Niobian rutile in Cr-V-bearing rocks of the Sludyanka metamorphic complex (Southern Baikal area)

Cr-V-bearing rocks of the Sludyanka metamorphic complex in the Southern Baikal area contain accessory niobian rutile with Nb contents unusually high for metamorphic rocks (10-12 to 20-25 wt.% Nb2O5, or, occasionally, up to 36-37 wt.%). Incorporation of Nb5 + into the rutile structure is balanced by Cr3 + and V3 +, which reach 16 wt.% Cr2O3 and 8 wt.% (or, rarely, up to 20 wt.%) V2O3. The distribution of Nb, Cr, and V in rutile is very uneven, down to the microscale. It does not depend on PT conditions, being rather controlled by crystallization kinetics of minerals competing with rutile in the paragenesis.