Bagbe (Maho)

The Bagbe complex is an elongate body extending in a northeasterly direction over 13 km. It is closely associated with the major Maho fault which appears to have controlled emplacement. The rock types involved are nepheline syenite, syenite and peralkaline granite. The complex was mapped by Wilson (1965) who, apart from late dykes, interpreted all the major rock types as resulting from metasomatism, including nephelinisation, by fault-controlled solutions. The relative ages of the rocks are not, therefore, clear. The nepheline syenite maps as three major and several smaller bodies that are in contact either with syenite, which tends to completely envelop the smaller bodies, or Archaean charnockitic rocks. It also forms dykes. Peralkaline granite makes a substantial body at the southern end of the complex and a smaller one in the north; it interdigitates with the syenites and in places is in contact with nepheline syenite. Areas mapped as 'Incipient fenitization' by Wilson (1965) appear to be principally zones marginal to large inclusions of country rocks in contact with peralkaline granite. Areas of potassium metasomatism are also distinguished. The nepheline syenites are sometimes markedly banded, vary from very fine-grained to pegmatitic and consist of perthite, albite, nepheline, cancrinite, patches or veins of blue sodalite, and a little aegirine-augite, biotite and amphibole. Accessories include apatite, magnetite, pyrite, pyrrhotite, bastnasite, pyrochlore, fluorite and calcite. The syenites are essentially quartz-free perthite rocks with a little aegirine-augite, biotite and an unspecified amphibole. The peralkaline granites contain a little aegirine-augite, biotite and an amphibole but, as with the fenites, few textural and mineralogical details are available. Analyses of two granites, a perthosite and two nepheline syenites are given by Wilson (1965) and a further one is in Allen and Charsley (1968).