Carbonatites and carbonatite-related rocks are the premier source for light rare earth
element (LREE) deposits. Here we outline a simplified ore formation model for LREE
mineralised carbonatites, reconciling field and petrological observations with recent
experimental and isotopic advances. REE can strongly partition to carbonatite ...
Carbonatites and carbonatite-related rocks are the premier source for light rare earth
element (LREE) deposits. Here we outline a simplified ore formation model for LREE
mineralised carbonatites, reconciling field and petrological observations with recent
experimental and isotopic advances. REE can strongly partition to carbonatite melts, which
are either directly mantle-derived or immiscible from silicate melts. As carbonatite melts
evolve, alkalis and REE concentrate in the residual melt due to their incompatibility in early
crystallising minerals. In most carbonatites, additional fractionation of calcite or ferroan
dolomite leads to evolution into a mobile alkaline “brine-melt” from which primary alkali
REE carbonates can form. These carbonates are rarely preserved owing to dissolution by
later fluids and are replaced in-situ by monazite and alkali-free REE-(fluor)carbonates.