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. At the known extremities of the mineralisation, interpreted as a pepperitic apron, the porphyry host is less continuous and interchanges with mafic volcaniclastics.

The main gold related hydrothermal alteration assemblage comprises quartz-ankerite-arsenopyrite- pyrrhotite-galena and gold. Synmineralisation 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.

Dimensions
Thunderbox mineralisatio ........

The Thunderbox Open Pit Project includes the Thunderbox deposit, Rainbow and Otto Bore gold deposits, Kailis Stage 1 & 2 gold deposits, Bannockburn and North Well gold deposits; and the Orelia deposit.

Thunderbox
Mining method employed at Thunderbox mine is conventional open pit with hydraulic excavator and dump truck fleet, and drill and blast activity. Thunderbox Reserve pit is in operation and designed as successive cutbacks to achieve final life of mine Reserve such that it meets the operation efficiency, safety and production rate. Appropriate mine schedule, operating cost and lead time have been considered to maintain efficient mining operations.

A minimum mining width of 25m has been adopted for the primary excavation fleet. Where ‘pinch-points’ occur or “Good Bye” cuts are considered at the base of the pit, it is assumed that a smaller or more versatile excavator will be employed. The practice is very consistent across all open pit operations and reflects the suitability and efficiency of the mining performance.

Rainbow
The Rainbow deposit is amenable to mining by open pit methods. There has not been any previous mining at Rainbow. There are reasonable grounds to assume that in the future this deposit will be mined by conventional open pit methods given the close proximity to surface of the mineralisation.

Otto Bore
During 2023, commencement of mining at Otto Bore.

The mining method to be employed ........

The process consists of a double toggle jaw crusher followed by a SAG and Ball milling circuit.

Metso Outotec has been chosen to supply its Premier SAG Mill for Northern Star Resources’ Thunderbox gold mine expansion. The expansion should double the throughput of the Thunderbox operation.

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