Diamba Sud Gold Project, Senegal

Targeting construction decision in H1 2026

Overview

Acquired in September 2023, the Diamba Sud Gold Project is located in the highly prospective Kenieba-Koudougou Inlier (KKI) which hosts several world class gold deposits in eastern Senegal and western Mali. Associated with north north-east trending fertile splays from the regionally significant Senegal Mali Shear Zone, the Diamba Sud Gold Project hosts seven deposits with resources totaling 724,000 oz Au Indicated, and 285,000 oz Au Inferred as of July 7, 2025.

The results of the PEA were announced on October 15, 2025, and supports robust project economics for the development of an open-pit mine and conventional carbon-in-leach (CIL) processing plant. At a gold price of $2,750 per ounce, the assessment unveils an after-tax NPV_5% of $563 million, an IRR of 72 percent, and a payback period of ten months. During the first three years of production, Diamba Sud is projected to deliver an average of 147,000 ounces of gold per year at an All-In Sustaining Cost (AISC) of $904 per ounce.

The PEA estimates construction capital costs at approximately $283.2 million. Project funding is derisked by the strength of Fortuna’s balance sheet and robust cash flow generation.

A technical report supporting the results of the PEA was released on November 26, 2025.

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.

PEA Key Highlights

Metrics	Units	Results
Gold Price	$/oz	2,750
Life of mine	years	8.1
Processing Duration	years	7.9
Total mineralized material mined¹	kt	17.8
Contained gold in mineralized material mined¹	koz	932
Strip ratio	Waste: mineralized material	5.5:1
Throughput initial 3 years (primarily oxide)	Mtpa	2.5
Throughput after 3 years (primarily fresh)	Mtpa	2.0
LOM grade	g/t	1.63
Recoveries	%	90
Gold production
Total Production over LOM	koz	840
Average annual production over LOM	koz	106
Average annual production over first 3 years	koz	146
Per unit costs LOM
Mining	$/t, mined	4.82
Processing	$/t, processed	13.9
G&A	$/t, processed	6.7
Cash costs¹
Average operating cash costs², over LOM	$/oz	1,081
Average operating cash costs², over first 3 years	$/oz	759
AISC¹
Average AISC², over LOM	$/oz	1,238
Average AISC², over first 3 years	$/oz	904
Capital costs
Initial capital expenditure	$M	283
Sustaining capital expenditure + Infrastructure (includes closure costs)	$M	48
Returns
NPV5%, pre-tax (100% Project basis)	$M	772
Pre-tax IRR	%	86
NPV5%, after-tax (100% Project basis)	$M	563
After-tax IRR	%	72
After-tax payback period	years	0.8
Annual EBITDA²
Average EBITDA² over LOM	$M	167
Average EBITDA² over first 3 years	$M	277

Notes

The pit optimization shells used for the mine plan were generated using a gold price of $2,300 per ounce.
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.
Average operating cash costs and average AISC represent costs for projected production for the LOM at the time of gold sales.
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.
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.
The IRR on total investment that is presented in the economic analysis was calculated assuming a 100% ownership in Diamba Sud.
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.
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.
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.
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.

Exploration Upside: Resource Delineation and Exploration Drilling

Opportunities exist to further strengthen and enhance Diamba Sud’s economic foundation through continued drilling, resource extension testing, and definition of new targets. Successful exploration programs are expected to extend the Life of Mine (LOM) gold production profile to beyond a decade.

Exploration programs are focused on:

Infill drilling at Area A, Area D, Karakara, Moungoundi, and Southern Arc to convert Inferred Resources to Indicated Resources in support of the forthcoming Definitive Feasibility Study (DFS) and Mineral Reserve estimate.
Step-out and resource expansion drilling at Southern Arc aimed at increasing the Mineral Resource and enhancing the LOM gold-production profile from year four onward.
Testing prospective targets identified across the broader Diamba Sud tenement package, which offer additional growth potential.
Continuing exploration at Fortuna’s Bondala properties, adjacent to Diamba Sud, where geophysical surveys and auger drilling have identified anomalies to be followed up with targeted drill programs.

PEA Overview

The PEA outlines the design of an open pit gold mining operation targeting a series of deposits including Area A, Area D, Karakara, Western Splay, Kassassoko, Moungoundi, and Southern Arc which will feed a central gold processing facility over the current 8.1-year LOM. The assessment is based on Diamba Sud´s Mineral Resource estimate, which comprises an Indicated Mineral Resource of 14.2 million tonnes (Mt) at an average gold grade of 1.59 grams per tonne (g/t), containing 724,000 ounces of gold, and an Inferred Mineral Resource of 6.2 Mt at an average grade of 1.44 g/t gold, containing 285,000 ounces of gold, reported as of July 7, 2025.

Indicated Mineral Resource

26.0 million tonnes

averaging 1.50 g/t, containing 1,254,000 oz Au

Inferred Mineral Resource

2.1 million tonnes

averaging 1.13 g/t, containing 77,000 oz Au

Refer to Mineral Reserves and Resources table below for full disclosure

Mining and Processing

The PEA and mine plan outline the design of an open pit gold mining operation feeding a central gold processing facility over the 8.1-year LOM. The assessment anticipates the concurrent development of multiple deposits, including Area A, Area D, Karakara, Western Splay, Kassassoko, Moungoundi, and Southern Arc, with no more than three pits mined at any one time.

Mining activities at Diamba Sud will employ conventional open pit methods. Drilling and blasting are planned for both oxide and fresh mineralized material, followed by conventional truck-and-shovel operations for the movement of potentially mineralized material and waste within the pits.

