Mining, begun in the Congo in 1905, was the most important sector of the economy and was dominated by crude oil, which contributed 15% of GDP in 1996 and accounted for 90% of exports in 2002. Diamonds were a leading export commodity, and cement was the second-leading industry in 2002. In 2000, gold and lime were the only nonfuel minerals extracted, and in small amounts. A formal cease-fire between the government and rebel forces in 2000 appeared to end the civil war begun in 1997, which significantly damaged the economy and the land-based infrastructure. The year 2000 saw the beginning of a long process of restoring the government, establishing a national dialogue, adopting a new constitution, and resettling more than 800,000 people displaced during the civil war. A sharp upturn in oil prices and renewed efforts to finance a major magnesium development suggested that the minerals sector could be a catalyst for economic renewal of the country. Other mineral deposits, in addition to petroleum and natural gas, were bauxite, bentonite, granite, gypsum, kaolin, marble, talc, potassium, potash, phosphate, limestone, lead, zinc, copper, and iron. Mining has generally been carried out by the state or through state-owned joint ventures.
Potash was the main mining product before the rapid growth of oil. Production was not enough to make operations profitable and ceased after 1977. Gold, mined in the Mayombé area, reached 158 kg in 1967 but fell to 10 kg in 1996–2000. Copper production at Mindouli ceased in 1978. Production of zinc and lead, extracted at Mfouati since 1938, was suspended in 1984. Iron deposits estimated at 400 million tons have been found. AfriOre Ltd., of Canada, though inactive in the Congo in 2000, held exploration permits on the Boko Songo copper prospect, with 2 million tons of ore, and the Yanga Koubanza lead-zinccopper prospect, with 5.5 million tons, both west of Brazzaville, and the company located high-grade copper mineralization at four other drilled prospects. Significant resources of magnesium, with byproducts of salt, potash, and possibly chlorine, were being evaluated for development in the Makola and the Youbi magnesium salt evaporite deposits, in the Kouilou region.