The Marange diamond fields, a 300 square-mile alluvial deposit in Zimbabwe, was ranked the worlds largest source of diamonds in 2013 in terms of total carats produced, estimated to have produced almost 17 million carats or 13% of global supply. However, It appears that 2013 production levels will not be sustained in 2014 as grades have decreased and easily minable loose gravel has been rapidly depleted leaving more difficult-to-mine conglomerate stone. While Marange is a relatively new project with formal mining commencing only 5 years ago, alluvial projects like Marange tend to have a much shorter life span than open-pit or underground diamond mines, as the economic resource is limited to the easily accessible surface stones; mining deeper solid conglomerate rock is not economic in a lot of cases. None of the 7 private companies operating in Marange provide specific production guidance, but representatives of the companies have publically expressed frustration with decreased operating economics resulting from depleted resource. In 2014, Marange production is estimated to drop to 8-12 million carats or less.