Quarterly report pursuant to Section 13 or 15(d)

ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS (Asset Retirement Obligation Disclosure) (Details)

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ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS (Asset Retirement Obligation Disclosure) (Details) - USD ($)
$ in Millions
6 Months Ended 12 Months Ended
Jun. 30, 2015
Dec. 31, 2014
Asset Retirement Obligation [Roll Forward]    
Asset retirement obligation at beginning of period $ 142.4 $ 177.6
Accretion expense 2.5 5.7
Exchange rate changes (1.3) (2.4)
Revision in estimated cash flows 46.8 (38.5)
Asset retirement obligation at end of period $ 190.4 $ 142.4