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Thursday, June 7, 2012

Gold Occurrences in Benin

Map of Benin

Mineral resource development is controlled by the Office Béninoise des Mines (OBEMINES). Benin has been revising its mining laws in order to attract foreign investment.

Benin has gold, iron ore and phosphate potential and has awarded several exploration licenses for gold exploration in the country to foreign investors. There are deposits of brick and china clay, feldspar, the Loumbu Loumbo low grade iron ore deposits and the Mekrou phosphate deposits. The development of the Loumbu Loumbu and Mekrou deposits hinges on the proposed development of a hydro electric power scheme that is to be constructed on the Mekrou River. Gold mineralization has been identified in the Atacora and Alibori regions, where hard rock and alluvial deposits are known to exist. At Alibori, a 350 km2 prospective area includes alluvial and vein hosted gold occurrences.

Major sources of alluvial gold and diamonds can be found in the Birimian rocks that are found in Ghana, the Ivory Coast, Mali and Burkina Faso   These rocks derive their name from the Birim River thay are one of the main tributaries of the Pra River of Ghana.  The same rocks also contain the country’s most important diamond deposits.  Diamonds are produced in Ghana and Mali that are the second and third largest producers in Africa.

The gold and diamond bearing rocks are called the Birimian Terranes that are composed of a mix 0f meta-volcanics, meta-sedimentary and rocks that are plutonic in nature.  Almost half of the rocks found in the southern part of the West African Craton are alkaline granites.  These rocks formed in a period of about 50 million years between 2,200 and 2,100 Ga years ago.

It is believed the Birimian Rocks that stretch across the countries that are to the north of the Gulf of Guinea formed when a series of island arcs were driven together forming a series of parallel belts that trend to the northeast in a belt that is about 40 to 50 kilometers wide.  Many of the volcanic rocks have been metamorphosed into greenschist facies.

Although most of the gold mined in the country is recovered by artisanal miners from the Birimian Terrane it has recently discovered more gold is found in the overlaying conglomerate of the Tarkewian formation.  The gold does not have its origin in the Birimian Terrane. 

There are several varying theories about the origin of the Birimian Terrane.  One theory holds the rocks were formed by the collision of the Archean Cupixi-Carajas craton of the Southern Guiana Shield.  Another theory that is more widely accepted is the terrane has it origins in a mid-oceanic series of volcanic island arcs that formed a crust that was then thrust faulted onto the West African Craton that was later compressed into a series of folds.

During the recent civil war in Benin foreign investment literally dried up, but with the onset of peace it is beginning to flow once again.

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