UNIVERZITA KOMENSKÉHO V BRATISLAVE VZÁCNOPRVKOVÁ ...

Tungstenian ixiolite was found in a form of discrete irregular crystals up to 500
µm in size, usually associated with wolframite (ferberite). Content of W reached up to 35
wt.% WO3 and decrease with increasing content of Ta. Chemical composition of ixiolite
is almost constant with low Ta/(Ta+Nb) = 0.05-0.09 and Mn/(Mn+Fe) = 0.32-0.33.
Tungsten and titanium content in columbite group minerals and tungstenian ixiolite are
introduced by the substitution W 6+ + Ti 4+ ↔ 2(Nb+Ta) 5+ .
Minerals of the pyrochlore group are represented mostly by microlite, rarely by
pyrochlore and uranmicrolite. Pyrochlore to microlite and uranmicrolite was found in a
form of discrete anhedral to subhedral crystals up to 250 µm in size. The Ta/(Ta+Nb) =
0.45-0.86 values in these crystals increase with increasing content of U (up to 20.4 wt.%
UO2) and Ti (up to 5.6 wt.% TiO2). On the other hand content of W (up to 4 wt. % WO3)
decrease with increasing value of Ta/(Ta+Nb) ratio. Microlite in a form of irregular
overgrowths on manganocolumbite is characterized by lower content of minor element (W
– up to 5 wt.% WO3, Ti – up to 2 wt.% TiO2, U – up to 11 wt.% UO2) and relatively
constant Ta/(Ta+Nb) = 0,60-0,80. The content of Na (up to 6 wt.% Na2O, up to 0.98 apfu)
slightly dominated over Ca (up to 10 wt.% CaO, up to 0,90 apfu) in all pyrochlore group
members.
Characteristics feature of leucogranite from Dlhá dolina is elevated content of W,
expressed also by increased content in Nb-Ta phases. The highest concentration are in
tungstenian ixiolite (up to 35 wt.% WO3) and manganocolumbite (up to 10 wt.% WO3).
Another specific feature is decrease of Mn/(Mn+Fe) ratio with increasing value of
Ta/(Ta+Nb) ratio in the outer parts of some manganocolumbite crystals. This feature can
be connected with crystallization of apatite, which is often found at the contact with
manganocolumbite. The crystallization of apatite (with content Mn up to 2 wt.% MnO)
could deplete the melt in Mn and caused decrease of Mn/(Mn+Fe) ratio in outermost parts
of manganocolumbite crystals.
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