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 % |
