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Assets Held for Sale (Details) - USD ($)
6 Months Ended 12 Months Ended
Jun. 30, 2021
Dec. 31, 2020
Assets held for sale    
Mineral properties $ 2,413,000 $ 0
Liabilities associated with assets held for sale    
Asset retirement obligations 875,000 0
Net assets held for sale $ 1,538,000 $ 0