Fortuna Mining Corp. (NYSE: FSM) (TSX: FVI) is pleased to report additional exploration drilling results from the Southern Arc deposit at its Diamba Sud Gold Project in Senegal. Diamba Sud is a PEA-stage project with robust economics, highlighted by an estimated after-tax NPV_5% of US$563 million and an IRR of 72% at a gold price of US$2,750 per ounce. The project is currently advancing toward a feasibility study and a construction decision targeted for the second quarter of 2026.

Paul Weedon, Senior Vice President of Exploration, commented “Southern Arc continues to deliver strong results with high grade intersections from both infill and extension drilling. Infill highlights include drillhole DSDD555, which returned 6.8 g/t gold over an estimated true width of 35.5 meters.” Mr. Weedon continued, “Importantly, drilling to the southwest of the current optimized pit shell is expanding mineralization, returning broad and consistent gold intervals. This includes drill hole DSDD574, which intersected 1.7 g/t gold over an estimated true width of 29.6 meters, and a further 2.0 g/t over an estimated true width of 20.0 meters.” Mr. Weedon concluded, “These results will feed into an updated resource estimate expected in the first quarter of 2026.”

The PEA is preliminary in nature and includes inferred mineral resources that are considered too speculative geologically to have the economic considerations applied to them that would enable them to be categorized as mineral reserves; as such, there is no certainty that the PEA results will be realized. Mineral resources that are not mineral reserves do not have demonstrated economic viability¹

Southern Arc Prospect Drilling Highlights

A further 63 reverse-circulation and diamond drill hole, totalling 9,619 meters, have been completed at Southern Arc (see Figure 1) since the Company´s previous exploration update (refer to Fortuna news release dated May 27, 2025). Drilling is continuing with five drill rigs, with key objectives including:

• ongoing infill drilling to support increased resource confidence, and
• continued step-out drilling to the southwest, east, and south, where mineralization remains open

Mineralization at Southern Arc occurs as variably developed fine stockwork vein arrays to diffuse pyrite-silica flooding, showing strong correlation with several tectonic breccia and carbonate units (see Figures 2 and 3). Alteration commonly includes extensive hematite development, consistent with mineralized systems elsewhere at Diamba Sud.

Overall, the latest drilling reinforces the strong potential for continued resource growth at Diamba Sud. Southern Arc remains open to the south, east, and at depth, with drilling to date testing to only approximately 150 meters below surface.

Figure 1: Location plan showing Diamba Sud drilling and Mineral Resource Deposits

Figure 2: Diamba Sud Gold Project: Southern Arc Prospect, cross section 550NE

Figure 3: Diamba Sud Gold Project: Southern Arc Prospect, cross section 450NE

Refer to Appendix 1 for complete drill hole collars, significant intercepts, and assay results for this drill program.

Quality Assurance & Quality Control

All drilling data completed by the Company utilized the following procedures and methodologies. All drilling was carried out under the supervision of the Company’s personnel.

All reverse circulation drilling used a 5.25-inch face sampling pneumatic hammer with samples collected into 60-liter plastic bags. Samples were kept dry by maintaining enough air pressure to exclude groundwater inflow. If water ingress exceeded the air pressure, RC drilling was stopped, and drilling converted to diamond core tails. Once collected, RC samples were riffle split through a three-tier splitter to yield a 12.5 percent representative sample for submission to the analytical laboratory. The residual 87.5 percent samples were stored at the drill site until assay results were received and validated. Coarse reject samples for all mineralized samples corresponding to significant intervals are retained and stored on-site at the Company-controlled core yard.

All diamond drilling drill holes started with HQ sized diameter, before reducing to NQ diameter diamond drill bits on intersecting fresh rock. The core was logged, marked up for sampling using standard lengths of one meter or to a geological boundary. Samples were then cut into equal halves using a diamond saw. One half of the core was left in the original core box and stored in a secure location at the Company core yard at the project site. The other half was sampled, catalogued, and placed into sealed bags and securely stored at the site until shipment.

