The Mt Thirsty cobalt-nickel project is a proposed open-pit mining development located in the Eastern Goldfields region of Western Australia. The project is being undertaken by the Mt Thirsty Joint Venture (MTJV), a 50:50 joint venture between Barra Resources and Conico.
A pre-feasibility study (PFS) for the Mt Thirsty cobalt-nickel project was completed in February 2020 making it the most advanced cobalt project in Australia.
The Mt Thirsty open-pit mine is estimated to produce up to 19,100 tonnes (t) of cobalt and 24,800t of nickel as a mixed sulphide product (MSP) at a dry ore feed rate of 1.8 million tonnes per annum (Mtpa), over a mine life of up to 12 years.
The pre-production capital investment for the project is estimated to be approximate £201.65m (A$371m).
Project location and geology
The Mt Thirsty cobalt-nickel project is located in the Eastern Goldfields region of Western Australia, approximately 16km north-west of Norseman. The project encompasses four adjacent mineral exploration tenements covering an area of approximately 1,768 hectares.
The Mt Thirsty cobalt-nickel project has two identified deposits on the tenements namely Mt Thirsty Main and Mt Thirsty North.
It is an oxide cobalt-nickel deposit located at the southern end of the Norseman-Wiluna greenstone belt, underlain by the Archaean Mt Kirk formation.
The Mt Kirk formation comprises a metamorphosed sequence of sediments, peridotite, pyroxenite, gabbro, and mafic-felsic volcanic rocks with granite and pegmatite dyke intrusions on its western side, while the eastern side is in faulted contact with the Woolyeenyer formation.
Mineralisation and reserves
The mineralisation at the Mt Thirsty cobalt-nickel project occurs within intensely weathered ultramafic peridotite orthocumulate rocks overlain by a Tertiary laterite capping. The host peridotite mineral is sandwiched between sediment–ultramafic-basalt sequence to the west and a pyroxenite unit to the east.
The majority of the cobalt and some of the nickel mineralisation is associated with manganese, while the majority of the nickel mineralisation is contained in goethite with smaller amounts occurring in silicate minerals.
The probable ore reserves for the Mt Thirsty project were estimated to be 18.8 million dry tonnes (Mdt) grading 0.126% cobalt and 0.54% nickel, as of February 2020.
The Mt. Thirsty cobalt-nickel project will utilise conventional open-pit mining methods on 10m benches with drilling and blasting required for extracting the laterite ore that comprises approximately 13% of the deposit. The remaining rock is expected to be mined by free digging on 2m flitches.
The load and haul fleet will comprise excavators, front end loaders, graders, dozers, and off-road trucks.
The current pit designs feature an overall slope of 35 degrees and batters varying between 30 and 55 degrees, and berms at every 10m.
The run-of-the-mine (ROM) ore will be introduced into a mineral sizer via a static grizzly, after which it will undergo wet scrubbing in an open circuit semi-autogenous (SAG) grinding mill. The grounded ore will then be transferred to a closed circuit ball mill to grind it to a leach feed size of 53um.
The ball mill cyclone overflow will be thickened in hypersaline process water and leached at 70-90ºC using sulphur dioxide (SO2) and air. The sulphur dioxide required for leaching will be produced by burning sulphur at the site.
Limestone will be used to neutralise the leached slurry in two stages. The cobalt and nickel from the neutralised solution will be recovered via mixed sulphide precipitation.
The resultant precipitate will be dried by filters to produce the final mixed sulphide product (MSP).
Access to the Mt Thirsty cobalt-nickel project is available from the Coolgardie-Esperance Highway which lies approximately 4km east of the project site.
A 21.2MW combined diesel-solar power station is expected to be developed on a build-own-operate basis for the project.
The project is estimated to require up to 1.8 gigalitres (GL) of water per annum which is planned to be met through bore fields from the nearby paleochannel aquifers. The potable and demineralised water will be produced by treating the bore water in a reverse osmosis plant.
Tasman Resources prepared the geological report for the PFS, while Golder Associates was engaged for the mineral resource estimates as well as for a hydrogeological desktop study for the project.
The metallurgical studies were compiled by AMEC Foster Wheeler while the mining studies were carried out by Snowden Mining Industry Consultants.
MACA and Hamptons Transport provided the cost estimates for the Mt Thirsty project mine plan.