Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2002 | 311927 | Metric tons, gross weight | NA |
| 2003 | 468677 | Metric tons, gross weight | 50.25% |
| 2004 | 527100 | Metric tons, gross weight | 12.47% |
| 2005 | 611373 | Metric tons, gross weight | 15.99% |
| 2006 | 634200 | Metric tons, gross weight | 3.73% |
