Rare-earth, yttrium and zirconium mobility associated with the uranium mineralisation at Okrouhla Radoun, Bohemian Massif, Czech Republic

The mobility of rare-earth elements (REE), Y and Zr during the Late-Variscan and post-Variscan mineralisation event in the Okrouhla Radoun uranium deposit has been investigated to elucidate their behaviour during the hydrothermal alteration of leucogranites and high-grade metamorphic rocks in the Moldanubian Zone (Bohemian Massif). The alteration of leucogranites has caused enrichment in Na, Ca, Fe3+, Zr and the bulk of REE while depleting K, Fe2+, Si, Th, Rb and Ba. The alteration of high-grade metasediments has also led to an enrichment in Na and Ca while depleting K, Si, Rb and Ba. However, this change is connected to the depletion of REE, as well as the enrichment of P and Th in the bulk. The high mobility of Y and Zr during formation of the uranium mineralisation is supported by the occurrence of Y- and Zr-rich coffinite (up to 3.4 wt.% Y2O3 and 13.8 wt.% ZrO2). The massive hydrothermal alteration of host rocks, as well as the high mobility of REE, Y and Zr indicate an influx of oxidised basinal fluids in the Permian to the crystalline rocks of the Moldanubian Zone.