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

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.

Mesozoic Tectonomagmatic Evolution and Gold Metallogeny in Jiaodong Area, East China

There were twice major collision orogenic events in Jiaodong area in Mesozoic period. It showed as three times of magmatic activities and stretching in Jiaodong area. In this paper, based on collecting age datas, referring to the previous classification scheme, a chronological frame pattern of Yanshanian granites had been put forward: Linglong-Kunyushan granite emplacement was in in 160~150Ma; the formation of Guojialing granodiorite was in 130~126Ma; Weideshan granodiorite-granite emplacement was in 120~110Ma; Laoshan A-type miarolitic cavity parlkaline alkali feldspar granite emplacement was in 110~100Ma and represented the end of Yanshan movement. Gold mineralization in three periods in this area had coupled relation with Linglong-Kunyushan granite, Guojialing granodiorite and Weideshan granodiorite-granite. Jiaodong tectonic-magmatic events and gold mineralization were controlled by the interactions among Tethyan tectonic domain, Paleo-ocean tectonic domain and the Pacific tectonic domain.

Xenotime-(Y) and Sn-rich thortveitite in miarolitic pegmatites from Baveno, Southern Alps, Italy

Xenotime-(Y), (Y,REE)PO4, and thortveitite, (Sc, Y)2Si2O7, in a miarolitic cavity in a niobium, yttrium, fluorine (NYF) granitic pegmatite at Baveno, Verbania, Southern Alps, Italy, were investigated by electron microprobe analysis and single-crystal X-ray diffraction. Fluorine has an important role as a complexing agent for Y and REEs in supercritical pegmatitic fluids; annitesiderophyllite and chamosite are the most likely sources of the Y and REEs. The thortveitite from Baveno contains up to 3.20 wt.% SnO2, an unusually high Sn content. Xenotime-(Y) is enriched in Gd in comparison to other Alpine xenotimes. Quantitative chemical data and measurements of the lattice parameters show that a higher scandium content results in a smaller unit-cell volume in thortveitite. The substitution of REEs for Y up to ∼20 mol.% has little effect on the unit cell of xenotime-(Y). The textures of xenotime-(Y) and thortveitite provide information about the dissolution and crystallization processes in the miarolitic cavity.

A new Czechoslovak occurrence of stokesite

SummaryThe third occurrence of stokesite was discovered in a desilicated pegmatite at Věžná, Western Moravia. In this locality, stokesite accompanies columbite, cassiterite, and stibian pyrochlore-microlite, in a miarolitic cavity of albite. The X-ray data and the optical properties of the Věžná stokesite agree well with those observed by previous authors.