REVENUE AND COST OF SALES (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Concentrate sales	$ 15,304	$ 31,417	$ 34,551
Provisional pricing adjustments	718	329	(435)
Total Revenue	$ 16,022	$ 31,746	$ 34,116

Expiry date 2020-01-01: 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. Effective 2020-01-01: The income arising in the course of an entity's ordinary activities. Income is increases in assets, or decreases in liabilities, that result in increases in equity, other than those relating to contributions from holders of equity claims.

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+ Details