Note 3 - Property, Plant and Equipment (Tables)

3 Months Ended

Mar. 31, 2020

Property, Plant and Equipment [Abstract]

Schedule of property, plant, and equipment

(In thousands)	March 31, 2020		December 31, 2019
Plant and equipment	$	145,347	$	142,773
Construction in process		14,144		11,986
Capitalized mine development cost		62,737		58,773
Less: accumulated depreciation and amortization		(40,332)		(35,330)
Total property, plant and equipment, net	$	181,896	$	178,202

Schedule of depreciation and amortization

	Three months ended March 31,
(In thousands)	2020		2019
Depreciation of plant and equipment	$	4,175	$	3,019
Amortization of capitalized
mine development costs		827		1,097
Total depreciation and amortization	$	5,002	$	4,116