Publication details
Niobium-tantalum oxide minerals in the Jezuitské Lesy granitic pegmatite, Bratislava Massif, Slovakia: Ta to Nb and Fe to Mn evolutionary trends in a narrow Be,Cs-richand Li,B-poor dike
| Authors | |
|---|---|
| Year of publication | 2011 |
| Type | Article in Periodical |
| Magazine / Source | Mineralogy and Petrology |
| MU Faculty or unit | |
| Citation | |
| Field | Geology and mineralogy |
| Keywords | columbite group minerals; tapiolite; ferrowodginite; pegmatite; evolution; Jezuitské Lesy; Slovakia |
| Description | A complex assemblage of Nb-Ta-(Sn) oxide minerals occur in a relatively narrow (similar to 1-2 m thick) extensively albitized, Hercynian granitic pegmatite dike intruding biotite granodiorites near Bratislava, SW Slovakia. The dike shows enrichment in beryl (locally Cs-rich) but absence of Li- and B-rich phases. Compositions and textural relationships indicate complex evolutions of Nb-Ta oxide phases with several generations presenting distinct textural and compositional features. The first generation of the Nb-Ta minerals from the quartz-microcline-muscovite zone show Ta, Fe-rich compositions with Ta# [Ta/(Ta + Nb)]= 0.52-0.70 (Ct I columbite-tantalite), 0.88-0.90 (Tap I ferrotapiolite) and 0.73-0.86 (Fw I ferrowodgin-ite); Mn# [Mn/(Mn + Fe)]= 0.32-0.49 (Ct I), 0.06-0.10 (Tap I) and 0.33-0.41 (Fw I). The 2nd generation is represented by ferrocolumbite to ferrotantalite (Ct II) in saccharoidal albite zone, replacement zones of Ct II in Ct I, and irregular overgrowths of ferrotapiolite (Tap II) and ferrowodginite (Fw II) on Tap I grains. The minerals of the 2nd generation show decreasing of Ta# in comparison to the 1st group: 0.10-0.60 (Ct II), 0.85-0.87 (Tap II) and 0.73-0.77 (Fw II); Mn# attains 0.30-0.45 (Ct II), 0.06-0.09 (Tap II) and 0.26-0.37 (Fw II). The 3rd generation includes fissure fillings, overgrowths and replacement zones of manganocolumbite and manganotantalite (Ct III), ferrotapiolite (Tap III) and ferrowodginite (Fw III) on the older Nb-Ta phases (Ct I, Tap I, Fw I, Fw II), in the coarse-grained unit. The 3rd population displays distinct Mn# increasing (Ct III: 0.51-0.69, Tap III: 0.11-0.24, Fw III: 0.40-0.41), Ta# values reach 0.16-0.79 (Ct III), 0.88-0.92 (Tap III) and 0.80-0.81 (Fw III). The latest, 4th generation of the Nb-Ta phases represents irregular veinlets and patches of fluorcalciomicrolite, replacing Ct I, Tap I, Fw I, Ct II and Tap III. Decrease of Ta/(Ta + Nb) values in Ct II from the saccharoidal albite unit can be explained by crystallization from the albite-rich melt, which was significantly impoverished in Ta with respect to Nb, after crystallization of Ta-rich phases from the 1st generation (ferrotapiolite I, ferrowodginite I). |