Axinit a doprovodné minerály z lokality Jezuitský rybník východně od Golčova Jeníkova (moldanubikum, Česká republika)

Abstract

A new occurrence of axinite at the locality Jezuitský rybník near Sirákovice (ENE from Golčův Jeníkov), situated in rocks of the Variegated (Drosendorf) Series (Moldanubian Zone of the Bohemian Massif), is a nice example of contaminated pegmatite in a Ca-skarn with intense superimposed hydrothermal overprint. Axinite [axinite-(Fe) to axinite-(Mg)] forms young hydrothermal infill of pocket/fissure in pegmatite cutting a brecciated Ca-skarn. The hydrothermal assemblage includes amphibole II (actinolite to ferro-actinolite), albite, K-feldspar II, chlorite, epidote (locally containing 0.20 - 0.30 apfu REE), muscovite and Al,F-enriched titanite (with up to 2 % SnO2) passing exceptionally to unnamed CaAlFSiO4. Quartz, plagioclase (andesine), K-feldspar I and amphibole I (mostly K-rich or even potassian ferro-pargasite to ferro-tschermakite) originated in magmatic stage associated with intrusion of externally derived pegmatite melt. Sporadic garnet (grossular-rich almandine) represents relics of mineral assemblage of the host skarn. Dominance of Nd among REE in the REE-rich epidote is explained in terms of chemical fractionation of REE, probably caused by the presence of strong REE-complexing ligands (F-, OH- and/or CO32-) in aqueous fluids enriched in MREE/HREE due to alteration of garnet. With regard to the presence of B, Cr and elevated XMg in some hydrothermal phases compared to the older Fe-Mg minerals, we suggest circulation of fluids affecting host rocks as well as additional rock types.