Journal of

GEOsciences

  (Formerly Journal of the Czech Geological Society)

Original Paper

Edvín Pivec, František V. Holub, Miloš Lang, Jiří K. Novák, Miroslav Štemprok

Rock-forming minerals of lamprophyres and associated mafic dykes from the Krušné hory/Erzgebirge (Czech Republic)

Journal of the Czech Geological Society, volume 47 (2002), issue 1-2, 23 - 34

Electron microprobe analyses were made on micas, amphiboles, feldspars, chlorites and accessory minerals in lamprophyric dykes (kersantites, minettes, spessartites), and in associated mafic diorite to tonalite porphyries (porphyrites) of the Krušné hory (Erzgebirge) area and Mariánské Lázně region in Western Bohemia (Czech Republic). All studied rocks are altered to various degrees during deuteric and/or postmagmatic stages of evolution. The only primary mafic mineral preserved in all rock types is Mg-biotite to phlogopite, in spessartites and some diorite porphyries also Ti-rich hornblende corresponding to titanian magnesiohastingsite to kaersutite. Magmatic biotites are relatively rich in Ti with limited variations in their Mg/Fe ratios, evidently re-equilibrated during cooling or re-heating. Olivine is totally replaced by pilitic pseudomorphs and by biotite-actinolite clots. Phenocrystic clinopyroxene is completely uralitized, often in well-preserved original shapes. The secondary amphiboles correspond to Si-rich magnesiohornblende to actinolite. Chlorite and epidote are rather scarce and their important occurrences are restricted to limited number of samples. Instead of chloritization typical of lamprophyres in other parts of the Bohemian Massif, most samples are affected by secondary biotitization. Effects of greisenization sensu stricto were observed in some lamprophyres from Krupka where Li-bearing dark micas rich in Si and Mg originated.