Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2009 | 611.81298828125 | Thousand metric tons | NA |
| 2010 | 428.484985351563 | Thousand metric tons | -29.96% |
| 2011 | 457.772003173828 | Thousand metric tons | 6.84% |
| 2012 | 307.184997558594 | Thousand metric tons | -32.90% |
| 2013 | 300 | Thousand metric tons | -2.34% |
