Announcement • Aug 01

Selkirk Copper Mines Inc. Announces Updated Mineral Resource Estimate for the Minto Project

Selkirk Copper Mines Inc. announced the results of an updated Mineral Resource Estimate for the Minto Project in the Yukon, Canada which is being used for the development of an updated Preliminary Economic Assessment. The 2026 Mineral Resource Estimate establishes a Measured & Indicated Resource of 47.8 million tonnes, representing a 280% increase in tonnage in these categories compared to the 2025 Mineral Resource Estimate. 47.8 million tonnes of Measured & Indicated Resources at 0.89% copper, 0.34 g/t gold, and 3.2 g/t silver totaling 940 million pounds copper, 530,000 ounces gold, and 4.97 million ounces silver; 182%, 184% and 188% increases respectively above the 2025 Mineral Resource Estimate. Measured & Indicated Resources include 26.0 million tonnes of underground resources at 1.14% Cu, 0.49 g/t Au, and 4.4 g/t Ag; and 21.8 million tonnes of open pit resources at 0.59% Cu, 0.17 g/t Au, and 1.8 g/t Ag. An additional 16.9 million tonnes of Inferred Resource have also been delineated: 16.9 million tonnes Inferred Resources at 0.76% copper, 0.26 g/t gold, and 2.7 g/t silver totalling 281 million pounds copper, 142,000 ounces gold, and 1.5 million ounces silver. Mineralization remains open laterally and at depth across central mine area, and there are several high potential drill targets for follow-up in future exploration, definition and delineation work. The ongoing 50,000 metre Phase 2 drill program is 75% complete, the results of which have not been included in this resource update. Initial assay results and visual drill logs continue to show expansion potential across each of the mineralized zones in the central mine area. The updated Mineral Resource Estimate contains both underground and open pit resources. The underground contains Measured & Indicated Resources of 26.0 million tonnes grading 1.14% Cu, 0.49 g/t Au, and 4.4 g/t Ag, plus an additional Inferred Resource of 9.8 million tonnes grading 0.91% Cu, 0.36 g/t Au, and 3.5 g/t Ag. The open pit contains an additional 21.8 million tonnes of Indicated Resources grading 0.59% Cu, 0.17 g/t Au, and 1.8 g/t Ag, plus Inferred Resources of 7.1 million tonnes grading 0.55% Cu, 0.13 g/t Au, and 1.6 g/t Ag. A small amount of Measured Resources have been established, representing a higher category of confidence for some underground mining areas. In total, the updated Mineral Resource Estimate contains 940 million lbs copper, 530 koz gold, and 4.97 million oz silver in the Measured & Indicated categories and an additional 281 million lbs copper, 142 koz gold, and 1.5 million oz silver in the Inferred category. The resource estimate is summarized in Table 1 below, with sensitivities to various NSR cut-offs detailed in Table 2 and Table 3. The updated Mineral Resource Estimate was prepared by Sue Bird, P.Eng., of Moose Mountain Technical Services who is independent of Selkirk Copper. The effective date of the resource is June 10, 2026. Resources are reported using the 2014 CIM Definition Standards and were estimated using the 2019 CIM Best Practices Guidelines. For the Net Smelter Proceeds calculations: Metal prices are USD 4.60/lb Cu, USD 3,300/oz Au, USD 40/oz Ag; A currency exchange rate of 0.72 USD per CAD; 97.5% payable Cu, 98% payable Au and 92% payable Ag; and the following inputs: Concentrate grade of 38% Cu with a moisture content of 8%; Unit deductions of 1gpt Au, 30gpt Ag; Offsite costs (refining, transport and insurance) of USD 200/dmt; Treatment for Cu Charges of USD 35, Refining Charges of USD 0.035/lb payable Cu, USD 5.00/oz Au and USD 0.50/oz Ag; Royalties of 1.5% NSR. Recoveries are as follows: CuRecov – 95.5%+1.07Cu%-113(ASCu/TCu), with a maximum of 98%; AuRecov = 35.63+0.58032Curecov-1.3341Cu%^ 0.8932, with a maximum of 85%; AgRecov = 69.4+1.9Aggpt, to a maximum of 85%. These inputs result in the following NSR and CuEq equations: NSR = CAD CuNSPCuRecovCu%22.0462 + CAD AuNSPAuRecovAugpt + CAD AgNSPAgRecovAggpt)/31.10348; CuEq = NSR/(CuNSPCuRecov22.0462). The Mineral Resource has been confined by a “reasonable prospects of eventual economic extraction” pit or underground shape using the 130% base case NSR for the Ridgetop and Area 118 open pits and by confining shapes for the underground. Mining costs are CAD 4.58/tonne for open pit, marginal mining costs of CAD 50/tonne for underground, Processing costs are CAD 30/tonne milled, and G&A costs are CAD 20/tonne milled.

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