Petrography and Geochemistry of Granitoids associated with Gold Mineralisation at Mpohor area in southeastern Ashanti Belt of Birimian, Ghana
Keywords:Petrography, Geochemistry, Gold mineralisation, Granitoids, Southeastern Ashanti belt, Birimian, Ghana
Mpohor area in Western Region of Ghana is located within the Birimian at the southeastern corridor of Ashantibelt. Diamond drilling in the area which encloses Father Brown concession intersected steeply dipping igneous rocks on which petrographic and whole rock XRF analyses were conducted to describe the rock types according to mineralogy, texture, alteration and mode of mineralisation. The study showed that gabbro and diorite are weakly deformed, partially altered and of greenschist facies. These rocks intruded into belt granitoids which accompanied metavolcanic rocks (well exposed at a coastal region at the southeast). Subsequent tonalite and granodiorite intrusives, into sheared areas of gabbro are deformed with foliation being parallel to the major foliation in the host rock. This ductile deformation was accompanied by brittle deformation and infiltrated by hydrothermal fluids leading to silicification, carbonatisation, sericitisation, pyritisation of second and third generations and gold mineralisation. On the contrary, chloritisation with fine chalcopyrite together with pyrite of first generation characterise host gabbro and diorite. Hence deformed pyrite porphyroblast of second generation is found in tonalite and partly in contact with magnetite and also associated with gold. The ore zone (Au grade between 1.78 to 48.80 g/t) in tonalite is characterised by lower TiO2 content (<0.73 wt %) in addition to Fe/Mg ratio above 2.4 and Zr values less than 100 ppm which may suggest that mineralised fluid was depleted of Ti and Zr and accompanied the more mafic host rocks.
Abouchami, W., Boher, M., Michard, A., Albarede, F. (1990), A major 2.1 Ga Event of Mantle Magmatism in West Africa, an Early Stage Crustal Accretion. Geophysical Research Bulletin, Vol. 95, p. 17605 - 17629.
Allibone, A., McCuaig T. C., Harris D., Etheridge, M., Munroe, S., Byrne, D. (2002a), Structural Controls on Gold Mineralisation at the Ashanti Gold Deposit. Economic Geology, Special Publication, Obuasi, Ghana, Vol. 9, p. 60 â€“ 94.
Allibone, A., Teasdale, J., Cameron, G., Etheridge, M., Uttley, P., Soboh, A., Appiah-Kubi, J., Adanu, A., Arthur, R., Mamphey, J., Odoom, B., Zuta J., Tsikata, A., Pataye, F. and Famiyeh, S. and Lamb, E. (2002b), Timing and Structural Controls on Gold Mineralisation at the Bogoso Gold Mine, Ghana, West Africa. Economic Geology, Vol. 97, p. 949 â€“ 969.
Allibone, A. H., Hayden, P., Cameron, G. and Duku, F. (2004), Palaeoproterozoic Gold Deposits Hosted by Albite and Carbonate Altered Tonalite in the Chirano District, Ghana, West Africa. Society Economic Geology, Vol. 99, p. 479 - 497.
Asihene, K. A. B. and Barning, K. (1975), A Contribution to the Stratigraphy of the Birimian System of Ghana, West Africa. Ghana Geological Survey Report 75/5, Accra, 30 pp.
Attoh, K. (1980), Structure, Stratigraphy, and some Chemical characteristics of an Early Proterozoic (Birimian) Volcanic belt, northeastern Ghana. Current Research, Part C, Geological Survey Canada Paper 80-1C, p. 69 - 80.
Attoh, K., Evans, M. J. and Bickford, M. E. (2006), Geochemistry of an Ultramafic-Rodingite Rock Association in the Palaeoproterozoic Dixcove Greenstone Belt Southwestern Ghana. Journal of African Earth Sciences, p. 333 - 346.
