Granite Creek Underground is a fully permitted and operational gold mine in Nevada, the US. It is the first property within mining firm i-80 Gold’s pipeline of assets to be redeveloped.
In March 2025, i-80 Gold announced the results of a preliminary economic assessment (PEA) for the Granite Greek Underground Project.
According to the PEA, the mine will have a life of around eight years. It will produce approximately 60,000 ounces of gold annually, after production ramp up.
The feasibility study, slated to be released in Q4 2025, will include an updated operational plan. It will also include an updated mineral resource estimate.
All drilling conducted since the beginning of 2023 is anticipated to be included in the planned feasibility study.
Granite Creek Project Location
The Granite Creek Project is situated in the Potosi mining district at the junction of the Getchell and Battle Mountain Trends, near Nevada Gold Mines’ Twin Creeks and Turquoise Ridge operations.
The site contains both high-grade open pit and underground mineral resources, with potential for further development. The project is 27 miles northeast of Winnemucca, in southeastern Humboldt County, Nevada.
The mine can be accessed via a mix of paved interstate and state highways, along with well-maintained unpaved private roads.
History
The Granite Creek Property has a long history of gold exploration and mining. Initial gold discoveries were made in the mid to late 1930s.
Between 1949 and 1950, approximately 10,000 troy ounces of gold were extracted. From 1980 to 1999, an additional 987,000 ounces were produced from various open pit mines.
Atna Resources conducted underground mining operations from 2012 to 2013, extracting around 30,148 tonnes of ore containing 7,915 ounces of gold, which were processed off-site.
In May 2016, Osgood Mining Company acquired the property following Atna’s Chapter 11 bankruptcy. i-80 became the owner of the property after it purchased OMC from Waterton Global Resource Management in June 2020.
Geology and Mineralisation
Granite Creek Project is located on the eastern flank of the Osgood Mountains at the intersection of the northeast-trending Getchell trend and the northwest-trending Battle Mountain trend. This area falls within the Basin and Range tectonic province of northern Nevada.
The mine is part of the Getchell gold trend, a northeast-trending structural corridor that includes several other gold deposits outside the property, such as Preble, Getchell, Turquoise Ridge, and Twin Creeks. These deposits are found in Palaeozoic marine sedimentary rocks.
The gold mineralisation at Granite Creek is identified as a Carlin-type, sedimentary-rock hosted system. It is structurally controlled, occurring mainly within a fault network near the eastern edge of the Osgood granodiorite and predominantly within the Comus Formation host rocks. This mineralisation is often associated with the decarbonatisation of carbonate rocks and the introduction of silica, fine-grained pyrite, arsenian pyrite, and remobilised carbon.
In underground areas, mineralisation is marked by pervasive argillisation and decarbonatization of host lithologies, along with the formation of dissolution collapse breccias and intense shearing.
Granite Creek Underground Mineral Resource Estimate
According to the PEA, Granite Creek Underground includes a measured and indicated gold mineral resource of 261,000 ounces at 10.5 grams per tonne (g/t) and an inferred gold mineral resource of 326,000 ounces at 13.0g/t.
The updated mineral resource estimate does not include infill drilling conducted within the Granite Creek Underground in 2023 and 2024.
Mining and Processing
The Granite Creek Project, located in northern Nevada, employs the underhand drift and fill mining method. This approach is chosen for its suitability to the site’s ground conditions, allowing for selectivity, productivity, and safety while minimizing dilution and enhancing recovery.
The main decline, accessible through portals in the north wall of the CX pit, facilitates movement of personnel and equipment, accommodating 30-tonne haul trucks. The decline is currently developed through over 700 vertical feet of mineralisation and will eventually extend to the 3200-ft elevation, providing access to four mineralised zones.
Over the next three years, refractory material mined will be processed at a third-party autoclave facility, resulting in approximately 30% lower payability on gold produced until the anticipated commissioning of i-80 Gold’s Lone Tree facility in 2028.
The project expects to process an average gold grade of 11.6 g/t with a recovery rate of 78%, through methods including oxide processing and pressure oxidation. Once the Lone Tree autoclave is operational, process recovery rates are projected to increase to about 92%, enhancing production and cash flow.
Granite Creek Underground is ramping up to full production, with commercial production anticipated in 2026. Initial mine life is projected at around eight years, with annual gold production peaking at approximately 80,000 ounces and averaging around 60,000 ounces post-ramp-up.
Gold recovery varies across different zones; the Ogee, Otto, and South Pacific zones generally require oxidation processes for optimal extraction. Economic recovery in the Ogee and South Pacific Zones is better in an alkaline environment, while the Otto deposit benefits from an acidic environment.
Contractors Involved
Global Resource Engineering (GRE) and Practical Mining (PM) completed the Preliminary Economic Assessment (PEA) of Granite Creek Underground Project.
