Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2004 | 131.235992431641 | Thousand metric tons | NA |
| 2005 | 150.585006713867 | Thousand metric tons | 14.74% |
| 2006 | 160 | Thousand metric tons | 6.25% |
| 2007 | 170 | Thousand metric tons | 6.25% |
| 2008 | 160 | Thousand metric tons | -5.88% |
| 2009 | 299.734985351563 | Thousand metric tons | 87.33% |
| 2010 | 344.033996582031 | Thousand metric tons | 14.78% |
| 2011 | 352.233001708984 | Thousand metric tons | 2.38% |
| 2012 | 313.171997070313 | Thousand metric tons | -11.09% |
| 2013 | 350 | Thousand metric tons | 11.76% |
