Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2002 | 427682 | Metric tons, gross weight | NA |
| 2003 | 429874 | Metric tons, gross weight | 0.51% |
| 2004 | 510430 | Metric tons, gross weight | 18.74% |
| 2005 | 543341 | Metric tons, gross weight | 6.45% |
| 2006 | 466093 | Metric tons, gross weight | -14.22% |
