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REVENUE AND COST OF SALES (Details 1) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Revenue And Cost Of Sales Details 1Abstract      
Production costs $ 24,619 $ 19,418 $ 21,060
Depreciation and depletion 3,231 2,688 1,901
Cost of sales $ 27,850 $ 22,106 $ 22,961