Acta Musei Moraviae

Evidence of rare earth elements (REE) mobilization in teschenites of the Beskydy Mts. region

Rocks of teschenite association form sills and submarine volcanic bodies in sediments of the Silesian Unit of the Moravo-Silesian Beskydy Mts. They represent foidic alkalic basaltoidic rocks. These rocks are enriched in REE which are bound mostly in fluorapatite. The occurrence of secondary REE minerals is documented. These REE minerals form grains in the range of micrometers. Rabdophane-(Ce) with increased content of La and Ca forms crystalline coatings on the surface of fluorapatite and in the microscopic pores of non-altered teschenites. In the fissures of teschenites as well as in the slightly contactmetamorphosed sediments, syntactic intergrowths of minerals from the group of bastnäsite-(Ce) – synchysite-(Ce) were found. These REE minerals were probably formed as a product of postvolcanic hydrothermal alterations. Following minerals were found at the fissure surfaces in partly weathered teschenites: rhabdophane-(Ce), rhabdophane-(La), rhabdophane with high content of brockite component, cerianite-(Ce) and probable wakefieldite-(Ce). The fractionation process can be interpreted as a result of immobilization of Ce⁺⁴ in oxidation conditions and also Ce⁺⁴ adsorption on oxihydroxides of Mn and Fe.