Demographics and Geographic Setting
Ghana is situated in West Africa, immediately north of the equator and on the Greenwich meridian. Ghana is bordered to the north and northwest by Burkina Faso, to the east by Togo, to the south by the Atlantic Ocean, and to the west by Côte d’Ivoire (Ivory Coast). Formerly a British colony known as the Gold Coast, Ghana was the first nation in sub-Saharan Africa to achieve independence from its colonial rulers in 1957.
Ghana has a total land area of 238,537km² (92,100 square miles). Its capital city is Accra, while other major cities include Kumasi, Tema, Tamale and Sekondi-Takoradi. Ghana has a tropical climate and a population of approximately 21 million (2005 estimate).
English is the official language of Ghana and is universally used in schools. The government has selected nine traditional Ghanaian languages, in addition to English and French, for use in educational institutions. Traditional religions are adhered to by more than one-fifth of the population while Christianity has been adopted by approximately three-fifths, and Muslim beliefs by about 16% of the population.
Natural resources include gold, timber, diamonds, bauxite and manganese, while agricultural products include cocoa, rubber, coconuts, coffee, pineapples, cashews, pepper and other food crops. Ghana’s industries are dominated by mining, timber processing, light manufacturing, fishing, aluminium production and tourism.
Political and Financial Status
Following cessation of colonial rule in 1957, Ghana has seen four republics, with intermittent military rule. The first republic extended from March 1957 to February 1966, under the first president, Dr Kwame Nkrumah. The second republic extended from June 1979 to September 1981, under President Dr Hilla Limann, while the third, under President Flt Lt Jerry Rawlings, was elected for the maximum 2 terms from June 1993 until December 2000. In a relatively peaceful process in December 2000, the Ghanaian people elected the New Patriotic Party (NPP) under Mr John Kuffour into government for a 4 year term. In December 2004 Mr John Kuffour won re-election for a further 4 years, in what were deemed free and fair elections by international monitoring groups.
Ghana’s GDP relies heavily on gold, cocoa, rubber and timber, amounting to US$48 billion in 2004. Well endowed with natural resources, Ghana has roughly twice the per capita output of the poorer countries in West Africa. Even so, Ghana remains heavily dependent on international financial and technical assistance. Gold, timber and cocoa production are major sources of foreign exchange. The domestic economy continues to revolve around subsistence agriculture, which accounts for 35% of GDP and employs 60% of the work force. Receipts from the gold sector should help sustain GDP growth in 2005.
Gold represents Ghana’s major export commodity, providing approximately 50% of GDP. Ghana is the world’s 10th and Africa’s 2nd largest producer of gold, with current production estimated at in excess of 2.4Moz per annum. High gold prices have resulted in a recent significant increase in expenditure on gold exploration in Ghana.
History of Gold Mining in Ghana
Ghana has been a producer of gold since the 16th century and today boasts one of the largest and richest reserves of gold in the world. The Ghanaian gold mining industry is a relative success story in the government’s attempts to turn the fledgling economy around. The gold sector followed the countries general trend of economic stagnation during the 1970s and, by the early 1980s, was starved of foreign investment to modernize and improve output. However, following the government’s policies of market liberalization aimed at increasing foreign investment, the industry was turned around, and in 2003 gold output exceeded 2.4Moz.
Regional Geological Setting
The gold deposits of West Africa largely lie within the Proterozoic domain of the Man Shield, the southernmost subdivision of the West African (or Guinean) Craton. The Man Shield represents approximately 45% of the exposed geology of Ghana, being largely restricted to the northern, western and south-western portions of the country. The shield area is confined to the southeast by the Proterozoic Togo Mobile Belt and the central-eastern portion is largely covered by late Proterozoic to early Palaeozoic sedimentary rocks of the Volta Basin.
Basement rocks of western Ghana comprise sedimentary and mafic volcanic rocks of the Birimian Supergroup, sedimentary rocks of the Tarkwaian Group, and various granitoid intrusions (Figure 1). Within the Birimian Supergroup, northeast-striking belts of mafic volcanic rocks are separated from intervening basins of dominantly turbiditic sedimentary rocks by major faults. Tarkwaian Group sedimentary rocks include conglomerates, various quartzose and arkosic sandstones, siltstones, and minor shales. Tarkwaian rocks are generally confined to belts of Birimian volcanic rocks where they occur as either fault-bounded slices or as unconformably overlying sequences.
The principal gold producing areas of Ghana occur within Palaeoproterozoic Birimian meta-volcanic and meta-sedimentary rocks, and within the marginally younger, overlying Tarkwaian meta-sedimentary succession.
Gold mineralisation in Ghana and the majority of the Birimian and Tarkwaian rocks of West Africa is found in three principal settings. Orogenic type gold mineralisation related to major structures at the Upper and Lower Birimian contact form the dominant deposit type. Examples of this style of mineralisation occur at Ashanti, Bogoso, Prestea, Akyem and Yamfo. Deposits are of numerous styles, including quartz veins hosted within frequently carbonaceous phyllites and greywackes associated with major shear structures and subsidiary oblique faults. Lower grade mineralisation may also be present as disseminations or associated with sheeted quartz veining within tuffs, greywackes and mafic dykes situated in close proximity to major structures.
The second and increasingly significant type of orogenic gold mineralisation is associated with sheeted vein swarms and stockwork zones within granitoids. Better examples include the Subika deposit at Ahafo and the Ayanfuri deposit near Obuasi. These deposits appear to be confined to the Dixcove suite granitoids and their regional equivalents.
Banket deposits represent the third significant style of mineralisation. These are paleao-placer deposits hosted in quartz pebble conglomerate towards the base of the Tarkwaian Series. The gold is detrital in origin and derived from erosion of older hydrothermal-related mineralisation. Epigenetic sheeted or stockwork quartz veining is, however, being increasingly recognised as an important source of gold within lower portions of the Tarkwaian Series.
Mike Ivey — Tarkwaian Sediments