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Mining concessions, development costs, property, plant and equipment, net (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Disclosure of Mining concessions, development costs, property, plant and equipment, net [Line Items]      
Opening balance $ 1,949,555 $ 1,960,025  
Balance as of December 1,847,615 1,949,555 $ 1,960,025
Gross carrying amount [member]      
Disclosure of Mining concessions, development costs, property, plant and equipment, net [Line Items]      
Opening balance 3,596,342 3,501,216  
Additions 172,509 277,824  
Disposals (9,725)   (18,056)
Sales (9,908) (122,906)  
Reclassifications and transfers (21,815) (41,736)  
Balance as of December 3,727,403 3,596,342 3,501,216
Accumulated depreciation, amortisation and impairment [member]      
Disclosure of Mining concessions, development costs, property, plant and equipment, net [Line Items]      
Opening balance 1,611,982 1,510,809  
Additions 253,968 222,495  
Disposals (262)   (3,043)
Sales (9,282) (101,259)  
Reclassifications and transfers (2,893) (17,020)  
Balance as of December 1,853,513 1,611,982 1,510,809
Accumulated impairment [member]      
Disclosure of Mining concessions, development costs, property, plant and equipment, net [Line Items]      
Opening balance 34,805 30,382  
Additions 0 21,620  
Disposals (8,530)   0
Sales 0 (17,197)  
Reclassifications and transfers 0 0  
Balance as of December 26,275 34,805 30,382
Land [Member] | Gross carrying amount [member]      
Disclosure of Mining concessions, development costs, property, plant and equipment, net [Line Items]      
Opening balance 22,690 22,958  
Additions 783 0  
Disposals (462)   0
Sales 0 0  
Reclassifications and transfers (1,250) (268)  
Balance as of December 21,761 22,690 22,958
Land [Member] | Accumulated depreciation, amortisation and impairment [member]      
Disclosure of Mining concessions, development costs, property, plant and equipment, net [Line Items]      
Opening balance 1,249 0  
Additions 0 0  
Disposals 0 0  
Sales 0 0  
Reclassifications and transfers (1,249) 1,249  
Balance as of December 0 1,249 0
Mining concessions [Member] | Gross carrying amount [member]      
Disclosure of Mining concessions, development costs, property, plant and equipment, net [Line Items]      
Opening balance 151,873 198,009  
Additions 0 2  
Disposals 0   0
Sales 0 (15,000)  
Reclassifications and transfers 0 (31,138)  
Balance as of December 151,873 151,873 198,009
Mining concessions [Member] | Accumulated depreciation, amortisation and impairment [member]      
Disclosure of Mining concessions, development costs, property, plant and equipment, net [Line Items]      
Opening balance 40,239 77,466  
Additions 10 8  
Disposals 0   0
Sales 0 (13,845)  
Reclassifications and transfers 0 (23,390)  
Balance as of December 40,249 40,239 77,466
Development costs [Member] | Gross carrying amount [member]      
Disclosure of Mining concessions, development costs, property, plant and equipment, net [Line Items]      
Opening balance 712,051 652,392  
Additions 32,059 69,335  
Disposals (2,656)   0
Sales 0 (10,107)  
Reclassifications and transfers 1,805 431  
Balance as of December 743,259 712,051 652,392
Development costs [Member] | Accumulated depreciation, amortisation and impairment [member]      
Disclosure of Mining concessions, development costs, property, plant and equipment, net [Line Items]      
Opening balance 263,122 241,636  
Additions 35,433 30,886  
Disposals 0   0
Sales 0 (7,910)  
Reclassifications and transfers (2) (1,490)  
Balance as of December 298,553 263,122 241,636
Development costs [Member] | Accumulated impairment [member]      
Disclosure of Mining concessions, development costs, property, plant and equipment, net [Line Items]      
Opening balance 10,153 9,487  
Additions 0 2,864  
Disposals 0   0
Sales 0 (2,198)  
Reclassifications and transfers 0 0  
Balance as of December 10,153 10,153 9,487
Buildings [member] | Gross carrying amount [member]      
Disclosure of Mining concessions, development costs, property, plant and equipment, net [Line Items]      
Opening balance 1,279,251 1,109,167  
Additions 0 835  
Disposals (2,837)   (387)
Sales 0 (28,751)  
Reclassifications and transfers 66,207 198,387  
Balance as of December 1,342,621 1,279,251 1,109,167
Buildings [member] | Accumulated depreciation, amortisation and impairment [member]      
Disclosure of Mining concessions, development costs, property, plant and equipment, net [Line Items]      
Opening balance 506,837 455,678  
Additions 84,244 73,314  
Disposals 0   (115)
Sales 0 (28,208)  
Reclassifications and transfers 562 6,168  
Balance as of December 591,643 506,837 455,678
Machinery [member] | Gross carrying amount [member]      
Disclosure of Mining concessions, development costs, property, plant and equipment, net [Line Items]      
Opening balance 929,023 986,032  
Additions 0 2,579  
Disposals (182)   (3,749)
Sales (9,205) (50,097)  
Reclassifications and transfers 38,830 (5,742)  
Balance as of December 958,466 929,023 986,032
Machinery [member] | Accumulated depreciation, amortisation and impairment [member]      
