Mineralogy of the elbaite-subtype pegmatite from Dolní RožínkaArticle PDF
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 Sps56–61Alm38–42 in the graphic zone to Sps72–79Alm23 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.
František Novotný, Department of Geological Sciences, Masaryk University, Brno, Kotlářská 2, 611 37 Brno, Czech Republic, e-mail: email@example.com
Jan Cempírek, Department of Geological Sciences, Masaryk University, Brno, Kotlářská 2, 611 37 Brno, Czech Republic