Chemistry of the Ta-Nb-Sn-W oxide minerals from the Yichun rare metal granite (SE China): genetic implications and comparison with Moroccan and French Hercynian examples

In the Yichun granite complex (SE China), columbite group minerals, microli te and cassiterite are the main Nb, Ta, Sn-bearing minerals. They are mainl y concentrated in the uppermost albite-lepidolite granite. Rutile is the on ly Nb, Ta-bearing phase in the geochemically primitive muscovite-zinnwaldit e granite. The chemical evolution of the columbite group minerals (the most abundant and commonly zoned Nb, Ta-bearing minerals) indicates a complex c rystallization history of the host granites with: (1) fractional crystalliz ation at depth, reflected by a strong increase of Mn/(Mn+Fe) ratios with a moderate increase of Ta/(Ta+Nb) ratios from the muscovite-zinnwaldite grani te to the Li-mica granite and then the most fractionated topaz-lepidolite g ranite; and (2) emplacement of successive magma batches corresponding to th e different units of the granite complex with progressive crystallization o f each unit, mainly reflected by a strong increase of Tai(Tai-Nb) ratios wi th moderate variation of Mn/(Mn+Fe) ratios during the growth of the zoned c rystals. The data are compared with those from the RMG of Ezzirari (Morocco ), Montebras, Beauvoir and Chedeville (France).