Minerály pegmatitových hnízd z okolí Jablonce nad Nisou (krkonošsko-jizerský pluton) - část I. silikáty

Abstract

We have studied silicate minerals in pegmatite nests from the Tanvald Granite (4 sites) and the Liberec Granite (1 site) in the vicinity of Jablonec n. Nisou, situated within the Variscan Krkonoše-Jizera Pluton. They contain major quartz, K-feldspar and plagioclase (An0-11), subordinate biotite, muscovite and locally schorl. Accessory phases include garnet (spessartine-almandine), andalusite, Hf-rich zircon and thorite. In addition, zinnwaldite was found in a single sample. The studied pegmatites show simple internal structure including aplitic, granitic and coarse-grained “blocky” units; the central zone commonly contains miarolitic cavity which is sometimes filled by tourmaline. The mineral composition and fractionation degree largely reflect those of the host granite; the more fractionated are pegmatites hosted by the Tanvald Granite. The pegmatite nest from Nová Ves nad Nisou II exhibits distinct mineral assemblage with zinnwaldite, pure albite and lack of biotite and garnet, therefore we suggest here a substantial modification of mineral assemblage by superimposed processes. Moreover, tourmaline (schorl) composition with local increasing of Mg toward rim indicates a possible contamination derived from adjacent rocks during tourmaline crystallization.

Fluid Evolution of Greisens from Krupka Sn-W Ore District, Bohemian Massif (Czech Republic)

“…; [40,41]). Compared to other localities with Sn-W or W mineralization, the non-aqueous phase in the fluid inclusions from Krupka shows a wider compositional range compared to the W mineralization from Tanvald granite from Jablonec nad Nisou [56], where CO 2 is always the dominant phase, and fluids have similar salinities (0-4.6 wt. % NaCl eq.).…”

“…The composition of the non-aqueous phase in the fluid inclusions suggests two possible trends, although the amount of data is small. One of these trends is already considered in [56] for W mineralization in Tanvald granite. In the primary inclusions from Krupka and from other Sn-W and W localities in the Bohemian Massif, a CO 2 -rich fluid is probably mixed with fluids with very similar CH 4 :N 2 ratios.…”