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 will be prepared on or before November 29, 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

	Units	Results
Gold Price	$/oz	2,750
Life of mine	year	8.1
Total mineralized material mined¹	Mt	17.75
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
Head grade	g/t Au	1.63
Recoveries	%	90%
Gold production
Total Production over LOM	koz	840
Average annual production, LOM	koz	106
Average annual production, first 3 years	koz	147
Per unit costs over LOM
Total mining costs	$/t, mined	$4.82
Processing	$/t, processed	$13.91
G&A	$/t, processed	$6.70
Cash costs¹
Average operating cash costs², LOM	$/oz	$1,081
Average operating cash costs², first 3 years	$/oz	$759
AISC¹
Average AISC², LOM	$/oz	$1,238
Average AISC², first 3 years	$/oz	$904
Capital costs
Initial capital expenditure	$ M	$283
Sustaining capital, operations + Infrastructure (includes closure costs)	$ M	$48
NPV5%, pre-tax (100% project basis)	$M	$772
Pre-tax IRR	%	86%
NPV5%, after-tax (100% project basis)	$M	$563
After-tax IRR	%	72%
Payback period	year	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 mining inventory were generated using a gold price of $2,300 per ounce.
This is a non-GAAP financial measure. The definition and purpose of this non-GAAP financial measure is included under “Privacy Policy & Disclaimer”. Non-GAAP 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 will be entitled to a 10 percent free-carried interest in the Project, 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. There can be no assurance that such provisions will not be renegotiated as part of the exploitation permit approval process.
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.

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

14.2 million tonnes

averaging 1.59 g/t, containing 724,000 oz Au

Inferred Mineral Resource

6.2 million tonnes

averaging 1.44 g/t, containing 285,000 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

Mineral Resources

Indicated

Deposit	Tonnes (000)	Au (g/t)	Contained Metal Au (koz)
Area A	3,891	1.47	184
Area D	4,877	1.75	274
Karakara	2,476	1.79	143
Western Splay	1,615	1.65	86
Kassassoko	1,294	0.90	38
Total	14,153	1.59	724

Inferred

Deposit	Tonnes (000)	Au (g/t)	Contained Metal Au (koz)
Area A	61	1.02	2
Area D	600	1.10	21
Karakara	510	1.61	26
Western Splay	101	2.11	7
Kassassoko	123	0.85	3
Southern Arc	3,854	1.57	194
Moungoundi	922	1.06	31
Total	6,171	1.44	285

Notes:

Mineral Reserves and Mineral Resources are as defined by the 2014 CIM Definition Standards for Mineral Resources and Mineral Reserves
Mineral Resources are exclusive of Mineral Reserves.
Mineral Resources that are not Mineral Reserves do not have demonstrated economic viability.
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, extend and/or retain mineral and surface rights, titles and permits, maintain environmental and other regulatory permits, and maintain the social license to operate.
Mineral Resources are reported as of July 7, 2025.
Mineral Resources for Diamba Sud are reported pit constrained on a 100% ownership basis at selective mining unit block sizes and at an incremental gold cutoff grade for oxide/transitional material of 31 g/t Au, with fresh material reported based on a cutoff of 0.35 g/t Au for Area A, 0.42 g/t Au for Area D, 0.35 g/t Au for Karakara, 0.41 g/t Au for Western Splay, 0.35 g/t Au for Kassassoko, 0.37 g/t Au for Southern Arc, and 0.39 g/t Au for Moungoundi in accordance with the varying ore differential parameters and varying metallurgical recoveries for oxide, transitional and fresh rock within pit shell optimizations, assuming a long-term gold metal price of $2,600/oz and metallurgical recoveries based on metallurgical testwork.
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

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Diamba Sud Gold Project, Senegal