Xenotime-(Y) veins in a Neoproterozoic metamudstone (Małopolska Block, S Poland)

First occurrence of xenotime-(Y) veins in the Neoproterozoic metamudstone, NW margin of the Małopolska Block, is reported here. The veins are <5 μm thick, inhomogeneous and of varied morphology. Their textural characteristics, exhibiting very low U and Th contents (<1 wt%) and relatively high heavy rare earth elements (REE) contents (12-24 REE₂O₃ wt%), suggest hydrothermal genesis, though diagenetic precursors of the veins are not excluded. The veins provide good evidence of the mobility of Y, REE, U and Th in low-temperature conditions (anchimetamorphic to greenschist facies). The observed differences in the chemical composition of the veins may indicate multiple stages of formation, possibly during several hydrothermal events that affected the area.