NIOBIAN TITANITE FROM THE HURON CLAIM PEGMATITE,

Niobian titanite occurs in the Be,Nb-Ta,Ti, REE,Y ,Zr,Th,U-bearing Huron Claim pegmatite, in the Winnipeg River pegmatite district of south­ eastern Manitoba. The titanite is found in vuggy albite and quartz, separate from other Nb,Ta­ bearing minerals. The Nb205 content is the highest ever found in this species ( 6.5 wt. % ) , and the combined (Nb,Ta).05 content (10.2 wt. %) is sec­ ond only to that of the tantalian titanite from Cra­ veggia (Clark 1974). Normalization to l:(RIV+Rv1) = 8 yields reasonable formulae for both Huron Claim and Craveggia titanites but with slight AI substitution for Si, which may improve local charge distribution at Nb,Ta-populated octahedra. Titanite­ bearing pegmatites are usually low in Nb and Ta, and complex Nb,Ta,Ti-bearing oxide minerals predominate in pegmatites enriched in these ele­ ments, suggesting a scarcity of Nb,Ta-rich titanites.