In all Sirius issued just under 129.4mln shares 18p each.
The cash injection will be used for “working capital purposes”, the firm said.
AIM-listed Sirius is the owner of the York Potash project in North Yorkshire, which recently received planning permission.
The high-volume operation could enjoy a mine life of more than 100 years even at a full production rate of 20mln tonnes per annum of polyhalite fertiliser.
The group is currently finalising its definitive, or bankable, feasibility study (DFS), which remains on track for completion this quarter.