Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2002 | 1970 | Metric tons of gross weight | NA |
| 2003 | 2100 | Metric tons of gross weight | 6.60% |
| 2004 | 2210 | Metric tons of gross weight | 5.24% |
| 2005 | 2780 | Metric tons of gross weight | 25.79% |
| 2005 | 2780 | Metric tons, gross weight | 0.00% |
| 2006 | 3830 | Metric tons, gross weight | 37.77% |
| 2006 | 3830 | Metric tons of gross weight | 0.00% |
| 2007 | 3810 | Metric tons, gross weight | -0.52% |
| 2008 | 4410 | Metric tons, gross weight | 15.75% |
| 2009 | 3030 | Metric tons, gross weight | -31.29% |
| 2009 | 3030 | Metric tons of gross weight | 0.00% |
| 2010 | 4460 | Metric tons of gross weight | 47.19% |
| 2011 | 5920 | Metric tons of gross weight | 32.74% |
| 2012 | 5570 | Metric tons of gross weight | -5.91% |
| 2013 | 5910 | Metric tons of gross weight | 6.10% |
