Rare earth deposits associated with carbonatites: little-known stats and facts every explorationist should know

English Abstract:

There are three principal types of rare-earth deposits associated with carbonatites, listed in order of decreasing historical importance: (1) primary magmatic, (2) supergene, and (3) hydrothermal-metasomatic. Primary magmatic deposits have been of historic significance, but are gradually giving way to supergene sources containing higher grades and a relatively larger proportion of heavy REE. Primary REE deposits are scarce for reasons that we are just beginning to understand and place in a global geodynamic context. Phosphorus cycling through mantle sources of carbonatitic melts and early apatite fractionation from these melts appear to figure prominently in REE metallogeny. For purely subjective reasons, igneous provinces that should have been at the forefront of REE exploration activities, have been largely neglected. Hydrothermal reworking of carbonatites has a significant effect on their REE budget, and is generally conducive to the development of high-grade, but localized mineralization. Development of hydrothermal-metasomatic deposits is hampered by their typically small size and mineralogical factors, such as elevated contents of REE-Ca(± Sr, Ba) carbonates. Supergene deposits in (reduced) laterites have very favorable economic parameters, but pose greater metallurgical challenges. Contrary to the popular opinion, carbonatite-hosted projects can compete with other bedrock deposit types in the critical REE market.