Fortuna Mining Corp. press release

Fortuna delivers robust Feasibility Study for the Diamba Sud Gold Project in Senegal: After-tax IRR of 60% and NPV5% of US$1 billion using US$3,500/oz

2026-06-29

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(All financial information contained herein are expressed in US dollars unless otherwise stated)

VANCOUVER, British Columbia, June 29, 2026 (GLOBE NEWSWIRE) -- FortunaMining Corp. (NYSE: FSM | TSX: FVI)announces positive results from the feasibility study (“FS”) for its Diamba Sud Gold Project in Senegal, confirming an economically robust open-pit conventional carbon-in-leach (“CIL”) gold mine and advancing one of Fortuna’s key growth opportunities.

Jorge A. Ganoza, President and CEO of Fortuna, commented, “Diamba Sud is a standout growth project with high returns, fast payback, and is expected to be our lowest-cost mine. Together with our Séguéla mine expansion, Diamba Sud supports our plan to grow our annual gold production rate by approximately 60% to more than 500,000 ounces in 2028.” Mr. Ganoza concluded, “With the recent receipt of the environmental decree from the Senegalese government and the feasibility study complete, we are ready to move Diamba Sud toward a final investment decision upon completion of the mining permit process.”

Feasibility Study Highlights

Financial

After-tax NPV5%of $1 billion, IRR of 60%, and 1-year payback at $3,500/oz gold At $4,000/oz gold, returns increase to NPV5%of $1.3 billion, IRR of 72%, and 11-month payback

Production and Cost

Strong first 4 years: Average annual gold production of 158,000 ounces 9.4-year life of mine (“LOM”) with an average annual gold production of 116,000 ounces Low-cost profile: Average AISC1of $1,056/oz over the first 4 years and $1,332/oz over LOM Final investment decision expected after receipt of the mining permit; first gold targeted by Q2 2028

CAPEX and Funding

Total initial capital of $397.5 million Funding secured by the Company's strong cash flow generation and liquidity of over $800 million2

Early Works

The Company continues advancing camp construction, office facilities and new site access road A letter of intent (“LOI”) has been executed with African Power Services (“APS”) as the power station engineering, procurement, and construction (“EPC”) contractor to secure the heavy-fuel oil (“HFO”) and light-fuel oil (“LFO”) generators Front-end engineering design (“FEED”) is being completed to support early procurement of critical-path equipment, including the SAG mill, to reduce project schedule risk

Notes:

1. This is a non-IFRS financial measure. The definition and purpose of this non-IFRS financial measure is included under the heading “Cautionary Note on Non-IFRS Measures” in this news release 2. Liquidity position as at March 31, 2026

DiambaSudFeasibility Study Overview

The Feasibility Study was prepared by Fortuna and supported by a team of independent industry experts, including Lycopodium, Knight Piesold, Kenmore Mine Consulting, SOJUFISC, Infinity Corporate Finance, Piteau Associates, Entech, and Earth Systems.

The Diamba Sud Gold Project is located in the Kédougou Region of southeastern Senegal, approximately 665 kilometers southeast of Dakar, 83 kilometers northeast of Kédougou, and 50 kilometers north of the Senegal-Guinea border. The Project comprises the contiguous DS1 and DS2 permit blocks, situated approximately 7 kilometers west of the Falémé River near the Senegal-Mali border.

Diamba Sud is operated by Boya S.A., a wholly owned indirect subsidiary of Fortuna. Boya holds full and unrestricted surface rights over the land covered by the exploration permit, subject to applicable mining regulations. Upon the granting of an exploitation permit, the State of Senegal will assume a 10% free-carried ownership interest in the Project.

Table 1 summarizes the key assumptions, operational parameters, economic results, and AISC values from the FS.

