Magmatic and post-magmatic Y-REE-Th phosphate, silicate and Nb-Ta-Y-REE oxide minerals in A-type metagranite: an example from the Turčok massif, the Western Carpathians, Slovakia

Abstract

An electron microprobe study of Y-REE-Th phosphate, silicate and Nb-Ta-Y-REE accessory-mineral assemblages revealed the compositional variations and evolution in post-orogenic, hypersolvus Permian A-type metagranite from Turčok, in the Gemeric Unit, of the Western Carpathians, eastern Slovakia. Prismatic zircon I and allanite-(Ce) are primary magmatic phases. However, the late-magmatic to early-subsolidus processes led to the formation of a more complex younger assemblage: bipyramidal zircon II, xenotime-(Y), thorite, gadolinite-hingganite-(Y), Nb-Ta-Y-REE oxide phases [fergusonite-(beta)/ samarskite-(Y), aeschynite/polycrase-(Y), and Nb-rich rutile?] and possibly monazite-(Ce). However, monazite-(Ce) and the partial alteration of allanite-(Ce), xenotime-(Y) and the Nb-Ta-Y-REE minerals are probably connected with a younger Alpine metamorphic overprint of the granite. Thorite appears as a solid solution in the thorite-xenotime-zircon series; it is also enriched in Al. Fergusonite-(beta)/ samarskite-(Y) and especially aeschynite/polycrase-(Y) show increased P, Si and Al contents.

Hydrothermal alteration of a chevkinite-group mineral to a bastnäsite-(Ce)-ilmenite- columbite-(Fe) assemblage: interaction with a F-, CO2-rich fluid

“…As examples, Uher et al (2009) found columbite-(Fe) forming rare irregular intergrowths with Nb-Ta-rich rutile in the Prašivá granitic pegmatites, Slovakia. Doroshkevich et al (2009Doroshkevich et al ( , p.1113 described columbite + quartz replacing pyrochlore in the Amba Dongar carbonatite complex, Gujarat, India, and Lahti (2000, p. 112) recorded pyrochlore-microlite replacing marginal parts of columbite crystals and small columbite-group phases occurring in pyrochlore samples from granitic pegmatites of the Eräjärvi district, South Finland.…”

“…The abundances of certain non-formula elements are high: P 2 O 5 ≤ 8.24 wt.%, CaO ≤3.02 wt.%; ΣREE 2 O 3 ≤22.44 wt.%; FeO* 4.05 wt.%, and TiO 2 ≤2.05 wt.%, the REE being dominated by the LREE. These elements are known to be incorporated into ThSiO 4 during interaction with hydrothermal fluids (Lumpkin and Chakoumakos 1988;Pointer et al 1988;Johan and Johan 2005;Förster 2006;Berger et al 2008;Uher et al 2009;Soman et al 2010;Piilonen et al 2013). The proportion of OH in the formulae was calculated from charge balance and ranged from 0.0 to 2.4 (Supplementary Table 2b).…”

Hydrothermal metasomatism of a peralkaline granite pegmatite, Khaldzan Buragtag massif, Mongolian Altai; complex evolution of REE-Nb minerals

“…The local presence of ilmenite may point to lower f O 2 condition there, consistent with the relatively high Mn content (≤4.65 wt.% MnO) (Cassidy et al 1988). (iii) The increasingly large positive Ce anomalies found in the phases during successive alteration stages may be taken to be a result of oxidising conditions affecting the valency of Ce (Gieré and Sorensen 2004;Pettke et al 2005;Mayer et al 2014;Berger et al 2008;Uher et al 2009). However, the anomalies may equally be related to preferential partitioning of Ce into the fluids.…”

Age and origin of fluorapatite-rich dyke from Baranec Mt. (Tatra Mts., Western Carpathians): a key to understanding of the post-orogenic processes and element mobility

“…The source of fluorine is still unknown, but the circulation of F-rich fluids was noted in supra-subduction zones, due to phengite and /or F-amphibole breakdown (Sheng et al 2013). The high activity of fluorine and phosphorus was noted during hydrothermal alterations elsewhere in the crystalline cores of the Central Western Carpathians (Burda & Dzierżanowski 2005;Szopa 2009;Uher et al 2009;Gawęda & Włodyka 2012;Ondrejka et al 2012).…”