Bessoles, B. (1977), GÃ©ologie de lâ€™Afrique, Vol. 1, Le Craton Ouest Africain MÃ©moire. Bureau Recherque GÃ©ologique MiniÃ¨re, OrlÃ©ans. 88, 402 pp.
Cooper, W. G. G. (1934), The Geology of the Prestea Goldfield. Memoir 3, Gold Coast Geological Survey, 20 pp.
Dampare, S. B., Shibata, T., Asiedu, D. K., Osae, S. and Banoeng-Yakubo, B. (2008), Geo- chemistry of Palaeoproterozoic Metavolcanic Rocks from the Southern Ashanti Volcanic Belt, Ghana, Petrogenetic and Tectonic Setting Implications. Precambrian Research 162, p. 403 - 423.
Davis, D., Hirdes, W., Schallegger, E. and Nunoo, E. A. (1994), U/Pb Age Constrains on Deposition and Provenance of Birimian and Gold Bearing Tarkwaian Sediments in Ghana Precambrian Research Journal 130, West Africa., p. 113 - 137.
Debon, F. and Le Fort, P. (1983), A Chemical and Mineralogical Classification of Common Plutonic Rocks and Associations Transactions of the Royal Society of Edinburgh, Earth Science, v. 73: p.135 - 149.
Dzigbodi-Adjimah, K. (1988), The Genesis of the Birimian Gold Deposits of Ghana A Paper Presented at the International Conference on the Geology of Ghana, Accra, Ghana, 9th -16th October, p.123 - 167.
Dzigbodiâ€“Adjimah, K. (1993), Geology and Geochemical Patterns of Birimian Gold Deposits, Ghana West Africa Journal of Geochemical Exploration. Elsevier Science, Publishers B. V. Amsterdam, Vol. 47 p. 305 - 320.
Eisenlohr, B. N. and Hirdes, W. (1992), The Structural Development of the Early Proterozoic Birimian and Tarkwaian Rocks of Southwest Ghana, West Africa Journal of African Earth Sciences 14, 3, p. 313 â€“ 325.
Flach, G. A. (1999), Terminal Exploration Report Hwini-Butre Concession Unpublished Ave Delta Press, p. 43 - 106.
Groves, D. I., Phillips, N., Ho, S. E., Houstoun, S. M. and Standing, C. A. (1987), Craton-Scale Distribution of Archaean Greenstone Gold Deposits: Predictive capacity of the Metamorphic Model Economic Geology, v. 82, p. 2045 - 2058.
Hirdes, W., Senger, R., Adjei, J., Efa, Loh, G. and Tettey, A. (1993), Explanatory Notes for the Geological Map Southwestern Ghana 1:100000 Geolosches Jarbuuch, Hanover Press, B83, 139 pp.
Huot, D., Sattran, V. and Zida, P. (1987), Gold in Birrimian Greenstone Belts of Burkina Faso, West Africa Economic Geology, Vol. 82, p. 2033 - 2044.
Hutchison, C. S. (1974), Laboratory Handbook of Petrographic Techniques John Wiley and Sons Press, 527 pp.
John, T., Kleimd, R., Hirdes, W. and Loh, G. (1999), The Metamorphic Evolution of the Palaeoproterozoic (Birimian) Volcanic Ashanti belt (Ghana, West Africa) Precambrian Research 98, p. 11 - 30.
Junner, R. N. (1935), Gold in the Gold Coast Gold Coast Geological Survey Memoir 4, 67 pp.
Kesse, G. O. (1985), The Mineral and Rock Resources of Ghana A. A Balkema, Rotterdam, 610 pp.
Leube, A., Hirdes, W., Mauer, R., Kesse, G. O. (1990), The Early Proterozoic Birimian Supergroup of Ghana and Some Aspects of its Associated Gold Mineralisation, Precambrian Research Vol. 46, p. 136 - 165.
Loh, G. and Hirdes, W. (1999), Explanation notes for the Geological Map of Southwest Ghana 1:100000 sheet Sekondi (0402A) and Axim (0403B). Geological Survey Bulletin, No. 49, BGR, Hannover, (unpublished), 149 pp.
