(Austria) and Leydsdorp (Transvaal, South Africa) Deposits

Classic schist-hosted emerald deposits are generally attributed to interaction between in-vading pegmatitic magma or vapor phases with preexisting metasediments, metavolcanics, and/or ultrabasic rocks. Detailed studies of the I-Iabachtal (Austria) and Leydsdorp (South Africa) emerald deposits indicate that the emerald formation was not due to a single-stage contact metamorphism at the border zone of magmatic intrusive bodies. On the contrary, the emeralds are found in metasomatic zones (blackwall zones) associated with ultramafic bodies formed by syn- to post-tectonic reactions during low-grade regional metamorphism. These reactions occur at the contact of preexisting beryl- and phenakite-bearing pegmatites and albitite pegmatoids with biotite-talc and actinolite schists (Leydsdorp), or at the contact of beryllium-rich garnet-mica schists and biotite-plagioclase-gneisses with serpentinites and talc-schists (Habachtal). Critical evidence for the regional metamorphic origin of emeralds includes the following points: 1. Augen textures occur in the metagranitic and metapegmatitic ountry rocks