Birim

BIRIM (EN: Birim; RU: Бирим) is the diamond-bearing region within Ghana, at the distance of 90-130 kilometres from the Accra city to the north-west. The industrial extraction has been started during the 1920. The overwhelming quantity of the diamonds is being extracted by the "Ghana Consolidated Diamonds" company. The riverbed and terraced placer deposits of the Neogene and Quaternary ages may be traced along the banks of the Birim river and its tributaries through the distance of up to 3 kilometres, rarely 12-14 kilometres, with the width of 10-120 metres, and with the average thicknesses of 0.2-1.0 metres, with the content of the diamonds of 2.5 karats per cubic metre. There have preserved themselves the placer deposits of the ancient river network on the watersheds, with the content of the diamonds of 0.5-1.0 karats per cubic metre. The individual findings of the diamonds have been recorded within the depositions of the crust of weathering on the rocks of the Lower (the Birim series) and Middle (the Tarkwa series) Proterozoic.

The placer deposits are being developed by excavators and bulldozers, the transportation is performed by the dump trucks. By the 1975, there have been extracted approximately 85 million carats, the reserves are approximately 80-100 million carats (1976, estimate). The rock mass (gravel) is being processed at the beneficiation plants, which are extracting approximately 2 million carats per year (2408 thousand carats during the 1966, 2424 thousand carats during the 1970, 1940 thousand carats during the 1977), with the average content of 2 karats per cubic metre. At the placer deposits, which are not suitable for the mechanical development, the extraction of the diamonds is conducted on the small scale by the private companies and prospectors. The average mass of the diamonds is 0.025-0.07 carats, within the ancient placer deposits is up to 0.1 carats. Approximately 10% of the extraction are amounted to the stones, which are suitable for the jewellery. The centres of the development are the Aquatia and Edubia cities. The reserves of the diamonds within the Aquatia city region are near to exhaustion. There have been started the works for the preparation for operation of the new diamond-bearing region within the lower reaches of the Birim river, where the reserves of the diamonds are estimated at approximately 50 million carats.