Columbite–Tantalite of the Kester Deposit (Eastern Yakutia).

Three mineral types of the columbite group have been revealed at the Kester Deposit (Eastern Yakutia), that is, columbite-(Fe), columbite-(Mn) and tantalite-(Mn), which are part of rare-metal granites, ongonites, albitites, and greisens. Columbite-(Mn) prevails: Ta/(Ta + Nb) = 0.30, and Mn/(Mn + Fe) = 0.64. The generalized formula of columbite–tantalite of the deposit is (Mn0.61Fe0.34)0.95(Nb1.37Ta0.58Ti0.04W0.03Sn0.01)2.03O6. Columbite–tantalite forms polymineral individuals with concentric growth zonality (from the core to the rim): columbite-(Fe) → columbite-(Mn) → tantalite-(Mn) + uranmicrolite → columbite-(Mn). In columbite of the Kester Deposit, WO3 is a typomorphic impurity, which is 2.67%, on average (formula coefficent, apfu is 0.04); the maximum value is 7.12% (apfu is 0.11). The isomorphic replacement of cations in the B position is assumed according to the following scheme: 2(Nb, Ta)5+ ↔ W6+ + Ti4+. In tantalite, SnO2 is a typomorphic impurity, which is 1.01%, on average (apfu is 0.03); the maximum value is 3.74% (apfu is 0.21). The paragenesis of the columbite group minerals includes albite, topaz, lepidolite, Nb-Ta-bearing cassiterite, wolframoixiolite, wolframite, U-Hf-bearing zircon, and struverite. At the Kester Deposit, the evolution of columbite–tantalite is accompanied by an increase in Ta/Nb, Mn/Fe, and Sn/W ratios manifested in the change of columbite by tantalite both in the process of the formation of ore-bearing rocks and in the rock series: rare-metal granites → albitites → greisens. The variation limits of Ta/(Ta + Nb) and Mn/(Mn + Fe) ratios are 0.07–0.74 and 0.16–0.96, respectively. The diversity and evolution of the columbite group minerals of the 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 small intrusions of rare-metal granites and ongonites in the deposit area allows the forecasting of new objects with bedrock and placer columbite–tantalite mineralization. [ABSTRACT FROM AUTHOR]