Applicant York Potash submitted plans to develop the mine on a 64-hectare site in the eastern section of the North York Moors national park.
A North York Moors National Park Authority planning report said the scheme would result in economic and social benefits to the surrounding areas, both during the construction and operation phases.
However, it added that a number of factors weighed heavily against approving the application, including concerns that the proposals would result in "substantial harm to the special qualities of the National Park in the area surrounding the minehead site".
It added: "Officers conclude that the policy conflict with the development plan and national policy is such that the proposal does not represent Exceptional Circumstances, which is the highest bar that planning policy requires.
"It is therefore considered that the economic benefits and extent of the mitigation/compensation offered through planning obligations do not outweigh the extent of the harm and clear conflict with the development plan."
However, the application was approved by members of the national park authority's planning committee on Tuesday.
According to the authority, members acknowledged the considerable harm the proposals would have on the special qualities of the North York Moors. However, it added that members felt the projected long-term economic and social benefits outweighed these concerns.
Andy Wilson, chief executive of the North York Moors National Park Authority, said: "Today’s decision is the culmination of hard work, of thorough examination and in-depth discussions of the largest planning application this National Park, and indeed any English National Park, has had to consider.
"I appreciate that there will be many disappointed by today’s decision but members felt that the long term benefits for the local, regional and national economy were transformational. This truly exceptional nature plus the measures proposed by the company to mitigate harm and deliver widespread environmental benefits to the park over a long period of time tipped the balance in favour of approval."