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. The complex consists principally of granites but there is little evidence of ring structures although the Dagga Allah granite porphyry forms a polygonal system of dykes to the south. The earliest rocks are rhyolitic agglomerates and ignimbrites that are confined to the northern part and form numerous rafts and roof pendants in later intrusions. The earliest intrusions, which are in the northern sector, are various types of porphyry some varieties of which contain hedenbergite phenocrysts and occasional anhedral amphibole crystals. The granites include a leucocratic porphyritic type which forms three major intrusions, biotite granites, which are concentrated in the south, and riebeckite granites that form substantial intrusions in the central and northwestern parts of the complex. The riebeckite granites usually also contain biotite and in a number of them aegirine is also present; fluorite is ubiquitous. The biotite granites are texturally variable and contain abundant quartz (33-35%), orthoclase or perthite, albite, a little biotite and accessory fluorite, topaz, zircon, ilmenite, thorite and xenotime. Mineralization is generally confined to the biotite granites and takes the form either of disseminated accessory cassiterite, commonly associated with columbite, and greisen veins containing the same minerals (Imeokparia, 1985a). A swarm of felsite cone sheets arc around the northwestern side of the complex. The Dagga Allah porphyry (Buchanan et al., 1971; Kinnaird, 1981) forms a system of mainly arcuate dykes cutting basement rocks between Tongolo and the Kwandonkaya (No. 122-00-028) complex to the south. The dykes are generally between 65 and 160 m wide and the rock consists of quartz and perthite phenocrysts in a granophyric or granitic textured groundmass of the same minerals together with occasional anhedral prisms of hedenbergite rimmed by sodic amphibole, which also forms felted clusters of fibres, minor biotite, and accessories including fluorite and allanite. Imeokparia (1985a) gives trace element data on the biotite granites and discusses the mineralization in some detail. A gravity traverse across the complex is described by Ajakaiye (1976).