The London-listed miner said the exercise period expired on March 31, but because due diligence and funding talks were still underway, they were seeking an extension.
The option, exercisable at its discretion, has an exercise price of $35 million.
“As a result of the size of the exercise price, the acquisition of the assets in question would be likely to constitute a reverse takeover under the AIM Rules for Companies and would therefore be, inter alia, subject to shareholder approval,” officials said.
Atlantic said discussions with the vendor should be finalized “shortly” and noted there was no certainty the extension would be granted or that it would be on terms that it found acceptable.
The company’s flagship complex is the Stockton mine in Hazleton, Pennsylvania.
That operation has recently been on a production run. In January the company said it had a double run-of-mine rate over 2011.
Stockton produced 161,500 tons clean over the year, 61% higher than 100,139t whole-year 2011 and notably exceeding its 2012 target of 155,000t.
Atlantic Coal managing director Steve Best said at the time that Stockton had been established as one of the top five anthracite producers in the state.