Sources of rare earth elements in Appin Group limestones, Dalradian, north-east Scotland

Abstract

Rare earth elements (REE) have been determined in 15 samples from three metamorphosed limestone units of the Appin Group of the Dalradian of north-east Scotland. Total REE contents range from about 7 to about 50 ppm and the light REEs are slightly enriched compared with REE in the North American Shale Composite (NASC). In the more impure limestones, the dominant control on REE content was the clay mineral content in siliciclastic impurities derived from terrestrial sources. In the purer limestones, the correlation between REEs and iron is consistent with the well-documented relationship between iron and REEs in the aqueous environment. REE associated with terrestrial, iron-rich, flocculated organic colloids or marine, authigenic iron-manganese coats may well have contributed significantly to the REE contents. Weak Ce anomalies on NASC-normalised, REE variation diagrams in two samples with very low REE contents suggest a marine influence on the REE distribution.