P-Al-Th-REE obohatený zirkón a fáza blízka cheralitu v apliticko-pegmatitickom granofýre na lokalite Dubová - Horné Trávniky pro Modré (Malé Karpaty, jz. Slovensko)
Martin Ondrejka, Pavel Uher
Accessory zircon and cheralite-like phase occur in Hercynian quartz - K-feldspar - albite aplitic granophyre dike cutting Devonian Ca-skarn and marbles in the Dubová, Horné Trávniky near Modra, SW Slovakia. Zircon forms euhedral to subhedral crystals. Zircon shows 1.5 to 2.7 wt. % HfO2, Zr/Hfwt. ratio attains 14 to 23. Some zircon compositions show low totals (82 - 92 wt. %), probably due to metamictization and hydration, elevated contents of P (up to 0.25 apfu, 7.6 wt. % P2O5), Al (up to 0.17 apfu, 3.8 wt. % Al2O3), Th (up to 0.12 apfu, 14 wt. % ThO2), Y+REE (up to 0.07 apfu, 4.3 wt. % (Y,REE)2O3), and also U, Fe and Ca (up to 0.1 apfu). Zircon associates with intermediate cheralite > huttonite phase, rich in Th (up to 0.63 apfu, 52 wt. % ThO2), Ca (up to 0.39 apfu, 6.9 wt. % CaO) and Y+REE (up to 0.13 apfu, 5.7 wt. % (Y,REE)2O3). The cheralite-like phase contains also elevated concentrations of Zr (up to 0.05 apfu, 2 wt. % ZrO2), Al (up to 0.17 apfu, 2.6 wt. % Al2O3), and low analytical totals (83 to 85 wt. oxide %). Textural and compositional relationships indicate a relatively rapid crystallization of the both zircon and cheralite-like phase during magmatic solidification of the host aplitic-pegmatitic granophyre which preserved their intermediate and probably metastable compositions.