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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Investments, Stockpiles, Proven and Probable Reserves (Details) $ in Millions | Jan. 01, 2018 USD ($)
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Marketable equity securities | Accounting Standards Update 2016-01 |
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES |
CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption | $ 3.0

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