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Mining concessions, development costs, property, plant and equipment, net (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Disclosure of Mining concessions, development costs, property, plant and equipment, net [Line Items]    
Opening balance $ 1,960,025 $ 1,747,624
Balance as of December 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 3,501,216 3,021,340
Additions 277,824 408,898
Disposals (18,056) (7,323)
Sales (122,906) (3,354)
Reclassifications of assets held for sale   78,660
Reclassifications and transfers (41,736) 2,995
Balance as of December 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 1,510,809 1,262,461
Additions 222,495 195,533
Disposals (3,043) (5,688)
Sales (101,259) (1,223)
Reclassifications of assets held for sale   60,846
Reclassifications and transfers (17,020) (1,120)
Balance as of December 1,611,982 1,510,809
Accumulated impairment [member]    
Disclosure of Mining concessions, development costs, property, plant and equipment, net [Line Items]    
Opening balance 30,382 11,255
Additions 21,620 0
Disposals 0 0
Sales (17,197) 0
Reclassifications of assets held for sale   19,127
Reclassifications and transfers 0 0
Balance as of December 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 22,958 22,454
Additions 0 162
Disposals 0 0
Sales 0 (6)
Reclassifications of assets held for sale   78
Reclassifications and transfers (268) 270
Balance as of December 22,690 22,958
Mining concessions [Member]    
Disclosure of Mining concessions, development costs, property, plant and equipment, net [Line Items]    
Reclassifications of assets held for sale   0
Reclassifications and transfers   0
Mining concessions [Member] | Gross carrying amount [member]    
Disclosure of Mining concessions, development costs, property, plant and equipment, net [Line Items]    
Opening balance 198,009 198,009
Additions 2 0
Disposals 0 0
Sales (15,000) 0
Reclassifications of assets held for sale   0
Reclassifications and transfers (31,138) 0
Balance as of December 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 77,466 77,450
Additions 8 16
Disposals 0 0
Sales (13,845) 0
Reclassifications and transfers (23,390)  
Balance as of December 40,239 77,466
Development costs [Member]    
Disclosure of Mining concessions, development costs, property, plant and equipment, net [Line Items]    
Reclassifications of assets held for sale   25,596
Reclassifications and transfers   (1,396)
Development costs [Member] | Gross carrying amount [member]    
Disclosure of Mining concessions, development costs, property, plant and equipment, net [Line Items]    
Opening balance 652,392 541,763
Additions 69,335 82,865
Disposals 0 0
Sales (10,107) 0
Reclassifications of assets held for sale   31,192
Reclassifications and transfers 431 (3,428)
Balance as of December 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 241,636 199,211
Additions 30,886 18,225
Disposals 0 0
Sales (7,910) 0
Reclassifications and transfers (241)  
Balance as of December 264,371 241,636
Development costs [Member] | Accumulated impairment [member]    
Disclosure of Mining concessions, development costs, property, plant and equipment, net [Line Items]    
Opening balance 9,487 3,803
Additions 2,864 0
Disposals 0 0
Sales (2,198) 0
Reclassifications of assets held for sale   5,684
Reclassifications and transfers 0 0
Balance as of December 10,153 9,487
Buildings [member]    
Disclosure of Mining concessions, development costs, property, plant and equipment, net [Line Items]    
Reclassifications of assets held for sale   8,598
Reclassifications and transfers   598
Buildings [member] | Gross carrying amount [member]    
Disclosure of Mining concessions, development costs, property, plant and equipment, net [Line Items]    
Opening balance 1,109,167 1,018,956
Additions 835 581
Disposals (387) 0
Sales (28,751) (20)
Reclassifications of assets held for sale   10,458
Reclassifications and transfers 198,387 79,192
Balance as of December 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 455,678 381,441
Additions 73,314 65,050
Disposals (115) 0
Sales (28,208) (9)
Reclassifications and transfers 6,168  
Balance as of December 506,837 455,678
Machinery [member]    
Disclosure of Mining concessions, development costs, property, plant and equipment, net [Line Items]    
Reclassifications of assets held for sale   6,640
Reclassifications and transfers   (68)
Machinery [member] | Gross carrying amount [member]    
Disclosure of Mining concessions, development costs, property, plant and equipment, net [Line Items]    
Opening balance 986,032 827,225
Additions 2,579 46,152
Disposals (3,749) (6,569)
Sales (50,097) (2,844)
Reclassifications of assets held for sale   9,425
Reclassifications and transfers (5,742) 112,643
Balance as of December 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 558,061 475,941
Additions 74,744 81,753
Disposals (2,662) (5,378)
Sales (41,595) (827)
Reclassifications and transfers (6,099)  
Balance as of December 582,449 558,061
Transportation units [member]    
Disclosure of Mining concessions, development costs, property, plant and equipment, net [Line Items]    
Reclassifications and transfers   14
Transportation units [member] | Gross carrying amount [member]    
Disclosure of Mining concessions, development costs, property, plant and equipment, net [Line Items]    
Opening balance 10,416 10,649
Additions 11 174
Disposals (190) (341)
Sales (1,079) (396)
Reclassifications of assets held for sale   357
Reclassifications and transfers 788 (27)
Balance as of December 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 8,792 7,932
Additions 837 1,103
Disposals (114) (250)
Sales (1,057) (365)
Reclassifications of assets held for sale   358
Reclassifications and transfers (68)  
Balance as of December 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 14,047 13,429
Additions 31 89
Disposals (157) (61)
Sales (487) (88)
Reclassifications of assets held for sale   359
Reclassifications and transfers 468 319
Balance as of December 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 9,172 7,577
Additions 1,109 1,156
Disposals (152) (60)
Sales (236) (22)
Reclassifications of assets held for sale   319
Reclassifications and transfers (13) 202
Balance as of December 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 30,051 26,291
Additions 2,822 15,797
Disposals 0 0
Sales 0 0
Reclassifications of assets held for sale   0
Reclassifications and transfers (28,124) (12,037)
Balance as of December 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 105,788 68,123
Additions 173,333 210,915
Disposals 0 (352)
Sales (190) 0
Reclassifications of assets held for sale   1,037
Reclassifications and transfers (177,809) (173,935)
Balance as of December 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 18,729 12,916
Additions 16,343 5,813
Disposals 0 0
Sales 0 0
Reclassifications of assets held for sale [1]   0
Reclassifications and transfers 6,623 (2) [1]
Balance as of December 41,695 18,729
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 [1] 124,467 106,838
Additions [1] 18,282 17,631
Disposals [1] (13,573) 0
Sales [1] 0 0
Reclassifications of assets held for sale   0
Reclassifications and transfers 1,271 [1] 0
Balance as of December [1] 130,447 124,467
Mine closure costs [Member] | Gross carrying amount [member]    
Disclosure of Mining concessions, development costs, property, plant and equipment, net [Line Items]    
Opening balance 247,889 187,603
Additions 10,594 34,532
Disposals 0 0
Sales (17,195) 0
Reclassifications of assets held for sale   25,754
Reclassifications and transfers 0 0
Balance as of December 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 141,275 99,993
Additions 25,254 22,417
Disposals 0 0
Sales (8,408) 0
Reclassifications of assets held for sale   19,335
Reclassifications and transfers 0 (470)
Balance as of December 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 10,990 4,080
Additions 17,916 0
Disposals 0 0
Sales (8,785) 0
Reclassifications of assets held for sale   6,910
Reclassifications and transfers 0 0
Balance as of December $ 20,121 $ 10,990
[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.