UNIVERZITA KOMENSKÉHO V BRATISLAVE VZÁCNOPRVKOVÁ ...

and 0.73-0.86 (Fw I); Mn/(Mn+Fe) = 0.32-0.49 (Ct I), 0.06-0.10 (Ft I) and 0.33-0.41 (Fw
I).
The second generation is represented by ferrocolumbite to ferrotantalite (Ct II) in
fine-grained saccharoidal albite zone and also by replacement zones of ferrotantalite II in
ferrotantalite I. To the second generation belongs also irregular overgrowths of
ferrotapiolite (Ft II) and ferrowodginite (Fw II) on ferrotapiolite I grains. The minerals of
the second generation show decreasing of Ta/(Ta+Nb) ratio in comparison to the first
generation: 0.10-0.60 (Ct II), 0.85-0.87 (Ft II) and 0.73-0.77 (Fw II); Mn/(Mn+Fe) ratio
attains 0.30-0.45 (Ct II), 0.06-0.09 (Ft II) and 0.26-0.37 (Fw II). The second generation is
characterized also by increased content of Ti (up to 1.7 wt.% TiO2 in Ct II, up to 5.4 in Ft
II, up to 5.6 in Fw II). Titanium is introduced by the substitution Ti 4+ + Fe 3+ ↔ (Nb+Ta) 5+
+ (Fe+Mn) 2+ .
The third generation includes fissure fillings, overgrowths and replacement zones
of manganocolumbite and manganotantalite (Ct III), ferrotapiolite (Ft III) and
ferrowodginite (Fw III) on the older Nb-Ta phases (Ct I, Ft I, Fw I, Fw II), in the coarsegrained
unit and also in the saccharoidal albite unit. The third generation displays distinct
increase in Mn/(Mn+Fe) ratio (Ct III: 0.51-0.69, Ft III: 0.11-0.24, Fw III: 0.40-0.41),
Ta/(Ta+Nb) ratio values reach 0.16-0.79 (Ct III), 0.88-0.92 (Ft III) and 0.80-0.81 (Fw III).
The latest Nb-Ta phase identified in the Jezuitské lesy pegmatite is represented by
irregular veinlets and patches of microlite, replacing mainly ferrotapiolite I and
ferotantalite I, rarely also ferrowodginite I, ferrocolumbite II and ferrotapiolite III.
Microlite is distinctly Ta-rich, the Ta/(Ta+Nb) values are evidently higher in microlite
penetrating ferrotapiolite I (0.90-0.97) than it associate with Ct1 (0.82-0.85).
The composition of Nb-Ta minerals shows unusual and complex fractionation
trends within the pegmatite dike. The first generation of Nb-Ta minerals (ferrotantalite I,
ferrotapiolite I and ferrowodginite I) originated during the crystallization of coarsegrained
quartz-microcline-muscovite zone and it is characterized by the relatively high
Ta/(Ta+Nb) ratio. The second generation of Nb-Ta minerals (ferrocolumbite to
ferrotantalite II, ferrotapiolite II, ferrowodginite II) formed during the crystallization of
fine-grained saccharoidal albite zone and it is characterized by the decrease of
Ta/(Ta+Nb) and Mn/(Mn+Fe) ratio. Low Ta/(Ta+Nb) values in ferrocolumbite to
ferrotantalite (Ct II) from the saccharoidal albite unit can be explained by crystallization
from the Ta-depleted, albite-rich melt, which was significantly impoverished in Ta, after
crystallization of Ta-rich phases (ferrotapiolite I, ferrowodginite I). The third generation
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