Plant and Equipment, Net - Components of plant and equipment, net (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2022	Dec. 31, 2021
Property, Plant and Equipment [Line Items]
Plant, equipment and mine development, gross	$ 87,880	$ 88,248
Less, accumulated depreciation and amortization	(31,198)	(29,764)
Total	56,682	58,484
Production leach pads
Property, Plant and Equipment [Line Items]
Plant, equipment and mine development, gross	$ 11,190	11,190
Test leach pads
Property, Plant and Equipment [Line Items]
Depreciation Life	18 months
Plant, equipment and mine development, gross	$ 6,241	6,241
Process equipment
Property, Plant and Equipment [Line Items]
Plant, equipment and mine development, gross	$ 17,712	17,735
Buildings and leasehold improvements
Property, Plant and Equipment [Line Items]
Depreciation Life	10 years
Plant, equipment and mine development, gross	$ 9,280	9,280
Mine equipment
Property, Plant and Equipment [Line Items]
Plant, equipment and mine development, gross	6,025	6,224
Vehicles
Property, Plant and Equipment [Line Items]
Plant, equipment and mine development, gross	$ 1,454	1,454
Furniture and office equipment
Property, Plant and Equipment [Line Items]
Depreciation Life	7 years
Plant, equipment and mine development, gross	$ 365	330
Construction in progress and other
Property, Plant and Equipment [Line Items]
Plant, equipment and mine development, gross	$ 35,613	$ 35,794
Minimum | Process equipment
Property, Plant and Equipment [Line Items]
Depreciation Life	5 years
Minimum | Mine equipment
Property, Plant and Equipment [Line Items]
Depreciation Life	5 years
Minimum | Vehicles
Property, Plant and Equipment [Line Items]
Depreciation Life	3 years
Maximum | Process equipment
Property, Plant and Equipment [Line Items]
Depreciation Life	15 years
Maximum | Mine equipment
Property, Plant and Equipment [Line Items]
Depreciation Life	7 years
Maximum | Vehicles
Property, Plant and Equipment [Line Items]
Depreciation Life	5 years