A wolframite-bearing greisen at Vykmanov, near Ostrov (Czech Republic) occurs at the contact of a small granite stock belonging to the Late Variscan Younger Intrusive Complex (YIC) of the Western Krušné hory/Erzgebirge pluton. The stock emerges as an outcrop of 0.8 × 0.3 km size from a hidden granite body in the eastern continuation of the Nejdek-Eibenstock granite massif. The lens-like greisen body consists mainly of quartz, topaz, protolithionite, and muscovite; it also contains wolframite (ferberite) and native bismuth mineralization. It was formed by replacement of a medium-grained, equigranular, slightly porphyritic Li-F granite of the Karlovy Vary pluton characterized by weak postmagmatic albitization and pervasive muscovitization. The greisen is geologically and compositionally transitional between the Li-rich greisens in albite granites (e.g. with zinnwaldite such as at Krásno) and the Li-poor greisens (e.g. phengite greisens at Gottesberg and Pøebuz) associated with weakly albitized granites of the Younger Intrusive Complex.
The Vykmanov greisen formed in a subsolidus stage of granite evolution by progressive alkali loss and fluorine metasomatism, leading to the formation of Li-mica quartz greisen subsequently replaced by topaz-quartz greisen at the granite/crystalline contact. These greisens were affected by late-stage muscovitization and argillitization (sericitization, the formation of clay minerals). The Li-Fe mica composition of the greisens corresponds to protolithionite (lithian siderophyllite) and is similar to the composition of micas in the enclosing granite.
The tungsten-bearing greisenization represents a postmagmatic episode in the development of the Krušné hory/Erzgebirge batholith, and is located at the eastern contact of highly evolved YIC granites of the Western Krušné hory pluton. The greisen formed from CO2-poor hydrothermal solutions, at about 400 °C, which evolved from highly saline brines as evidenced by fluid inclusion studies. The geological situation suggests that the mineralizing fluids were mostly magmatic and were responsible for the tungsten-bismuth specialization of the greisens, whereas meteoric waters participated in mineralization during later stages.

Key words: Krušné hory/Erzgebirge, ore-bearing granite, Variscan magmatism, greisen, feldspathite, protolithionite, ferberite, wall-rock alteration, tungsten mineralization
Bulletin of Geosciences, Vol. 80, No. 3, 163–184, 2005
© Czech Geological Survey, ISSN 1214-1119

Numerous specimens of the ankyroid Vizcainocarpus naimae sp. nov. (Stylophora, Echinodermata) have been found in middle Arenigian shallow-water, inner shelf, fine to medium grained siliciclastics of the Oum-er-Rbia Formation, located in the Imfout Syncline in Morocco’s western Meseta. Their occurrence in this sedimentary/ecological setting is atypical because ankyroids are most common in deeper water calcisiltites and limestones.

Aspects of orientation and feeding habits in the debate over stylophorans as echinoderms or calcichordates (ongoing since the 1960s) appear to be largely resolved by data derived from these specimens. The aulacophores of most specimens face into the prevailing sediment-depositing current and appear to have draped over the adjacent sand wave. There is no evidence that they were orientated in the calcichordate mode with the convex side of the theca facing down and aulacophore extending into the substrate, as proposed by Jefferies (1973, 1986, 2001) and Sutcliffe et al. (2000).

Key words: Echinodermata, stylophorans, Vizcainocarpus, middle Arenig, Imfout Syncline, Morocco
Bulletin of Geosciences, Vol. 80, No. 3, 185–192, 2005
© Czech Geological Survey, ISSN 1214-1119