The re-evaluation follows a royalty and share deal struck with an offshoot of Australia’s Hancock Prospecting.
Liberum estimates Hancock could end up paying as much as 170p a share in the equity portion of the funding.
This has knock-on implications as to the value of the giant polyhalite deposit, which it now reckons is worth US$6bn, up from US$4bn previously.
“We can also derive an implied valuation for the project based on the royalty agreement, although it of course relies on our own assumptions on volumes, price, and discount rate,” said analyst Richard Knights.
The Liberum stock picker reckons the shares are worth 50p each. At 8.40am they were trading at 36.35p each, up 2.4%.
On Tuesday Sirius said it said it had tied up a financing deal worth up to US$300mln.
The pact with a subsidiary Gina Rinehart’s Hancock Prospecting will form an important plank of the overall funding package for the AIM-listed group’s North Yorkshire Polyhalite Project.
Under the terms of the agreement, Hancock British Holdings is acquiring a 5% royalty on the first 13mln tonnes of fertiliser produced every year and 1% on anything over that output figure at a cost of US$250mln.
Hancock has also agreed to acquire US$50mln-worth of Sirius shares.
Chief executive Chris Fraser told investors: "We are delighted to have signed this agreement with such an experienced party in the mining industry, as well as one that has very successful and strong leadership and a long term and growing agricultural interest."