INCOME TAXES: - Tax assets and liabilities (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Assets:
Inventories	$ 55.7	$ 61.5
Capitalized exploration expenses	14.0	11.1
U.S. foreign tax credit carryforward, net of FIN 48 liability	731.8	483.4
U.S. tax effect of Peruvian deferred tax liability	131.3	165.1
Provisions	145.0	155.0
Mexican tax on consolidated dividends	9.0	14.8
Deferred workers participation	24.7	27.0
Accrued salaries, wages and vacations	10.0	9.1
Sales price adjustment (PUI)	3.0	2.7
Social responsibility expenses	2.1	2.1
Deferred charges	14.5	6.1
Valuation allowance on U.S. deferred tax assets, foreign tax credits and U.S. tax effect on Peruvian deferred	(1,097.0)	(819.1)
Other	9.9	10.1
Total deferred tax assets	54.0	128.9
Liabilities:
Property, plant and equipment	(45.4)	(137.3)
Other	(3.0)	(0.4)
Total deferred tax liabilities	(48.4)	(137.7)
Total net deferred tax assets	5.6
Total deferred tax liabilities		$ (8.8)
Increase in valuation allowance	$ 277.9
U.S. statutory rate (as a percent)	21.00%	21.00%	35.00%

Represents the amount as of the balance sheet date of the estimated future tax effects attributable to the difference between the methods used to account for capitalized exploration expenses for tax purposes and under generally accepted accounting principles.

No definition available.