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Mining interests - Narrative (Details) $ in Millions |  |  |  |  |  | 1 Months Ended | 2 Months Ended | 3 Months Ended | 11 Months Ended | 12 Months Ended |
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Aug. 08, 2018 USD ($) | Jun. 15, 2018 USD ($) shares | Jun. 14, 2018 | May 22, 2018 USD ($) | Jun. 07, 2017 CAD ($) | Aug. 31, 2017 | Nov. 30, 2017 USD ($) | Dec. 31, 2018 USD ($) | Sep. 30, 2018 USD ($) | Jun. 30, 2017 USD ($) | Nov. 30, 2017 USD ($) | Dec. 31, 2018 USD ($) $ / pound $ / Ounce | Dec. 31, 2017 USD ($) | Dec. 31, 2016 USD ($) | Dec. 31, 2015 USD ($) | Mar. 30, 2009 USD ($)
Disclosure of detailed information about property, plant and equipment [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Impairment loss |  |  |  |  |  |  |  |  |  |  |  | $ (55,353,000) | $ 0 |  |  |
Property, plant and equipment |  |  |  |  |  |  |  | $ 2,035,097,000 |  |  |  | 2,035,097,000 | 2,124,133,000 | $ 1,950,356,000 |  |
Capitalized to mining interests |  |  |  |  |  |  |  |  |  |  |  | (74,961,000) | (33,106,000) |  |  |
Interest expense, capitalized to mineral property interests |  |  |  |  |  |  |  |  |  |  |  | 0 | 20,052,000 |  |  |
Acquisition of non-controlling interest (Note 8) |  |  |  |  |  |  |  |  |  |  |  | 2,500,000 | 1,500,000 |  |  |
Gain on sale of Lynn Lake royalty (Note 8) |  |  |  |  |  |  |  |  |  |  |  | 0 | 6,593,000 |  |  |
Write-down mineral property interests |  |  |  |  |  |  |  |  |  |  |  | 9,398,000 | 4,150,000 |  |  |
Cost |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Property, plant and equipment |  |  |  |  |  |  |  | 3,113,126,000 |  |  |  | 3,113,126,000 | 2,909,819,000 | 2,546,361,000 |  |
Reclass |  |  |  |  |  |  |  |  |  |  |  | 1,633,000 | 2,464,000 |  |  |
Exploration and evaluation properties (non-depletable) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Property, plant and equipment |  |  |  |  |  |  |  | 152,649,000 |  |  |  | 152,649,000 | 150,971,000 | 123,962,000 |  |
Exploration and evaluation properties (non-depletable) | Cost |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Property, plant and equipment |  |  |  |  |  |  |  | 152,649,000 |  |  |  | 152,649,000 | 150,971,000 | 123,962,000 |  |
Reclass |  |  |  |  |  |  |  |  |  |  |  | (632,000) | 0 |  |  |
Property, plant and equipment (depletable) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Property, plant and equipment |  |  |  |  |  |  |  | 1,881,768,000 |  |  |  | 1,881,768,000 | 1,972,451,000 | 856,172,000 |  |
Property, plant and equipment (depletable) | Cost |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Property, plant and equipment |  |  |  |  |  |  |  | 2,957,959,000 |  |  |  | 2,957,959,000 | 2,756,584,000 | 1,450,837,000 |  |
Reclass |  |  |  |  |  |  |  |  |  |  |  | 2,265,000 | 1,131,551,000 |  |  |
Libertad |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Impairment loss |  |  |  |  |  |  |  | 34,000,000 | $ 16,000,000 |  |  |  |  |  |  |
Libertad | Property, plant and equipment (depletable) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Property, plant and equipment |  |  |  |  |  |  |  | 19,854,000 |  |  |  | 19,854,000 | 71,813,000 | 74,328,000 |  |
Libertad | Property, plant and equipment (depletable) | Cost |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Property, plant and equipment |  |  |  |  |  |  |  | 315,569,000 |  |  |  | 315,569,000 | 335,651,000 | 300,816,000 |  |
Reclass |  |  |  |  |  |  |  |  |  |  |  | 0 | 0 |  |  |
Limon |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Impairment loss |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 23,000,000 |
Tax effect of impairment in property, plant and equipment |  |  |  |  |  |  |  |  | 4,000,000 |  |  |  |  |  | (7,000,000) |
Impairment loss, net of tax |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 16,000,000 |
Reversal of impairment loss |  |  |  |  |  |  |  |  | 13,000,000 |  |  |  |  |  |  |
Reversal of impairment loss, net of tax |  |  |  |  |  |  |  |  | $ 9,000,000 |  |  |  |  |  |  |
Acquisition of non-controlling interest (Note 8) |  |  |  | $ 2,500,000 |  |  |  |  |  |  |  |  |  |  |  |
