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 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.
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.