Compositional Variation of Some Rare Earth Minerals from the Fen Complex (Telemark, SE Norway): Implications for the Mobility of Rare Earths in a Carbonatite System

Tom Andersen
Institutt for Geologi, Universitetet i Oslo, Boks 1047, Blindern, N0316 Oslo 3, Norway

Abstract: 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.

Keywords: rare earth minerals • monazite • allanite • carbonatite • rødberg • Fen complex • Norway

Mineralogical Magazine; September 1986 v. 50; no. 357; p. 503-509; DOI: 10.1180/minmag.1986.050.357.13
© 1986, The Mineralogical Society
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