The Four Mile Uranium mine is located in the Frome Basin in the state of South Australia. The operational uranium mine was first discovered in 2005 and is considered Australia’s third highest grade deposit after Jabiluka and Koongarra Uranium mines.
The Four Mile mine is fully owned and operated by Quasar Resources, a subsidiary of Heathgate Resources which operates the adjacent Beverley and Beverley North mining leases. The ore extracted from the Four Mile mine is processed at the nearby Beverley uranium mine site.
Quasar applied for a mining lease in May 2008 and secured it from the state and federal regulators in April 2012. An environmental assessment for the project was published in January 2009.
The construction of the mine started in 2013, while production began in 2014.
In 2021, the Four Mile Uranium mine’s output totalled 2,241 tonnes of triuranium octoxide (U3O8), accounting for approximately 5% of global production.
The project is expected to have an operational life of 15 years.
Location and site details
Four Mile is located around 550km north of Adelaide and east of the northern Flinders Ranges. The site is around 115km northeast of Leigh Creek and approximately 8km of Beverley Uranium Mine.
The ground surface of the site comprises around 15m of gravels of the Tertiary Willawortina formation over the Tertiary Upper Eyre Formation. Mineralisation is found within the Tertiary Lower Eyre Formation at an average depth of 180m.
Four Mile mine geology and mineralisation
The project comprises two mineralised zones within Tertiary age sediments- Four Mile West (FMW) and Four Mile East (FME).
Both the deposits FME and FMW are of the sandstone uranium type, associated with redox interfaces. At FMW, the Mesozoic sediments of the Frome Embayment host the mineralisation. It occurs within medium to fine sands in the upper half of a diamictite unit and is underlain by crystalline Meso or Palaeoproterozoic basements.
At FME, Tertiary sediments of the Callabonna Sub-basin of the Lake Eyre Basin contain mineralisation. This features multiple thin intercepts in sub-horizontal, sandy, materials below the water table and beneath a seal layer of predominantly clay or siltstone.
The Four Mile uranium deposit was considered the best greenfield discovery since the Kintyre Uranium deposit in 1985. The deposit is also prospective for iron-oxide copper-gold mineralisation.
As of November 2013, the project had a mineral resource estimate of 9.8 million tonnes at 0.33% U3O8.
The Four Mile West deposit had 14,000 tonnes of indicated resources and 4,700 tonnes of inferred resources, at 0.34%, while the east deposit had 13,000 tonnes of inferred resources of U3O8 at 0.31%.
The Four Mile mine uses the in-situ recovery (ISR) mining method.
The process uses specially designed wellfields to extract minerals from the host rock underground.
In the case of Four Mile, the ore exists in an underground aquifer. To extract the minerals, oxygen and a weak acid mining solution are injected through the ore body to dissolve the uranium minerals.
The dissolved uranium is then pumped to the surface from multiple wells and loaded onto resin at the Beverley North Pannikan plant.
Subsequently, it is transported to the Beverley Processing Plant for further processing leveraging the ion exchange (IX) process. The processed uranium is then dried, packaged and readied for export.
The waste products are then reconditioned with reagents and sent back to the mining zones.
Construction and infrastructure facilities
The Four Mile infrastructure consists of wellfields, pipelines, well houses, filter skids, ferric sulphate facilities, as well as trunklines to the Beverley North facilities among others.
The Four Mile wellfields are connected to the Pannikan satellite plant by trunklines built using high-density polyethylene (HDPE) pipelines.
Four Mile mine produced 935 tonnes of U3O8 in 2015. The production increased every year thereafter and touched 2,130 tonnes of U3O8 in 2020.