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PLANT AND EQUIPMENT AND MINERAL PROPERTIES - Schedule of Property, Plant and Equipment (Details) - USD ($)
$ in Thousands
Jun. 30, 2018
Dec. 31, 2017
Property, Plant and Equipment [Line Items]    
Cost $ 56,217 $ 56,203
Accumulated Depreciation (24,801) (23,127)
Net Book Value 31,416 33,076
Nichols Ranch    
Property, Plant and Equipment [Line Items]    
Cost 29,210 29,210
Accumulated Depreciation (10,996) (9,971)
Net Book Value 18,214 19,239
Alta Mesa    
Property, Plant and Equipment [Line Items]    
Cost 13,626 13,626
Accumulated Depreciation (1,854) (1,388)
Net Book Value 11,772 12,238
Equipment and other    
Property, Plant and Equipment [Line Items]    
Cost 13,381 13,367
Accumulated Depreciation (11,951) (11,768)
Net Book Value $ 1,430 $ 1,599