UNUSUAL (Na,Mg)-ENRICHED BERYL AND ITS BREAKDOWN PRODUCTS (BERYL II, BAZZITE, BAVENITE) FROM EUXENITE-TYPE NYF PEGMATITE RELATED TO THE OROGENIC ULTRAPOTASSIC TREBIC PLUTON, CZECH REPUBLIC

Abstract

Intragranitic, euxenite type NYF pegmatite Kožichovice II derived from ultrapotassic orogenic Třebic Pluton (syenogranite) contains pale green prismatic crystals of primary beryl Ienclosed in massive quartz. Beryl I is locally altered to the secondary mineral assemblage beryl II + bavenite + bazzite + smectite. Secondary mineral assemblage after beryl I including common bavenite and elevated Ca in bazzite suggest high activity of Ca in late fluids. The temperature slightly below 250 to 350 C and neutral to slightly alkaline conditions for the formation of the secondary assemblage are suggested.