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

Abstract

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 Mn 3 Ca 2 (PO 4 ) 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, H 2 O-undersaturated, Cl-enriched melts by an exsolved H 2 O-, 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.