Rare earth elements in rift-hosted ferromanganese nodules, Malawi, Central Africa

Ferromanganese nodules from Lake Malawi have been analysed for 13 rare earth elements by ICP mass spectrometry. Total REE levels are considerably higher than previously reported for lacustrine or continental margin nodules and shale-normalised profiles display many characteristics commonly associated with deep ocean concretions. While shale-normalised REE values for the nodules exceed 1.0 across the entire REE spectrum, the surrounding lake muds are enriched only in LREE. Significant fractionation, involving the preferential assimilation of HREE during nodule growth is thus inferred. The nodules are also characterised by positive Ce and negative Tb anomalies, generally consistent with REE incorporation through redox-mediated exchange processes.