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2. Butler, B.S. and Burbank, W.S., 1929. The Copper Deposits of Michigan, Professional Paper 144, US Geological Survey, Washington.
3. Cox, Denis P. and Singer, Donald A. ,Eds. (1996, and 1998 on the web), Mineral Deposit Models, US Geological Survey Bulletin 1693 (〈http://pubs.usgs.gov/bul/b1693〉).
4. Mine size and the structure of costs;Crowson;Resources Policy,2003
5. Copper production from the late 1990s- A paradox? Copper Studies, December 2009;Crowson,2009