Journal of

GEOsciences

  (Formerly Journal of the Czech Geological Society)

Original Paper

Milan Novák, Diviš

Compositional trends in manganocolumbite from the Puklice I pegmatite, western Moravia, Czech Republic

Journal of the Czech Geological Society, volume 41 (1996), issue 1-2, 1 - 6

Manganocolumbite occurs in the albite-muscovite-lepidolite unit of the zoned lepidolite pegmatite Puklice I near Jihlava. Its zoned blade-like crystals are embedded in various minerals. The cores show slight variation in Ta/(Ta+Nb) but extensive changes in Mn/(Mn+Fe), whereas the rims display variation in Mn/(Mn+Fe), and extensive Ta/(Ta+Nb) fractionation. Increased amounts of WO₃ (up to 8.96 wt. %; 0.555 W apfu) and TiO₂ (up to 1.64 wt. %; 0.299 Ti apfu) are typical in crystal cores. The substitution W⁶⁺Ti⁴⁺Nb⁵⁺_-2 is very likely at W and Ti concentration of < 0.2 apfu. A higher degree of fractionation in terms of Mn-Fe and Ta-Nb was observed in manganocolumbite from the lepidolite subunit relative to the muscovite subunit. The fractionation trends of manganocolumbite and overall chemical variation within a single textural-paragenetic unit are comparable with those in other lepidolite pegmatites. No differences in the chemical composition were observed in relation to the host mineral of manganocolumbite.