Journal of

GEOsciences

  (Formerly Journal of the Czech Geological Society)

Original Paper

Milan Novák, Stanislav Houzar, Vladimír Šrein

Gahnite-bearing marbles and their significance for regional classification of the eastern part of the Bohemian Massif

Journal of the Czech Geological Society, volume 42 (1997), issue 1-2, 33 - 40

Gahnite-bearing marbles in the Polička Unit and in the Hraničná Group were recognized as a distinct mineralogical and geochemical type of the marbles within the Bohemian Massif, typically rich in Zn and Mn (Fe). Gahnite seems to be the important Zn-carrier. Conditions of its origin are not explained sufficiently due to the simple mineral assemblages Cal+Dol+Tr+Phl+Di and its large stability field. The likely process of gahnite formation seems to be its crystallization from Zn, released during metamorphism from carbonate minerals, under conditions of a relatively high activity of Al in metamorphic fluids. Remarkably similar features of the studied marbles - lithology, chemical and mineral compositions, similar sulphide and Fe-oxide minerals, concentration and composition of gahnite - suggest the Polička Unit is closely related to the Hraničná Group (Staré Město Unit). Consequently, the Polička Unit may be lithologically a part of the Lugicum, which includes the Hraničná Group (Staré Město Unit).