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Retirement Obligation Asset (Tables)
3 Months Ended
Mar. 31, 2019
Asset Retirement Obligation Disclosure [Abstract]  
Reconciliation of the Aggregate Retirement Obligation Asset
Following is a reconciliation of the aggregate retirement obligation asset associated with our mining reclamation plans: 
 
Three Months Ended
 
Twelve Months
Ended
 
March 31, 2019
 
December 31, 2018
Retirement obligation asset — beginning of period
$
203,274

 
$
282,745

Additional obligations incurred

 

Amortization of retirement obligation asset
(16,939
)
 
(79,471
)
Retirement obligation asset — end of period
$
186,335

 
$
203,274