INVENTORIES: (Details) (USD $)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Metals at lower of average cost or market:
Finished goods	$ 103,400,000		$ 84,200,000
Work-in-process	339,300,000		305,400,000
Supplies at average cost	307,200,000		304,300,000
Total current inventory	749,940,000		693,942,000
Inventory, long-term:
Leach stockpiles	441,240,000		395,177,000
Leaching costs capitalized as long-term inventory of leachable material	86,100,000	68,200,000
Leachable material inventories recognized in cost of sales	$ 39,200,000	$ 26,700,000