Acta Musei Moraviae

Mineralogy of Th-rich granites and granodiorites from the Eastern margin of the Thaya Terrane in Brunovistulicum (Brno Batholith)

The slight positive Th-anomaly detected by the airborne gamma-ray spectrometry in the rocks Tetčice Suite at the western part Brno Batholith was confirmed by the field measurements. Irregular spatial distribution of Th in the biotite granites and amphibole-biotite granodiorites reflect complicated evolution including assimilation of metamorphic rocks, magma mixing and mingling. Granites and granodiorites with maximum content of Th are predominantly present near the boundary with the wall rocks of the batholith. The most important carriers of Th and U in the rocks Tetčice Suite are zircon, xenotime-(Y), thorite and allanite-(Ce). Contents of Th and U in another common accessory minerals such as apatite and titanite are below the detection limit of WDS electron-microprobe. The high content of Th in the biotite granites is related to presence of thorite, while the main carrier of Th in the amphibole-biotite granodiorites is allanite-(Ce).