Manu, J. (1993), Gold Deposits of Birimian Greenstone Belt in Ghana: Hydrothermal Alteration and thermodynamics Braunschweiger Geologisch- PalÃ¤ontologische Dissertationen, 17, 116 S., 44 abb. 14 Tab. 185 pp.
Mayer, M. and Saag, R. (1985), The Gold content of some Archaen rocks and their possible relationship to Epigenetic Gold-quartz Vein Deposits Mineralium Deposita, v. 20, p. 284 - 289.
MilÃ©si, J. P., Ledru, P., Ankrah, P., Johan, V., Marcoux, E., Vinchon, Ch. 1991, The Metallogenic Relationship between Birimian and Tarkwaian Gold Deposits in Ghana Mineralium Deposita Conference, v. 26 p. 228 - 238.
MÃ¼cke, A. and Dzigbodi-Adjimah, K. (1994), Ore texture and parageneses of the Prestea and Obuasi Gold deposits in the Ashanti belt of Ghana, An Ore Microscopic Study, Geologisches, Jahrbuch, Vol. D100, p. 167 - 199.
Mumin, A. H., Fleet, M. E. and Longstaffe, F. J. (1994), Gold Mineralisation in As-rich Mesothermal fluids in the Ashanti Gold belt, Ghana: Stable Isotope Geochemistry of Carbonates, Graphite and Quartz. Economic Geology, Vol. 31, p. 135 - 148.
OberthÃ¼r, T., Weiser, T., Amanor, J. A. and Chryssoulis, S. L. (1997), Mineralogical siting and Distribution of Gold in Quartz Veins and Sulphide Ores of the Ashanti Mine and other Deposits in the Ashanti Belt of Ghana: Genetic Implications Mineralium Deposita, Vol. 32, pp. 2 - 15.
OberthÃ¼r, T., Vetter, U., Davis, D.W. and Amanor, J.A. (1998), Age constraints on gold mineralisation and Palaeoproterozoic Crustal Evolution in the Ashanti belt of southern Ghana. Precambrian Research, Vol. 80, p. 129 - 143.
Papon, A. (1973), GÃ©ologie et MinÃ©ralisations du Sud-Ouest de la CÃ´te dâ€™Ivoire MÃ©moire Bureau Recherque GÃ©ologique MiniÃ¨re, France, 80, 284 pp.
Picot, P. and Johan, Z. (1982), Atlas of Ore Minerals Elsevier, Amsterdam, Adams Press, 275 pp.
Streckeisen, A. (1974), Classification and Nomenclature of Plutonic Rocks, Recommendation of the IUGS Subcommission on Systematics of Igneous Rocks. Geologische Rundschau. Internationale Zeitschrift fur Geologie, Stuttgart, Vol. 63, p. 773 - 785.
Spry, P. G., Gedlinske, B. L. (1987), Tables for the Determination of Opaque Common Minerals. Economic Geology Publishing Company, 5 pp.
Tagini, B. 1971, Esquisse structurale de la CÃ´te dâ€™Ivoire, Essai de GÃ©otechnique RÃ©gionale ThÃ¨se UniversitÃ© Lausanne, SODEMI, Republique de CÃ´te dâ€™Ivoire, 302 pp.
Taylor, P. N., Moorbath, S., Leube, A. and Hirdes, W. 1992, Early Proterozoic Crustal Evolution in the Birimian of Ghana Constraints from Geochronology and Isotope Geology. Precambrian Research 56, p. 97 - 111.
Trashliev, S. S. (1972), The Geology of 1/4Â° Field Sheets No. 82 and 46, Wiawso, S. E. and Asangragwa, N. E, Report of the Ghana Geological Survey (unpublished), 88 pp.
Whitney, D. L. and Evans, B. W. (2010), Abbreviations for Names of Rock-Forming Minerals. American Mineralogist, Vol. 95, p. 185 - 187.
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