The fundraising for the project in northeast England was already on the way to hitting its target after Austrialia's richest woman Gina Rinehart, last week poured $300 million into the firm, a step analysts read as a major endorsement of the potential for polyhalite.

On Thursday Sirus said a placing of convertible bonds and shares announced on Wednesday had successfully raised the rest of the funds, provided they were approved by shareholders at a meeting on Nov. 24.

The initial funding will cover the first three years of construction at the site in Yorkshire.

It will be followed by another round of funding in between 18 months and two years' time to meet requirements to reach first production, expected at the end of 2021, Chief Executive Chris Fraser told Reuters.

Polyhalite is a naturally occurring mineral containing four of the six nutrients that ensure plant growth – potassium, sulphur, magnesium and calcium.

Fraser says it is superior to potash, which is far more widely used, because it contains four vital nutrients, not just one - potassium - and does not leave a damaging residue of chloride, which can result from using potash.

He said he already has offtake sales agreements with China and expects to sell to Europe, meaning his firm can benefit from the weaker pound resulting from Britain's vote to leave the European Union.

"Europe will be an important market," he said, adding that for a firm focused on export, Brexit should not have negative implications, apart from general uncertainty.

"The project is so robust economically, it does not have much of an impact except no-one likes uncertainty," he said.

(Reporting by Barbara Lewis; Editing by Greg Mahlich)