The Julianna pegmatite vein system at the Piława Górna Mine, Góry Sowie Block, SW Poland – preliminary data on geology and descriptive mineralogy

Abstract

The newly discovered Julianna pegmatitic system from the Piława Górna Quarry (the Góry Sowie Block, Sudetes Mts., NE margin of the Bohemian Massif) is described in terms of geological setting, petrography and descriptive mineralogy. The system represents the largest pegmatitic occurrence in the Polish Sudetes and consists of a complex network of cogenetic rare-element granitic pegmatites that intruded into tectonized amphibolite as discordant dikes. The pegmatites range from barren and weakly zoned to texturally well-differentiated ones that are composed of a fine-grained border zone, coarse-grained wall zone, graphic and blocky feldspar intermediate zones and a quartz core. Unidirectional and skeletal solidification textures are well-developed. The Julianna pegmatites consist of rock-forming plagioclase (ŁAn39), microcline, quartz and biotite accompanied mostly by accessory to minor muscovite, tourmaline, garnet and beryl. They crystallized from anatectic melt of hybrid NYF (niobium-yttrium-fluorine) + LCT (lithium-cesium-tantalum) geochemical characteristics. Pegmatites with a low to moderate degree of fractionation, that dominate in the Julianna system, bear NYF-signature accessory minerals, such as allanite-(Ce), columbite-, euxenite- and samarskite-group minerals, fergusonite-(Y) and gadolinite-(Y). However rare dikes that attained a very high degree of fractionation contain typical minerals of LCT-signature including tourmalines of the elbaite-olenite-rossmanite series, lepidolite, lithiophilite, spodumene, Cs-rich beryl and pollucite.