Apatite-rich inclusions in some basaltic rocks from eastern Australia are interpreted as mantle crystallization products of a carbonatitic/kimberlitic fluid enriched in low atomic number rare earth elements (l.r.e.e.), and are a priori evidence for mantle heterogeneity. The chondrite-normalized rare earth abundances of separated apatite, clinopyroxene, amphiboles and micas are high, with La in apatite being up to 4600 times chondrite. Apatites show a significant variation in rare earth content and in La:Lu ratios, indicating the occurrence of some crystal fractionation. The absence of europium anomalies from all mineral phases is indicative of a relatively high oxygen fugacity for the parent magma. The nature of the rare earth element distribution between mineral pairs suggests that some xenoliths represent equilibrium assemblages while some of the amphibole-bearing ones do not. The fluid from which these xenoliths crystallized would be an ideal agent for the metasomatism of upper mantle material and may account for l.r.e.e. enriched patterns of primary magmas in some alkaline provinces.