1. Aydin, H., 1998. Labor Productivity Growth in the U.S. Copper Industry. Unpublished PhD dissertation, Colorado School of Mines, Golden, CO.
2. Scarcity and growth revisited;Barnett,1979
3. Scarcity and Growth;Barnett,1963
4. Natural resource prices: will they ever turn up?;Berck;Journal of Environmental Economics and Management,1996
5. Metallic Mineral Exploration: An Economic Analysis;Eggert,1987