Rare earth minerals in ankeritic ferrocar-bonatite and associated magnetite ore, as well as in hematite-calcite-(dolomite) carbonatite (rødberg) derived from the ferrocarbonatite by post-magmatic alteration, have been studied by electron microprobe. The minerals found are monazite, parisite, and bastnäsite (identifications confirmed by X-ray diffraction) as well as an aluminous silicate with allanite composition, and possibly, synchysite. The rare earth element (REE) distribution patterns of the minerals change from light rare earth (LREE)-enriched in magnetite ore and ferrocarbonatite to less LREE-enriched, or middle REE-enriched in the most strongly re-equilibrated carbonatites. Two distinct mineral varieties, monazite-(Ce,Nd) and a Nd-fluorocarbonate, have been found in rødberg. The LREE were leached from their host minerals during re-equilibration of the carbonatite, most likely because of the influence of fluoride-bearing hydrothermal solutions.

In the Fen complex (Telemark, S.E. Norway), carbonatites of different compositions have penetrated feldspathic fenites (alkali feldspar(s) + aegirine augite ± alkali amphibole) or older carbonatites, inducing different types of contact metasomatic alterations in their wall-rocks. (1) Pyroxene søvite has induced alkali metasomatism (i.e. fenitization s.s.), with alkali feldspars remaining stable and aegirine-augite transformed to nearly pure aegirine. (2) Søvite and dolomite carbonatite with phlogopite and/or alkali or alkali-calcic amphibole have caused replacement of feldspathic fenite by phlogopite, i.e. magnesium metasomatism. (3) Granular (dyke facies) ferrocarbonatite has increased the ferromagnesian components in calcite in wall-rock søvite. (4) Heterogeneous (pyroclastic) ferrocarbonatite induced pseudomorphic replacement of phlogopite by chlorite (leaching of alkalis). The different contact metasomatic processes reflect contrasts in compositional character among carbonatite magmas in the Fen complex, which may be evaluated in terms of differences in alkali and magnesium carbonate activities. The different types of carbonatite magma represent the products of local evolutionary trends, and are genetically related to spatially associated silicate rocks, rather than to a single ‘primitive’ carbonatite parent magma.