|Résumé||(disponible en anglais seulement)|
Columbite-tantalite series minerals are a main constituent of Ta and Nb ores. They are also present in Li, REE, Be, Zr, W, Sn, and Cs -bearing deposits
associated with granitoids, pegmatites, carbonatites, peralkaline intrusions, in saprolites overlying these deposits, in associated stream and lake sediments, and in till. Compositionally, following classification of Cerný and Ercit (1989), based on
Ta/(Nb+Ta) and Mn/(Mn+Fe) atomic ratios, members of the columbite-tantalite series can be divided into tantalite-(Fe), columbite-(Fe), columbite-(Mn), and tantalite-(Mn). Li-F-Rb-Cs-Be-Nb-Ta-REE-Sn-U-Th-Zr enriched granites are known to contain
predominantly columbite-Fe) with a Mn/(Mn + Fe) atomic ratio > 0.2, columbite-(Mn), and tantalite-(Mn). Pegmatite related deposits are known to contain tapiolite, all major varieties of tantalite, and Ta-rich end members of columbite. There is a
paucity of columbite analyses from carbonatite-hosted deposits; however, preliminary compilation suggests that they contain Nb-rich columbite-(Fe) with Mn/(Mn+Fe) atomic ratio <=0.2. Mineral groups belonging to the pyrochlore supergroup (betafite,
microlite, and pyrochlore) as defined by Atencio et al. (2010) are associated with the same deposits as columbite-tantalite minerals. Betafite group minerals [(Ca,U)2(Ti,Nb,Ta)2O6(OH)] are common in granite pegmatites and present in some
carbonatites; microlite group minerals [(Na,Ca)2Ta2O6(O,OH,F)] are found predominantly in rare element pegmatites and in miarolitic cavities in granites; and pyrochlore group minerals [(Na,Ca)2Nb2O6(OH,F)] are characteristic of carbonatites, but are
also present in other alkaline rocks. Discrimination diagrams based on composition of columbite-tantalite and/or pyrochlore minerals may allow exploration geologist to relate mineral chemistry of these minerals to established deposit models. For
example, Nb-rich pyrochlore and columbite-(Fe) with Mn/Mn+Fe atomic ratio <=0.2 are expected in carbonatite-related specialty metal deposits, while tapiolite, microlite and Ta-rich betafite are characteristic of pegmatite-related mineralisation.
Weathering is known to affect chemical composition of minerals belonging to the columbite-tantalite series and pyrochlore supergroup and should be taken into consideration.