Rare earth elements in sovitic carbonatites and their mineral phases

Abstract

Rare earth element (REE) concentrations were analysed by atom emission spectrometry (ICP-AES) in whole-rock samples and mineral separates of plutonic carbonatites from different localities. Calcite, dolomite, apatite, and unaltered pyrochlore show parallel to subparallel REE distribution patterns at different enrichment levels. The REE distribution in the whole rocks is controlled by that of the carbonates because of their high modal amounts and by that of apatite because of its high REE abundances. REE-rich accessory phases such as pyrochlore will influence the whole-rock pattern only when present in sufficient amounts. On the basis of variations in REE distributions and mineral chemistry, several groups of sovites can be distinguished among the samples studied here. The highest REE concentrations and the strongest light REE (LREE) enrichment is found in sovites from Oka, Kaiserstuhl, and Alno that contain Mg-poor calcites, Si-rich apatites and Ca-bearing silicates. These sovites are associated with melilititic or nephelinitic rocks. Less pronounced LREE enrichment is found in sovites, dolomitic carbonatites and phoscorites from Sokli, Siilinjarvi, Phalaborwa, Jacupiranga and Fen, which contain Mg-rich calcites and/or dolomite, Si-poor apatite and Mg,Fe-silicates (olivine, phlogopite). These carbonatites are associated with potassium-rich peralkaline ultramafic rocks and lamprophyres.