Fractionation of the REE during hydrothermal processes: constraints from the Bayan Obo Fe-REE-Nb deposit, Inner Mongolia, China.

The composition of REE minerals from the Bayan Obo Fe-REE-Nb deposit, China, varies widely with paragenesis. The properties of fluid inclusions also vary with paragenesis, indicating changing fluid conditions during the deposits formation. In early disseminated monazite and in the main stage banded ores, the chondrite normalised La/Nd ratio varies from ∼3 to 7, whilst vein-hosted bastnäsite and monazite show ratios in the range ∼4.8 to 5.8. The...