NOVÝ VÝSKYT SKARNU V GFÖHLSKÉ JEDNOTCE U VEVČIC U JEVIŠOVIC: MINERÁLNÍ ASOCIACE SKARNU A KONTAMINOVANÝCH AMFIBOLICKÝCH PEGMATITŮ

Abstract

This work provides detailed information about a new occurrence of skarn near Vevčice (near Jevišovice, western Moravia), which is one of the most important outcrops of these rocks in the southeastern part of the Moldanubian Zone (Gföhl Unit). The skarn is characterized by a strong migmatization, which resulted in contaminated amphibole pegmatite veins penetrating the skarn. The mineral assemblage of the skarn is simple, with dominant garnets, both grossular-almandine (Alm55–57 Grs31–37 Adr3–8) and grossular-andradite-almandine (Grs45–53 Adr20–34 Alm20–24). Garnets clearly predominate over clinopyroxene, hedenbergite with a slightly increased “fassaite component”. The very low amount of quartz contrasts with that in the skarns in the surrounding Gföhl unit. Amphibole (potassium-rich hastingsite) is younger mineral in the skarn, and especially in contaminated pegmatites. Epidote after garnets, and eventually prehnite, belong to the youngest minerals in some types of rocks. Accessory titanite, sometimes rich in Sn, was found frequently, as well as metamict REE-rich epidote. Magnetite is rather exceptional, mainly in assemblages replacing garnet; fluorapatite, ilmenite and zircon are rare. The studied skarn is part of a lithologically varied sequence of the Gföhl Unit, with intercalations of Ca-metasediments, appearing in several non-contiguous horizons around the boundary of so-called Běhařovice-Vémyslice synform, with a granulite–serpentinite complex in its center. This sequence of strongly migmatized biotite paragneiss to leucocratic migmatites also contains diopside and scapolite-diopside gneiss, garnet-pyroxene and phlogopite-diopside skarns containing magnetite and exceptionally Au-Co-Bi and REE mineralization as well as rare occurrences of spinel-forsterite dolomitic marbles.