Disclosure of Mining concessions, development costs, property, plant and equipment, net [Line Items]      
Opening balance 582,449 558,061  
Additions 93,722 74,744  
Disposals (177)   (2,662)
Sales (8,659) (41,595)  
Reclassifications and transfers (1,978) (6,099)  
Balance as of December 665,357 582,449 558,061
Transportation units [member] | Gross carrying amount [member]      
Disclosure of Mining concessions, development costs, property, plant and equipment, net [Line Items]      
Opening balance 9,946 10,416  
Additions 42 11  
Disposals (138)   (190)
Sales (510) (1,079)  
Reclassifications and transfers 1,545 788  
Balance as of December 10,885 9,946 10,416
Transportation units [member] | Accumulated depreciation, amortisation and impairment [member]      
Disclosure of Mining concessions, development costs, property, plant and equipment, net [Line Items]      
Opening balance 8,390 8,792  
Additions 745 837  
Disposals (85)   (114)
Sales (436) (1,057)  
Reclassifications and transfers (15) (68)  
Balance as of December 8,599 8,390 8,792
Fixtures and fittings [member] | Gross carrying amount [member]      
Disclosure of Mining concessions, development costs, property, plant and equipment, net [Line Items]      
Opening balance 13,902 14,047  
Additions 0 31  
Disposals 0   (157)
Sales (193) (487)  
Reclassifications and transfers (403) 468  
Balance as of December 13,306 13,902 14,047
Fixtures and fittings [member] | Accumulated depreciation, amortisation and impairment [member]      
Disclosure of Mining concessions, development costs, property, plant and equipment, net [Line Items]      
Opening balance 9,880 9,172  
Additions 644 1,109  
Disposals 0   (152)
Sales (187) (236)  
Reclassifications and transfers (214) (13)  
Balance as of December 10,123 9,880 9,172
Units in transit [Member] | Gross carrying amount [member]      
Disclosure of Mining concessions, development costs, property, plant and equipment, net [Line Items]      
Opening balance 4,749 30,051  
Additions 11 2,822  
Disposals 0   0
Sales 0 0  
Reclassifications and transfers (2,078) (28,124)  
Balance as of December 2,682 4,749 30,051
Construction in Progress [Member] | Gross carrying amount [member]      
Disclosure of Mining concessions, development costs, property, plant and equipment, net [Line Items]      
Opening balance 101,122 105,788  
Additions 67,096 173,333  
Disposals (3,450)   0
Sales 0 (190)  
Reclassifications and transfers (108,106) (177,809)  
Balance as of December 56,662 101,122 105,788
Stripping activity asset [Member] | Gross carrying amount [member]      
Disclosure of Mining concessions, development costs, property, plant and equipment, net [Line Items]      
Opening balance [1] 130,447 124,467  
Additions [1] 11,279 18,282  
Disposals [1] 0   (13,573)
Sales [1] 0 0  
Reclassifications and transfers [1] 0 1,271  
Balance as of December [1] 141,726 130,447 124,467
Stripping activity asset [Member] | Accumulated depreciation, amortisation and impairment [member]      
Disclosure of Mining concessions, development costs, property, plant and equipment, net [Line Items]      
Opening balance 41,695 18,729  
Additions 28,820 16,343  
Disposals 0   0
Sales 0 0  
Reclassifications and transfers 3 6,623  
Balance as of December 70,518 41,695 18,729
Mine closure costs [Member] | Gross carrying amount [member]      
Disclosure of Mining concessions, development costs, property, plant and equipment, net [Line Items]      
Opening balance 241,288 247,889  
Additions 61,239 10,594  
Disposals 0   0
Sales 0 (17,195)  
Reclassifications and transfers (18,365) 0  
Balance as of December 284,162 241,288 247,889
Mine closure costs [Member] | Accumulated depreciation, amortisation and impairment [member]      
Disclosure of Mining concessions, development costs, property, plant and equipment, net [Line Items]      
Opening balance 158,121 141,275  
Additions 10,350 25,254  
Disposals 0   0
Sales 0 (8,408)  
Reclassifications and transfers 0 0  
Balance as of December 168,471 158,121 141,275
Mine closure costs [Member] | Accumulated impairment [member]      
Disclosure of Mining concessions, development costs, property, plant and equipment, net [Line Items]      
Opening balance 20,121 10,990  
Additions 0 17,916  
Disposals (5,693)   0
Sales 0 (8,785)  
Reclassifications and transfers (1,221) 0  
Balance as of December 13,207 20,121 10,990
Mining Concessions And Development Costs [Member] | Accumulated impairment [member]      
Disclosure of Mining concessions, development costs, property, plant and equipment, net [Line Items]      
Opening balance 4,531 9,905  
Additions 0 840  
Disposals (2,837) 0  
Sales 0 (6,214)  
Reclassifications and transfers 1,221 0  
Balance as of December $ 2,915 $ 4,531 $ 9,905
[1] In mid-2016, a landslide occurred in the west wall of the Tajo Norte; consequently, it was decided not to mine this area due to stability and operational design issues. According to the distribution of reserves, this area (Phase 10) contained 5.5 MT of ore and 9.2 MT of waste valued at US$13,573,000, which were withdrawn from the reserves in the year 2017.