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OPERATING SEGMENT REPORTING - El Gallo Project (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019
Operating Segment Reporting |  |
Inventory | $ 26,964 | $ 38,376
El Gallo Project |  |
Operating Segment Reporting |  |
Production costs applicable to sales | 15,700 | 18,500
Residual leaching and other site costs | 8,400 | 8,200
Inventory | 3,000 | 3,400
Operating expenditures | $ 7,300 | $ 10,300

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