Annual report pursuant to Section 13 and 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, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Asset Retirement Obligation [Roll Forward]    
Asset retirement obligation at beginning of period $ 290.6us-gaap_AssetRetirementObligation $ 231.1us-gaap_AssetRetirementObligation
Accretion expense 14.5us-gaap_AssetRetirementObligationAccretionExpense 18.1us-gaap_AssetRetirementObligationAccretionExpense
Exchange rate changes (2.4)us-gaap_AssetRetirementObligationForeignCurrencyTranslation (3.4)us-gaap_AssetRetirementObligationForeignCurrencyTranslation
Revision in estimated cash flows (65.2)us-gaap_AssetRetirementObligationRevisionOfEstimate 44.8us-gaap_AssetRetirementObligationRevisionOfEstimate
Payments 4.7us-gaap_AssetRetirementObligationLiabilitiesSettled 0us-gaap_AssetRetirementObligationLiabilitiesSettled
Asset retirement obligation at end of period $ 232.8us-gaap_AssetRetirementObligation $ 290.6us-gaap_AssetRetirementObligation