Sirius Minerals shares slumped today after the miner said its North Yorkshire potash mine could cost up to $3.5bn (£2.4bn).
The first phase will cost $1.6bn, followed by another $1.9bn in the second phase, according to a widely anticipated study into the project.
This helped send the company's shares down as much as 17.8 per cent to 18.7p in early morning trading.
Sirius also expects initial production to start in 2021, but the mine won't start producing at its initial installed capacity of 10m tonnes per year until 2023.
It's previously said that the development will create at least 1,000 jobs, as well as adding over £1bn to the UK economy.
"The business that is created from this project will sit as a world leader in the fertilizer industry based here in the UK," Chris Fraser, managing director and chief executive of Sirius, said.
"In delivering this project we can create thousands of jobs in North Yorkshire and Teesside, deliver billions of pounds of investment to the UK and put the country at the forefront of the multi-nutrient fertiliser industry."
Sirius wants to build the mine which will eventually produce potash, a form of fertiliser, between Whitby and Scarborough in North Yorkshire.
However, it's been politically contentious, attracting opposition from environmental campaigners who are worried about its impact on the moors.