Alamos Gold Announces Island Gold District Base Case Life of Mine Plan Outlining One of the Largest and Lowest-Cost Gold Mines in Canada with Significant Upside

Press Release

TORONTO, June 23, 2025 —  Alamos Gold Inc. (TSX:AGI; NYSE:AGI) (“Alamos” or the “Company”) today reported results of the Base Case Life of Mine Plan (“Base Case LOM Plan”) completed on the Island Gold District operation, located in Ontario, Canada. The Base Case LOM Plan integrates Island Gold and Magino as one consolidated long-life operation that is expected to become one of the largest, lowest-cost, and most profitable gold mines in Canada. An Expansion Study is expected to be released in the fourth quarter of 2025 detailing the significant upside potential within the Island Gold District beyond the Base Case LOM Plan.

The Base Case LOM Plan has been updated to reflect the current costing environment, significant growth in Mineral Reserves at Island Gold, operating savings resulting from the use of a larger and more efficient Magino mill, and scope changes since the Phase 3+ Expansion Study (“Phase 3+ Study”), which was completed in 2022. The Base Case LOM Plan includes Mineral Reserves only at Island Gold and Magino. Both deposits have significant Measured, Indicated and Inferred Mineral Resources, which have not been factored into the Base Case LOM Plan and economic analysis. All amounts are in United States dollars, unless otherwise stated.

“The Base Case Plan for the Island Gold District outlines an attractive, long-life operation that is expected to become one of Canada’s largest, lowest-cost, and most profitable gold mines. This is a first look at an operation with significant upside potential which we expect to detail in an Expansion Study later this year. We expect this to include a larger Mineral Reserve through ongoing Mineral Resource conversion, and a potential further expansion up to 20,000 tonnes per day, supporting an even larger, more valuable, and profitable operation. Longer-term, we see excellent opportunities for that value to continue to grow through ongoing exploration success at Island Gold, and a number of emerging higher-grade regional targets that have the potential to support multiple sources of ore within an expanded mill,” said John A. McCluskey, President and Chief Executive Officer.

Base Case LOM Plan Highlights:

Average annual gold production of 411,000 ounces starting in 2026 and over the initial 12 years, a 43% increase from the mid-point of 2025 production guidance driven by the completion of the Phase 3+ Expansion

• Average annual production of 306,000 ounces over the 20-year Mineral Reserve life
• Significant upside potential through a further expansion of the operation, and the expected conversion of a significant portion of the large Mineral Resource base to Mineral Reserves through ongoing delineation drilling

Low-cost structure: average mine-site all-in sustaining costs (“mine-site AISC”) of $915 per ounce over the initial 12 years (2026+), a 19% decrease from the mid-point of 2025 guidance

• Average total cash costs of $581 per ounce over the initial 12 years (average $699 per ounce over the life of mine)
• Average AISC of $1,003 per ounce over the life of mine, an 11% decrease from 2025 guidance

Long-life operation supported by a large and growing Mineral Reserve base

• 48% increase in total Mineral Reserves to 6.3 million ounces (88.6 million tonnes (“mt”) grading 2.23 grams per tonne (“g/t Au”), including:
  • 4.1 million ounces grading 10.85 g/t Au (11.8 mt) at Island Gold underground, up 80% from the end of 2024 reflecting the conversion of Mineral Resources
  • 2.2 million ounces grading 0.91 g/t Au (76.9 mt) at Magino open pit, up 12% from the end of 2024

Significant upside potential expected to be outlined in an Expansion Study in the fourth quarter of 2025

• Base Case LOM Plan based only on Mineral Reserves and long-term milling rates of 12,400 tonnes per day (“tpd”)
• Expansion Study expected to include an increase in milling rates potentially to between 18,000 and 20,000 tpd supporting higher throughput rates from both Island Gold and Magino, and

• The incorporation of a larger Mineral Reserve through the expected conversion of a significant portion of existing Mineral Resources, which consist of:
  • Island Gold Underground
    • M&I Mineral Resources: 1.0M oz grading 10.49 g/t Au (3.1 mt)
    • Inferred Mineral Resources: 1.3M oz grading 16.88 g/t Au (2.4 mt)
  • Magino Open Pit
    • M&I Mineral Resources: 1.8M oz grading 0.91 g/t Au (60.3 mt)
    • Inferred Mineral Resources: 1.2M oz grading 0.92 g/t Au (40.3 mt)

Low capital intensity

• Growth capital of $453 million with the majority to be spent over the next two years, focused on completing the Phase 3+ Expansion and Magino mill expansion to 12,400 tpd
• Sustaining capital of $1,808 million over the life of mine, or $304 per ounce
• Sustaining capital intensity expected to decrease within Expansion Study reflecting a larger Mineral Reserve leveraging existing infrastructure
• Total all-in cost of $1,079 per ounce, including total capital intensity of $380 per ounce

Attractive base case economics with significant upside

• After-tax net present value (“NPV”) (5%) of $4.5 billion, (base case long-term gold price assumption of $2,400 per ounce and USD/CAD foreign exchange rate of $0.75:1)
• After-tax NPV (5%) of $6.7 billion, at current gold prices of approximately $3,300 per ounce
• Expansion Study is expected to demonstrate attractive economics with a further increase in value reflecting a larger Mineral Reserve and higher throughput rates

Phase 3+ Expansion expected to be completed during the second half of 2026

• Base Case LOM Plan is consistent with existing three-year production guidance
• The slight delay in the completion of the Phase 3+ Expansion (from the first half of 2026 previously) is not expected to impact production or cost guidance in 2026 and 2027
• Work on the Phase 3+ Expansion has been largely de-risked with a number of key projects substantially complete including the shaft surface infrastructure, and shaft development which is currently at 92% of its ultimate planned depth

Low and decreasing Greenhouse Gas (“GHG”) emission intensity

• 29% reduction of GHG emissions per ounce from already low levels which are currently 57% below the industry average. This is expected to be achieved through the completion of the Phase 3+ Expansion, and connection of the Magino mill to grid power in 2026

Fully funded growth: ongoing free cash flow with significant growth expected in 2026

• Island Gold District is expected to self finance all remaining growth capital at current gold prices with significant free cash flow growth following the completion of the Phase 3+ Expansion in 2026

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