First Mining Announces Updated Pre-Feasibility Study for the Springpole Gold Project, Ontario, Canada

Press Release

November 18, 2025 – Vancouver, Canada – First Mining Gold Corp. (“First Mining” or the “Company”) (TSX: FF) (OTCQX: FFMGF) (FRANKFURT: FMG) is pleased to announce the positive results of an updated Pre-Feasibility Study (“2025 PFS”) completed for its 100%-owned Springpole Gold Project (the “Project” or “Springpole”) located in Ontario, Canada. The 2025 PFS results support a 30,000 tonnes-per-day (“tpd”) open pit mining operation.

2025 PFS Highlights^{1 2}

• US$3.2 billion pre-tax net present value at a 5% discount rate (“NPV_5%”) at US$3,100/oz gold (“Au”), increasing to US$5.6 billion at US$4,200/oz Au²
• US$2.1 billion after-tax NPV_5% at US$3,100/oz Au, increasing to US$3.8 billion at US$4,200/oz Au
• 54% pre-tax internal rate of return (“IRR”) at US$3,100/oz increasing to 82% at $4,200/oz Au
• 41% after-tax IRR at US$3,100/oz Au increasing to 63% at US$4,200/oz Au
• Life of mine (“LOM”) of 9.4 years
• After-tax payback of 1.8 years and reducing to 1.2 years at US$4,200/oz Au
• Initial capital costs estimated at US$1,104 million, sustaining capital costs estimated at US$323 million, plus US$40 million in closure costs (excluding plant closure)
• Average annual payable gold production of 330 koz per year (Years 1 to 5); 281 koz per year LOM
• Total net cash costs³ of US$742/oz (Years 1 to 5); and US$802/oz LOM
• Net All-In Sustaining Costs (“AISC”)³ of US$877/oz (Years 1 to 5), and AISC US$938/oz (LOM)

“We are pleased to announce a very positive updated PFS at our Springpole Gold Project that reinforces its position as one of the largest and most robust undeveloped gold and silver projects in Canada”, stated Dan Wilton, CEO of First Mining.  “Since our original PFS was published in 2021, we have completed significant engineering work, the results of which have been reflected in the updated infrastructure and design plans that First Mining has carried through the Environmental Assessment process.  At the same time, this study demonstrates the strong leverage to gold price the Project possesses, and clearly demonstrates the potential for Springpole to be one of the largest economic drivers in northwestern Ontario for a generation to come, delivering hundreds of jobs and careers in the region, significant contracting opportunities for regional and Indigenous businesses and more than $7 billion in gross domestic product, as well as generational opportunities and potential infrastructure improvements for the Indigenous communities in the area.  First Mining continues to make progress on the Federal and Provincial Environmental Assessment processes, important consultation processes with Indigenous communities, and expects to provide updates in the coming months.”

This 2025 PFS for the Springpole Gold Project was prepared by Ausenco Engineering Canada ULC (“Ausenco”) of Vancouver, Canada, and a technical report summarizing the 2025 PFS will be filed by the Company on SEDAR+ within 45 days of this news release.

2025 PFS Overview

The Springpole Gold Project, located in Ontario, Canada, is one of the largest undeveloped gold resources in North America. The Project is located approximately 110 kilometres northeast of Red Lake and within 18 km of road access. The 2025 PFS provides for an updated resource model for Springpole including an Indicated Mineral Resource of 191Mt at 0.78 g/t Au for 4.8 million ounces (“Moz”) of gold and 4.6 g/t Ag for 28 Moz of silver.  The Inferred Mineral Resource category hosts 64 Mt at 0.38 g/t Au for 0.8 Moz of gold and 3.1 g/t Ag for 6.5 Moz of silver.

The 2025 PFS evaluates recovery of gold and silver from a 30,000 tpd open pit operation, with a process plant planned to include crushing, grinding, and flotation, with fine grinding of the flotation concentrate and separate agitated leaching circuits for both the reground flotation concentrate and the flotation tailings, followed by a carbon-in-pulp recovery process and a Merrill-Crowe circuit to produce doré bars. Tailings and mine rock are proposed to be securely stored at the Project’s Co-Disposal Facility (“CDF”) designed by WSP Canada, Inc. and reviewed by the Independent Tailings and Geotechnical Review Board established for the Project in 2023. The leached sulphur containing (“PAG”) flotation tailings are stored in a downstream constructed and raised CDF south cell which is lined.  The desulphurized flotation (“NAG”) tailings are thickened and co-disposed with mine rock in the CDF north cell.

Certain important parameters of the 2025 PFS are presented in the following table:

Table 1: Key Parameters

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Economic Sensitivities

The Project economics and cash flows are highly sensitive to changes to the gold price as presented in the following tables.

