| Summary: | The plutonic members of the complexes that comprise the Younger Granite province of Northern Nigeria, include gebbros, syenites, amphibole-fayalite granites and porphyries, amphibole-biotite, biotite, and riebeckite granites, and a short petrographic account of these rocks is riven. Mineralogically the plutonic rocks are characterised by a varied assemblage of mafic minerals, of which the most important are members of the olivine, pyroxene, amphibole and biotite groups; all the ferromagnesian minerals are iron-rich. Analyses nave been made of calcium and soda-rich pyroxenes, calciferous and alkali amphiboles, biotites, cossyrite and ilmenites, that come from some of the above mentioned rocks, and the analytical results are presented and discussed. Whenever possible an attempt has been mane to correlate changes in chemical composition of the analysed minerals with variations in optical properties and, in the case of the amphiboles, variations in unit-cell parameters. Compositional trends in the analysed ferromagnesian minerals have been discussed and compared with compositional trends in the plutonic rocks of the Younger Granite complexes. The possible conditions of formation of some of the analysed ferromagnesian minerals have been considered in the light of experimental studies. The distribution of the complexes throughout the Younger Granites Province is commented upon, and several problems of the evolution of the Younger Granites are discussed.
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