Note 10 - Derivative Instruments (Tables)

12 Months Ended

Dec. 31, 2017

Notes Tables

Schedule of Notional Amounts of Outstanding Derivative Positions [Table Text Block]

December 31, 2017	Ounces/pounds under contract (in 000's)								Average price per ounce/pound
	Silver		Gold		Zinc		Lead		Silver		Gold		Zinc		Lead
	(ounces)		(ounces)		(pounds)		(pounds)		(ounces)		(ounces)		(pounds)		(pounds)
Contracts on provisional sales
2018 settlements		1,447		5		21,550		4,740	$	16.64	$	1,279	$	1.45	$	1.11
Contracts on forecasted sales
2018 settlements		—		—		32,187		16,645		N/A		N/A	$	1.29	$	1.06
2019 settlements		—		—		23,589		18,078		N/A		N/A	$	1.33	$	1.09
2020 settlements		—		—		3,307		2,866		N/A		N/A	$	1.27	$	1.08

December 31, 2016	Ounces/pounds under contract (in 000's)								Average price per ounce/pound
	Silver		Gold		Zinc		Lead		Silver		Gold		Zinc		Lead
	(ounces)		(ounces)		(pounds)		(pounds)		(ounces)		(ounces)		(pounds)		(pounds)
Contracts on provisional sales
2017 settlements		1,295		4		19,070		7,441	$	16.29	$	1,172	$	1.18	$	0.97
Contracts on forecasted sales
2017 settlements		N/A		N/A		35,384		17,637		N/A		N/A	$	1.19	$	1.03
2018 settlements		N/A		N/A		13,779		5,732		N/A		N/A	$	1.21	$	1.05