The results announced in this press release are supported by two technical reports prepared for Granite Creek Underground: (1) a technical report prepared under National Instrument 43-101 – Standards of Disclosure for Mineral Projects ("NI 43-101") which, in the opinion of the qualified persons, constitutes a feasibility study under NI 43-101 (the "NI 43-101 FS" or the "FS"); and (2) a technical report summary prepared under Subpart 1300 of Regulation S-K ("S-K 1300") which, in the opinion of the qualified persons, constitutes a pre-feasibility study under S-K 1300 (the "S-K 1300 PFS" and, together with the NI 43-101 FS, the "Technical Reports"). The Technical Reports are based on the same underlying technical and economic data and analysis but have different study classifications resulting from differences in the substantive criteria applied under each of S-K 1300 and NI 43-101. As a result, the same body of technical work satisfies the definition of a feasibility study under NI 43-101 but constitutes a pre-feasibility study under S-K 1300. The mineral resource and mineral reserve estimates and the project economics presented in the Technical Reports are derived from the same underlying technical and economic work.
"The Granite Creek Underground Feasibility Study outlines robust project economics based on a significantly expanded mineral resource base, increased production rate, and longer mine life relative to the preliminary economic assessment ("PEA")(1) published in March 2025, despite over a year of mining depletion and only a modest drilling program focused primarily on infill drilling to support the FS," stated Richard Young, President & CEO. "The drill program successfully delineated and expanded the mineralized zones, demonstrated continuity within the mineralized structures, and identified a number of additional prospective targets that suggest the potential for further mineral resource growth. The Project is expected to be a key source of feed for our wholly owned Lone Tree autoclave and carbon-in-leach processing plant for many years to come, together with mineralized material from Archimedes underground where production mining is expected to commence later this year. With the Lone Tree Plant anticipated to be operational by the end of 2027, these assets are expected to support i-80 Gold's transformation into a Nevada-focused mid-tier producer generating strong free cash flow."
Granite Creek Underground Feasibility Study Highlights
- Initial Proven and Probable Mineral Reserves of 2.20 million tonnes ("Mt") grading 7.87 grams per tonne ("g/t") gold ("Au") containing 556,500 ounces ("oz") of gold ("Au").
- Measured and Indicated underground Mineral Resources increased by 229% to 3.73 Mt grading 7.17 g/t Au containing 859,500 oz Au, compared to the PEA(1); Inferred Mineral Resources decreased by 38% to 0.89 Mt grading 7.06 g/t Au containing 202,800 oz Au as the infill program converted a portion of Inferred Mineral Resources into the higher classification categories.(2)
- Mine life of approximately 8.5 years (the "LOM") supported by successful South Pacific Zone drill results and improved resource definition, after accounting for 15 months of mining since the PEA.(3)
- At a base case gold price of $2,750/oz, total undiscounted after-tax cash flow of $153 million with an after-tax net present value(5%) ("NPV") of $118 million.(3)
- At an illustrative spot gold price sensitivity of $4,500/oz, total undiscounted after-tax cash flow of $744 million with an after-tax NPV(5%) of $598 million.(3)
- At an illustrative gold price sensitivity of $6,000/oz, total undiscounted after-tax cash flow of $1.2 billion with an after-tax NPV(5%) of $985 million.(3)
- Annual gold production of approximately 75,000 oz for the five-year period from 2028 to 2032, following completion of the Company's Lone Tree Plant refurbishment, representing an increase of approximately 15,000 oz Au per year compared to the PEA.(1)
- Estimated cash costs(4) of $1,827/oz and all-in-sustaining costs ("AISC")(4,5) of $1,915/oz for the five-year steady-state period following commissioning of the Lone Tree Plant (2028 to 2032), excluding the allocated Lone Tree Plant refurbishment capital.
- Lower sustaining capital of $83 million compared to the PEA,(1) despite increased development at depth, higher planned tonnage, and additional equipment following successful South Pacific Zone drilling, as well as an expanded infill drilling program and water treatment infrastructure.
- Optimized processing strategy whereby refractory and oxide ores are expected to be processed by a third-party through mid-2027, followed by approximately six months of stockpiling prior to the planned fourth quarter 2027 commissioning of the Company's wholly owned Lone Tree autoclave and carbon-in-leach plant at significantly lower processing costs.
