Fortuna Expands Southern Arc Mineralization with Drill Intercept of 1.7 g/t Au over 29.6 meters and a further 2.0 g/t Au over 20.0 meters from DSDD574 at the Diamba Sud Gold Project, Senegal

Vancouver, December 8, 2025: Fortuna Mining Corp. (NYSE: FSM | TSX: FVI) (-https://www.commodity-tv.com/play/fortuna-mining-ceo-on-strong-q3-results-and-diamba-sud-development-plans/ -) 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 NPV5% 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

1 Refer to the table in Appendix 2 (page 14) of this release for a summary of the key assumptions, operational parameters and economic results and values from the PEA

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 (QA - QC)

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 (RC) 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 (DD) 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

ON BEHALF OF THE BOARD

Jorge A. Ganoza

President, CEO, and Director

Fortuna Mining Corp.

Investor Relations:

Carlos Baca | info@fmcmail.com | fortunamining.com | X | LinkedIn | YouTube

In Europe

Swiss Resource Capital AG

Jochen Staiger & Marc Ollinger

info@resource-capital.ch 

www.resource-capital.ch

Forward looking Statements

This news release contains forward-looking statements which constitute “forward-looking information” within the meaning of applicable Canadian securities legislation and “forward-looking statements” within the meaning of the “safe harbor” provisions of the Private Securities Litigation Reform Act of 1995 (collectively, “Forward-looking Statements”). All statements included herein, other than statements of historical fact, are Forward-looking Statements and are subject to a variety of known and unknown risks and uncertainties which could cause actual events or results to differ materially from those reflected in the Forward-looking Statements.  The Forward-looking Statements in this news release may include, without limitation, the projected economics of the Diamba Sud Project, including the net present value of the Diamba Sud Project and the internal rate of return of the Diamba Sud Project; the Company’s expectation that a construction decision will be targeted for the second quarter of 2026; statements regarding continued resource growth at the Diamba Sud Project and the expected timing of an updated resource estimate; the Company’s proposed exploration plans at Diamba Sud statements about the Company’s business strategies, plans and outlook; the Company’s plans for its mines and mineral properties; changes in general economic conditions and financial markets; the impact of inflationary pressures on the Company’s business and operations;  the future results of exploration activities; expectations with respect to metal grade estimates and the impact of any variations relative to metals grades experienced;  assumed and future metal prices; the merit of the Company’s mines and mineral properties; and the future financial or operating performance of the Company.  Often, but not always, these Forward-looking Statements can be identified by the use of words such as “estimated”, “potential”, “open”, “future”, “assumed”, “projected”, “proposed”, “used”, “detailed”, “has been”, “gain”, “planned”, “reflecting”, “will”, “anticipated”, “estimated”   “containing”, “remaining”, “to be”, or statements that events, “could” or “should” occur or be achieved and similar expressions, including negative variations.   

