Correlations between microstructures, K-feldspar triclinicity and trace element geochemistry in stanniferous and barren granites, northern Nigeria

摘要: Abstract The biotite granites in the Nigerian Younger Granites are a major source of economic metals Sn, Nb, Zn and W. textural variations these rocks considered together with composition structural state K-feldspars. curious disparity degree mineralization similar mineral assemblage is to be related variations. stanniferous characterized by medium- fine-grained texture, miarolitic cavities, subsolidus crystallization albite; turbidity, coarsening incoherent perthitic texture K-feldspar. barren usually coarse-grained few druses, silvery irridescent feldspar grains coherent texture. K-feldspars mainly maximum microcline structure while ones intermediate structure. Compositionally, all have less than 3% An; they crystallized binary system at temperatures close 700°C but now re-equilibrated various lower as result variable rock-fluid interaction. Positive correlations observed between Rb, Li F triclinicity their Enhancement Rb-values both K-feldspar constituents. textures, Al, Si order feldspars enrichment ore trace elements attributed presence abundance fluid phase. It suggested that course magmatic evolution an alkali-rich volatile phase developed, accumulated was trapped roof zone granites.