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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.

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