1. R. R. Conry and K. D.Karlin , in Encyclopedia of Inorganic Chemistry , ed. R. B. King , Wiley , Chichester , 1994 , vol. 2 , p. 829
2. https://www.copper.org/education/history/timeline/timeline.html
3. The copper rush of the nineties
4. https://www.usgs.gov/centers/nmic/copper-statistics-and-information