REVIEW OF STRUCTURES, FLUID FLOW AND GOLD DEPOSIT IN NIGERIA

The study indicates the relationship between the geologic structures, fluid flow and gold deposits in Nigeria. Nigerian gold major deposits are found in 9 locations and are all within the Schist belts of northwest and southwest Nigeria. They are; Maru, Anka, Malele, Tsohon Birnin Gwari, Kwaga, Bin Yauri, Gurmana, Okolom-Dogondaji, and Iperindo areas. The Duki and Maraba mines of Maru are associated with anticlinal axis of tight folds trending N-S direction. The Anka gold mineralisation is associated with sub-regional fault structures, that are subsidiary to the trascurrent anka fault system. They are concordant with the host rock foliation. In Malele area, the gold-bearing quartz vein appear parallel to foliation of the host rocks, apparently along a sub-regional fold axis. The Tsohon Birnin Gwari and Kwaga are within a series of metasediments that lie in a number of Isoclinal fold structures trending N-S and a strong foliation parallel to the axial plane of the folds. The Bin yauri gold- sulphide-carbonate occur in a brittle fault zone cutting hornfels. The brittle fault is a NW-SE-trending subsidiary structure of the transcurrent Anka fault. In Okolom-Dogodaji, series of gold- quartz is hosted by N-S and NNE trending shear zone which cut gneisses, schists and amphibolites. The shear zone appear to have exploited the mains chistosity and anticlinal axes of tight isoclinal folds. Silicification of the wall rock is the main hydrothermal alteration type. The Iperindo metasomatism is bounded to the east by the Ifewara transcurrent fault system.

The Nigerian gold mineralisation appears to be product of potassium , characterised by co-enrichment of K, Rb, and Ba. The K/Rb, K/Ba, Ba/Rb and Rb/Sr ratios in all these areas are not significantly different indicating a common or similar Ore-fluid.The REE pattern observed in all the Nigerian gold deposits so far studied is similar to post- Archean shales and unlike that of Calc-alkaline granitoids, late stage magmatic pegmatites and hydrothermal veins or of sub-marine exhalative ore deposits. This is interpreted to mean derivation from metamorphic hydrothermal fluids of upper crustal origin. The generally positive ó34S values of the Nigeria gold mineralisation offer further support to the upper crustal sedimentary source of the ore fluids. The structural settings suggest also the emplacement of the gold mineralisation to be late Pan-African.