Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2002 | 20400 | Metric tons, gross weight | NA |
| 2003 | 33300 | Metric tons, gross weight | 63.24% |
| 2004 | 40300 | Metric tons, gross weight | 21.02% |
| 2005 | 34000 | Metric tons, gross weight | -15.63% |
| 2006 | 27900 | Metric tons, gross weight | -17.94% |
| 2007 | 25000 | Metric tons, gross weight | -10.39% |
| 2008 | 25000 | Metric tons, gross weight | 0.00% |
