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Deferred income tax (Tables) | 12 Months Ended
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Dec. 31, 2018
Disclosure of Deferred income tax [Abstract] |
Disclosure of temporary difference, unused tax losses and unused tax credits [text block] |
| (a) | The Group recognizes the effects of timing differences between the accounting and tax basis. This caption is made up as follows:
|  | As of January 1, 2017 |  |  | Credit (debit) to the Consolidated statement of profit or loss |  |  | Credit (debit) to consolidated statements of other comprehensive income |  |  | As of December 31, 2017 |  |  | Credit (debit) to the Consolidated statement of profit or loss |  |  | Credit (debit) to consolidated statements of other comprehensive income |  |  | Others movements |  |  | As of December 31, 2018 |
|  | US$(000) |  |  | US$(000) |  |  | US$(000) |  |  | US$(000) |  |  | US$(000) |  |  | US$(000) |  |  | US$(000) |  |  | US$(000) |
Deferred asset for income tax included in results |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Tax - loss carryforward |  |  | 93,050 |  |  |  | 1,889 |  |  |  | - |  |  |  | 94,939 |  |  |  | 11,680 |  |  |  | - |  |  |  | (396 | ) |  |  | 106,223 |
Difference in depreciation and amortization rates |  |  | 60,883 |  |  |  | 734 |  |  |  | - |  |  |  | 61,617 |  |  |  | 6,497 |  |  |  | - |  |  |  | - |  |  |  | 68,114 |
Provision for closure of mining units, net |  |  | 39,538 |  |  |  | 5,030 |  |  |  | - |  |  |  | 44,568 |  |  |  | 3,291 |  |  |  | - |  |  |  | - |  |  |  | 47,859 |
Impairment loss of long-lived assets |  |  | 7,592 |  |  |  | 2,328 |  |  |  | - |  |  |  | 9,920 |  |  |  | (2,448 | ) |  |  | - |  |  |  | - |  |  |  | 7,472 |
Other minor |  |  | 14,650 |  |  |  | 809 |  |  |  | - |  |  |  | 15,459 |  |  |  | 5,369 |  |  |  | - |  |  |  | (146 | ) |  |  | 20,682 |
|  |  | 215,713 |  |  |  | 10,790 |  |  |  | - |  |  |  | 226,503 |  |  |  | 24,389 |  |  |  | - |  |  |  | (542 | ) |  |  | 250,350 |
Less - Allowance for deferred asset |  |  | (37,012 | ) |  |  | (1,898 | ) |  |  | - |  |  |  | (38,910 | ) |  |  | (2,038 | ) |  |  | - |  |  |  | - |  |  |  | (40,948 | )
|  |  | 178,701 |  |  |  | 8,892 |  |  |  | - |  |  |  | 187,593 |  |  |  | 22,351 |  |  |  | - |  |  |  | (542 | ) |  |  | 209,402 |
Deferred asset included in retained earnings |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivative financial instruments |  |  | 1,140 |  |  |  | - |  |  |  | 7,963 |  |  |  | 9,103 |  |  |  | - |  |  |  | (9,103 | ) |  |  | - |  |  |  | - |
|  |  | 179,841 |  |  |  | 8,892 |  |  |  | 7,963 |  |  |  | 196,696 |  |  |  | 22,351 |  |  |  | (9,103 | ) |  |  | (542 | ) |  |  | 209,402 |
Deferred assets for mining royalties and special mining tax included in results |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Other minors |  |  | 43 |  |  |  | 80 |  |  |  | - |  |  |  | 123 |  |  |  | (87 | ) |  |  | - |  |  |  | - |  |  |  | 36 |
|  |  | 43 |  |  |  | 80 |  |  |  | - |  |  |  | 123 |  |  |  | (87 | ) |  |  | - |  |  |  | - |  |  |  | 36 |
Total deferred asset |  |  | 179,884 |  |  |  | 8,972 |  |  |  | 7,963 |  |  |  | 196,819 |  |  |  | 22,264 |  |  |  | (9,103 | ) |  |  | (542 | ) |  |  | 209,438 |
Deferred liability for income tax included in results |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Differences in amortization rates for development costs |  |  | (51,788 | ) |  |  | 6,095 |  |  |  | - |  |  |  | (45,693 | ) |  |  | (20,295 | ) |  |  | - |  |  |  | - |  |  |  | (65,988 | )
Effect of translation into U.S. dollars |  |  | (70,525 | ) |  |  | 24,502 |  |  |  | - |  |  |  | (46,023 | ) |  |  | (15,248 | ) |  |  | - |  |  |  | - |  |  |  | (61,271 | )
Other minors |  |  | (43,985 | ) |  |  | (33,618 | ) |  |  | - |  |  |  | (77,603 | ) |  |  | 3,123 |  |  |  | - |  |  |  | - |  |  |  | (74,480 | )
|  |  | (166,298 | ) |  |  | (3,021 | ) |  |  | - |  |  |  | (169,319 | ) |  |  | (32,420 | ) |  |  | - |  |  |  | - |  |  |  | (201,739 | )
