Fortuna Mining Corp. (NYSE: FSM and TSX: FVI) was down 1.5% in US premarket trade Thursday after it provided an updated consolidated Mineral Reserve and Mineral Resource estimates for its operating mines and projects in West Africa and Latin America.
Mineral Reserves increased by 15% year-over-year, after accounting for production related depletion, Fortuna said in a statement.
An updated estimate for Seguela as of March 31, 2026, reported an increase of 34% in underground Mineral Reserves and a 55% increase in Inferred Mineral Resources for the Sunbird deposit "as a result of the successful infill and exploration drilling program executed in the second half of 2025", the company added.
Among highlights, Consolidated Proven and Probable Mineral Reserves are reported containing 3.0 million gold equivalent ounces representing a year-over-year increase of 15%, the company said. Changes are due to the upgrading of resources to reserves representing 819,000 GEOs, primarily at Seguela, offset by production related depletion of 378,000 GEOs, it added.
Consolidated Measured and Indicated Resources exclusive of Mineral Reserves are reported containing 2.1 million GEOs representing a year-over-year increase of 56%, Fortuna said. Primary drivers for the net increase are the result of drilling at Diamba Sud, upgrading 781,000 GEOs, a 165% increase, offset by the upgrading of resources to reserves at Seguela, it added.
Consolidated Inferred Mineral Resources are reported containing 2.2 million GEOs representing a year-over-year increase of 4%, the company said. The change is the result of drilling discovering 726,000 GEOs counteracting the impact of upgrading 628,000 GEOs, it added.
Underground Mineral Reserves for Seguela's Sunbird deposit are reported as 4.4 Mt averaging 3.80 g/t Au containing 539,000 ounces of gold, an increase of 34% to its maiden estimate, Fortuna said. Inferred Mineral Resources are reported as 2.9 Mt averaging 4.45 g/t Au containing 417,000 ounces of gold, a 55% increase, it added.
Diamba Sud's feasibility study remains on track for first-time reporting of Mineral Reserves in support of a construction decision by the end of this quarter, the company said.
Mineral Reserves are estimated using a gold price of US$2,300/oz and Mineral Resources are estimated using a gold price of $2,600/oz, except for the Diamba Sud Project where Mineral Resources are estimated using a gold price of $3,300/oz, the company noted.
Shares in Fortuna were up 2.75% in Canada and 2.7% in the U.S. yesterday.