In this paper we present textural and compositional data for columbite group minerals (CGM) and associated Nb-Ta-Sn oxides from lithium-beryllium-tantalum pegmatite deposits of the Kolmozero-Voronja belt, NW Russia, with the aim of deciphering the above mentioned features for minerals from deposits with different mineral signatures and lithium ore grade. Minerals from four deposits, including two of world-class (Kolmozero and Polmostundra), are examined. It is shown that the main controlling factors are the diversity and rate of magmatic fractionation, hydrothermal overprint and mineral paragenesis followed from the specific geochemical signature of the different pegmatite deposits. CGM from Kolmozero include several mineral species (columbite-(Fe), columbite-(Mn), tantalite-(Fe), tantalite-(Mn)) showing large compositional variations, mainly controlled by Nb-Ta fractionation (Ta/(Ta+Nb) = 0.16-0.70; Mn/(Mn + Fe) = 0.45-0.63). Textural patterns are extremely various (oscillatory, homogeneous, patchy, spongy, somewhere with over-growing Ta-rich rims) and indicate the involvement of numerous magmatic and hydrothermal processes. The Polmostundra CGM are represented by columbite-(Fe) with Ta/(Ta+Nb) ranging from 0.05 to 0.39 with homogeneous, mottled, oscillatory, patchy and irregular reverse textures. The Okhmylk CGM are irregular normal, patchy and homogeneous columbite-(Fe) and columbite-(Mn) with Ta/(Ta+Nb) = 0.09-0.24 and Mn/(Mn + Fe) = 0.29-0.92, indicating the suppressed magmatic fractionation and iron drop due to precipitation of Fe minerals. Columbite-(Fe) and columbite-(Mn) from the Be-Ta Shongui deposit are less evolved with Ta/(Ta+Nb) = 0.07-0.23 and Mn/(Mn + Fe) = 0.31-0.55. The minerals are characterized by progressive normal, oscillatory, homogeneous and ir-regular reverse patterns. Associated pyrochlore minerals occur both as early magmatic (Kolmozero) and late hydrothermal (Polmostundra, Okhmylk). Cassiterite is found only in the Okhmylk dykes and is apparently of hydrothermal origin. CGM from Li pegmatites have impurities of Ti (0.01-0.05 apfu) and W (up to 0.02 apfu), whereas CGM from Be pegmatites contains elevated Ti (up to 0.09 apfu). The mineral systems analysis presented here is relevant for exploration.

The intensive variables, geochemical, mineralogical and petrogenetic constraints of the Iberian rare metal granites, many of them unknown, are presented. It allows to distinguish two main granitic types with contrasting characteristics: Nb-Ta-rich granites and Nb-Ta-poor granites. The former have lower emplacement temperatures, higher water contents and probably lower emplacement pressures than Nb-Ta-poor granites. Nb-Ta-rich granites also have higher fluoride contents, strong fractionation into twin pairs such as Zr-Hf, Y-Ho and Nb-Ta, and an abundant, probably exsolved, fluid phase, which is not or not as evident in Nb-Ta-poor granites, probably in part because the Nb-Ta-rich granites reach their solidus later (about 550 ºC). The geochemical signature of the Iberian rare metal granites follows the trends of mainly two-mica granites and P-rich cordierite granites, but also of granodiorites and even type I granites, suggesting that the rare metal granites may have different parental magmas. Thermodynamic modeling shows that many of the geochemical characteristics of the RMGs can be explained by a process of extreme differentiation, while others cannot, e.g. Na evolution. In terms of ore deposition, white mica plays a very important role in explaining the variation of the Ta/Nb ratio, although the latter could also be controlled by late Nb-Ta oxides crystallization and even by acidic fluids that remove Nb relative to Ta from earlier Nb-Ta oxides.