The Diamba Sud process plant design is based on a metallurgical flowsheet developed to produce gold doré at optimum recovery while minimizing initial capital and operating costs. The flowsheet comprises conventional crushing, milling (single-stage semi-autogenous grinding mill in closed circuit with cyclones), gravity recovery, carbon-in-leach processing, carbon elution, and gold recovery.

Tailings, Water and Power

The tailings management system will comprise a tailings pipeline and a water return pipeline housed within a geomembrane-lined trench, with associated tailings pumps. The Tailings Storage Facility (TSF) will be fully lined with a geomembrane and will be developed as a side-valley storage facility formed by robust, multi-zoned earth-fill embankments. It is designed to accommodate 17.8 Mt of tailings and will be constructed using the downstream methodology, in accordance with industry best practices and the Global Industry Standard on Tailings Management.

A water storage dam will serve as the main collection and storage facility for clean, raw, and process water. Raw water is currently assumed to be supplied via a pipeline from the Falémé River, supplemented by pit dewatering activities. Ongoing studies are evaluating the potential to develop a water harvesting facility as an alternative source. Process water from the TSF will be recycled back to the plant, with site operations designed as a closed-circuit system to maximize water reuse and minimize environmental impacts on surrounding communities.

Power for Diamba Sud is expected to be self-supplied through an on-site power plant. The current plan envisages a heavy fuel oil power plant constructed in an N+1 configuration, supported by light fuel oil generators to meet site-wide demand. In parallel, a hybrid solar photovoltaic system is being evaluated as part of the preparation of the DFS.

Financial Analysis

Diamba Sud has been evaluated on a discounted cash flow basis and the results of the PEA demonstrate that it is potentially economically robust. The base case, using a gold price of $2,750 per ounce, generates an after-tax NPV at a 5 percent discount rate of $563 million, an IRR of 72 percent, and a payback period of approximately ten months.

The sensitivity of Diamba Sud’s NPV to changes in the applied discount rate and gold price is presented in the table below:

		Gold Price ($/oz)
		$2,000	$2,250	$2,500	$2,750	$3,000	$3,250	$3,500	$3,750
Discount Rate (%)	3.0	$230	$362	$494	$622	$750	$878	$1,007	$1,134
	5.0	$200	$322	$444	$563	$682	$800	$919	$1,037
	7.0	$173	$287	$400	$511	$621	$731	$841	$951

Environmental and Permitting

On October 6, 2025, Fortuna filed an Environmental and Social Impact Assessment (ESIA) with the Direction de la Réglementation Environnementale et du Contrôle, a division of the Ministry of the Environment and Sustainable Development of Senegal. The filing of the ESIA marks an important milestone in the permitting process.

Fortuna expects to apply and receive an exploitation permit for Diamba Sud before the expiry of its exploration permit in June 2026.

Next Steps: Definitive Feasibility Study and Early Works

Fortuna has approved a supplementary budget of $17 million to de-risk Diamba Sud’s development schedule by advancing early work planning and permitting in parallel with early works construction activities to establish site access and a new accommodation camp. In addition, subject to Board approval, front-end engineering and design is scheduled to commence this quarter, followed by the procurement of long-lead items in the second quarter of 2026 to ensure readiness for project execution.

The DFS is expected to be completed towards the end of the second quarter of 2026, leading to an anticipated construction decision shortly thereafter. A positive construction decision would position Diamba Sud to begin full construction in the fourth quarter of 2026, following the wet season, with first gold pour targeted for the second quarter of 2028.

Projected timeline for development and key milestones

Technical reports

Download the latest Diamba Sud Technical Report, effective date: October 15, 2025 (27 MB)

Mineral Resources

Indicated

Deposit	Tonnes (000)	Au (g/t)	Contained Metal Au (koz)
Area A	5,037	1.39	225
Area D	5,952	1.52	292
Southern Arc	5,993	1.91	367
Karakara	3,296	1.70	180
Western Splay	2,345	1.27	96
Kassassoko	1,697	0.78	43
Moungoundi	1,707	0.93	51
Total	26,027	1.50	1,254

Inferred

Deposit	Tonnes (000)	Au (g/t)	Contained Metal Au (koz)
Area A	207	1.24	8
Area D	329	0.86	9
Southern Arc	841	1.28	34
Karakara	31	1.30	1
Western Splay	262	1.42	12
Kassassoko	182	0.74	4
Moungoundi	253	0.89	7
Total	2,105	1.13	77

Notes:

Mineral Resources are reported using the 2014 CIM Definition Standards.
Mineral Resources are reported insitu, on a 100% basis as of January 16, 2026. The Government 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% interest in Boya SA at a “fair price” as determined through an independent valuation upon the granting of the exploitation permit.
Mineral Resources are reported from a regularized block model derived from the original subblocked model to account for mining dilution.
Factors that could materially affect the reported Mineral Resources 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 also applied for an exploitation permit and an environmental impact assessment permit for the Project. If the aforementioned permits are not granted, this will have a material impact on the potential development of the Project.
Mineral Resources that are not Mineral Reserves do not have demonstrated economic viability.
Mineral Resources are reported inside constraining 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 in accordance estimated average base mining costs of $4.57/t for all material mined, average processing and G&A costs of $21.45/t milled, and sales and transportation costs of $7.00/oz of gold. Pit slope angles applied are 33? for weathered material and 46? for fresh rock. The long-term gold price was US$3,300/oz. Metallurgical recoveries are estimated using grade versus recovery relationship formulas developed for oxide/transition rock (all deposits) and separate formulas for fresh rock in each of the seven deposits A royalty of 3.5% has been considered in the generation of the pit shell and cut-off grade determination.
Eric Chapman, P. Geo. (EGBC #36328), is the Qualified Person responsible for Mineral Resources, being an employee of Fortuna Mining Corp.
Totals may not add due to rounding

Photo gallery

Diamba Sud Gold Project, Senegal