Forward-looking Statements involve known and unknown risks, uncertainties and other factors which may cause the actual results, performance, or achievements of the Company to be materially different from any results, performance or achievements expressed or implied by the Forward-looking Statements. Such uncertainties and factors include, among others, operational risks associated with mining and mineral processing; uncertainty relating to Mineral Resource and Mineral Reserve estimates; uncertainty relating to capital and operating costs, production schedules and economic returns; risks relating to the Company’s ability to replace its Mineral Reserves; risks related to the conversion of Mineral Resources to Mineral Reserves; risks associated with mineral exploration and project development; uncertainty relating to the repatriation of funds as a result of currency controls; environmental matters including obtaining or renewing environmental permits and potential liability claims; uncertainty relating to nature and climate conditions; laws and regulations regarding the protection of the environment (including greenhouse gas emission reduction and other decarbonization requirements and the uncertainty surrounding the interpretation of omnibus Bill C-59 and the related amendments to the Competition Act (Canada); risks associated with political instability and changes to the regulations governing the Company’s business operations; changes in national and local government legislation, taxation, controls, regulations and political or economic developments in countries in which the Company does or may carry on business; risks associated with war, hostilities or other conflicts, such as the Ukrainian – Russian, and Israeli – Hamas  conflicts, and the impacts they may have on global economic activity; risks relating to the termination of the Company’s mining concessions in certain circumstances; developing and maintaining relationships with local communities and stakeholders; risks associated with losing control of public perception as a result of social media and other web-based applications; potential opposition to the Company’s exploration, development and operational activities; risks related to the Company’s ability to obtain adequate financing for planned exploration and development activities; property title matters; risks related to the ability to retain or extend title to the Company’s mineral properties; risks relating to the integration of businesses and assets acquired by the Company; impairments; risks associated with climate change legislation; reliance on key personnel; adequacy of insurance coverage; operational safety and security risks; legal proceedings and potential legal proceedings; uncertainties relating to general economic conditions; risks relating to a global pandemic, which could impact the Company’s business, operations, financial condition and share price; competition; fluctuations in metal prices; risks associated with entering into commodity forward and option contracts for base metals production; fluctuations in currency exchange rates and interest rates; tax audits and reassessments; risks related to hedging; uncertainty relating to concentrate treatment charges and transportation costs; sufficiency of monies allotted by the Company for land reclamation; risks associated with dependence upon information technology systems, which are subject to disruption, damage, failure and risks with implementation and integration; labor relations issues; as well as those factors discussed under “Risk Factors” in the Company's Annual Information Form for the fiscal year ended December 31, 2024. Although the Company has attempted to identify important factors that could cause actual actions, events, or results to differ materially from those described in Forward-looking Statements, there may be other factors that cause actions, events or results to differ from those anticipated, estimated or intended.

Forward-looking Statements contained herein are based on the assumptions, beliefs, expectations and opinions of management, including, but not limited to, the accuracy of the Company’s current Mineral Resource and Mineral Reserve estimates; that the Company’s activities will be conducted in accordance with the Company’s public statements and stated goals; that there will be no material adverse change affecting the Company, its properties or its production estimates (which assume accuracy of projected ore grade, mining rates, recovery timing, and recovery rate estimates and may be impacted by unscheduled maintenance, labor and contractor availability and other operating or technical difficulties); the duration and effect of global and local inflation; the duration and impacts of geo-political uncertainties on the Company’s production, workforce, business, operations and financial condition; the expected trends in mineral prices, inflation and currency exchange rates; that all required approvals and permits will be obtained for the Company’s business and operations on acceptable terms; that there will be no significant disruptions affecting the Company's operations and such other assumptions as set out herein. Forward-looking Statements are made as of the date hereof and the Company disclaims any obligation to update any Forward-looking Statements, whether as a result of new information, future events, or results or otherwise, except as required by law. There can be no assurance that these Forward-looking Statements will prove to be accurate, as actual results and future events could differ materially from those anticipated in such statements. Accordingly, investors should not place undue reliance on Forward-looking Statements.

Cautionary Note to United States Investors Concerning Estimates of Reserves and Resources

All reserve and resource estimates included in this news release have been prepared in accordance with National Instrument 43-101 Standards of Disclosure for Mineral Projects ("NI 43-101") and the Canadian Institute of Mining, Metallurgy, and Petroleum Definition Standards on Mineral Resources and Mineral Reserves. NI 43-101 is a rule developed by the Canadian Securities Administrators that establishes standards for public disclosure by a Canadian company of scientific and technical information concerning mineral projects. All Mineral Reserve and Mineral Resource estimates contained in the technical disclosure have been prepared in accordance with NI 43-101 and the Canadian Institute of Mining, Metallurgy and Petroleum Definition Standards on Mineral Resources and Reserves. Canadian standards, including NI 43-101, differ significantly from the requirements of the Securities and Exchange Commission, and mineral reserve and resource information included in this news release may not be comparable to similar information disclosed by U.S. companies.

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