A Decade of Change—Mineral Exploration in West Africa in Its Usefulness

A decade of change—mineral exploration in West Africa by D. Pohl* Introduction Geological survey departments and Ministries have changed dramatically for the The past decade has seen rapid expansion in better during the last decade, largely through the West African mineral exploration donor funding for reorganization, computeri- environment. This expansion has been largely zation and fundamental field surveys. This has driven by changes in resulted in greater transparency of operation, ➤ Political climate faster processing of, or the reduction of, red ➤ Fiscal and legal regimes tape, and better availability and distribution of ➤ Exploration approaches new geological and technical data. ➤ West African geology. But a note caution of is in order. The Major regional mapping and geochemical recent move to make local geological survey surveys by the UNDP, and the BRGM in the departments self-sufficient enterprises may be late 1970s and early 1980s laid the foundation counter-productive and as such should be resisted by the minerals industry. After an for the rapid development of mineral initial capacity building effort largely funded exploration and resources during the past by foreign aid, local geological surveys became decade. An additional driving impetus was the very responsive to the minerals industry. discovery by native artisanal miners of many However, of late, the pressure to generate significant new gold occurrences at Libiri, income has seen dramatic rises in costs and Essakan, Bouda and Tirahori, during the great fees for the mining industry without any droughts of the late seventies and early corresponding increase in quality or services eighties. rendered. In some instances there has even The successful democratization of Ghana’s been a decline in service. The concept of public military-led regime, the replacement of military service and essential national investment must regimes in Mali and Guinea by multiparty be reinforced. governments and the peaceful passing of Côte On the exploration side, the trend has been d’Ivoire’s Houphouet-Boigny signalled a more to utilize new geochemical survey techniques mature political climate, conducive to resource developed in Australia which has similar extraction, particularly by foreign entities. problems of deeply weathered soils and cover, Unfortunately the positive political and to extensively use airborne magnetics and developments in Ghana, Mali, Burkina Faso, radiometrics to look through deep overburden. Niger, and Côte d’Ivoire have been offset by Responsible analytical laboratories have been political instability in Togo and Benin, civil established in most West African countries and war in Liberia, Sierra Leone, Congo and offer healthy competition to the previously Guinea Bissau, as well as a secessionist monopolistic government laboratories. The movement in Senegal. availability of low-cost percussion drills has Ghana led the way with major positive fueled a movement toward pattern drilling and changes in mining law and fiscal regimes even regional sampling by drilling. covering the mining industry. Mining laws in Interestingly, one of the earliest and best Mali, Burkina Faso, Côte d’Ivoire have now geochemical indicators used in West Africa, converged toward those in Ghana, Australia, artisanal mining activity, may be diminishing Canada and the U.S.A. However, a vestige of socialist-marxist idealogy remains in that most governments retain a carried interest in all mineral properties. Even this attitude may fall by the wayside also, as has been the case in * Sanu Resource Inc. Los Angeles, U.S.A. Tanzania. Tax laws are now, generally, in line © The South African Institute of Mining and Metallurgy, 1998. SA ISSN 0038–223X/3.00 + with those in developed countries and in many 0.00. This paper was presented at the SAIMM instances countries offer favorable tax Symposium: Mining in Africa ’98, 14–15 Sep. treatment to the mining industry. 1998. The Journal of The South African Institute of Mining and Metallurgy NOVEMBER/DECEMBER 1998 311 ▲ A decade of change—mineral exploration in West Africa in its usefulness. Native mining has a detection limit of about Junner (1940) also defined the Tarkwaian System 200 ppb gold. Rising standards of living, the low price of gold consisting of a succession of arenaceous sediments and absence of catastrophic drought all put downward unconformably overlying the Birimian. The succession pressure on artisanal exploration and exploitation. Artisanal begins with basal heterolithic conglomerates and arenites of miners are now following exploration companies rather than the Kawere Group followed by quartz pebble conglomerates vice versa. and arenites of the Banket Series which are in turn overlain Political, fiscal and legal change may have been the key by two sequences of sandstone and phyllite, the Upper and in bringing mining companies to West Africa but it will be Lower Huni Sandstones and Phyllites. the expansion of the understanding of the geological Junner’s proposed stratigraphy became the paradigm for framework of West Africa that will keep them there. From a the Birimian in West Africa. geological perspective there has been a revolutionary change The tonalite-trondjheimite-granodiorite (TTG) complex in the knowledge and understanding of West African granitoids associated with Birimian greenstone belts in geology. The discovery of new styles of mineralization, such Ghana were divided into three major groups (Kesse 1985), a as Sadiola, Essakan, Ayenfuri, Abosso and diverse tectonic foliated, biotite-bearing batholithic plutonic series, the Cape environments are expanding the possibilities for discovery of Coast type, and interpreted as pre- or syntectonic; a gold and basemetal resources in West Africa. It has been the hornblende-bearing, porphyritic, post-tectonic granodiorite, use of detailed mapping, high-precision age determinations the Dixcove type and the post-orogenic Bongo granites. The coupled with high-resolution airborne magnetics and EM inferred age relationships between these granitoid groups data that fueled these changes. But our knowledge base is has recently been challenged and modified by German work still fragmentary and contains many unresolved questions. on the Birimian in Ghana. They divide the granitoids into For progress in understanding to grow, cooperation and those intrusive into the volcanic belts (functionally funding from mining companies, universities and equivalent to the Dixcove type), those intrusive into government agencies will be required. sedimentary basins (broadly equivalent to the Cape Coast type) and post-orogenic plutons (Bongo type). Early Proterozoic geology of West Africa Francophone concepts and contributions Fundamental to the understanding of the Birimian supercrustals, is the reconciliation of conflicting paradigms of The concept of an ensialic rift setting for Birimian sedimen- the stratigraphy and geodynamics established locally by tation and volcanism was first introduced by Arnould (1961) different groups of geologists and researchers and then and enthusiastically supported by most subsequent extrapolated throughout the Early Proterozoic Birimian francophone workers in spite of the absence of basement- province. Birimian sedimentary contacts or rift-filling sedimentary All the Early Proterozoic supracrustal rocks with the successions. The extension of this geodynamic model of the exception of some late silici-clastic basins in Ghana and Côte Birimian led to the concept that each Birimian belt or basin d’Ivoire (Tarkwaian System) have been assigned to the recorded the same history. Birimian Supergroup (Archambault, 1935, 1943; Tagini, Problems with this global stratigraphy and in particular 1971; Bessoles, 1977; Kesse, 1985). (A note on with correlation of conglomerates within volcanic sequences nomenclature: Kitson’s original definition used the term with the Tarkwaian of Ghana led Tagini (1971) to invert the Birrimian to describe rocks in the Birim River valley of stratigraphy of the Birimian in Côte d’Ivoire. He proposed a southern Ghana but following a request by the Ghana lower volcanic and sedimentary sequence separated in time Geological Survey (Kesse and Barning, 1985) the spelling by a weak tectono-metamorphic episode from an upper has been changed to Birimian to conform to the official place sedimentary unit. The hypothesis was based on a postulated name of the type locality.)

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