Alpine eclogite-facies modification of Li-Cs-Ta pegmatite from the Wolfsberg lithium deposit, Austria

Abstract

The Wolfsberg lithium deposit in Austria is one of the largest Li-Cs-Ta pegmatite resources in Europe. The deposit is part of the Austroalpine Unit Pegmatite Province in the Eastern Alps that formed during the high-temperature, low-pressure Permian extensional event and was subsequently overprinted by Cretaceous eclogite-facies metamorphism during the Alpine orogeny. The two pegmatite types distinguished at the deposit, amphibolite hosted-(AHP) and mica schist hosted-(MHP) pegmatite, consist of quartz, albite, K-feldspar, muscovite and spodumene with accessory apatite, beryl and columbite. Both pegmatite types have similar peraluminous granitic compositions and element distribution patterns. However, the AHP contains higher Li and Cs concentrations. Both pegmatite types display LREE-enriched/HREE-depleted chondrite-normalized REY patterns that suggest derivation from partial melting of basement mica schist during the Permian HT/LP extensional event. The Alpine metamorphism more strongly affected the MHP relative to the AHP, resulting in recrystallization of primary assemblages by metamorphic assemblages with lower rare-metal concentrations, and development of a strong foliation, during which (re)mobilized elements (e.g., Li, Cs) were concentrated along localized shear zones. Recognition of element remobilization in MHP associated with metamorphic overprinting may bear important implications towards mineral exploration for Li-Cs-Ta pegmatite in other strongly metamorphosed terranes.