COLUMBITE-TANTALITE OF THE KESTER DEPOSIT (EASTERN YAKUTIA)

Three mineral species of the columbite group were installed at the Kester deposit (Eastern Yakutia): columbite-(Fe), columbite-(Mn) and tantalite-(Mn), which are part of rare-metal granites and ongonites, albitites and greisens. Columbite-(Mn) prevails: Ta/(Ta + Nb) = 0.30, Mn/(Mn + Fe) = 0.64. The generalized formula for the columbite-tantalite of deposit is (Mn0.61Fe0.34)0.95(Nb1.37Ta0.58Ti0.04W0.03Sn0.01)2.03O6. Columbite tantalite combine the polymineral individuals with concentric growth zonality (from core to rim): columbite-(Fe) → columbite-(Mn) → tantalite-(Mn) + uranmicrolite → columbite-(Mn). A typomorphic impurity in the columbite of Kester deposit – WO3: an average of 2.67 % (apfu 0.04); maximum 7.12 % (apfu 0.11). Isomorphic substitution of cations in position B is assumed according to the scheme: 2(Nb,Ta)5+ ↔ W6+ + Ti4+. Typomorphic impurity in tantalite – SnO2: on average 1.01 % (apfu 0.03); maximum 3.74 % (apfu 0.21). Paragenesis of columbite-group minerals includes: albite, topaz, lepidolite, Nb-Ta-containing cassiterite, wolframoixiolite, wolframite, U-Hf-containing zircon, struverite. The evolution of columbite-tantalite of the Kester deposit is accompanied by an increase in the relations of Ta/Nb, Mn/Fe, Sn/W, expressed in the change of columbite by tantalite both in the process of formation of ore-bearing rocks and in the series of these rocks: rare-metal granites → albitites → greisens. Fluctuation limits of ratios Ta/(Ta + Nb) 0.07–0.74, Mn/(Mn + Fe) 0.16–0.96. The diversity and evolution of the columbite-group minerals of Kester deposit indicate their belonging to the rare-metal ore- magmatic system, which includes ore-bearing rare-metal granites, albitites and greisens. The presence of the small intrusions of rare-metal granites and ongonites in the area of the deposit allows predicting the discovery of new objects of bed-rock and placer columbite-tantalite mineralization.