Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2002 | 2000 | Thousand metric tons | NA |
| 2003 | 2000 | Thousand metric tons | 0.00% |
| 2004 | 2200 | Thousand metric tons | 10.00% |
| 2005 | 2400 | Thousand metric tons | 9.09% |
| 2006 | 2500 | Thousand metric tons | 4.17% |
| 2007 | 2500 | Thousand metric tons | 0.00% |
| 2008 | 2500 | Thousand metric tons | 0.00% |
| 2009 | 1500 | Thousand metric tons | -40.00% |
| 2010 | 2650 | Thousand metric tons | 76.67% |
| 2011 | 2820 | Thousand metric tons | 6.42% |
| 2012 | 2900 | Thousand metric tons | 2.84% |
