Note 3 - Property, Plant and Equipment (Tables)

9 Months Ended

Sep. 30, 2021

Property, Plant and Equipment [Abstract]

Schedule of property, plant, and equipment

(In thousands)	September 30, 2021		December 31, 2020
Plant and equipment	$	161,566	$	155,173
Construction in process		4,890		7,245
Capitalized mine development costs		88,713		74,279
Less: accumulated depreciation and amortization		(73,494)		(56,242)
Total property, plant and equipment, net	$	181,675	$	180,455

Schedule of depreciation and amortization

	Three months ended September 30,				Nine months ended September 30,
(In thousands)	2021		2020		2021		2020
Depreciation of plant and equipment	$	4,484	$	4,326	$	13,354	$	12,740
Depreciation of right of use assets		413		—		540		—
Amortization of capitalized
mine development costs		1,854		932		4,967		2,861
Total depreciation and amortization	$	6,751	$	5,258	$	18,861	$	15,601