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PLANT AND EQUIPMENT AND MINERAL PROPERTIES (Narrative) (Details) - USD ($) |  | 12 Months Ended
--- | --- | ---
May 27, 2016 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Property, Plant and Equipment [Line Items] |  |  |  |
Abandonment of mineral properties |  | $ 287,000 | $ 1,036,000 | $ 2,770,000
Nichols Ranch |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |
Depreciation |  | $ 3,170,000 | $ 4,430,000 | $ 2,370,000.00
Roca Honda |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |
Number of shares issued (in shares) | 1,212,173 |  |  |
Percentage of voting interests acquired | 40.00% |  |  |
Value assigned of equity interest issued | $ 2,630,000 |  |  |
Cash payable | $ 4,500,000 |  |  |

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