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REVENUE AND COST OF SALES (Details 1) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Production costs $ 11,443 $ 27,949 $ 24,619
Stand-by costs 2,394    
Inventory net realizable adjustment   387 0
Depreciation and depletion 1,995 3,680 3,231
Cost of sales $ 15,832 $ 32,016 $ 27,850