Limon | Property, plant and equipment (depletable) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Property, plant and equipment |  |  |  |  |  |  |  | 67,722,000 |  |  |  | 67,722,000 | 45,618,000 | 43,931,000 |  |
Limon | Property, plant and equipment (depletable) | Cost |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Property, plant and equipment |  |  |  |  |  |  |  | 217,263,000 |  |  |  | 217,263,000 | 173,358,000 | 151,186,000 |  |
Reclass |  |  |  |  |  |  |  |  |  |  |  | 0 | 0 |  |  |
Mocoa |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Impairment loss |  |  |  |  |  |  |  |  |  |  |  | 18,000,000 |  |  |  |
Mocoa | Exploration and evaluation properties (non-depletable) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Property, plant and equipment |  |  |  |  |  |  |  |  |  |  |  |  | 29,041,000 | 29,004,000 |  |
Mocoa | Exploration and evaluation properties (non-depletable) | Cost |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Property, plant and equipment |  |  |  |  |  |  |  | 11,000,000 |  |  |  | 11,000,000 | 29,041,000 | 29,004,000 |  |
Reclass |  |  |  |  |  |  |  |  |  |  |  |  | 0 |  |  |
Fekola |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Sales proceeds from pre-commercial production period |  |  |  |  |  |  | $ 101,000,000 |  |  |  |  |  |  |  |  |
Capitalized to mining interests |  |  |  |  |  |  | $ 28,000,000 |  |  |  |  |  |  |  |  |
Interest expense, capitalized to mineral property interests |  |  |  |  |  |  |  |  |  |  | $ 20,000,000 |  |  |  |  |
Fekola | Property, plant and equipment (depletable) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Property, plant and equipment |  |  |  |  |  |  |  | 1,024,156,000 |  |  |  | 1,024,156,000 | 1,059,307,000 | 0 |  |
Fekola | Property, plant and equipment (depletable) | Cost |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Property, plant and equipment |  |  |  |  |  |  |  | 1,168,491,000 |  |  |  | 1,168,491,000 | 1,094,784,000 | 0 |  |
Reclass |  |  |  |  |  |  |  |  |  |  |  | 2,265,000 | 1,068,207,000 |  |  |
Masbate | Property, plant and equipment (depletable) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Property, plant and equipment |  |  |  |  |  |  |  | 433,488,000 |  |  |  | 433,488,000 | 431,797,000 | 352,233,000 |  |
Masbate | Property, plant and equipment (depletable) | Cost |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Property, plant and equipment |  |  |  |  |  |  |  | $ 681,509,000 |  |  |  | 681,509,000 | 625,722,000 | $ 517,457,000 |  |
Reclass |  |  |  |  |  |  |  |  |  |  |  | 0 | 60,880,000 |  |  |
Lynn Lake Royalty |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Consideration paid (received) |  |  |  |  | $ 9 |  |  |  |  |  |  |  |  |  |  |
Net smelter royalty |  |  |  |  | 2.00% |  |  |  |  |  |  |  |  |  |  |
Increase (decrease) in contingent consideration asset (liability) |  |  |  |  | $ 6 |  |  |  |  | $ 0 |  |  |  |  |  |
Contingent consideration period |  |  |  |  | 24 months |  |  |  |  |  |  |  |  |  |  |
Gain on sale of Lynn Lake royalty (Note 8) |  |  |  |  |  |  |  |  |  | $ 7,000,000 |  |  |  |  |  |
Namibia and Mali |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Write-down mineral property interests |  |  |  |  |  |  |  |  |  |  |  | $ 9,000,000 | $ 4,000,000 |  |  |
Libero Copper Corp | Mocoa |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of shares received (in shares) | shares |  | 10,400,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from sale of property, plant and equipment |  | $ 1,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net smelter royalty receivable |  | 2.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net smelter royalty recognized as of acquisition date |  | $ 10,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Central Sun | Lynn Lake Royalty |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net smelter royalty recognized as of acquisition date |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 0
Fekola SA |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proportion of ownership interests held by non-controlling interests | 20.00% |  |  |  |  | 10.00% |  |  |  |  |  |  |  |  |  |
Percentage of ownership interest in subsidiary | 80.00% |  |  |  |  |  |  |  |  |  |  |  |  | 100.00% |  |
