The nonfuel sector of the Libyan mining industry was negligible. Petroleum was Libya's leading industry in 2002—Libya was the second-largest crude oil producer in Africa, after Nigeria—cement production ranked fifth, and the hydrocarbon sector accounted for 98% of foreign exchange revenues. Estimated production in 2000 included 270,000 tons of lime, 175,000 tons of gypsum, and 13,000 tons of sulfur (byproduct of petroleum and natural gas). Also produced were hydraulic cement, clay, calcined dolomite, limestone, nitrogen, salt, crude construction stone, and possibly natron (soda ash). Libya had large reserves of iron ore in the Fezzan. The Wadi ash-Shatti iron ore deposit, near Brach, was estimated to contain 1,600 million tons of oolitic hematite, limonite, chamosite, and siderite with a grade range of 30%–48% iron. There were also deposits of magnesium salts (7.5 million tons) and potassium salts (1.6 million tons) in Maradah, south of the Port Brega oil terminal; potash in the Sirte Desert; and magnetite, phosphate rock, and sulfur.