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NATURE OF OPERATIONS AND RECENT ACCOUNTING PRONOUNCEMENTS (Details) | 3 Months Ended |
--- | --- | ---
Mar. 31, 2018 | Mar. 31, 2017
MSC |  |
Ownership interest (as a percent) | 49.00% | 49.00%
El Gallo 1 mine |  |
Option to sell prior to the completion of refining (as a percent) | 90.00% |
Period of completion of refining | 10 days |
Minimum |  |
Period over which concentrates are provisionally priced at the end of a period after delivery to the customer | 30 days |
Maximum |  |
Period over which concentrates are provisionally priced at the end of a period after delivery to the customer | 90 days |

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- Definition Period over which concentrates are provisionally priced, whereby the selling price is subject to final adjustments at the end of a period after delivery to the customer. + References No definition available. + Details
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- Definition The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 323 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=66011266&loc=d3e33918-111571 + Details
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