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Lower Proterozic Birimian 'Greenstone Belt' of West Africa And

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Lower Proterozic Birimian 'Greenstone Belt' of West Africa And Lower Proterozic Birimian ‘Greenstone belt’ of 2. Sources of Mn in the Birimian West Africa and sources of Manganese Various sources of manganese have been proposed in the Birimian. Example, mineralization in Ghana Melcher (1995), on the Nangodi belt, showed that manganese was formed in George M. Tetteh (University of Mines and Technology, P. O. relatively oxidised to more reducing environment. At Nsuta deposit, Service (1943) Box 237, Tarkwa. Ghana), Frank K. Nyame (Dept. of Geology, linked the lenticular manganese ore to contemporaneously deposited volcano- University of Ghana) sedimentary rocks. Consequently, Mn sources have been related to volcanism (Kleinschrot et al., 1994); volcanic exhalation (Ntiamoah-Agyakwa, 1979) and 1. Introduction hydrothermal fluids (Dzigbodi-Adjimah and Sorgbor, 1993). Continental sources At the eastern flank of the West African craton are Palaeoproterozoic rocks, were suggested by Mücke et al. (1999). Nyame and Beukes (2006) showed that which were affected by 2100 Ma Eburnean thermotectonic event, referred to as the minor fluid infiltration with organic matter could produce the manganese carbonate 13 18 Birimian (Kitson, 1918). Early stratigraphic subdivision by Junner (1940) into protore at Nsuta that has lighter δ CPDB and heavier δ OPDB. At Mankwadzi Lower Birimian Series made up mainly of metasedimentary rocks and Upper (Winneba-Kibi belt), Dzigbodi-Adjimah (2003) identified Fe as indigenous to Birimian Series comprising of metavolcanic rocks and greywacke was contested by sedimentation in quartzites but Mn is hydrothermal. neighbouring Francophone geologists as their scheme was reversed comprising of References Asihene, K. A. B. and K. Barning, 1975, A contribution to the stratigraphy of the Birimian lower formation volcanique, middle formation volcano-sedimentaires and an upper System of Ghana, West Africa. Ghana Geological Survey Report, 75/5; Accra, Ghana. 1-30. formation sedimentaire (Tagini, 1971). Currently, Leube et al. (1990) consider the Condie, K. C., 2005, Earth as an Evolving Planetary System. Elsevier Academic Press, rock types as deposited contemporaneously and form a lateral facies. The Birimian, London, UK, 1-447. Dzigbodi-Adjimah, K., 2003, The mineralogy and petrology of the ferruginous manganese on the basis of isotopic age, is Middle Precambrian having been deposited between rocks at Mankwadzi, Ghana. Journal of African Earth Sciences, 38, 293-315. 2100 and 1900 Ma (Asihene and Barning, 1975). Four types of granitoids that lack Dzigbodi-Adjimah, K. and F. Sorgbor, 1993, The mineralogy and genetic significance of the cross-cutting relationships are present in the Birimian. Associated with the manganese carbonate ore at Nsuta, Ghana, Proceedings of National Seminar on current Developments in the Minerals Industry of Ghana, Kumasi, Ghana, 25-32. metasedimentary rocks are basin granitoids which are foliated and were emplaced John, T., R. Klemd, , W. Hirdes, and G. Loh, 1999, The metamorphic evolution of the before the belt granitoids, which are mainly amphibole-rich granodiorite and found Paleoproterozoic (Birimian) volcanic Ashanti belt Ghana, West Africa Precambrian Research, in association with the metavolcanic rocks. Localised Winneba granites are 98, 11-30. Junner, N. R., 1940, The geology of the Gold Coast and western Togoland, Gold Coast restricted to the area occupied by the metasedimentary rocks and cut by the basin Geological Survey, Bulletin, 11, 40. granites and so considered as having Achaean precursor. Kitson, E. A.,1918, Annual Report for 1916/1917 Gold Coast Geological Survey Accra, The Tarkwaian sedimentary rocks are regarded as younger than the Birimian as Kleinschrot, D., R. Klemd, M. Bröcker, M. Okrusch, L. Franz, and, K.Schmidt, 1994, Protores and country rocks of the Nsuta manganese deposit (Ghana). Neues Jahrbuch für Kawere conglomerate at the base consists of reworked polymictic pebbles of Mineralogie, Abhandlungen 168, 67-108. various Birimian rocks. The Tarkwaian rocks are intruded by diabase/dolerite sills Leube, A., W. Hirdes, R. Mauer and G. O. Kesse, 1990, The Early Proterozoic Birimian and dykes and also the Bongo granitoid which is K-rich and located at Bole- Supergroup of Ghana and its associated gold mineralisation, Precambrian Research, 46, 139-165. Navorongo belt. The Birimian rocks have generally been metamorphosed to lower Melcher, F. 1995, Genesis of chemical sediments in Birimian greenstone belts: evidence from greenschist facies but amphibolite facies may occur as contact metamorphic gondites and related manganese bearing rocks from northern Ghana. Mineralogical Magazine, aureoles (John et al., 1999). Structurally, Junner (1940) identified two main 59, 229-251. Mücke, A., K. Dzigbodi-Adjimah, and A. Annor, 1999, The mineralogy, petrology, deformations in the Birimian. Thus the lower Proterozoic Birimian has many geochemistry and genesis of manganese deposits of Proterozoic Birimian rocks of Nsuta, similarities as the Achaean greenstone belts described by Condie (2005) and so it is Ghana. Mineralium Deposita, 34, 297-311. loosely referred to as a greenstone belt although no komatiitic volcanic rocks occur Ntiamoah-Agyakwa, Y., 1979, The relationship between gold and manganese mineralisations in the Birimian of Ghana West Africa, Mineralogical Magazine, 116, 345-352. as in the Achaean counterparts. The Birimian is rich in gold and manganese deposits Nyame, F. K. and N. J. Beukes, 2006, The genetic significance of carbon and oxygen isotopic in addition to bauxite and localised diamond, derived from the Achaean rocks out of variations in Mn-bearing carbonates from the Proterozoic (~2.2 Ga) Nsuta Deposit in the which the sediments were originated. There are many occurrences of manganese Birimian of Ghana. Carbonates and Evaporites, 21, 1, 21-31. Service, H., 1943, The geology of the Nsuta manganese ore deposits. Gold Coast Geological deposits in almost all the six NE trending volcanic belts in Ghana, located at the Survey Memoir, 5, 1-32. contact between the metavolcanic and metasedimentary rocks and enclosed within Tagini, B., 1971, Esquisse structurale de La Côte D’ivoire, Essai de géotechnique régionale. schists, phyllites and metavolcanic rocks. Thèse Université Lausanne, Sodemi, Republique de Côte d’Ivoire, 302. .
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