Abstract:
For complex natural bodies, which undoubtedly include plutons of autometasomatized rare-metal granite, one interpretation of the origin of all rare-metal minerals often cannot be regarded as satisfactory. To determine the granite phases and facies to which such minerals belong, we should employ the various methods now used to analyze their typomorphic properties. As revealed by our work, the composition of tantalite-columbite and wolframite from different granite facies of the Central pluton and their physical properties, distribution and relationships can be explained quite clearly and satisfactorily on the basis of the following theory. Tantalite-columbite occurs as at least two major generations, magmatic and autometasomatic; the first generation (ferrocolumbite) crystallizes faster than the second (manganotantalite-columbite), and during its crystallization there is a gradual change in the conditions of mineral formation, accompanied by the replacement of ferrocolumbite by manganotantalite-columbite, and of the latter by microlite and by wolframite, which is related to columbite in its crystal chemistry.