GEOLOGY

Habachtal mine is in the Tuaern window where the tectonic contact between the Central gneisses (ortho-augengneisses) and Habac Formation (amphibolites, mica schist and black phyllites with interlayered serpentinites, part of the Untere Schieferhulle) occurs. Both formations belong to the lowest tectonic unit of Eastern Alps (Penninicum). The Habac formation is considered an alpine nappe above Central gneisses. (A nappe is a large sheetlike body of rock that has been moved far from its original position.)

Generally, classic schist-hosted emerald deposits are due to interaction between pegmatitic magma or vaphor phases with preexisting metasediments, metavolcanics and/or ultrabasic rocks. The Habachtal deposit, however, was formed during regional metamorphism in lithologies of  chromium-rich ultrabasic and beryllium-rich metapelites and metavolcanics and juxtaposed by pre- or synmethamorphic tectonism. This schist hosted emerald deposit is explained by a mutual interaction of a granitic fluid phase and a melanocratic basic rock. Classified, according to Sinkankas, as an exomethamorphic cause the major compound to form beryl are derived from granitic pegmatites and then transferred to the adjoining basic rock. The emerald mineralization is located in a sequence of metasomatic blackwall zones developed between a series of metamorphosed pelites, mafic volcanics and ultramafics. The emeralds are predominantly in biotite, chlorite actinolite and talc schist. Habachtal deposit is very similar to an emerald deposit of the same type in the Urals.