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Asset Retirement Obligation | 12 Months Ended
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Dec. 31, 2017
Asset Retirement Obligation Disclosure [Abstract] |
Asset Retirement Obligation | 7. ASSET RETIREMENT OBLIGATION The Company’s mining and exploration activities are subject to various state and federal law and regulations governing the protection of the environment. The Company conducts its operations to protect public health and the environment and believes its operations are in compliance with the applicable laws and regulations in all material respects. The Company has made, and expects to make in the future, expenditures to comply with such laws and regulations, but cannot predict the full amount of such future expenditures. Estimated future restoration and reclamation costs are based principally on legal and regulatory requirements. Changes to the Company’s asset retirement obligation are summarized below:
|  | December 31, 2017 |  |  | December 31, 2016 |
|  | (thousands of dollars) |
Balance, beginning of period |  | $ | 4,789 |  |  | $ | 4,468 |
Liabilities settled |  |  | (97 | ) |  |  | (54 | )
Accretion expense |  |  | 1,039 |  |  |  | 480 |
Balance, end of period |  |  | 5,731 |  |  |  | 4,894 |
Less: Included in liabilities held for sale |  |  | - |  |  |  | (105 | )
Less: Current portion |  |  | (1,078 | ) |  |  | (121 | )
Non-current portion |  | $ | 4,653 |  |  | $ | 4,668 |
As of December 31, 2017, the Company’s asset retirement obligation was fully secured by surety bonds totaling $9.1 million, which were partially collateralized with restricted cash totaling $3.7 million.

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- Definition The entire disclosure for an asset retirement obligation and the associated long-lived asset. An asset retirement obligation is a legal obligation associated with the disposal or retirement from service of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -URI http://asc.fasb.org/subtopic&trid=2175671 + Details
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