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Geochemical Journal
Geochemical Journal An open access journal for geochemistry
Published for geochemistry community from Geochemical Society of Japan.

Rare earth element abundances in high phosphorus and low iron groundwaters from the Nishinomiya district, Japan: Variations in Ce anomaly, redox state and heavy rare earth enrichment

Michiyo Otsuka, Yasutaka Terakado
Geochemical Journal, Vol. 37, No. 1, P. 1-19, 2003


High phosphorus and low iron-content groundwaters from the southern Nishinomya district (Miyamizu groundwater), Japan, were analyzed for rare earth element (REE) and some major element concentrations. The chondrite-normalized REE patterns of these groundwaters are characterized by strong heavy REE enrichments relative to light REE, and slight-to-moderate negative Ce anomalies. The magnitude of Ce anomaly increases with decreasing Fe and increasing NO3- contents and pH. Such correlations are explained by the redox changes with depth in the area. The heavy REE inclinations of the chondrite-normalized REE patterns correlate positively with Ca and Mg contents and negatively with Fe contents. Heavy REE enrichment is explained by successive water-rock interactions supplying REE to the water in which differential scavenging of light REE by particulate matters occurs. The high P characteristic is achieved by the decomposition of biogenic materials under oxidizing conditions. The low Fe concentration of these groundwaters is ascribed to precipitation of Fe-hydroxides and their subsequent filtration as groundwater flows through the aquifer. The low P and high Fe groundwaters are thought to originate from a deeper aquifer experiencing reducing conditions. The unique geochemical characteristics of the groundwaters of the study area may be closely related to a peculiar geological situation in which an organic-rich layer is seated at relatively shallow depths within an aquifer of relatively large permeability.

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