| $000 | | Dec 31, 2017 | | Dec 31, 2016 | | ||
| Mine properties, mine development costs and mine plant facilities and equipment cost | | | | | | | |
| At the beginning of year | | | 2,462,421 | | | 2,272,985 | |
| Additions | | | 199,324 | | | 189,436 | |
| | | | 2,661,745 | | | 2,462,421 | |
| Accumulated depreciation and amortization | | | | | | | |
| At beginning of year | | | 901,561 | | | 726,218 | |
| Charge for the year | | | 182,900 | | | 175,343 | |
| | | | 1,084,461 | | | 901,561 | |
| Net book value | | | 1,577,284 | | | 1,560,860 | |