Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2005 | 400 | Thousand metric tons | NA |
| 2006 | 377 | Thousand metric tons | -5.75% |
| 2007 | 320 | Thousand metric tons | -15.12% |
| 2008 | 320 | Thousand metric tons | 0.00% |
| 2009 | 251.091995239258 | Thousand metric tons | -21.53% |
| 2010 | 239.468002319336 | Thousand metric tons | -4.63% |
| 2011 | 273.714996337891 | Thousand metric tons | 14.30% |
| 2012 | 238.555999755859 | Thousand metric tons | -12.85% |
| 2013 | 240 | Thousand metric tons | 0.61% |
