PLANT AND EQUIPMENT, MINE DEVELOPMENT AND CONSTRUCTION IN PROGRESS - By Type (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
PROPERTY AND EQUIPMENT
Subtotal	$ 60,134	$ 20,016
Less: accumulated depreciation	(9,088)	(5,764)
Total	51,046	14,252
Land
PROPERTY AND EQUIPMENT
Subtotal	8,699	8,699
Plant and equipment
PROPERTY AND EQUIPMENT
Subtotal	43,257	8,505
Construction in process
PROPERTY AND EQUIPMENT
Subtotal	$ 8,178	$ 2,812

Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 50
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
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Amount before accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Amount after accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business to produce goods and services and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(13))
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