A mining company says it has found the world's biggest and best quality supply of a valuable mineral under the North York Moors National Park.
York Potash today said it is pressing ahead with plans to build a mine after surveys discovered an estimated 1.3 billion tonnes of polyhalite, which is processed to make premium potash fertiliser, below the protected Yorkshire coastline.
The firm, owned by international mining conglomerate Sirius Minerals, said the find was of "global relevance" and could create 1,000 jobs.
But conservationists say it would be the largest intrusion in a national park in 40 years.
York Potash wants to sink a 1,500-metre mine under the park, tunnel outwards and pump the polyhalite underground to Teesside, around 30 miles north, where it would be processed.
An exact location for the development has yet to be identified after boreholes were drilled at several sites in the conservation area between Scarborough and Whitby.
York Potash spokesman Gareth Edmunds said: "It's the biggest polyhalite resource and the highest quality in the world.
"We are confident that this is a project of national importance, but also one that will deliver numerous local benefits.
"It's a proposal that's going to create around a thousand direct jobs - many of those are highly skilled jobs - and many more in supporting roles."
The site, about 15 miles south of the UK's only existing potash mine in Boulby, near Redcar, could generate £1.5 billion a year if plans are approved, York Potash said
About 0.5% of annual revenue would be invested into the local community through a project fund.
Mr Edmunds said the mineral, in high demand for food production in the developing world, would be processed outside the national park and the shaft head would be sunken to avoid scarring the landscape.
He said: "All our focus is on reducing the surface impact and reducing the environmental impact.
"And people won't know the pipeline is there once it has been installed."
Conservationists are fighting the plans, saying the mining process and its associated infrastructure would be catastrophic for the landscape and the environment.
Tom Chadwick, chairman of the North Yorkshire Moors Association, said: "We are completely opposed to a major industrial development in the national park. That's what it amounts to.
"It will be the largest intrusion in a national park in 40 years. It will diminish the national park."
He added that no plans had been put forward to dispose of the mining spoil, which could create half a million to three quarters of a million cubic metres of rubble.
"The only thing they can do with it is create an artificial landscape," he said.
"The North Yorkshire Moors is an exquisite area of wild moorland.
"If you're going to have this in a moorland area, clearly it's going to reduce the habitat for moorland birds, some of which are endangered. That would have to be addressed.
"There will be an effect, there's no question about that. It will reduce wildlife habitat for everything from small mammals to reptiles."
North York Moors National Park said the planned development would be the biggest ever single investment in one of Britain's national parks.
Director of planning, Chris French, said it was a "huge" project and the organisation has been "closely involved in giving application advice".
He said he expects to receive a full planning application from the company in late autumn.
However, the final decision may ultimately be made by the Secretary of State, depending on how complicated the application is and the level of opposition to it.
A National Park spokesperson said government guidelines state it had to be "supportive" while helping York Potash explore mineral deposits in the area.
However, now polyhalite has been found, the emphasis switches and the firm must prove there is an "overriding public interest" to extract it, it said.