Table1: Feasibility Study Summary

| Metrics | Units | Results | | | | Gold price | $/oz | | 3,500 | | | Life of mine | year | | 9.4 | | | Total ore mined1 | Mt | | 20.5 | | | Contained gold in ore mined1 | koz | | 1,151 | | | Strip ratio | w:o | | 6.3:1 | | | Throughput (oxide) | Mtpa | | 2.5 | | | Throughput (fresh) | Mtpa | | 2.0 | | | Head grade | g/t Au | | 1.75 | | | Recovery | % | | 91% | | | Goldproduction | | | | | | Total production over LOM | koz | | 1,053 | | | Average annual production, LOM | koz | | 116 | | | Average annual production, first 4 years | koz | | 158 | | | PerunitcostsoverLOM | | | | | | Total mining costs | $/t, mined | | $4.8 | | | Processing | $/t, processed | | $16.1 | | | G&A | $/t, processed | | $8.6 | | | Cashcosts2 | | | | | | Average operating cash costs2, LOM | $/oz | | $1,146 | | | Average operating cash costs2, first 4 years | $/oz | | $856 | | | AISC2 | | | | | | Average AISC2, LOM | $/oz | | $1,332 | | | Average AISC2, first 4 years | $/oz | | $1,056 | | | Capitalcosts | | | | | | Initial capital expenditure | $ M | | $398 | | | Sustaining capital, operations + Infrastructure (includesclosurecosts) | $ M | | $79 | | | NPV5%,pre-tax (100%project basis) | $ M | | $1,379 | | | Pre-tax IRR | % | | 70% | | | NPV5%,after-tax_(100%projectbasis)_ | $ M | | $1,009 | | | After-tax IRR | % | | 60% | | | Payback period | years | | 1 | | | AnnualEBITDA2 | | | | | | Average EBITDA2over LOM | $ M | | $258 | | | Average EBITDA2over first 4 years | $ M | | $398 | |

Notes:

1. The pit optimization shells used for the Mineral Reserves were generated using a gold price of $2,900/oz. 2. This is a non-IFRS financial measure. The definition and purpose of this non-IFRS financial measure is included under the heading “Cautionary Note on Non-IFRS Measures” in this news release. Non-IFRS financial measures have no standardized meaning under the International Financial Reporting Standards (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 FS is presented on a 100% project basis. However, upon the granting of the exploitation permit, the State of Senegal will be entitled to a 10% free-carried interest in the Project, with the right for the State to acquire an additional contributory interest of up to 25%. 5. The economic analysis was carried out using a discounted cash flow approach on a pre-tax and after-tax basis, based on a gold price of $3,500/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%. 8. The FS assumes that the percentage of certain royalties and taxes payable to the State, the percentage of the investment tax credit available to Boya S.A. 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. There can be no assurance that such provisions will not be renegotiated by the State as part of the exploitation permit approval process.

Figure 1 illustrates the Diamba Sud FS LOM production and cost profile and highlights average production of 158,000 ounces per year over the initial four years at an AISC of $1,056/oz.

Figure 1:Diamba Sud FS LOM Production and Cost Profile

Key Improvements from the 2025 PEA

The 2026 Diamba Sud FS supersedes the Preliminary Economic Assessment (“PEA”) dated October 15, 2025, and reflects a more advanced, higher-confidence project with stronger production, a longer mine life, improved technical definition, and reduced execution risk. Key optimizations to the Project include:

Higher production profile:Average annual gold production increases from 106,000 ounces per year in the PEA to 116,000 ounces per year in the FS, including average production of 158,000 ounces per year over the first four years compared with 147,000 ounces per year over the first three years in the PEA. Longer mine life:Project life increases from 8.1 years in the PEA to 9.4 years in the FS, supporting an extended production and cash-flow profile. Reserve conversion and Resource growth:Material growth in the Indicated Mineral Resource category supports conversion to Probable Mineral Reserves, establishing a stronger foundation for the FS mine plan. Improved grade profile:Average feed grade increases from 1.63 g/t Au in the PEA to 1.75 g/t Au in the FS. Improved metallurgical performance:Metallurgical recoveries increased from 90% in the PEA to 91% in the FS. Higher-confidence cost and execution basis:The FS advances the Project to a level of accuracy considered consistent with an Association for the Advancement of Cost Engineering (“AACE”) Class 3 estimate, typically corresponding to an accuracy range of approximately -10% to +15%. Reduced execution risk:Further advancement of early works to enable a rapid construction ramp-up following FID, to secure long-lead equipment, and to protect the project’s critical-path.

Exploration Upside: Resource Growth and Continued Expansion Potential

The initial Mineral Reserve estimate for Diamba Sud (see Table 2 below) represents a major milestone and provides the foundation for a long-life, low-cost open pit operation with strong production and cash flow potential. The Probable Mineral Reserves total 20.5 million tonnes averaging 1.75 g/t Au, containing 1.15 million ounces of gold. Importantly, Diamba Sud remains open for further growth. The FS mine plan is based on the current Mineral Reserve, while additional opportunities remain to convert Mineral Resources into Mineral Reserves and to expand the resource base through continued drilling. This provides Fortuna with a clear pathway to potentially extend mine life, enhance future production, and increase the overall value of the Project.

