Diamond mining was the country's leading industry and top export commodity in 2002. Mining accounted for about 4% of GDP and 40%–50% of export earnings. Diamonds were discovered in alluvial deposits in various parts of the country in 1935 and 1947. Production, which reached 609,360 carats in 1968, was estimated at 530,000 carats in 2000, 75% of gem quality. Sizable quantities were smuggled out of the country. About 60% of the nation's diamonds came from the upper Sangha region. Gold production, which began in 1930 and peaked at 521 kg in 1980, fell to 26 kg in 1982; it was 100 kg in 2000. Diamonds and gold were still mined in alluvial deposits, by about 40,000 artisanal miners, primarily in the Bandas and the Bogoin-Boali greenstone belts.
Uranium was discovered in 1966 in the Bakouma region in the eastern part of the country, and there was further prospecting in the Berbérati and Bangassou areas; exploitation has not occurred, because of high start-up costs and poor transportation. Reserves were estimated at 18,000 tons. Iron deposits estimated at 3.5 million tons have been exploited, but production has ceased. The country also had deposits of nickel, graphite, ilmenite, lignite, monazite, rutile, manganese, cobalt, tin, copper, china clay, and limestone. The lack of adequate transportation and industrial infrastructure hindered the development of the nation's mineral industry. Little of the country's 400,000-sq-km Precambrian terrane has been explored using modern exploration techniques.