RARE-EARTH ELEMENT CONCENTRATIONS AND SPECIATION IN ALKALINE LAKES FROM THE WESTERN USA

The rare earth element (REE) concentrations of lake water from five al kaline lakes (i.e., Mono, Walker, Abert, Summer, and Goose Lakes) with in the Great Basin of the western U.S.A. are reported. All of the lake s exhibit HREE-enriched shale-normalized patterns. The speciation of t he REEs was determined and, in all cases, species greater than 99% of each of the REEs exist as Ln(CO3)2-complexes. The only exception to th is is Summer Lake where minor amounts of phosphate species were also p redicted. The large enrichments in the HREEs observed in these lakes a re the result of the formation of stable carbonate complexes in soluti on where the HREEs preferentially form stronger carbonate complexes th an the LREEs. Activity product calculations for REE phosphate coprecip itates in these lakes indicate the lakes are close to saturation with respect to these phases and suggest that these precipitates may limit the maximum dissolved REE concentrations in the lakes.