Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2002 | 265 | Thousand metric tons | NA |
| 2003 | 331 | Thousand metric tons | 24.91% |
| 2004 | 402.5 | Thousand metric tons | 21.60% |
| 2005 | 511 | Thousand metric tons | 26.96% |
| 2006 | 530 | Thousand metric tons | 3.72% |
| 2007 | 520 | Thousand metric tons | -1.89% |
| 2008 | 411 | Thousand metric tons | -20.96% |
| 2009 | 460 | Thousand metric tons | 11.92% |
| 2010 | 490 | Thousand metric tons | 6.52% |
| 2011 | 458 | Thousand metric tons | -6.53% |
| 2012 | 377 | Thousand metric tons | -17.69% |
