NB-RICH, TA-RICH AND SN-RICH TITANITE AND ITS ALTERATION IN PEGMATITES FROM ZOLKIEWKA, POLAND

Titanite enriched in Nb ((x) over bar = 5.84 wt% Nb2O5), Ta ((x) over bar = 2.88 wt% Ta2O5), Sn ((x) over bar = 2.81 wt% SnO2), and also in Al ((x) over bar = 2.69 wt% Al2O3) and Fe ((x) over bar = 1.96 wt% FeO ) has been found in a miarolitic pegmatite near Strzegom in SW Poland in association with microcline, albite, Fe-chlorite, fluorite, pyrite and stilbite. Between 25% to 35% of the Ti was substituted by other ca tions in this titanite. The principal substitution mechanisms include: Al3+ + (Nb, Ta)(5+) = 2Ti(4+); Al3+ + (F, OH)(-) = Ti4+ + O2-; and Sn 4+ = Ti4+. Based on stoichiometric considerations, Fe in titanite is, at least in part, divalent. The titanite was partially altered due to leaching of Nb, Sn, Fe and Ta by low-temperature hydrothermal solution s. As the result of the preferential leaching of Nb over Ta, the Nb/Ta ratio changed from 3.42 in primary titanite to 0.46 in the altered pa rts.