The rare earth element contents and the origin of the sparry magnesite mineralizations of Tux-Lanersbach, Entachen Alm, Spiessnaegel, and Hochfilzen, Austria, and the lacustrine magnesite deposits of Aiani-Kozani, Greece, and Bela Stena, Yugoslavia

The rare earth element distribution patterns of magnesite and dolomite samples from the magnesite mineralizations of Tux-Lanersbach (Innsbruck quartz phyllite), Entachen Alm, Spiessngel, and Hochfilzen (graywacke zone) have been determined by neutron activation spectrometry. The finely dispersed magnesite in the dolomitic country rock shows rather flat rare earth element patterns. The magnesite and dolomite from veins exhibit extremely low light rare earth element contents. This feature is attributed to long-range mobilization of magnesite.The tectonic structure of the graywacke zone and of the Innsbruck quartz phyllite suggests that a maior perturbation of the regional geothermal gradient was produced by overthrusting. Owing to the irregular form of the geothermal gradient, low temperature Mg (super +2) ion-rich solutions, generated by dehydration reactions and equilibrated with calcite and dolomite, penetrated dolomite-bearing sheets at higher temperatures during their ascent. The dolomite of the higher tectonic units was thereby metasomatically altered to magnesite. Such a regional metamorphism is displayed by the positive Eu anomalies in the rare earth element distribution patterns of the Spiessngel dolomites. This Eu anomaly indicates that the dolomite from this locality crystallized from solutions involved in the decomposition of feldspars. The rare earth element contents of the magnesites and huntites from lacustrine basins of Bela Stena and of Aiani-Kozani are lower than those of the sparry magnesites. This reflects the different sources of the Mg (super +2) -bearing solutions and depositional environments.