The Thunderbox Operations (TBO) are located in the highly prospective Yandal Belt and the Agnew-Wiluna Belt in the North Eastern Goldfields of Western Australia. Northern Star acquired TBO in 2014 and commenced commercial gold production in 2016. TBO includes the Thunderbox, Kailis, Bannockburn and Waterloo Projects.
In 2019, Northern Star acquired ASX-listed Bligh Resources Limited. Bligh’s Bundarra project is located less than 30km south of TBO and adjacent to the sealed Goldfields Highway. The Bundarra project consists of five mining leases and six prospecting licences that host four known gold deposits including the key Wonder gold deposit.
In the same year, Northern Star acquired the Sinclair project from ASX-listed Talisman Mining Limited. Sinclair is located 25km south-west of TBO in the world class Agnew-Wiluna greenstone belt. In addition to acquiring significant mine site infrastructure, Sinclair also includes a 207km2 tenement package covering more than 80km of prospective ultramafic host rocks with gold exploration potential as well as the Sinclair nickel deposit which complements Northern Star’s existing nickel portfolio in the region.
GEOLOGY & MINERALISATION
Thunderbox is a mesothermal lode gold deposit located at the southern end of the Yandal greenstone belt in an area where several major shear zones converge and join with the Perseverance Fault.
The shear zone dips at 30° to 60° WSW, with the exception in the vicinity of the mineralisation, where the shear is vertical to steeply dipping. Mineralisation is hosted by strongly deformed, silicified and carbonate altered albite-quartz porphyry in the hangingwall of the shear zone. The shear juxtaposes foliated basalts and intrusive porphyries in the hangingwall against sedimentary rocks in the footwall. The zone of shearing is over 200m wide. An ultramafic unit occurs within the shear, in the footwall of the deposit and is attenuated along the shear.
The main gold related hydrothermal alteration assemblage comprises quartz-ankerite-arsenopyrite-pyrrhotite-galena and gold. This assemblage has been overprinted by a retrograde chlorite-epidote-white mica-biotite-quartz and pyrite assemblage. Syn-mineralisation veins have a continuum of vein textures ranging from laminated to pseudo-breccias.
Throughout the Thunderbox Deposit, elevated grades occur within southerly plunging ore shoots that are more evident in the lateral extents of the orebody. Whilst the shoots persist centrally, the gold distribution is for more uniform and ubiquitous than in other areas.
MINING
Mining at Thunderbox is by bulk, low-cost open pit and underground methods. Current open pit mining involves an excavator in backhoe configuration supported by a fleet of rear dump trucks.
The underground operation is a modern mechanised trackless mine employing a combination of longhole open stoping methods based on ore zone widths. Paste fill has recently been introduced to maximise recovery of the orebody and ensure stability of the mining areas.
PROCESSING
The Thunderbox processing circuit is a conventional CIL plant with a hard rock processing capacity of approximately 3.0M tonnes per year. The process consists of a double toggle jaw crusher followed by a SAG and Ball milling circuit incorporating gravity recovery and CIP process achieving 94% recoveries.