Fractionation of REE in the xenotime and florencite paragenetic association from Au-REE mineral occurrences of the Nether-Polar Urals.

A detailed survey of REE distribution in the xenotime and florencite paragenetic association from quartz veins of Au-REE mineral occurrences of the Nether-Polar Urals revealed maximum contents of Ce, Nd, Sm, Gd, Dy, and Y. Four of these elements form their own minerals: florencite-( Ce), -( Nd), and -( Sm) and xenotime-( Y) containing up to 25% GdO. The compositions of the minerals are isomorphous mixtures of two different groups: Yb (Y, Ho, Er, Yb, Lu, Nd, and As) and Gd (Gd, Tb, Dy, Eu, and Sm) in xenotime and La (La, Ce, Pr, Eu, and As) and Sm (Nd, Sm, Gd, Sr, Ca, and S) in florencite. Both minerals display strong heterogeneities in the distribution of isomorphous components and two types of zoning, oscillatory and trend. The crystal cores are enriched in HREE. Variations in the composition of isomorphous mixtures are accompanied by a change in the dominant crystal forms of florencite. Redeposited varieties are distinguished by homogeneous composition, the absence of impurities, and weak correlations between elements. The REE fractionation is interpreted in terms of quantum mechanics. [ABSTRACT FROM AUTHOR]