Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2002 | 250 | Thousand metric tons | NA |
| 2003 | 459 | Thousand metric tons | 83.60% |
| 2004 | 459.496002197266 | Thousand metric tons | 0.11% |
| 2005 | 370.143005371094 | Thousand metric tons | -19.45% |
| 2006 | 355.640991210938 | Thousand metric tons | -3.92% |
| 2007 | 350 | Thousand metric tons | -1.59% |
| 2008 | 350 | Thousand metric tons | 0.00% |
| 2009 | 201.067001342773 | Thousand metric tons | -42.55% |
| 2010 | 159.248001098633 | Thousand metric tons | -20.80% |
| 2011 | 92.2839965820313 | Thousand metric tons | -42.05% |
| 2012 | 87.3789978027344 | Thousand metric tons | -5.32% |
| 2013 | 68.4869995117188 | Thousand metric tons | -21.62% |