The Mineral Reserve estimate is supported by FS-level technical work, including metallurgical, geotechnical, hydrogeological, environmental, mine planning, processing, infrastructure, and cost studies. Mineral Reserves are reported at the point of delivery to the process plant using the 2014 CIM Definition Standards, on a 100% basis, and are classified as Probable Mineral Reserves. Mineral Reserves are estimated and reported as at April 10, 2026, and are summarized in Table 2. Mineral Resources, reported exclusive of Mineral Reserves, are summarized in Table 3.

Table 2:Mineral Reserve Estimate

| Classification | Deposit | Tonnes (kt) | Au (g/t) | Au (koz) | | Probable Mineral Reserves | Area A | 4,136 | 1.59 | 211 | | | Area D | 5,103 | 1.70 | 279 | | | Karakara | 2,859 | 1.87 | 172 | | | Kassasoko | 1,164 | 0.96 | 36 | | | Moungoundi | 1,069 | 1.10 | 38 | | | Southern Arc | 4,464 | 2.31 | 332 | | | Western Splay | 1,706 | 1.51 | 83 | | Total | | 20,500 | 1.75 | 1,151 |

Table 3:Mineral Resource Estimate, exclusive of Mineral Reserves

| Classification | Deposit | Tonnes (kt) | Au (g/t) | Au (koz) | | Indicated Mineral Resources | Area A | 288 | 0.50 | 5 | | | Area D | 436 | 0.53 | 8 | | | Karakara | 221 | 0.61 | 4 | | | Kassasoko | 206 | 0.49 | 3 | | | Moungoundi | 279 | 0.75 | 7 | | | Southern Arc | 1,701 | 1.62 | 89 | | | Western Splay | 233 | 0.74 | 6 | | Total | | 3,364 | 1.12 | 121 | | Inferred | Area A | 152 | 1.45 | 7 | | | Area D | 264 | 0.95 | 8 | | | Karakara | 26 | 1.47 | 1 | | | Kassasoko | 138 | 0.86 | 4 | | | Moungoundi | 107 | 1.09 | 4 | | | Southern Arc | 734 | 1.42 | 33 | | | Western Splay | 211 | 1.64 | 11 | | Total | | 1,632 | 1.30 | 68 |

Notes:

