MINERAL PROPERTY INTERESTS AND PLANT AND EQUIPMENT (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Subtotal	$ 144,721	$ 132,920
Less: accumulated depreciation	(37,150)	(18,186)
Net carrying value	107,571	114,734
Mineral property interests
Property, Plant and Equipment [Line Items]
Subtotal	339,374	326,086
Less: accumulated depreciation	(28,154)	(16,941)
Net carrying value	311,220	309,145
Land
Property, Plant and Equipment [Line Items]
Subtotal	8,746	8,699
Construction in process
Property, Plant and Equipment [Line Items]
Subtotal	2,961	74,643
Plant and equipment
Property, Plant and Equipment [Line Items]
Subtotal	133,014	49,578
Mineral property interests and plant and equipment
Property, Plant and Equipment [Line Items]
Net carrying value	$ 418,791	$ 423,879