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PLANT AND EQUIPMENT AND MINERAL PROPERTIES - Schedule of Property, Plant and Equipment (Details) - USD ($)
$ in Thousands
Mar. 31, 2018
Dec. 31, 2017
Property, Plant and Equipment [Line Items]    
Cost $ 56,217 $ 56,203
Accumulated Depreciation (23,966) (23,127)
Net Book Value 32,251 33,076
Nichols Ranch    
Property, Plant and Equipment [Line Items]    
Cost 29,210 29,210
Accumulated Depreciation (10,483) (9,971)
Net Book Value 18,727 19,239
Alta Mesa    
Property, Plant and Equipment [Line Items]    
Cost 13,626 13,626
Accumulated Depreciation (1,621) (1,388)
Net Book Value 12,005 12,238
Equipment and other    
Property, Plant and Equipment [Line Items]    
Cost 13,381 13,367
Accumulated Depreciation (11,862) (11,768)
Net Book Value $ 1,519 $ 1,599