Rare earth elements and yttrium in ferromanganese deposits from the South China Sea: distribution, composition and resource considerations

Ferromanganese nodules and crusts contain relatively high concentration of rare earth elements (REE) and yttrium (REY), with a growing interest in exploitation as an alternative to land-based REY resources. On the basis of comprehensive geochemical approach, the abundance and distribution of REY in the ferromanganese nodules from the South China Sea are analyzed. The results indicate that the REY contents in ferromanganese deposits show a clear geographic regularity. Total REY contents range from 69.1×10^–6 to 2 919.4×10^–6, with an average value of 1 459.5×10^–6. Especially, the enrichment rate of Ce content is high, accounting for almost 60% of the total REY. This REE enrichment is controlled mainly by the sorption of ferromanganese oxides and clay minerals in the nodules and crusts. Moreover, the total REY are higher in ferromanganese deposits of hydrogenous origin than of diagenetic origin. Finally, Light REE (LREE) and heavy REE (HREE) oxides of the ferromanganese deposits in the study area can be classified into four grades: non-enriched type, weakly enriched type, enriched type, and extremely enriched type. According to the classification criteria of rare earth resources, the Xisha and Zhongsha platform-central deep basin areas show a great potential for these rare earth metals.