YREE QUANTITIES, ENRICHMENT, AND DISTRIBUTION IN KARST SPRINGS AND COAL MINE DISCHARGES

Rare earth elements and yttrium, commonly referred to as YREE, are of interest as environmental tracers and as potential economic resources. Studies have used YREE to “fingerprint” hydrogeological flow systems, study mixing in estuaries, and to gain insight into a wide variety of geochemical processes. Two common settings for YREE research are coal mine drainage and karst water systems. By comparing the YREE distribution, enrichment/depletion trends, and overall concentrations of these two dissimilar systems, a deeper insight into YREE sources and geochemical processes can be explored.

Water chemistry was compared between mine waters and karst water systems for total concentrations and distribution patterns relative to the North American Shale Composite (NASC). The coal mine sites include flow from a down-dip mine (pH 3-5.5) and from a wetland downstream of a portal (pH 4-5); the karst sites include surface waters, springs, tufa-depositing sites, and warm springs. In general, the coal mine waters tend to have a greater total YREE concentration by at least one order-of-magnitude and have different enrichment and distribution trends than found in the karst waters. The coal mine waters are generally enriched in the middle REE (i.e. Eu, Gd, Tb, Dy, and Y) with a slight depletion of Ce and La and a slight enrichment of Y, Gd and Eu. The karst waters tends to be enriched in Y and depleted in Ce. Karst waters also generally enriched in middle REE, largely due to their sizeable Y enrichment.

Comparison of the YREE concentrations and distributions in these two datasets helps to identify the water sources and flowpaths. Whereas many studies focus on one water type, looking at different systems simultaneously provides a better understanding of the mechanisms of YREE mobility.