Abstract
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.
Highlights
Xenotime-(Y) is a tetragonal orthophosphate of Y and heavy rare earth elements that can incorporate some U and Th (Ni et al 1995)
Identification of minerals observed in scanning electron microscope (SEM) was based on chemical composition determined by energy-dispersive X-ray spectrometry (EDS) using NORAN Vantage analyser
Lamination of the rock is clearly visible under optical microscope due to differences between laminae colours in transmitted light ranging from grey to brown tones
Summary
Xenotime-(Y) is a tetragonal orthophosphate of Y and heavy rare earth elements that can incorporate some U and Th (Ni et al 1995). Its applications are especially promising in Precambrian suits, where fossils are not preserved, and in lower temperature environments where reliable dating methods are scarce.While hydrothermal veins containing crystals of xenotime-(Y) appear to be quite common, few authors mention veinlets of xenotime-(Y) filling fractures in zircon grains (Kositcin et al 2003), apatite (Rojkoviè et al 1999), pegmatitic feldspar (Michalik, Szuszkiewicz 2003) and U-Ti oxides (Rojkoviè, Koneèný 2005). This contribution reports the first occurrence of xenotime-(Y) veins in a Neoproterozoic metamudstone from Poland and discusses their possible genesis.
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