ABSTRACT
Greisenized lamprophyres were studied in the contact zone of the eastern Krušné hory-Erzgebirge granite pluton in the Krupka Sn-W ore district, Czech Republic. These rocks consist mainly of Libearing biotite, topaz and fluorite and correspond petrologically to metasomatic glimmerites poor in quartz, in contrast to quartz-rich greisens produced by the same process in underlying granitoids or enclosing migmatites. The differences in mineral assemblage formed by greisenization were observed also in an en masse greisenized intrusive breccia of lamprophyre fragments cemented by a microgranite (aplite) matrix. Despite of total recrystallization and some compositional changes of biotite, the sharp contrasts in mica compositions between greisenized lamprophyres and surrounding acidic rocks is maintained. During greisenization, K, Rb, Cs and Li which can be accommodated in biotite are enriched whereas Ca, Na and Sr are significantly decreased. Not only the Al but also Si, Fe and Mg are almost constant in lamprophyres up to very progressed stage of greisenization. Relatively high contents of Sn in moderately altered lamprophyres from the Krupka district appear to be spatially unrelated to tin mineralization. They could be due to a high sensitivity of lamprophyres to postmagmatic alterations and elemental enrichments. However, at least a part of increased Sn could reflect the enrichment processes in the mantle sources of lamprophyric magmas.
