The deal completes the private placement phase of the amended strategic agreement between Prospero and Fortuna which was announced in May last year.
Fortuna currently owns 20.32% of the Prospero shares and after the placing will have around 26.9%.
Prospero says the proceeds will be aimed at drilling its Bermudez project in Chihuahua State, Mexico.
Drilling began at Bermudez in late August and Prospero plans to complete a three hole, approximately 1,500m, diamond drill program at Bermudez.
The 430-hectare Bermudez project is in Chihuahua, about 150km west of the City of Chihuahua.
Fortuna will buy around 4.74mln Prospero shares at C$0.075 per share.