Consideration paid (received) | $ (57,000,000) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gain (loss) on sale of mineral properties | 10,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Receivables from sale of properties | $ 47,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Triton Minera S.A. |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of ownership interest in subsidiary |  |  |  | 5.00% |  |  |  |  |  |  |  |  |  |  |  |
Triton Minera S.A. | Limon |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of ownership interest in subsidiary |  |  |  | 100.00% |  |  |  |  |  |  |  |  |  |  |  |
Libero Copper Corp |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proportion of ownership interest in associate |  | 19.00% | 0.00% |  |  |  |  |  |  |  |  |  |  |  |  |
Interest rate risk | Libertad |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Reasonably possible change in risk variable, percent |  |  |  |  |  |  |  |  |  |  |  | 0.005% |  |  |  |
Reasonably possible change in risk variable impact on property, plant and equipment |  |  |  |  |  |  |  |  |  |  |  | $ 0 |  |  |  |
Interest rate risk | Limon |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Reasonably possible change in risk variable, percent |  |  |  |  |  |  |  |  |  |  |  | 0.005% |  |  |  |
Reasonably possible change in risk variable impact on property, plant and equipment |  |  |  |  |  |  |  |  |  |  |  | $ 0 |  |  |  |
Interest rate risk | Mocoa |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Reasonably possible change in risk variable, percent |  |  |  |  |  |  |  |  |  |  |  | 0.005% |  |  |  |
Reasonably possible change in risk variable impact on property, plant and equipment |  |  |  |  |  |  |  |  |  |  |  | $ 1,000,000 |  |  |  |
Commodity price risk | Libertad |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Reasonably possible change in risk variable impact on property, plant and equipment |  |  |  |  |  |  |  |  |  |  |  | 8,000,000 |  |  |  |
Commodity price risk | Limon |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Reasonably possible change in risk variable impact on property, plant and equipment |  |  |  |  |  |  |  |  |  |  |  | 0 |  |  |  |
Commodity price risk | Mocoa |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Reasonably possible change in risk variable impact on property, plant and equipment |  |  |  |  |  |  |  |  |  |  |  | $ 1,000,000 |  |  |  |
Long-term gold price | Commodity price risk | Libertad |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Reasonably possible change in price per unit (in usd per unit) | $ / Ounce |  |  |  |  |  |  |  |  |  |  |  | 50 |  |  |  |
Long-term gold price | Commodity price risk | Limon |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Reasonably possible change in price per unit (in usd per unit) | $ / Ounce |  |  |  |  |  |  |  |  |  |  |  | 50 |  |  |  |
Molybdenum Price | Commodity price risk | Mocoa |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Reasonably possible change in price per unit (in usd per unit) | $ / pound |  |  |  |  |  |  |  |  |  |  |  | 0.40 |  |  |  |
Copper Price | Commodity price risk | Mocoa |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Reasonably possible change in price per unit (in usd per unit) | $ / pound |  |  |  |  |  |  |  |  |  |  |  | 0.15 |  |  |  |
Non-participating Share Capital | Fekola SA |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proportion of ownership interests held by non-controlling interests | 10.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Priority dividend rate to non-controlling interest | 10.00% |  |  |  |  |  |  |  |  |  |  | 10.00% |  |  |  |
Fully Participating Share Capital | Fekola SA |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proportion of ownership interests held by non-controlling interests | 10.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Central Bank Of West African States Prime Rate | Receivables From Sale Of Properties | Fekola SA |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Borrowings, adjustment to interest rate basis | 3.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |

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