Annual report pursuant to Section 13 and 15(d)

Income taxes (Schedule of Deferred Tax Assets and (Liabilities)) (Details)

v3.19.1
Income taxes (Schedule of Deferred Tax Assets and (Liabilities)) (Details) - USD ($)
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Deferred tax assets (liabilities):      
Net operating loss carryforwards $ 30,745,000 $ 25,837,000  
Research and development credit carryforwards 989,000 989,000  
Stock option expense 1,384,000 252,000  
Impairment of mining related assets and other 8,779,000 14,000  
Total deferred tax assets 41,897,000 27,092,000  
Valuation allowance (41,897,000) (27,092,000)  
Net deferred tax assets  
Deferred income tax liabilities:      
Indefinite life intangible assets (142,709) (699,000)  
Net deferred tax liabilities $ (142,709) $ (699,000)