Acta Musei Moraviae

Mineralogy of the elbaite-subtype pegmatite from Dolní Rožínka

The elbaite-subtype granitic pegmatite from Dolní Rožínka, Czech Republic, is a highly fractionatedpegmatite with complex mineralogy and distinct evolution of mineral composition. The pegmatite dike is zoned and from the contact inward can be divided into a graphic unit with biotite (and graphic intergrowths of quartz with tourmaline or garnet), a graphic unit with beryl, blocky unit, albite unit, and pockets. Compositional evolution of tourmaline, beryl, garnet, mica, and Nb,Ta,Sn-oxides was studied in detail. Primary tourmaline develops from Mg-rich, slightly Al-deficient schorl, through Li-rich schorl, to Mn-rich elbaite, in pockets with increased Ca and F contents. Boron-rich fluid allowed formation of metasomatic vein tourmaline enriched in F, Ca, Mn and Mg (schorl, fluor-schorl, fluor-elbaite, elbaite) and secondary metasomatic tourmalines; tourmaline after biotite is rich in Mg and strongly Al-deficient, tourmaline after plagioclase evolves from fluor-elbaite, to fluor-liddicoatite and liddicoatite. Early beryl is partially enriched in Na and Mg, whereas content of Na and Cs increase towards the pegmatite center; secondary beryl is strongly enriched in Cs and Na (pezzottaite and very rare avdeevite). Garnet (Fe-bearing spessartine) evolves from Sps_56–61Alm_38–42 in the graphic zone to Sps_72–79Alm₂₃ in the albite zone. From micas, biotite is the most common whereas polylithionite (in pockets) and secondary muscovite are rare; polylithionite locally contains inclusions of Cs-rich polylithionite to sokolovaite. Columbite-group minerals show evolution trend with high Mn/(Mn+Fe) that corresponds to F-rich pegmatites. Albite zone contains common Mn-enriched fluorapatite and secondary bertrandite after beryl. Other accessory minerals include pyrochlore-microlite, cassiterite, zircon, and in submicroscopic inclusions also pollucite and petalite. Textural and compositional evolution of the pegmatite from Dolní Rožínka is similar to the elbaite-subtype pegmatites from Pikárec, Rudolfov, and Ctidružice by the presence of common cleavelandite, common graphic textures and complex mineralogy; on the other hand, the Řečice pegmatite has distinctly different, less complex textural development.