INVENTORIES: (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Metals at average cost:
Finished goods	$ 69.6	$ 48.8
Work-in-process	256.8	308.0
Ore stockpiles on leach pads	328.0	320.9
Supplies at average cost	378.3	364.2
Total current inventory	1,032.7	1,041.9
Inventory, long-term:
Ore stockpiles on leach pads	1,177.4	977.4
Total leaching costs added as long-term inventory of ore stockpiles in leach pads	506.6	513.9	$ 439.0
Long-term leaching inventories recognized as cost of sales	$ 299.4	$ 333.5	$ 316.6

Represents the capitalized costs of ore stockpile material contained on a leach pad, such as copper or gold ore.

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- Definition

The current inventory balance before last-in first-out (LIFO) and valuation reserves of ore stockpile material contained on a leach pad, for example, but not limited to, copper or gold ore.

+ References

No definition available.

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- Definition

Represents the costs recognized under cost of sales of ore stockpile material contained on a leach pad, such as copper or gold ore.

+ References

No definition available.

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- References

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- Definition

Carrying amount, net of valuation reserves and adjustments, as of the balance sheet date of merchandise or goods held by the company that are readily available for sale.

+ References

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- Definition

Amount after valuation and LIFO reserves of inventory expected to be sold, or consumed within one year or operating cycle, if longer.

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Amount before last-in first-out (LIFO) and valuation reserves of ore stockpile material contained on a leach pad, for example, but not limited to, copper or gold ore.

+ References

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Carrying amount, net of valuation reserves and adjustments, as of the balance sheet date of products used directly or indirectly in the manufacturing or production process, which may or may not become part of the final product. May also include items used in the storage, presentation or transportation of physical goods.

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Carrying amount, net of reserves and adjustments, as of the balance sheet date of merchandise or goods which are partially completed. This inventory is generally comprised of raw materials, labor and factory overhead costs, which require further materials, labor and overhead to be converted into finished goods, and which generally require the use of estimates to determine percentage complete and pricing.

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