All RC and DD samples were transported by Company vehicle or commercial courier to ALS Global’s preparation laboratories in Kedougou, Senegal or Bamako, Mali, with prepared sample pulps then transported via commercial courier to ALS Global’s analytical facility in Ouagadougou, Burkina Faso. Routine gold analysis using a 50-gram charge and fire assay with an atomic absorption finish was completed for all samples. Samples returning assays >10 parts per million Au were reanalyzed using a 50-gram charge and fire assay with a gravimetric finish. Quality control procedures included the systematic insertion of blanks, duplicates and sample standards into the sample stream. In addition, the ALS Global laboratory inserted its own quality control samples.

Qualified Person

Paul Weedon, Senior Vice President, Exploration for Fortuna Mining Corp., is a Qualified Person as defined by National Instrument 43-101 being a member of the Australian Institute of Geoscientists (Membership #6001). Mr. Weedon has reviewed and approved the scientific and technical information contained in this news release. Mr. Weedon has verified the data disclosed, including the sampling, analytical and test data underlying the information or opinions contained herein by reviewing geochemical and geological databases and reviewing diamond drill core. There were no limitations to the verification process.

About Fortuna Mining Corp.

Fortuna Mining Corp. is a Canadian precious metals mining company with three operating mines and a portfolio of exploration projects in Argentina, Côte d’Ivoire, Mexico, and Peru, as well as the Diamba Sud Gold Project in Senegal. Sustainability is at the core of our operations and stakeholder relationships. We produce gold and silver while creating long-term shared value through efficient production, environmental stewardship, and social responsibility. For more information, please visit our website at www.fortunamining.com

Appendix 1: Diamba Sud drill program details of the drill holes and assay results for Southern Arc Prospect

Notes:
1. EOH: End of hole
2. Depths and widths reported to nearest significant decimal place
3. NSI: No significant intercepts
4. ETW: Estimated true width
5. RC: reverse circulation drilling | DD: diamond drilling tail | RCD: reverse circulation drilling with diamond tail

Appendix 2 – PEA Key Highlights

Notes:

1. The pit optimization shells used for the mine plan were generated using a gold price of $2,300 per ounce.
2. This is a non-IFRS financial measure. The definition and purpose of this non-IFRS financial measure is included in the Company’s management’s discussion and analysis for the three and nine months ended September 30, 2025, under the heading “Non-IFRS Measures”. Non-IFRS financial measures have no standardized meaning under IFRS and therefore, may not be comparable to similar measures presented by other issuers.
3. Average operating cash costs and average AISC represent costs for projected production for the LOM at the time of gold sales.
4. The PEA is presented on a 100 percent project basis. However, upon the granting of the exploitation permit, the Senegalese Government is entitled to a 10 percent free-carried interest in Boya , with the right for the State to acquire an additional contributory interest of up to 25 percent.
5. The economic analysis was carried out using a discounted cash flow approach on a pre-tax and after-tax basis, based on the gold price of $2,750/oz.
6. The IRR on total investment that is presented in the economic analysis was calculated assuming a 100% ownership in Diamba Sud.
7. The NPV was calculated from the after-tax cash flow generated by the Project, based on a discounted rate of 5% and an effective date of October 10, 2025.
8. The PEA assumes that the percentage of certain royalties and taxes payable to the State, the percentage of the investment tax credit available to the company and the percentage payable to the social development fund will be in accordance with the provisions of the Mining Convention between Boya S.A. and the State of Senegal dated April 8, 2015. It should be noted, however, that the State retains the sovereign prerogative to review or revisit certain fiscal terms during the exploitation permit approval process, and as such, the current framework may be subject to amendment.
9. The PEA is preliminary in nature, and it includes inferred mineral resources that are considered too speculative geologically to have the economic considerations applied to them that would enable them to be categorized as mineral reserves, and, as such, there is no certainty that the PEA results will be realized. Mineral resources that are not mineral reserves do not have demonstrated economic viability.
10. Further information regarding the PEA, including details on key assumptions, parameters, opportunities, risks and other factors are contained in the Technical Report prepared for the Company entitled “Diamba Sud Gold Project, Kedougou Region, Senegal” with an effective date of October 15, 2025, which has been filed on SEDAR+ and on EDGAR under the Company’s profile.