Rare-earth elements in geothermal waters from Oregon, Nevada, and California

Abstract

The concentrations of rare-earth elements (REE) were determined in thermal waters from hot springs in the Oregon Cascades and southeastern Oregon, and from wells in the Beowawe (NV), Dixie Valley (NV) and Heber (CA) geothermal fields. The waters are all near-neutral to slightly alkaline, and dominated by sodium chloride or sodium bicarbonate. Concentrations of REE range from <10−6 to approximately 10−3 times chondrite. In general, filtered aliquots of the fluids contain substantially less REE (sometimes by an order of magnitude or more) than corresponding unfiltered aliquots, suggesting a considerable particulate contribution to the total REE. Concentrations of REE in the waters from Beowawe and Dixie Valley are generally quite low, possibly owing to loss of REE on boiling. Most of the waters exhibit LREE-enriched, chondrite-normalized REE patterns, with slight or non-existent Eu anomalies. The main exceptions are the waters from Heber, which exhibit a concave-upward pattern with a prominent, positive Eu anomaly (“Mexican hat” pattern). The behavior of REE in waters from continental geothermal systems is a useful indicator of water–rock interaction and holds promise as a potential tool for exploration.