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FAIR VALUE MEASUREMENTS (Details) - USD ($)
$ in Thousands
Sep. 30, 2017
Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Commodity price risk derivatives $ 29  
Outstanding warrant liability 580 $ 1,030
Recurring Measurements [Member] | Total [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Commodity price risk derivatives 29
Total 493 946
Outstanding warrant liability 580 1,030
Recurring Measurements [Member] | Equity Securities [Member] | Total [Member] | Sutter Gold Mining Company [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Marketable equity securities 7 16
Commodity price risk derivatives  
Recurring Measurements [Member] | Equity Securities [Member] | Total [Member] | Anfield Resources, Inc. [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Marketable equity securities 457 930
Level 1 [Member] | Recurring Measurements [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Commodity price risk derivatives
Total 464 946
Outstanding warrant liability  
Level 1 [Member] | Recurring Measurements [Member] | Equity Securities [Member] | Sutter Gold Mining Company [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Marketable equity securities 7 16
Level 1 [Member] | Recurring Measurements [Member] | Equity Securities [Member] | Anfield Resources, Inc. [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Marketable equity securities 457 930
Level 2 [Member] | Recurring Measurements [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Commodity price risk derivatives 29
Total 29  
Outstanding warrant liability  
Level 2 [Member] | Recurring Measurements [Member] | Equity Securities [Member] | Sutter Gold Mining Company [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Marketable equity securities
Level 2 [Member] | Recurring Measurements [Member] | Equity Securities [Member] | Anfield Resources, Inc. [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Marketable equity securities
Level 3 [Member] | Recurring Measurements [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Commodity price risk derivatives
Total
Outstanding warrant liability 580 1,030
Level 3 [Member] | Recurring Measurements [Member] | Equity Securities [Member] | Sutter Gold Mining Company [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Marketable equity securities
Level 3 [Member] | Recurring Measurements [Member] | Equity Securities [Member] | Anfield Resources, Inc. [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Marketable equity securities