Note 3 - Property, Plant and Equipment (Tables)

3 Months Ended

Mar. 31, 2021

Property, Plant and Equipment [Abstract]

Schedule of property, plant, and equipment

(In thousands)	March 31, 2021		December 31, 2020
Plant and equipment	$	157,424	$	155,173
Construction in process		5,551		7,245
Capitalized mine development costs		77,158		74,279
Less: accumulated depreciation and amortization		(62,397)		(56,242)
Total property, plant and equipment, net	$	177,736	$	180,455

Schedule of depreciation and amortization

	Three months ended March 31,
(In thousands)	2021		2020
Depreciation of plant and equipment	$	4,399	$	4,175
Amortization of capitalized
mine development costs		1,756		827
Total depreciation and amortization	$	6,155	$	5,002