Abstract

The Jurassic Younger Granites of northern Nigeria are closely associated with tin and niobium deposits. Primary mineralization which is confined almost exclusively to the biotite granites occurs as disseminations in albitzed granites, and as greisen lodes and veins. Distributions of Sn and other trace elements in more than 200 samples from various but related intrusive phases of biotite granites are examined with the main objective of determining geochemical criteria that may be useful in discriminating between tin-bearing and tin-barren granites.Concentrations of Sn are generally erratic, and mean values show only a subtle geochemical contrast between tin-bearing and tin-poor granites. However, a nonuniform distribution of Sn and a high coefficient of variance in which a large proportion of values exceed 25 ppm provide criteria for recognizing tin-bearing granites. The abundance and interrelationships of Rb, Li, K, Ba, Sr, Zr, Nb, Th, rare earth elements, and Mn are most useful as indicators of mineralizing processes and ore-bearing potential. Thus, the tin-bearing granites are characterized by low K/Rb and Ba/Rb and high Rb/Zr ratios.However, the ability of the stanniferous biotite granites to yield tin deposits depends on the development of an alkali-volatile phase during crystallization of the magma, and ore formation is considered a product of postmagmatic processes.

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