- Ongoing 2026 infill and step-out drilling supports continued reserve development and resource growth in the South Pacific, Rangefront, Otto and Ogee zones, with the high-grade portion of CX Zone targeted for further evaluation as part of an anticipated extensive multi-year drill program planned to commence in 2027.
Table 1: Granite Creek Underground FS Key Operating and Financial Metrics
For detailed metrics presented on an annual basis, see the Granite Creek Underground Detailed Cash Flow Model in Table 1 in the Appendix.
"The FS incorporates several improvements relative to the PEA,(1) including an optimized mine design, improved geological definition, increased mining flexibility, and additional working faces particularly within the Ogee Zone," stated Paul Chawrun, EVP & COO. "Successful infill and definition drilling within the South Pacific Zone closed mineralized gaps, improved continuity, and upgraded the existing mineral resources into higher-confidence categories, supporting a larger mineable inventory and longer mine life following over a year of mining. Improved geological definition also increased the number of available ore faces and increased total ore mined, contributing to higher planned production and reduced waste development. These improvements are further supported by ongoing infrastructure upgrades, including increased water treatment and dewatering capacity, and ventilation optimization."
Mr. Chawrun added, "The Study also incorporates an optimized processing strategy which includes stockpiling the Project's sulfide and oxide ore ahead of the planned commissioning of the Lone Tree Plant in the fourth quarter of 2027. This strategy is expected to increase the amount of Granite Creek ore processed at the Lone Tree Plant at more favorable processing costs, while reducing reliance on third-party processing."
Initial Mineral Reserve Estimate and Updated Mineral Resource Estimate
The updated underground mineral resource estimate included in the FS incorporates approximately 36,470 meters of drilling from 164 core holes conducted between 2023 through the end of 2025, relative to the resource estimate that formed the basis of the PEA published in March 2025.(1) Numerous step-out drill holes have resulted in a larger mineralized envelope, while infill drilling increased definition and confidence in the mineral resource and supported conversion of a majority of the resource to mineral reserves. Relative to the PEA mineable resources, and accounting for mining depletion in 2025 and a portion of 2026, approximately 65,000 ounces have been added to mineral inventory (see Figures 1 and 2).(3)
The FS includes an initial mineral reserve estimate of 556,500 oz Au at 7.87 g/t Au in the proven and probable categories (see Table 2). The updated underground mineral resource estimate includes 859,500 oz Au at 7.17 g/t Au in the measured and indicated categories, and an additional 202,800 oz at 7.06 g/t Au in the inferred category (see Table 3).(2) These mineral resources are hosted within the Ogee, Otto and South Pacific zones (see Figures 3 and 4). Relative to the PEA,(1) measured and indicated resources increased by 229%, while inferred resources decreased by 38% as material was converted into higher classification categories.
The resource estimate was prepared using stope optimization software which is in line with industry recommended best practices for the assessment of the in-situ mineralization which satisfies the reporting criteria of the Reasonable Prospects for Eventual Economic Extraction (RPEEE). Additionally, a more conservative approach was applied to establish the creation of grade shell domains to match current mining methods, resulting in lower grades than in the previously published PEA. These updated grades are in line with the average grade currently mined at Granite Creek and are believed to more accurately reflect the expected grades of the orebody.
Exploration
The ongoing 2026 exploration program includes a combination of infill drilling to support continued reserve development for optimized ongoing mine operations and step-out drilling to expand the current and known mineralization within the South Pacific Zone, which remains open to the north and at depth, and the Rangefront, Otto, and Ogee zones.
Additional near-mine exploration targets include the CX Zone beneath the historical CX pit, which is not currently included in the underground mineral resource. Previous drilling in the CX Zone includes high-grade intercepts from legacy holes, including 18.0 g/t Au over 9.1 m in hole HPR 078 and 15.3 g/t Au over 9.1 m in RHC-1763, and i-80 hole of 36.4 g/t Au over 9.1 m in iGM21-06.(9) A successful drill program in the CX Zone has the potential to add high-grade ounces to the mineral resource and near-term mine plan. The Company intends to evaluate the high-grade portion of the CX Zone as an underground target as part of an anticipated extensive multi-year drill program planned to commence in 2027.
