Origin of topaz-granite of the Krudum granite body


Grant No.:


Grant Agency:

Czech Science Foundation (GAČR)

Resolved in:

2009 - 2011

Principal investigator:

RNDr. Miloš René, CSc.,


Dr. Jaromír Leichmann, PhD., Masaryk University, Faculty of Science
Dr. Vojtěch Janoušek, PhD., Czech Geological Survey
Dr. Zuzana Kratinová, PhD., Insitute of Geophysics ASCR
Dr. Zdeněk Dolnicek, PhD., Palacký University Olomouc, Faculty of Science


The Krudum granite body represents a reversely-zoned intrusion with the oldest, least fractionated biotite granite in the centre, surrounded to the NW by younger topaz-bearing, two-mica granite. The youngest, topaz–albite granite forms the outermost shell. From geochemical point of view, all these are subaluminous to strongly peraluminous (leuco-) granites which form a compositional continuum. Going from biotite to topaz–albite granites, the A/CNK and Rb values increase, whereas the Ti, Fe, Mg, K, Ba, Sr, Th, Zr and REE contents with K/Rb, Ba/Sr and Zr/Hf ratios drop dramatically. The inverse major- and trace-element modelling indicates that the observed trends in barren granites can be explained by extensive (~40–60 %) fractionation driven mainly by K-feldspar. Important role of accessory minerals, most importantly zircon and monazite, is clear in view of the sharp decrease in Zr and REE contents with fractionation. Two distinct magmatic fabrics have been recognized based on AMS measurements. The dominant one, present in all granite types, is subhorizontal with distributed shallow-dipping lineations. Steep WNW–ESE trending magnetic foliations with subhorizontal lineations, characterizes the minor fabric developed mainly in two-mica granite. Fluid evolution of the Horní Slavkov–Krásno Sn–W ore district records almost continuously the post-magmatic cooling history of the granite body from 500 to 50 C. The greisenization was related to near-critical low salinity (0–7 wt% NaCl eq.) aqueous fluids. Nb–Ta-bearing rutile and columbite-group minerals represent the most common Nb–Ta hosts in topaz–albite granites. Tungsten-bearing columbite-(Fe), W-bearing ixiolite, wodginite and tapiolite-(Fe) are extremely rare in these rocks.