Plans by York Potash for a mine at Sneaton, near Whitby, and a 37km underground tunnel were due to be considered by planners next month but it will be now May, at the earliest, before a decision is made.
The latest delay is the result of requests for detailed information by North York Moors National Park Authority, which has raised fresh concerns about the potential impact on the environment.
A report to the Authority’s planning committee next week said “very important and potentially significant issues” emerged during the initial assessment of the application.
Planners have asked for extra information about mitigation measures to deal with nitrogen emissions from diesel generators.
They have also asked for figures relating to lorry movements to be looked at again.
The Authority said its consultants found a “series of anomalies and omissions” in the HGV traffic calculations during the construction phase.
Planners have also asked whether the company intended to transport polyhalite - a mineral used as a fertilizer - by road in the event of the transportation tunnel going behind schedule.
If the tunnel is not available, it could mean 53,000 tonnes being moved by road over a 2-3 month period, which will affect local communities.
Questions are also being asked about alternative proposals for dealing with sewage to avoid the risk of polluting Sneaton Thorpe and Rigg Mill Becks.
York Potash has said it wants to submit a revised environmental statement to address these concerns.
An Authority spokesman said the delay would add to the estimated £750,000 planning bill and would also require further discussions with communities.
Park authority planners meet January 15 to discuss the latest developments.