1. Mineral Reserves and Mineral Resources are as defined by the 2014 CIM Definition Standards for Mineral Resources and Mineral Reserves. 2. Mineral Resources are exclusive of Mineral Reserves. 3. Mineral Resources that are not Mineral Reserves do not have demonstrated economic viability. 4. Factors that could materially affect the reported Mineral Resources or Mineral Reserves include; changes in metal price and exchange rate assumptions; changes in local interpretations of mineralization; changes to assumed metallurgical recoveries, mining dilution and recovery; and assumptions as to the continued ability to access the site, retain mineral and surface rights titles, maintain environmental and other regulatory permits, and maintain the social license to operate. Boya SA has applied for an exploitation permit for the Project, and if not granted, it will have a material impact on the potential development of the Project. 5. Mineral Resources and Reserves for the Diamba Sud are estimated and reported as at April 10, 2026. The State of Senegal will assume a 10% free-carried ownership interest in the Project when an exploitation permit is granted and may elect to purchase up to an additional 25% contributory interest in Boya SA at a “fair price” as determined through an independent valuation. 6. Mineral Reserves for the Diamba Sud Project are reported at the point of delivery to the process plant on a 100% ownership basis and have been estimated using incremental gold cutoff grades for open-pit oxide and transitional material as follows: 0.38 g/t Au for Area A, Moungoundi, and Western Splay; 0.37 g/t Au for Kassasoko and Southern Arc; 0.36 g/t Au for Karakara; and 0.35 g/t Au for Area D. For fresh material, the applied cut-off grades are 0.40 g/t Au for Karakara and Kassasoko, 0.42 g/t Au for Area A, 0.43 g/t Au for Southern Arc, 0.45 g/t Au for Moungoundi, 0.46 g/t Au for Area D, and 0.49 g/t Au for the Western Splay deposit. The cutoff grades were derived using a gold price assumption of $2,900/oz, metallurgical recovery rates ranging from 72% to 97% depending on grade and material type by deposit, and surface mining costs of $5.77/t for Area A, $5.26/t for Area D, $5.28/t for Karakara, $6.27/t for Western Splay, $6.09/t for Kassasoko, $6.18/t for Moungoundi, and $6.27/t for Southern Arc. Average processing and general and administrative (G&A) costs are estimated at $24.92/t milled for oxide and transitional material and $30.23/t for fresh material. Refining and selling costs are estimated at $5.50/oz of gold, with an applicable royalty rate of 3.5%. Pit slope angles of 32° for weathered material and 46° for fresh rock have been applied in the pit optimization. Metallurgical recoveries have been estimated using grade–recovery relationship models developed for oxide and transitional material across all deposits, with deposit-specific recovery models applied to fresh rock across the seven deposits. 7. Mineral Resources are reported insitu and constrained within pit shells using selective mining unit block sizes and at an incremental gold cutoff grade for oxide/transitional material of 0.26 g/t Au, with fresh material reported based on a cutoff of 0.29 g/t Au for Area A, 0.37 g/t Au for Area D, 0.31 g/t Au for Karakara, 0.33 g/t Au for Western Splay, 0.28 g/t Au for Kassassoko, 0.31 g/t Au for Southern Arc, and 0.33 g/t Au for Moungoundi. Mineral Resource estimates are based on the same parameters used for Mineral Reserve estimates except gold price, where $3,300/oz was applied. 8. Eric Chapman is the Qualified Person responsible for Mineral Resources, and is a full-time employee of Fortuna, Raul Espinoza is the Qualified Person responsible for Mineral Reserves, and is a full-time employee of Fortuna. 9. Totals may not add due to rounding procedures.

Since 2023, Fortuna has invested meaningfully in mineral exploration at Diamba Sud, with the growth reflected in the maiden Mineral Reserve estimate summarized in Table 2. This work has increased both the scale and confidence of the resource base and supports the feasibility study mine plan. The Project retains further upside, particularly at Southern Arc, where recent drilling indicates the potential to extend mineralization.

Ongoing drilling is expected to test open extensions, improve geological confidence in areas currently classified as Inferred Resources, and identify additional mineralization beyond the current feasibility study mine plan. This work provides a clear pathway to further expand and upgrade the resource base, with the potential to support future mine life extensions and additional value creation.

MiningandProcessing

The FS outlines a conventional open pit gold mining operation feeding a central processing facility over a 9.4-year project life. The mine plan incorporates the Area A, Area D, Karakara, Kassassoko, Moungoudi, Southern Arc, and Western Splay deposits, with mining sequenced to support a consistent production profile over the LOM. The proposed general arrangement of the site infrastructure is shown in Figure 2.

The pit optimization shells used to constrain the Mineral Reserve were generated using a gold price of $2,900/oz and a revenue factor of 1.0. Optimization parameters included government royalties, refining, mining, processing, and general and administrative costs to support realistic pit designs and economic assumptions.

Based on the Mineral Reserve estimate, the mine plan includes the mining of 20.5 million tonnes of ore at an average gold grade of 1.75 g/t, containing 1.15 million ounces of gold. A total of 130 million tonnes of waste will be mined, resulting in a LOM strip ratio of 6.3:1.

Mining will use conventional open pit methods, including drilling and blasting for both oxide and fresh ore, followed by truck-and-shovel mining operations. Ore from the open pits will be processed through a conventional CIL plant designed to produce gold doré, incorporating crushing, milling, gravity recovery, CIL processing, carbon elution, and gold recovery.

The process plant is designed to treat the ore at an average annual processing rate of approximately 2.26 million tonnes, as shown in Figure 3, producing 1.05 million ounces of gold at a LOM metallurgical recovery of 91%.

Figure 2:Diamba Sud Mine General Site Infrastructure General Arrangement

Figure 3:Diamba Sud FS LOM processing schedule

A summary of the key operating and production statistics from the FS is presented in Table 4. The Area A and D deposits are combined for planning purposes as they are to be mined from a single contiguous pit.

