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Long-term investments - Schedule of Long-Term Investments (Details) - USD ($) $ in Thousands | Dec. 31, 2018 | Dec. 31, 2017
--- | --- | ---
Disclosure of financial assets [line items] |  |
Investments | $ 4,155 | $ 9,744
Accumulated other comprehensive loss | (146,153) | (94,294)
Calibre Mining Corp. |  |
Disclosure of financial assets [line items] |  |
Investments | 1,449 | 5,526
Accumulated other comprehensive loss | (6,395) | 2,012
RTG Mining Inc. |  |
Disclosure of financial assets [line items] |  |
Investments | 1,094 | 2,588
Accumulated other comprehensive loss | (12,306) | 1,283
St. Augustine Gold & Copper Ltd. |  |
Disclosure of financial assets [line items] |  |
Investments | 999 | 1,626
Accumulated other comprehensive loss | (19,194) | 91
Libero Copper Corp |  |
Disclosure of financial assets [line items] |  |
Investments | 610 | 0
Accumulated other comprehensive loss | (22) | 0
Goldstone Resources Ltd. |  |
Disclosure of financial assets [line items] |  |
Investments | 3 | 4
Accumulated other comprehensive loss | (17) | 2
Investments in Equity Instruments Designated At Fair Value Through Other Comprehensive Income |  |
Disclosure of financial assets [line items] |  |
Accumulated other comprehensive loss | (37,934) | 3,388
Cost |  |
Disclosure of financial assets [line items] |  |
Investments | 42,089 | 41,457
Cost | Calibre Mining Corp. |  |
Disclosure of financial assets [line items] |  |
Investments | 7,844 | 7,844
Cost | RTG Mining Inc. |  |
Disclosure of financial assets [line items] |  |
Investments | 13,400 | 13,400
Cost | St. Augustine Gold & Copper Ltd. |  |
Disclosure of financial assets [line items] |  |
Investments | 20,193 | 20,193
Cost | Libero Copper Corp |  |
Disclosure of financial assets [line items] |  |
Investments | 632 | 0
Cost | Goldstone Resources Ltd. |  |
Disclosure of financial assets [line items] |  |
Investments | $ 20 | 20
Total Impairment |  |
Disclosure of financial assets [line items] |  |
Investments |  | (35,101)
Total Impairment | Calibre Mining Corp. |  |
Disclosure of financial assets [line items] |  |
Investments |  | (4,330)
Total Impairment | RTG Mining Inc. |  |
Disclosure of financial assets [line items] |  |
Investments |  | (12,095)
Total Impairment | St. Augustine Gold & Copper Ltd. |  |
Disclosure of financial assets [line items] |  |
Investments |  | (18,658)
Total Impairment | Libero Copper Corp |  |
Disclosure of financial assets [line items] |  |
Investments |  | 0
Total Impairment | Goldstone Resources Ltd. |  |
Disclosure of financial assets [line items] |  |
Investments |  | $ (18)

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