Birim River
Coordinates: 5°59′30″N 0°50′0″W / 5.99167°N 0.83333°W
The Birim River is one of the main tributaries of the Pra River in Ghana and the country's most important diamond-producing area, flowing through most of the width of the Eastern region. The river rises in the east of the Atewa Range, flows north through the gap between this range and the Kwahu Plateau, then runs roughly south-west until it joins the Pra. It gives its name to the Birimian rock formation, which yields most of the gold in the region. Ghana is the second largest producer of gold in Africa.
The Birim River basin lies in the Man Shield area of the West African craton, which has been overlaid by Early Proterozoic metasedimentary Birimian rocks. These rocks appear to have originated in mid-oceanic arcs of volcanoes, which formed a crust that collided with and rode over the Man shield portion of the West African Craton and was compressed to form a series of folds generally trending northeasterly. The Birimian rocks include Akwatian formations, named after the town of Akwatia in the Birim valley, which have yielded more than 100,000,000 carats (20,000 kg) of diamonds. The great majority of the diamonds are found in Harzburgitic rocks and seem to have crystallized at unusually high temperatures and pressures deep in the lithosphere.
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