Burkina Faso's economy has grown on average 6.3% during the decade 2003-2013 partly due to economic reforms the government has put in place to improve the country's business environment. In 2014, IMF forecasts 6.4% growth, against 6.5% % in 2013 and 9% in 2012. Gold is the chief export, having surpassed cotton in 2009. The first of nine industrial-scale gold mines came on line in 2008. The sector directly employs between 6,000 and 8,000 workers and produced approximately 40 tons of gold in 2013. In that year it contributed 76% of exports, 19% of government revenues and 5.5% of GDP growth. The reserves of the nine mines are estimated at 260 tons with a lifetime ranging from 6 to 15 years. Manganese and zinc deposits have also attracted significant interest from international mining firms. Burkina Faso is the largest cotton producer in Sub-Saharan Africa, producing conventional, organic, and genetically engineered (GE) cotton. The country is a leader in GE cotton production in Africa, with GE cotton accounting for 50% - 60% of cotton harvested. Cotton is critically important to the economy as roughly 50% of the population derive their income from it. Virtually all cotton is produced on small-scale, family-owned or communal plots. Eighty percent of the country's 17 million people are engaged in small-scale, rain-fed subsistence farming. Burkina Faso's per capita gross national income is US$1,513 in 2012, when adjusted for Purchasing Power Parity, making it one of world's poorest countries. Forty-seven percent of the population lives below the poverty line. Burkina Faso was the United States' 180th largest goods export market in 2013. U.S. goods exports to Burkina Faso in 2013 were $77.5 million against $47. 3 million in 2012. The top export categories for 2013 were Machinery, Vehicles, Cereal (rice), and Electrical Machinery.