Lanthanide Abundances in Coexisting Skarn Minerals, as Determined by X-Ray Fluorescence Analysis

Abstract

<p> A method is presented for the determination of trace quantities of the rare earth elements and yttrium in calcareous minerals by X-ray fluorescence analysis. Initial chemical concentration of the rare earths is accomplished by scavenging their insoluble hydroxides on a ferric hydroxide precipitate and serves the further purpose of elimination of matrix absorption effects which dampen sensitivity when the raw minerals are analysed.</p> <p> Triplicate analyses are given for La, Ce, Sm and Y in a calcite-fluorite-apatite skarn rock and for each of the three minerals of this rock. Apatite and calcite are enriched in all the rare earths investigated relative to the whole rock, while fluorite shows a relative depletion. The apatite is enriched in the rare earths relative to the calcite. Peak height ratios of Nd, Eu, Er, Lu, Gd+Ho and Dy+Tm in each of the separated minerals to the whole rock show the same trends as the quantitative data and also indicate that apatite and fluorite show a stronger affinity for the lanthanides of low atomic number than for those of higher atomic number. The abundances of the rare earths in the apatite show the same dependence on ionic radius as has been noted by other workers. The whole rock and each of the minerals which it contains are enriched in all the rare earths relative to chondrites.</p> <p> The rare earths have preferentially entered the lattices of those minerals which provide a stronger rare earth-anion bond.</p>