According to the Helsingin Sanomat daily, the area being mined would almost double if the proposal is accepted.
The company expects the billion-euro development to produce five times as much nickel and create about 1,000 new jobs in the Kainuu region.
The company applied to Finnish Safety and Chemicals Agency (Tukes) for the expansion permit in the summer of 2011.
Tukes said it won’t begin processing the permit before 2013 due to a backlog of applications and a shortage of staff.
However Talvivaara said it is prepared for a long approval process and has not yet organised financing for the venture.
Mining activities are currently suspended, with operations focusing on extracting nickel from available ore. Mining operations are scheduled to recommence by the end of the year.
Last month the Kainuu centre for economic development slapped the company with a raft of new and tighter water management and environmental permit requirements. That followed a long string of allegations that the mine is polluting the surrounding area.