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Other current and non-current non-financial assets (Details 1) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Disclosure of other non-financials asset [Abstract]      
Opening balance $ 18,654 $ 26,189 $ 17,721
Change in assets for exploration and evaluation of mineral resources      
Additions 0 0 11,298
Short-term reclassifications (526) (1,311) 1,987
Increase (decrease) due to transfers and other charges (245) (6,224) (4,817)
Total changes (771) (7,535) 8,468
Total $ 17,883 $ 18,654 $ 26,189