Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2002 | 22000 | Metric tons, gross weight | NA |
| 2003 | 33780 | Metric tons, gross weight | 53.55% |
| 2004 | 42140 | Metric tons, gross weight | 24.75% |
| 2005 | 38081 | Metric tons, gross weight | -9.63% |
| 2006 | 46728 | Metric tons, gross weight | 22.71% |
| 2007 | 31592 | Metric tons, gross weight | -32.39% |
| 2008 | 15268 | Metric tons, gross weight | -51.67% |
| 2009 | 14322 | Metric tons, gross weight | -6.20% |
| 2010 | 14807 | Metric tons, gross weight | 3.39% |
| 2011 | 22794 | Metric tons, gross weight | 53.94% |
| 2012 | 23890 | Metric tons, gross weight | 4.81% |
