Abstract

Columbite is an accessory constituent of various biotite granites in the Jos-Bukuru complex, central Nigeria, and occurs in greatest abundance in granite of the Rayfield-Gona phase, a fine-grained, closely and irregularly jointed rock which is particularly susceptible to deep weathering. Extensive areas of this intensely decomposed rock have been preserved beneath a cover of laterite or Tertiary fluvial and volcanic deposits. Fragmental petrographic techniques, here described, have been developed for identification of different types of decomposed granites, based mainly on heavy mineral assemblages and the type and grain size of quartz in drill samples.

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