REFERENCES
- U.S., Bureau of Mines , South Africa and Critical Materials , a Report Prepared for the Subcommittee on Transportation , Aviation and Materials, Committee on Science and Technology, U.S. House of Representatives, March 1986 .
- Bureau of Mines and the U.S. Department of Commerce , Domestic Consumption Trends, 1972-1982, and Forecasts to 1993 for Twelve Major Metals , January 1986 .