Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2003 | 229.432006835938 | Thousand metric tons | NA |
| 2004 | 208.319000244141 | Thousand metric tons | -9.20% |
| 2005 | 210 | Thousand metric tons | 0.81% |
| 2006 | 210 | Thousand metric tons | 0.00% |
| 2007 | 210 | Thousand metric tons | 0.00% |
| 2008 | 210 | Thousand metric tons | 0.00% |
| 2009 | 241.113998413086 | Thousand metric tons | 14.82% |
| 2010 | 364.760986328125 | Thousand metric tons | 51.28% |
| 2011 | 446.524993896484 | Thousand metric tons | 22.42% |
| 2012 | 289.480987548828 | Thousand metric tons | -35.17% |
| 2013 | 300 | Thousand metric tons | 3.63% |