Table 2: Springpole Economic Sensitivity to Gold Price

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Table 3: Springpole Economic Sensitivity to Initial Capital Costs

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Table 4: Springpole Economic Sensitivity to Operating Costs

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Key Changes from 2021 Pre-Feasibility Study

Since the release of the 2021 PFS, First Mining has continued to advance Project engineering in support of addressing the Provincial and Federal Environmental Assessment processes, and the consultation processes with local and Indigenous communities.  This work, which remains on-going has resulted in several updates to the Project design since 2021.  The following areas reflect the key design optimizations from the 2021 PFS to date that have been brought forward in the 2025 PFS:

• The filter plant for NAG tailings was removed from the flowsheet given the optimization to a thickened tailings product instead of dry filtered tailings.
• The tailings and mine rock management strategy has been advanced since the 2021 PFS.  A separate flotation and leach circuit will sequester the sulphur concentrate PAG tailings.  This allows the PAG tailings to be isolated and placed saturated during operations in the CDF south cell to mitigate the potential onset of acid generation.
• PAG mine rock will be placed in the centre of the north cell.  Thickened NAG tailings, hydraulically transported via a pipeline, will encapsulate the PAG mine rock significantly reducing oxygen ingress to prevent oxidation of PAG mine rock improving environmental performance.
• A Merrill-Crowe circuit was added to the gold recovery circuits in order to manage ore variability and high silver grades.
• An airstrip was added to the site layout to be co-located adjacent to the mine access road that will facilitate up to Dash-8 size aircraft.
• A contact water management system will collect and treat site runoff and intercept potential seepage from the CDF.
• The closure design has been advanced to include a new enhanced fish habitat development area of 46 hectares which results in a net gain in Springpole Lake surface area at closure with corresponding benefits for fish and fish habitat.
• Two construction phase quarry sources within the Project footprint have been identified to source clean construction material early on with one adjacent to the two dikes and the second within the CDF footprint. This results in readily available material to initiate the construction of key Project infrastructure early on at low cost while maintaining a small overall Project footprint.
• The tonnes processed has been reduced from the 2021 PFS as a result of an updated pit design requiring reduced pit slope angles in the southwest portion of the open pit.  Opportunities exist to optimize the pit design as the Project advances with additional drilling programs planned in support of a feasibility study.  The reduction in the tonnes is partially offset by the 154% increase in contained gold ounces in the Inferred Resource category which will continue to be defined with further drilling and opportunities at Springpole Southwest and East targets. See Project Enhancement Opportunities section.
• Process and equipment changes are as follows:
  • Flotation Tails Thickener diameter reduced to 40 m (previously 41 m)
  • Flotation Concentrate Thickener diameter reduced to 23 m (previously 30 m)
  • CCD Thickeners diameter reduced to 23 m (previously 30 m)
  • Clarifier diameter reduced to 29 m (previously 33 m)
  • Flotation Tailings Leach Tanks diameter decreased to 17.0 m (previously 19.3 m)
  • Concentrate Pre-Oxidation Tank diameter decreased to 14.7 m (previously 15.2 m)
  • Tails Cyanide Detox Tanks diameter increased to 11.9 m (previously 6.4 m)
  • Concentrate Cyanide Detox Tanks diameter increased to 7.1 m (previously 6.4 m)
  • Tailings Surge Tanks diameter decreased to 15.9 m (previously 19.6 m)
  • Regrind Mills quantity reduced to two (2) (previously three (3))
  • Concentrate Leach Tanks quantity reduced to four (4) and the diameter reduced to 10.5 m (previously six (6) with a diameter of 12.3 m)
  • Flotation Cells quantity reduced to five (5) and capacity increased to 300 m³ (previously six (6) with a capacity of 200 m³)

Mineral Processing and Metallurgical Testing

The 2025 PFS reflects updated recoveries for both gold and silver that resulted from updated metallurgical test work completed since the 2021 PFS. The test work focused on understanding the variability in gold and silver recoveries as well as optimizing the process flowsheet.

Based on the test work carried out, a flowsheet that includes flotation followed by leaching of reground concentrate and flotation tails presents as the most beneficial processing route for the Project. This flowsheet is based on a primary grind size of 80% passing or P₈₀ 150 micrometres (“µm”) ahead of flotation, with flotation concentrate being reground to approximately 17 µm ahead of agitated leaching. The overall recoveries expected and used for the economics presented in the 2025 PFS are 86.0% for gold and 86.2% for silver. The increase in gold / decrease in silver recoveries in the 2025 PFS stems primarily from a better understanding of the ore variability. First Mining plans to undertake follow-up metallurgical test work to investigate additional opportunities to further increase recoveries and believes that this remains an important focus area for further improving the economics of the Project.

Mineral Resource and Mineral Reserve Estimates

The updated 2025 mineral resource model prepared by SRK Consulting (Canada) Inc. (“SRK”) utilizes results from 499 core boreholes drilled by First Mining and previous property owners. The Mineral Resource Estimate (“MRE”) at the Springpole Gold Project is shown below.

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