Tongolo And Dagga Allah
The 270 km2 Tongolo complex lies northeast of Saiya-Shokobo (No. 122-00-021) and is cut by a biotite granite related to that centre.
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.
The 270 km2 Tongolo complex lies northeast of Saiya-Shokobo (No. 122-00-021) and is cut by a biotite granite related to that centre.
This rather small occurrence consists of an approximately circular, 3 km-diameter biotite granite, an earlier concentric arfvedsonite granite along its southern margin, and an overlapping system of cone sheets and radial dykes.
This is a somewhat isolated centre forming a prominent hill having an elevation of 600 m above the surrounding plains. It is circular, 5 km in diameter and unusual for the province in consisting predominantly of syenitic rocks. Bennett et al.
This is a small hill composed of steeply dipping rhyolites and vent agglomerates. Few petrographic details are available.
Sutumi is a volcanic plug in which most of the plug materials have been displaced by later intrusions of granite. Rhyolites and agglomerates form screens between the granite and the basement rocks at several places around the plug.
Emplaced within Archaean gneisses the Kwandonkaya complex covers 190 km2 and is formed wholly of granites with some granite porphyry dykes. There are no associated volcanic rocks.
The small complex of Kofai may represent a southerly continuation of the Kwandonkaya intrusion (No. 122-00-028) being separated from it by only about 1 km of migmatitic basement rocks. As in Kwandonkaya there are no alkaline rocks.
This intrusion, like Kwandonkaya (No. 122-00-028) to the north, contains no truly alkaline rocks. It consists of an early hornblende-biotite granite and later biotite granite and biotite microgranite. The chemistry of these rocks is described by Imeokparia (1985b).
Jos-Bukuru is a large ring-complex lying approximately at the centre of the province and covers about 430 km2. In the northeastern corner a small ring structure, the Shere complex, is superimposed on Jos-Bukuru.
Approximately circular in shape and extending over 77 km2 the Buji complex is in contact with Rukuba (No. 122-00-033) lying to the west. It comprises two superimposed ring complexes the earlier eastern one being partly obliterated by the western.