The Fimiston open-pit mine is located in the Kalgoorlie region of Western Australia. It is the largest open-pit gold mine in Australia.
The mine was owned by a 50:50 joint venture named Kalgoorlie Consolidated Gold Mines (KCGM) between Barrick Gold and Newmont Mining until November 2019 and January 2020.
Barrick Gold and Newmont Mining sold their respective interests to Saracen Mineral and Northern Star Resources in January 2020.
In February 2021, Saracen Mineral and Northern Star Resources announced a merger of equals and the latter became the sole owner of KCGM. The KCGM joint venture was dissolved in June 2021.
Northern Star is currently undertaking an A$1.5bn ($1.01bn) expansion of the Fimiston processing facility, which is expected to be completed in 2029. It will enable the mine to produce 900,000oz of gold annually.
The Fimiston open-pit mine is located on the south-eastern edge of Kalgoorlie-boulder, approximately 600km east of Perth in Western Australia.
The mine is part of KCGM Operations, which includes the Fimiston open pit mine, Mt Charlotte underground mine, apart from the Fimiston and Gidji processing plants.
Geology and mineralisation
The gold mine deposit in the Kalgoorlie terrane lies within the southern portion of the NNW trending Archaean Norseman-Wiluna greenstone belt of Western Australia. Gold-bearing ore lodes formed by a series of steeply plunging ancient shears are hosted within the mine in a massive rock unit known as Golden Mile Dolerite.
The Golden Mile Dolerite hosts the maximum gold found in Kalgoorlie. The rock unit is a tholeiitic gabbro and a layered sill with multiple fractionation.
Mineralisation is localised in lodes as breccia veins. It includes breccia-dominated veins and open space-filling vein textures that are occasionally overprinted by a foliation. The best-grade mineralisation is found in areas where lodes converge and form a pervasive mineralisation zone with their large alteration haloes. The mineralisation at Fimiston consists of 1m-2m wide vertically and laterally extensive lodes.
The Fimiston open pit is estimated to contain 8.1 million ounces (Moz), as of May 2023.
Mining and ore processing
Mining at the Fimiston Super Pit is carried out using conventional open pit mining with drilling, blasting, excavation and hauling using trucks and shovels.
Ore extracted from Super Pit is treated at the Fimiston processing plant, which has a capacity of 13.4 million tonnes per annum (Mtpa). The processing plant comprises two mills, including the Fimiston plant and the Mt Charlotte plant.
The Fimiston plant circuit comprises single-stage crushing, semi-autogenous grinding (SAG), ball milling, gravity concentration and flotation circuit. The Mt Charlotte plant circuit comprises three-stage crushing, SAG ball milling, gravity concentration and flotation circuit.
The concentration from the two circuits is combined and treated in ultra-fine grinding (UFG) and high-cyanide leach at the Gidji plant to produce dore bars.
Fimiston processing facility expansion
In June 2023, Northern Star announced the final investment in the expansion of the Fimiston processing plant. The project will expand the capacity of the plant from 13Mtpa to 27Mtpa and simplify the plant design.
The Gidji processing plant will be decommissioned after the completion of the expansion.
Fimiston South project
Fimiston South is located at the southern end of the Fimiston super pit. It is being developed in stages and will extend the life of the mine to 2034.
The project includes the development of a new tailings storage facility, waste rock facilities, topsoil stockpiles and related infrastructure.
Stage one is expected to commence in 2023, followed by stage two in 2024.
Fimiston underground development
In April 2021, Northern Star cut the first underground portal at the Super Pit to expand the underground resource at the mine.
Drilling operations are currently ongoing to deliver the maiden reserves and choose the optimum mining methods. Production from the underground development is expected to commence in 2026 and further extend the mine life of the project.
The project will consist of two cutbacks named Great Boulder and Ivanhoe.
Primero Group, an engineering, procurement and construction company, was awarded a A$973m ($647.4m) contract to undertake the expansion of the processing facility.
Delonix Solutions, an engineering company, provided engineering design for enabling earthworks and civil design in addition to full plant 3D scanning and surveying services for the Fimiston South project.