Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2003 | 240 | Thousand metric tons | NA |
| 2004 | 240 | Thousand metric tons | 0.00% |
| 2005 | 260 | Thousand metric tons | 8.33% |
| 2006 | 250 | Thousand metric tons | -3.85% |
| 2007 | 260 | Thousand metric tons | 4.00% |
| 2008 | 250 | Thousand metric tons | -3.85% |
| 2009 | 260 | Thousand metric tons | 4.00% |
| 2010 | 378 | Thousand metric tons | 45.38% |
| 2011 | 335 | Thousand metric tons | -11.38% |
| 2012 | 410 | Thousand metric tons | 22.39% |
| 2013 | 400 | Thousand metric tons | -2.44% |
