REE and Y Mineralogy of the Krudum Granite Body (Saxothuringian Zone)

Abstract

The Krudum granite body comprises highly fractionated granitic rocks ranging from medium-F biotite granites to high-F, high-P2O5 Li-mica granites. This unique assemblage is an ideal site to continue recent efforts in petrology to characterize the role of zircon, monazite and xenotime as hosts to REEs. The granitic rocks of the Krudum body analysed in this study were found to contain variable concentrations of monazite and zircon, while xenotime was only found in the high-F, high-P2O5 Li-mica granites and in the alkali-feldspar syenites of the Vysoký Kámen stock. For analysed monazites of all magmatic suites cheralite substitution was significant. The highest concentration of cheralite was found in monazites from the high-F, Li-mica granites and from the alkali-feldspar syenites. The proportion of YPO4 in all analysed xenotimes ranges from 71 to 84 mol. %. Some xenotimes were found to be hydrated and the observed water content estimated from analytical data ranged from 5 to 11 wt. % H2O. Preprints (www.preprints.org) | NOT PEER-REVIEWED | Analysed xenotimes were commonly enriched in HREEs (9.3-19.5 wt. % HREE2O3) and thorite-coffinite and cheralite exchange was observed. Analysed zircons from granite suites of the Krudum granite body contained moderate Hf concentrations (1.0-4.7 wt. % HfO2; 0.010-0.047 apfu Hf). The highest concentrations of HfO2 were found in zircons from the high-F, high P2O5 Li-mica granites (1.2-4.7 wt. % HfO2) and from the alkalifeldspar syenites (1.3-4.1 wt. % HfO2). Zircons from the high-F, high-P2O5 Li-mica granites were often hydrated and fluorised. The concentrations of F in zircon from partly greisenised high-F, high-P2O5 Li-mica granites reached up to 1.2 wt. % (0.26 apfu F). In zircons from the alkali-feldspar syenites enrichment in P, which is not associated with a simultaneous enrichment in Y + REE, was also observed. Analysed zircons from the high-F, high P2O5 Li-mica granites were enriched in Y (up to 5.5 wt. % Y2O3; 0.10 apfu Y) and Sc (up to 1.17 wt. % Sc2O3; 0.03 apfu Sc).