosciences, University of São Paulo, São Paulo CEP 05508-080, Brazil
Academic Editors: Massimo D’Antonio and Ilenia Arienzo
Minerals 2022, 12(5), 628; https://doi.org/10.3390/min12050628
Received: 31 March 2022 / Revised: 4 May 2022 / Accepted: 10 May 2022 / Published: 14 May 2022
Singular crypto- and microcrystalline hydrothermal zircon aggregates occur in peralkaline granites from the Corupá Pluton of “A-type” granites and syenites in Graciosa Province, Southern Brazil, and are herein characterized for their morphological, textural and geochemical (major, minor and trace elements, and Lu-Hf isotopes) properties. The aggregates were found to present a variety of habits, such as dendritic, oolitic, botryoidal and spherulitic, and they are associated with typical hydrothermal minerals (alkali-feldspars, quartz, fluorite, epidote-group minerals, phyllosilicates and Fe oxides) in micro-fractures and small miarolitic cavities in the host rock. They precipitated directly from a hydrothermal fluid and, compared to magmatic zircon crystals from the host, were found to contain relatively high abundances of the “non-formula” elements (e.g., Fe, Al, and Ca) and HFSEs (High-Field-Strength Elements), particularly the L- and MREEs (Light and Medium Rare Earth Elements), features most typical of hydrothermal zircon, as well as high Th/U ratios, whereas the Lu-Hf isotopic signatures were found to be similar. The formation of the zircon aggregates and the associated epidote-groups minerals was probably due to the interaction between an orthomagmatic, F-bearing, aqueous fluid transporting the HFSEs with the host-rock and/or with an external meteoritic fluid from the country rocks. The preservation of an amorphous-like Zr-silicate compound and crypto-to-microcrystalline zircon varieties is arguably related to the inefficient fluid flux and/or elemental diffusion in a low-temperature oxidizing environment. View Full-Text
Keywords: hydrothermal zircon; crypto- and microcrystalline aggregates; zircon geochemistry and Lu-Hf isotopes; peralkaline granite hydrothermal zircon; crypto- and microcrystalline aggregates; zircon geochemistry and Lu-Hf isotopes; peralkaline granite
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MDPI and ACS Style

Vlach, S.R.F. On the Morphology and Geochemistry of Hydrothermal Crypto- and Microcrystalline Zircon Aggregates in a Peralkaline Granite. Minerals 2022, 12, 628. https://doi.org/10.3390/min12050628

AMA Style

Vlach SRF. On the Morphology and Geochemistry of Hydrothermal Crypto- and Microcrystalline Zircon Aggregates in a Peralkaline Granite. Minerals. 2022; 12(5):628. https://doi.org/10.3390/min12050628

Chicago/Turabian Style

Vlach, Silvio R.F. 2022. "On the Morphology and Geochemistry of Hydrothermal Crypto- and Microcrystalline Zircon Aggregates in a Peralkaline Granite" Minerals 12, no. 5: 628. https://doi.org/10.3390/min12050628

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