The Murchinson gold project is a brownfield open-pit and underground gold mining project being developed by Meeka Metals in Western Australia (WA).
The project was previously owned by Silver Lake Resources. The mining activity started at Murchinson with the commencement of open-pit mining at the Andy Well deposit in September 2012, followed by the first gold pour in February 2013.
However, the project was placed on care and maintenance in September 2017.
Meeka Metals acquired Andy Well and the adjacent Gnaweeda gold project containing Turnberry and St Anne deposits from Silver Lake Resources in February 2021.
It completed a feasibility study for the Murchinson gold project in July 2023, which highlighted an average annual production of 663 thousand ounces (koz) of gold for a period of 9.3 years with an estimated pre-production capital investment of A$136m ($92.6m).
Murchinson Project location
The project is located between the towns of Mount Magnet and Cue, 46km north-east of Meekatharra and 800km north-east of Perth, WA. The project tenure comprises five exploration licences and two mining leases, totalling 281km².
The project focuses on three deposits, including Andy Well located within mining lease (ML) M51/870, and Turnberry and St Anne located within ML M51/882.
Murchison gold mine geology and mineralisation
The Murchison gold field contains volcanic rocks of the Gabanintha and Golconda Formations. The rocks host high-grade volcanogenic massive sulphide mineralisation.
Gold mineralisation is mostly within banded iron formations. It is also found in the quartz-feldspar margins and in the rafts of greenstone stratigraphy.
Fine-grained basalt rocks are found at the project site. Coarse-grained gold occurs as iron-rich sediments divided into footwall and hanging wall lodes. Higher grades occur in steeply dipping shoots.
Gold reserves at Murchinson
The probable ore reserves at Murchinson were estimated at 4.1 million tonnes (mt) grading 3.1 grams per tonne (g/t) of gold, as of June 2023.
Mining methods at Murchison
Murchinson will utilise a combination of open-pit and underground mining methods at Andy Well and Turnberry while mining the St Anne’s deposit will involve only the open-pit method. Mining operations will be carried out simultaneously at each site.
All open pits are planned to be developed using a conventional load and haul mining fleet with contract-based mining services. Underground mining will be carried out using the long-hole stoping (LHS) method with contractors for development and production activities.
The mining fleet is proposed to include 200t class excavators in a backhoe configuration supported by 140t haul trucks, as well as a smaller fleet of 100t excavators and 95t haul trucks.
The Andy Well and the bigger Turnberry deposits are planned to be developed with two and five open pits, respectively, in addition to underground mines with limited or no interaction between underground and open-pit activities. The St Anne’s deposit is planned to be developed with two open pits.
Ore from all the locations will be trucked to the processing facility at Turnberry.
Processing at Turnberry
The processing plant at the Turnberry site will have the capacity to treat 1mtpa of ore. It will use carbon-in-leach (CIL) and flotation processes for gold recovery.
The run-of-mine (ROM) ore will undergo three-stage crushing in a primary jaw crusher followed by secondary and tertiary cone crushers. The crushed ore will feed a ball mill operating in closed circuit with cyclone classification.
The cyclone underflow will feed the centrifugal concentrator and the resultant concentrate will feed the gravity leach unit. Recovered gold from the gravity concentrator will be dissolved in the intensive leach reactor. The clarified solution containing gold will be retrieved through electrowinning.
A flotation circuit will be installed in year three to optimise the recovery and coincide with the development of the Turnberry underground mine. Cyclone overflow from the ball mill circuit will feed a trash screen and the undersize slurry will be pumped to an agitated dilution tank. The diluted slurry will be conditioned and pumped into the flotation cells. The underflow will be pumped to the CIL circuit while the final concentrate will be pumped to a concentrate thickener.
The thickened flotation tails from the pre-leach thickener and the leached flotation concentrate will be fed to the CIL tanks. Gold from the solution will be adsorbed onto carbon in the adsorption tanks. The loaded carbon will be recovered and acid washed.
The washed solution will be transferred to the elution circuit, with the resultant gold-bearing solution flowing to the dual electrowinning cell. The resultant sludge containing gold will be filter pressed to recover a sludge cake, which will be dried in a drying oven. The dried gold sludge will be mixed with fluxes and smelted in a furnace to produce dore bars.
The project is accessible via the existing Andy Well mine turnoff from the Great Northern Highway that runs on the western side of the project area. New haul roads will be constructed to connect Andy Well and St Anne’s to the Turnberry site.
Two modular diesel-fired power stations, including a 10MW facility at Turnberry and a 2.4MW facility at Andy Well will be constructed as part of the project.
water required for the project will be sourced from open pit dewatering bores, as well as a bore field is to be developed to the south-east of the processing plant.
RSC consultants conducted the geological studies and provided mineral resource estimates for the feasibility study.
Peter O’Bryan and Associates, MineGeoTech and AMC Consultants were engaged for the geotechnical studies.
Mine planning consultancy Oreology was responsible for the mine design and scheduling of the open pits.
Metallurgy and comminution works were provided by Como Engineers and ALS Metallurgy. Como Engineers also provided the process plant design including its operating and capital cost estimates.
Hydrology and hydrogeological studies were provided by Rockwater, RPS Aquaterra and CDM Smith.
Australia-based Malcolm Thompson Pumps (MTP Pumps) and UON were responsible for the mine dewatering studies.
Mattiske Consulting, Bamford Consulting, Ecologists Bennelongia Environmental Consultants, Stantec, SoilWater and Atheos Consulting were engaged for environmental studies for the project.
Enviro Mining Support, Stantec and Atheos Consulting were engaged for the project’s permitting and approvals.
The financial modelling review was prepared by Professional Cost Consultants International.