Table4:Diamba Sud LOM Mining and Processing Plan Metrics

| | Y0 | Y1 | Y2 | Y3 | Y4 | Y5 | Y6 | Y7 | Y8 | Y9 | Y10 | LOM | | Area AD | | | | | | | | | | | | | | Ore mined (kt) | 81 | 1,825 | 284 | 16 | 1,034 | 2,393 | 1,515 | 2,090 | - | - | - | 9,239 | | Au grade (g/t) | 0.84 | 2.39 | 2.31 | 1.14 | 1.25 | 1.32 | 1.93 | 1.32 | - | - | - | 1.65 | | Karakara | | | | | | | | | | | | | | Ore mined (kt) | - | - | 30 | 819 | 1,972 | 37 | - | - | - | - | - | 2,859 | | Au grade (g/t) | - | - | 1.24 | 2.04 | 1.79 | 2.85 | - | - | - | - | - | 1.87 | | Kassasoko | | | | | | | | | | | | | | Ore mined (kt) | - | - | - | - | - | - | 25 | 82 | 136 | 922 | - | 1,164 | | Au grade (g/t) | - | - | - | - | - | - | 0.99 | 0.70 | 0.87 | 0.99 | - | 0.96 | | Moungoudi | | | | | | | | | | | | | | Ore mined (kt) | - | - | - | - | - | - | - | - | 97 | 923 | 49 | 1,069 | | Au grade (g/t) | - | - | - | - | - | - | - | - | 0.95 | 1.10 | 1.49 | 1.10 | | South Arc | | | | | | | | | | | | | | Ore mined (kt) | 234 | 1,348 | 1,321 | 1,561 | - | - | - | - | - | - | - | 4,464 | | Au grade (g/t) | 1.72 | 1.95 | 2.50 | 2.56 | - | - | - | - | - | - | - | 2.32 | | Western Splay | | | | | | | | | | | | | | Ore mined (kt) | - | - | - | - | - | - | 59 | 767 | 879 | - | - | 1,706 | | Au grade (g/t) | - | - | - | - | - | - | 1.08 | 1.29 | 1.73 | - | - | 1.51 | | Total | | | | | | | | | | | | | | Ore mined (kt) | 315 | 3,173 | 1,635 | 2,396 | 3,006 | 2,430 | 1,599 | 2,939 | 1,112 | 1,845 | 49 | 20,500 | | Au grade (g/t) | 1.50 | 2.21 | 2.45 | 2.37 | 1.61 | 1.34 | 1.88 | 1.30 | 1.56 | 1.04 | 1.49 | 1.75 | | Contained gold (koz) | 15 | 225 | 129 | 183 | 155 | 105 | 97 | 123 | 56 | 62 | 2 | 1,151 | | Waste mined (kt) | 3,644 | 15,439 | 16,606 | 16,259 | 16,020 | 16,612 | 17,438 | 12,664 | 8,114 | 6,768 | 53 | 129,618 | | Total mined (kt) | 3,959 | 18,612 | 18,242 | 18,656 | 19,027 | 19,042 | 19,037 | 15,603 | 9,226 | 8,613 | 102 | 150,118 | | Stockpile | | | | | | | | | | | | | | End of period (kt) | 315 | 1,322 | 584 | 730 | 1,360 | 1,373 | 722 | 1,412 | 292 | 106 | - | n/a | | Grade (g/t) | 1.5 | 0.98 | 0.57 | 0.57 | 0.64 | 0.58 | 0.58 | 0.59 | 0.60 | 0.57 | - | n/a | | Processing | | | | | | | | | | | | | | Material milled (kt) | - | 2,166 | 2,374 | 2,250 | 2,376 | 2,416 | 2,250 | 2,250 | 2,231 | 2,031 | 155 | 20,500 | | Head grade (g/t) | - | 2.85 | 2.09 | 2.49 | 1.84 | 1.38 | 1.51 | 1.51 | 1.07 | 1.01 | 0.86 | 1.75 | | Contained gold (koz) | - | 199 | 160 | 180 | 141 | 107 | 109 | 109 | 77 | 66 | 4 | 1,151 | | Recovery (%) | - | 93 | 93 | 94 | 93 | 87 | 93 | 90 | 86 | 87 | 86 | 91 | | Gold production (koz) | - | 184 | 149 | 169 | 131 | 93 | 101 | 98 | 67 | 57 | 4 | 1,053 |