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Deferred income tax (Tables) | 12 Months Ended
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Dec. 31, 2017
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:
|  |  |  |  |  |  |  |  |  |  |  | Credit (debit) to |  |  |
|  |  |  |  |  | Credit (debit) to |  |  |  | Credit (debit) |  | consolidated |  |  |
|  |  |  | Credit (debit) to the |  | consolidated |  |  |  | to the |  | statements of |  |  |
|  |  |  | Consolidated |  | statements of other |  | As of |  | Consolidated |  | other |  | As of |
|  | As of January 1, |  | statement of |  | comprehensive |  | December 31, |  | statement of |  | comprehensive |  | December 31, |
|  | 2016 |  | profit or loss |  | income |  | 2016 |  | profit or loss |  | income |  | 2017 |
|  | 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 |  |  | 78,409 |  |  | 14,641 |  |  | - |  |  | 93,050 |  |  | 1,889 |  |  | - |  |  | 94,939 |
Difference in depreciation and amortization rates |  |  | 52,377 |  |  | 8,506 |  |  | - |  |  | 60,883 |  |  | 734 |  |  | - |  |  | 61,617 |
Provision for closure of mining units, net |  |  | 32,644 |  |  | 6,894 |  |  | - |  |  | 39,538 |  |  | 5,030 |  |  | - |  |  | 44,568 |
Impairment loss of long-lived assets |  |  | 5,185 |  |  | 2,407 |  |  | - |  |  | 7,592 |  |  | 2,328 |  |  | - |  |  | 9,920 |
Environmental liability for Santa Barbara mine |  |  | 1,556 |  |  | 13 |  |  | - |  |  | 1,569 |  |  | (273) |  |  | - |  |  | 1,296 |
Other minor |  |  | 14,866 |  |  | (1,785) |  |  | - |  |  | 13,081 |  |  | 1,082 |  |  | - |  |  | 14,163 |
|  |  | 185,037 |  |  | 30,676 |  |  | - |  |  | 215,713 |  |  | 10,790 |  |  | - |  |  | 226,503 |
Less - Allowance for deferred asset |  |  | (18,166) |  |  | (18,846) |  |  | - |  |  | (37,012) |  |  | (1,898) |  |  | - |  |  | (38,910) |
|  |  | 166,871 |  |  | 11,830 |  |  | - |  |  | 178,701 |  |  | 8,892 |  |  | - |  |  | 187,593 |
Deferred asset included in retained earnings |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivative financial instruments |  |  | 2,441 |  |  | - |  |  | (1,301) |  |  | 1,140 |  |  | - |  |  | 7,963 |  |  | 9,103 |
|  |  | 169,312 |  |  | 11,830 |  |  | (1,301) |  |  | 179,841 |  |  | 8,892 |  |  | 7,963 |  |  | 196,696 |
Deferred assets for mining royalties and special mining tax included in results |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Exploration expenses |  |  | (326) |  |  | 364 |  |  | - |  |  | 38 |  |  | (38) |  |  | - |  |  | - |
Other minors |  |  | 185 |  |  | (180) |  |  | - |  |  | 5 |  |  | 118 |  |  | - |  |  | 123 |
|  |  | (141) |  |  | 184 |  |  | - |  |  | 43 |  |  | 80 |  |  | - |  |  | 123 |
Total deferred asset |  |  | 169,171 |  |  | 12,014 |  |  | (1,301) |  |  | 179,884 |  |  | 8,972 |  |  | 7,963 |  |  | 196,819 |
Deferred liability for income tax included in results |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Effect of translation into U.S. dollars |  |  | (73,537) |  |  | 3,012 |  |  | - |  |  | (70,525) |  |  | 24,502 |  |  | - |  |  | (46,023) |
Differences in amortization rates for development costs |  |  | (32,304) |  |  | (19,484) |  |  | - |  |  | (51,788) |  |  | 6,095 |  |  | - |  |  | (45,693) |
Other minors |  |  | (34,582) |  |  | (9,403) |  |  | - |  |  | (43,985) |  |  | (33,618) |  |  | - |  |  | (77,603) |
|  |  | (140,423) |  |  | (25,875) |  |  | - |  |  | (166,298) |  |  | (3,021) |  |  | - |  |  | (169,319) |
Deferred liability for mining royalties and special mining tax |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Other minors |  |  | 164 |  |  | (199) |  |  | - |  |  | (35) |  |  | (126) |  |  | - |  |  | (161) |
|  |  | 164 |  |  | (199) |  |  | - |  |  | (35) |  |  | (126) |  |  | - |  |  | (161) |
Total deferred liability |  |  | (140,259) |  |  | (26,074) |  |  | - |  |  | (166,333) |  |  | (3,147) |  |  | - |  |  | (169,480) |
Deferred income tax asset, net |  |  | 28,912 |  |  | (14,060) |  |  | (1,301) |  |  | 13,551 |  |  | 5,825 |  |  | 7,963 |  |  | 27,339 |
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:
|  | 2017 |  | 2016 |
|  | US$(000) |  | US$(000) |
Deferred income tax asset, net |  |  | 43,129 |  |  | 25,881 |
Deferred income tax liability, net |  |  | (15,790) |  |  | (12,330) |
|  |  | 27,339 |  |  | 13,551 |
Disclosure of detailed information about provision for income taxes [Text Block] |
| (c) | The following is the composition of the provision for income taxes shown in the consolidated statement of income for the years 2017, 2016 and 2015:
|  | 2017 |  | 2016 |  | 2015 |
|  | US$(000) |  | US$(000) |  | US$(000) |
Current |  |  | (23,837) |  |  | (39,444) |  |  | (14,222) |
Deferred |  |  | 5,825 |  |  | (14,060) |  |  | (541) |
|  |  | (18,012) |  |  | (53,504) |  |  | (14,763) |
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 2017, 2016 and 2015:
|  | 2017 |  | 2016 |  | 2015 |
|  | US$(000) |  | US$(000) |  | US$(000) |
Profit (loss) before income tax |  |  | 92,545 |  |  | (255,237) |  |  | (340,549) |
Loss before income tax for discontinued operations |  |  | (10,098) |  |  | (19,073) |  |  | (20,230) |
Profit (loss) before income tax |  |  | 82,447 |  |  | (274,310) |  |  | (360,779) |
Theoretical loss (gain) for income tax |  |  | 24,322 |  |  | (76,807) |  |  | (101,018) |
Permanent items and others: |  |  |  |  |  |  |  |  |  |
Effect of translation into U.S. dollars |  |  | (24,502) |  |  | (3,012) |  |  | 42,044 |
Share in the results of associates |  |  | (3,896) |  |  | 102,290 |  |  | 48,545 |
Mining royalties and special mining tax |  |  | (1,538) |  |  | 247 |  |  | 663 |
Permanent items |  |  | 16,513 |  |  | 6,577 |  |  | 4,447 |
Allowance of deferred tax asset |  |  | 1,898 |  |  | 18,846 |  |  | 13,929 |
Effect of change in income tax rate net |  |  | - |  |  | (1,431) |  |  | 2,347 |
Income tax expense |  |  | 12,797 |  |  | 46,710 |  |  | 10,957 |
Mining Royalties and Special Mining Tax |  |  | 5,215 |  |  | 6,794 |  |  | 3,806 |
Total income tax |  |  | 18,012 |  |  | 53,504 |  |  | 14,763 |

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