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BEUSITE AND AN UNUSUAL Mn-RICH APATITE FROM THE SZKLARY GRANITIC PEGMATITE, LOWER SILESIA, SOUTHWESTERN POLAND

Adam Pieczka

Department of Mineralogy, Petrography and Geochemistry, AGH – University of Science and Technology, al. Mickiewicza 30, 30-059 Kraków, Poland

E-mail address: pieczka{at}uci.agh.edu.pl

An assemblage of phosphate minerals, including beusite, Mn-rich fluorapatite, chlorapatite, hydroxylapatite and traces of alluaudite and mitridatite, usually accompanied by Mn-rich oxides also enriched in Ba, Ca, Mg and Ni, and Bi and Pb, has been recognized in a granitic pegmatite occurring within serpentinites of the Szklary massif in Lower Silesia, Poland. This pegmatite is a representative of the MSREL–REE subclass of the muscovite – rare-element pegmatites. The beusite usually occurs there as a Mn-dominant, (Ca,Fe)-bearing, Mg-enriched phase devoid of the typical lamellar intergrowths with triphylite or sarcopside, evolving toward more and more Mn-enriched varieties, stabilized by the earlier crystallization of tourmaline and fluorapatite. In terms of enrichment in Mn, the beusite from Szklary is on a level with that from the Cross Lake pegmatite in Canada, considered as the example richest in Mn worldwide. Similarly, Mn-rich fluorapatite containing up to 19.3 wt.% MnO, and a Mn-dominant apatite-group mineral containing up to 31.5 wt.% MnO, are two apatite species richest in Mn worldwide, the second close to the ideal Mn₃Ca₂(PO₄)₃(Cl,F,OH) composition. The progressive removal of Fe over Mn, a decrease in the activities of F and Fe due to crystallization of abundant Fe-bearing tourmaline and fluorapatite, extraction of Mn from pegmatite-forming, H₂O-undersaturated, Cl-enriched melts by an exsolved H₂O-, F- and Cl-bearing volatile phase, and metasomatic alteration induced by residual Mn- and Cl-bearing fluids additionally enriched in Mn released during the dissolution of metastable beusite are the main reasons of such a high degree of Mn enrichment in the phosphates from the Szklary pegmatite.

Keywords: beusite, Mn-rich apatite, Szklary granitic pegmatite, Poland.