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Long-term investments (Tables) | 12 Months Ended
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Dec. 31, 2018
Available-for-sale financial assets [abstract] |
Schedule of Long-Term Investments |
| 2018 |  | 2017
| Cost |  | AOCI |  | Fair Value |  |  | Cost |  | Total Impairment |  | AOCI |  | Fair Value |
| $ |  | $ |  | $ |  |  | $ |  | $ |  | $ |  | $ |
Calibre Mining Corp. | 7,844 |  | (6,395 | ) | 1,449 |  |  | 7,844 |  | (4,330 | ) | 2,012 |  | 5,526 |
RTG Mining Inc. | 13,400 |  | (12,306 | ) | 1,094 |  |  | 13,400 |  | (12,095 | ) | 1,283 |  | 2,588 |
St. Augustine Gold & Copper Ltd. | 20,193 |  | (19,194 | ) | 999 |  |  | 20,193 |  | (18,658 | ) | 91 |  | 1,626 |
Libero Copper Corp. (Note 8) | 632 |  | (22 | ) | 610 |  |  | — |  | — |  | — |  | — |
Goldstone Resources Ltd. | 20 |  | (17 | ) | 3 |  |  | 20 |  | (18 | ) | 2 |  | 4 |
Balance, end of year | 42,089 |  | (37,934 | ) | 4,155 |  |  | 41,457 |  | (35,101 | ) | 3,388 |  | 9,744 |

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