Kudaru

It was at Kudaru that fayalite-bearing granites were first recorded in Nigeria, this being the first of the ring-complexes to be recognised. The central area of the complex forms prominent hills flanked by high cliffs, the highest of which rise to over 300 m; the periphery is marked by an annular ridge along the line of a ring-dyke. A considerable area of basement rocks is included within the ring-dyke but the most extensive rock of the complex is a riebeckite granite with lesser areas of pyroxene-fayalite granite and biotite granite. There are no volcanic rocks, in contrast to the other complexes in this part of the province, but dense swarms of cone-sheets are better developed here than anywhere else in the province. The ring-dyke, which is nearly 40 km in length, is the earliest manifestation of igneous activity. The rock is generally porphyritic with phenocrysts of quartz and alkali feldspar and smaller ones of fayalite, zoned aegirine-augite, which may be rimmed by amphibole, prisms of amphibole zoned to riebeckitic, with accessory opaques, allanite and zircon. The pyroxene-fayalite granite consists of perthite, albite-oligoclase, quartz, aegirine-augite, amphibole and fayalite. An early suite of minor intrusions having inward dips of 30-65( was then injected and comprises microgranite, rhyolite and quartz porphyry showing granophyric intergrowths of quartz and feldspar. The large riebeckite granite was then intruded and contains xenoliths of earlier rock types as well as roof pendants of basement gneiss. The typical rock consists of perthite, albite-oligoclase, quartz, riebeckite, which is often fringed by aegirine, and accessories including astrophyllite, allanite, fluorite and zircon. Small areas of biotite granite were then emplaced followed by a second generation of microgranitic cone-sheets, that in places form an intense swarm of several hundred dykes. The dyke rocks contain riebeckite and/or aegirine and astrophyllite. The division of the cone-sheets into earlier and later series was made by Bain (1934) but Jacobson and MacLeod (1977) consider that this interpretation is open to question. Bain (1934) gives the fullest description of the complex including rock analyses and analyses of riebeckite and biotite.