New Zealand’s Environmental Protection Authority (EPA) approved Trans-Tasman Resources’ application to mine 50 Mt/a (55 million stpy) of iron sand in a 66 km (41 mile) area of seabed off the Taranaki Bight.
The company said the mine will create 300 jobs and add $160 million to the New Zealand’s GDP.
EPA chief executive Allan Freeth said it was a split decision, with decision-making committee chairman Alick Shaw issuing a casting vote in favor.
Radio New Zealand reported that the decision is facing stiff opposition from environmental groups including Kiwis Against Seabed Mining.
Kiwis Against Seabed Mining chairman Phil McCabe said appealing the decision was "the only responsible route."
"We are stunned that the EPA could have given this experimental industry the go-ahead, given the startling lack of available crucial information," he said.
Trans-Tasman Resources' first application in 2014 was turned down by the authority, which found there was uncertainty about the potential of effects on the environment and on existing fishing and iwi interests.
During a four-month hearing that ended in May, Greenpeace and Kiwis Against Seabed Mining said the authority should say no again.
The extra information backing the proposal was still too sketchy, the groups said.
The groups won a court case late last year demanding the release of further documents that Trans-Tasman Resources had redacted, saying they were commercially sensitive.
Trans-Tasman Resources said during the hearing that dredging and backfilling of sand would have a negligible effect, compared to passing ships or from oil and gas-drilling.
The mining would not take place in a pristine environment as the area already had a lot of commercial activity, the company argued.