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Inventories - Summary of inventories (Details) - USD ($)
$ in Thousands
Dec. 31, 2021
Dec. 31, 2020
Classes of current inventories [abstract]    
Ore stockpiles $ 10,097 $ 6,327
In-process inventory and finished goods 63,513 68,984
Materials and supplies 104,553 88,824
Inventories $ 178,163 $ 164,135