The open-case producer and processor said on Wednesday that the option for the assets, which were not named, had an exercise price of $US35 million and an exercise period deadline of October 31.
Because of the size of the deal and triggering of the reserve transaction, it will be subject to shareholder approval.
Atlantic had not yet commenced due diligence on the property, which could take months to complete and it did not provide a timeline for the process.
In January, the producer began due diligence on the Pott and Bannon anthracite property in Schuylkill County, a 410-acre asset about 25 miles from its existing Stockton open-cast mine.
It also has an open option to purchase the property.
Atlantic did not indicate the size of the newest asset option but last month it said Pott and Bannon was estimated to contain 12 million tons of run of mine reserves at a 3:9 ratio with 4.1Mt of clean coal.
If it takes the latter option for P&B, it will pay $6 million in cash and shares as well as $3 million in warrants to Reading Anthracite.
Earlier this year, Atlantic managing director Steve Best said it was focused on expanding its Pennsylvania foothold to become a major US producer of anthracite coal.
