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INVENTORY (Details) - USD ($)
$ in Thousands
Dec. 31, 2019
Dec. 31, 2018
Classes of current inventories [abstract]    
Process material stockpiles $ 1,079 $ 4,486
Concentrate inventory 3,055 3,095
Materials and supplies 1,458 1,650
Inventories $ 5,592 $ 9,231