Minerály řady bavenit-bohseit z pegmatitu Schinderhübel I v Maršíkově (silezikum, Česká republika)

Abstract

Bavenite and bohseite were found in an archive sample from Schinderhübel I granitic pegmatite, situated ca. 50 m NE from the famous chrysoberyl-bearing pegmatite body Schinderhübel III near Maršíkov (Silesicum, Czech Republic). Minerals of the bavenite-bohseite series together with minor quartz, muscovite and albite form chalky white radial aggregates up to 3.5 cm in size within a fissure cutting the pegmatite. The electron microprobe data revealed 29.0 - 65.4 mol. % of bavenite component, 0.03 - 0.12 apfu Na and 0.05 - 0.20 apfu F. Bavenite seems to be older than bohseite in the studied aggregate. The collected data suggest significant increase of Be/Al during growth of the studied aggregate, which could be explained in two ways. First, one can assume that different primary minerals with contrasting Be/Al ratios were dissolved during different stages of alteration (i.e., chrysoberyl in the early stage giving rise to bavenite-rich compositions and beryl during late stage giving rise to bohseite-rich members). Second, chemical fractionation of Be and Al due to complexation by fluoride anions is suggested from negative correlation between Al and F in the studied members of the bavenite-bohseite series. Identical behaviour is observed also in bavenite-bohseite from Piława Górna and Maršíkov D6e pegmatites, suggesting potential importance of fluoride complexation during hydrothermal stage of evolution of granitic pegmatites.

Mineral assemblages and compositional variations in bavenite–bohseite from granitic pegmatites of the Bohemian Massif, Czech Republic

“…The measured concentrations of Al are critical for the discussion, whereas Na, Fe, Mn, P and F are of secondary importance as only trace amounts are usually present (Table 5). Data obtained during our study and from the published papers of Novák and Filip (2010), Dolníček et al (2020) and Zachař et al (2020) revealed high variability in Al (and Be) and significant heterogeneity of some samples (Fig. 4).…”

“…3f) whereas textural relations of bavenite-bohseite with associated albite, muscovite and quartz on fractures are not clear. They are likely fragments of the fracture surface where late bavenite-bohseite crystallised (see also Dolníček et al, 2020); however, euhedral shape of quartz grains (see Fig. 3e) indicates that it recrystallised during or slightly before the formation of bavenite-bohseite.…”

Chrysoberyl and associated beryllium minerals resulting from metamorphic overprinting of the Maršíkov–Schinderhübel III pegmatite, Czech Republic

“…The most fractionated pegmatites show an affinity to the LCT (lithium-caesium-tantalum) family and beryl–columbite subtype of the rare-element class according to the classification of Černý and Ercit (2005), as were documented by their mineral assemblages (e.g. Černý et al , 1992, 1995; Novák 1988, 2005; Novák et al , 2003, 2023; Chládek and Zimák, 2016; Chládek et al , 2020, 2021; Dolníček et al , 2020a, 2020b).…”