INCOME TAXES: (Tables)

6 Months Ended

Jun. 30, 2017

INCOME TAXES:

Schedule of income tax provision and effective income tax rate

The income tax provision and the effective income tax rate for the first six months of 2017 and 2016 consisted of ($ in millions):

	2017			2016
Statutory income tax provision	$	289.1		$	175.5
Peruvian royalty	0.4			—
Mexican royalty	32.3			13.7
Peruvian special mining tax	14.8			5.0
Total income tax provision	$	336.6		$	194.2
Effective income tax rate	35.7		%	32.7		%

Summary of income tax rate and dividend tax rate due to change in enacted tax law

Year	Income Tax Rate		Dividend Tax Rate
2016	28.0	%	6.8	%
2017 and later	29.5	%	5	%