Deferred liability for mining royalties and special mining tax included in results |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivative financial instruments |  |  | - |  |  |  | - |  |  |  | - |  |  |  | - |  |  |  | - |  |  |  | (813 | ) |  |  | - |  |  |  | (813 | )
|  |  | - |  |  |  | - |  |  |  | - |  |  |  | - |  |  |  | - |  |  |  | (813 | ) |  |  | - |  |  |  | (813 | )
Deferred assets for mining royalties and special mining tax |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Other minors |  |  | (35 | ) |  |  | (126 | ) |  |  | - |  |  |  | (161 | ) |  |  | 158 |  |  |  | - |  |  |  | - |  |  |  | (2 | )
|  |  | (35 | ) |  |  | (126 | ) |  |  | - |  |  |  | (161 | ) |  |  | 158 |  |  |  | - |  |  |  | - |  |  |  | (2 | )
Total deferred liability |  |  | (166,333 | ) |  |  | (3,147 | ) |  |  | - |  |  |  | (169,480 | ) |  |  | (32,262 | ) |  |  | (813 | ) |  |  | - |  |  |  | (202,554 | )
Deferred income tax asset, net |  |  | 13,551 |  |  |  | 5,825 |  |  |  | 7,963 |  |  |  | 27,339 |  |  |  | (9,998 | ) |  |  | (9,916 | ) |  |  | (542 | ) |  |  | 6,883 |
Disclosure of detailed information about net deferred tax asset [Text Block] |
| (b) | The deferred tax asset is presented in the consolidated statement of financial position:
|  | 2018 |  |  | 2017 |
|  | US$(000) |  |  | US$(000) |
Deferred income tax asset, net |  |  | 38,305 |  |  |  | 43,129 |
Deferred income tax liability, net |  |  | (31,422 | ) |  |  | (15,790 | )
|  |  | 6,883 |  |  |  | 27,339 |
Disclosure of detailed information about provision for income taxes [Text Block] |
| (c) | The following is the composition of the provision for income taxes shown in the consolidated statement of income for the years 2018, 2017 and 2016:
|  | 2018 |  |  | 2017 |  |  | 2016 |
|  | US$(000) |  |  | US$(000) |  |  | US$(000) |
Income tax expense |  |  |  |  |  |  |  |  |  |  |  |
Current |  |  | 12,433 |  |  |  | 18,781 |  |  |  | 32,902 |
Deferred |  |  | 10,069 |  |  |  | (5,984 | ) |  |  | 13,808 |
|  |  | 22,502 |  |  |  | 12,797 |  |  |  | 46,710 |
Mining Royalties and Special Mining Tax |  |  |  |  |  |  |  |  |  |  |  |
Current |  |  | 4,495 |  |  |  | 5,056 |  |  |  | 6,542 |
Deferred |  |  | (71 | ) |  |  | 159 |  |  |  | 252 |
|  |  | 4,424 |  |  |  | 5,215 |  |  |  | 6,794 |
Total income tax |  |  | 26,926 |  |  |  | 18,012 |  |  |  | 53,504 |
Disclosure of reconciliation of accounting profit multiplied by applicable tax rates [Text Block] |
| (d) | Below is a reconciliation of tax expense and the accounting profit multiplied by the statutory tax rate for the years 2018, 2017 and 2016:
|  | 2018 |  |  | 2017 |  |  | 2016 |
|  | US$(000) |  |  | US$(000) |  |  | US$(000) |
Profit (loss) before income tax |  |  | 22,475 |  |  |  | 92,545 |  |  |  | (255,327 | )
Loss for discontinued operations |  |  | (7,203 | ) |  |  | (10,098 | ) |  |  | (19,073 | )
Profit (loss) before income tax |  |  | 15,272 |  |  |  | 82,447 |  |  |  | (274,400 | )
Theoretical loss (gain) for income tax |  |  | 4,505 |  |  |  | 24,322 |  |  |  | (76,807 | )
Permanent items and others: |  |  |  |  |  |  |  |  |  |  |  |
Effect of translation into U.S. dollars |  |  | 15,248 |  |  |  | (24,502 | ) |  |  | (3,012 | )
Permanent items |  |  | 3,492 |  |  |  | 16,513 |  |  |  | 6,577 |
Allowance of deferred tax asset |  |  | 2,038 |  |  |  | 1,898 |  |  |  | 18,846 |
Share in the results of associates |  |  | 337 |  |  |  | (3,896 | ) |  |  | 102,290 |
Mining royalties and special mining tax |  |  | (3,118 | ) |  |  | (1,538 | ) |  |  | 247 |
Effect of change in income tax rate net |  |  | - |  |  |  | - |  |  |  | (1,431 | )
Income tax expense |  |  | 22,502 |  |  |  | 12,797 |  |  |  | 46,710 |
Mining Royalties and Special Mining Tax |  |  | 4,424 |  |  |  | 5,215 |  |  |  | 6,794 |
|  |  | 26,926 |  |  |  | 18,012 |  |  |  | 53,504 |

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