Quarterly report pursuant to Section 13 or 15(d)

ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS (Narrative) (Details)

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ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS (Narrative) (Details) (USD $)
In Millions, unless otherwise specified
Mar. 31, 2014
Dec. 31, 2013
Environmental Remediation Obligations [Abstract]    
Total environmental and mine closure obligations $ 306.3 $ 321.0