PROPERTY, PLANT AND EQUIPMENT - Mineral Property Expenses (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Total mineral property expenses for the period	$ 2,640	$ 2,736
(Less) Mineral Property expenses attributable to Discontinued Operations	(2,606)	(2,416)
Mineral property expenses for continued operations	34	320
Kingsville Dome Project, Texas
Property, Plant and Equipment [Line Items]
Total mineral property expenses for the period	907	716
Rosita Project, Texas
Property, Plant and Equipment [Line Items]
Total mineral property expenses for the period	464	530
Vasquez Project, Texas
Property, Plant and Equipment [Line Items]
Total mineral property expenses for the period	600	495
Other Projects, Texas
Property, Plant and Equipment [Line Items]
Total mineral property expenses for the period	20	(4)
Total Texas Projects
Property, Plant and Equipment [Line Items]
Total mineral property expenses for the period	1,991	1,737
Cebolleta Project, New Mexico
Property, Plant and Equipment [Line Items]
Total mineral property expenses for the period	390	440
Juan Tafoya Project, New Mexico
Property, Plant and Equipment [Line Items]
Total mineral property expenses for the period	224	223
West Largo
Property, Plant and Equipment [Line Items]
Total mineral property expenses for the period		13
Total New Mexico Projects
Property, Plant and Equipment [Line Items]
Total mineral property expenses for the period	614	676
Columbus Basin Project, Nevada
Property, Plant and Equipment [Line Items]
Total mineral property expenses for the period		126
Total Nevada Projects
Property, Plant and Equipment [Line Items]
Total mineral property expenses for the period		126
Sal Rica Project, Utah
Property, Plant and Equipment [Line Items]
Total mineral property expenses for the period	1	111
Total Utah Projects
Property, Plant and Equipment [Line Items]
Total mineral property expenses for the period	1	111
Coosa Project, Alabama
Property, Plant and Equipment [Line Items]
Total mineral property expenses for the period	34	86
Total Alabama Projects
Property, Plant and Equipment [Line Items]
Total mineral property expenses for the period	$ 34	$ 86