Chatham Islands mayor Alfred Preece is concerned that mining in nearby waters will not bring economic benefits to residents.
Chatham Rock Phosphate has been given a 20-year permit to mine 820 square kilometres of seabed on the Chatham Rise.
It is the first permit to be awarded under the amended Crown Minerals Act, which came into force earlier this year.
Phosphate from the Chatham Rise can be used as direct application fertiliser and will reduce the need to import phosphate from Morocco.
But Mr Preece said on Friday that the strong fishing community would like more information on how disturbed sediment will affect them.
"That's always a concern to us. We're a small community forgotten at times that relies a lot on the waters around us to make our living. Certainly if there are any economic benefits, we'd like to see that dealt with in the next part of this process."
Mr Preece said there were a lot of unknowns about the project, particularly the side-effects of mining.
Chatham Rock Phosphate must now apply for a marine consent, which takes into account the environmental impact of the project, and will be subject to a consultation process.
Managing director Chris Castle said the granting of the permit was a milestone for the company, even though it could be several years before mining actually started.
Mr Castle moved to reassure residents over plumes of sediment created by the drilling, saying they should stay close to where the mining actually takes place.
"In fact, the plumes don't go anywhere near the island, they only move a few kilometres from where we are, and that's 250km away from the island.
"The plumes that do move around are all almost clear water. In fact, we have demonstration towers where we show what the water actually looks like, and it's water you would probably drink without even noticing."
Shares in the company on Friday jumped 17% at the news the permit had been granted.
