Note 3 - Property, Plant and Equipment (Tables)

12 Months Ended

Dec. 31, 2020

Property, Plant and Equipment [Abstract]

Schedule of property, plant, and equipment

	December 31,
(In thousands)	2020		2019
Plant and equipment	$	155,173	$	142,773
Construction in process		7,245		11,986
Capitalized mine development costs		74,279		58,773
Less: accumulated depreciation and amortization		(56,242)		(35,330)
Total property, plant and equipment, net	$	180,455	$	178,202

Schedule of depreciation and amortization

	Years ended December 31,
(In thousands)	2020		2019		2018
Depreciation of plant and equipment	$	17,094	$	14,219	$	9,751
Amortization of capitalized
mine development costs		3,818		5,302		2,672
Total depreciation and amortization	$	20,912	$	19,521	$	12,423