COMMITMENTS AND CONTINGENCIES: - Others (Details) PEN in Millions, $ in Millions	1 Months Ended			9 Months Ended		12 Months Ended
	May 31, 2016 MW	Jul. 31, 2014 MW	Jun. 30, 2014 MW	Sep. 30, 2016 PEN item m km T	Sep. 30, 2016 USD ($) item m km T	Dec. 31, 1997
Other commitments:
Commitment for capital projects					$ 308.2
Tia Maria | Peru
Other commitments:
Project budget					1,400.0
Amount spend as of the current date					$ 362.8
Annual production ( in tons) | T				120,000	120,000
Distance of sea water transportation | km				25	25
Height above sea level of the desalinization plant | m				1,000	1,000
Additional investment in desalinization plant					$ 95.0
Number of jobs expected to be generated | item				3,500	3,500
Number of workers expected to be directly employed | item				600	600
Number of workers expected to be indirectly employed | item				2,000	2,000
Term life of environmental project (in years)				20 years	20 years
Amount committed to funding for social and infrastructure improvement projects				PEN 38.0	$ 11.0
Toquepala Concentrator Expansion | Peru
Other commitments:
Project budget					1,200.0
Amount spend as of the current date					476.6
Amount committed to funding for social and infrastructure improvement projects				400.0	118.0
Development Fund Moquegua Region | Peru
Other commitments:
Amount committed to funding for social and infrastructure improvement projects				PEN 108.5	$ 32.0
Copper | Toquepala Concentrator Expansion | Peru
Other commitments:
Estimated increase in annual production (in tons) | T				100,000	100,000
Molybdenum | Toquepala Concentrator Expansion | Peru
Other commitments:
Estimated increase in annual production (in tons) | T				3,100	3,100
Enersur | Power purchase agreements
Other commitments:
Term of power purchase agreement related to sale of power plant						20 years
Electroperu S.A | Power purchase agreements
Other commitments:
Term of power purchase agreement related to sale of power plant			20 years
Purchase agreement, contracted power capacity (in megawatts) | MW			120
Kallpa | Power purchase agreements
Other commitments:
Term of power purchase agreement related to sale of power plant	10 years	10 years
Purchase agreement, contracted power capacity (in megawatts) | MW		120
Kallpa | Power purchase agreements | Maximum
Other commitments:
Purchase agreement, contracted power capacity (in megawatts) | MW	80