Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2002 | 300 | Thousand metric tons | NA |
| 2003 | 260 | Thousand metric tons | -13.33% |
| 2004 | 255 | Thousand metric tons | -1.92% |
| 2005 | 260 | Thousand metric tons | 1.96% |
| 2006 | 250 | Thousand metric tons | -3.85% |
| 2007 | 250 | Thousand metric tons | 0.00% |
| 2008 | 250 | Thousand metric tons | 0.00% |
| 2009 | 217.679992675781 | Thousand metric tons | -12.93% |
| 2010 | 240.136001586914 | Thousand metric tons | 10.32% |
| 2011 | 335 | Thousand metric tons | 39.50% |
| 2012 | 327.799987792969 | Thousand metric tons | -2.15% |
| 2013 | 315 | Thousand metric tons | -3.90% |
