Ririwai (Liruei)
Ririwai is one of the most studied of the Nigerian ring-complexes with an extensive literature on the geology, petrology and mineralization.
Alkaline rocks are concentrated in two areas in Nigeria; the Jos Plateau of central and northern Nigeria and the Benue Valley in the southeast and along the border with Cameroon. The Jos Plateau suite consists of a remarkable series of essentially granitic intrusions, which are known as the Younger Granites and also as the Nigerian Anorogenic ring complexes, with less extensive extrusive rocks. Many of the granite complexes form spectacular ring structures, some formed of numerous intrusions. Non-alkaline rocks are more voluminous than alkaline ones amongst the Younger Granites but most occurrences include a greater or lesser proportion of peralkaline granite and/or syenite, with extrusive peralkaline rocks also present in some centres. A preliminary review of the province was given by Jacobson et al. (1958) with much fuller accounts of most of the individual complexes by MacLeod et al. (1971) and Buchanan et al. (1971). Further detailed accounts of nine of the complexes are in Bennett et al. (1984) and Turner (1976) also reviews the province. The province as a whole is clearly depicted on a geological map at a scale of 1:500,000 compiled by Kinnaird (1981), while a map of the northern part of the province only, at a scale of 1:250,000, has been compiled by Turner (1979). Reviews of the geology and mineralization are given by Bowden et al. (1984), Bowden and Kinnaird (1984), and Pastor and Turaki (1985) while Hossain and Turaki (1983) have compiled a bibliography of the province and the associated tin mineralization.
The volcanic rocks of the Benue Valley consist of a number of lava plateau together with several concentrations of plugs and other minor intrusions. Little detailed work has been done on these rocks and although a proportion of the plugs are known to be alkaline information on the lavas is sparse. Wright (1976) reviewed the data available at that time.
Ririwai is one of the most studied of the Nigerian ring-complexes with an extensive literature on the geology, petrology and mineralization.
The 17.5x15 km Banke complex is bounded by a ring-fault but one third of the enclosed area is occupied by basement rocks.
This intrusion, just over 3 km in diameter, is expressed as a group of small hills. Most of the intrusion is occupied by biotite granite, which underlies most of the high ground. It is made of perthite, a little albite, quartz and fluorite.
It was at Kudaru that fayalite-bearing granites were first recorded in Nigeria, this being the first of the ring-complexes to be recognised.
This occurrence is little known, a photographic interpretation on the 1:250 000 geological map (Turner, 1979) indicating an approximately circular 3 km diameter intrusion, while Raeburn et al. (1927, 1:125,000 sheet) indicate an intrusion somewhat elongated east-west.
This complex has not been mapped in detail.
Only provisional mapping of this occurrence is available (Raeburn et al., 1927) which, together with photo-interpretation (Turner, 1979), indicates the presence of two overlapping intrusions of which, like Rishiwa (No.
This is a ring-complex composed predominantly of granite but there are also significant areas of volcanic rocks.
This complex is contiguous with Jere-Sanga (No. 122-00-022) to the south, a ring-dyke of which cuts rocks of the southern part of Saiya-Shokobo, and Tongolo (No. 122-00-023) to the northeast.
This complex overlaps Saiya-Shokobo (No. 122-00-021) to the north the peripheral ring-dyke enclosing rocks of the southern end of that complex together with large areas of basement granite gneiss.