SOURCES OF RARE-EARTH ELEMENTS IN APPIN GROUP LIMESTONES, DALRADIAN, NORTHEAST SCOTLAND

Rare earth elements (REE) have been determined in 15 samples from thre e metamorphosed limestone units of the Appin Group of the Dalradian of north-east Scotland. Total REE contents range from about 7 to about 5 0 ppm and the light REEs are slightly enriched compared with REE in th e 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 pure r 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 h ave contributed significantly to the REE contents. Weak Ce anomalies o n NASC-normalised, REE variation diagrams in two samples with very low REE contents suggest a marine influence on the REE distribution.