REVENUE AND COST OF SALES (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue And Cost Of Sales
Concentrate sales	$ 34,551	$ 33,327	$ 34,925
Provisional pricing adjustments	(435)	32	(233)
Total Revenue	$ 34,116	$ 33,359	$ 34,692

The income arising in the course of an entity's ordinary activities. Income is increases in economic benefits during the accounting period in the form of inflows or enhancements of assets or decreases of liabilities that result in an increase in equity, other than those relating to contributions from equity participants.

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+ Details