Thunderbox Operation (TBO) includes the Thunderbox Project (comprised of the Thunderbox, Rainbow and Otto Bore gold deposits), the Kailis Project (comprised of the Kailis Stage 1 & 2 gold deposits), the Bannockburn Project (comprised of the Bannockburn and North Well gold deposits) and the Waterloo Project (comprised of the Waterloo and Amorac nickel deposits).

Thunderbox
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.

Rainbow
Regionally the Rainbow deposit occurs on the southern end of the Yandal greenstone belt in an area where several major intra-greenstone shear zones converge and join with the Perseverance Fault.

This shear system appears to be a major geological discontinuity, defining the boundary between two potentially distinct geological domains. The western domain is continuous with the Wiluna – Mt Keith – Leinster – Mt Clifford sequence and is characterised by deformed and metamorphosed ultramafic and mafic dominated greenstone stratigraphy intruded by granitoid plutons. The eastern domain is dominated by sediments, felsic volcanics and felsic intrusive complexes in addition to mafics and contains copper-zinc volcanogenic massive sulphide mineralisation (at Teutonic Bore). Locally the deposit is contained with a sheared unit with sediments in the footwall and mafics in the hanging wall. The shear dips to the west at approximately 450 and strikes 340 degrees.

Gold mineralisation at Rainbow occurs in shallow west dipping quartz +/-sulphide lodes within sheared basalts/sediments. Mineralisation occurs as one main lode, however other smaller lodes are apparent as is some supergene enrichment.

Otto Bore
Otto Bore is located within the Kurnalpi terrane to the east of the Ockerburry Fault, separating the Kalgoorlie and Kurnalpi terranes. The deposit is hosted within a greenstone package consisting of basalts, high-Mg basalts, dolerites and ultramafics with minor intermediate porphyries observed within the upper portion of the stratigraphy. Locally Otto Bore is situated within a NNW trending shear zone that dips moderately (50-60degrees) to the west. The mineralised zone largely hugs the rheological contact between the high-mg basalts and basalts. To the north mineralisation is also associated with a series of dolerites. Cross cutting NW trending faults are interpreted to disrupt the strike continuity of the main mineralisation and the southern extent of the Otto Bore deposit is terminated by a regional NNE trending shear. At depth higher grade mineralisation is typically associated with pervasive quartz veining and form short range southerly plunging shoots.

Kailis
Gold mineralisation at Kailis - Trump is hosted in quartz-sericite schist within a broad east-west trending, shallow to moderately dipping (40-50 degrees SSE) shear zone with a strike length in excess of 1800m. Mineralised intervals are often narrow (1-3m) but thicken to 8-20m in places. The shear zone encapsulates a high nugget mineralisation style with common occurrences of visual gold. Structural studies identified narrow sub vertical NE-SW trending quartz vein sets/structures that crosscut the main shear zone as possible controls on high grade mineralisation. The best gold grades tend to occur in the oxide and transitional zones with lower grades in the fresh rock. Mineralisation is open at depth but closed along strike.

Bannockburn
The Bannockburn deposit is located along the western margin within the central portion of the Norseman Wiluna greenstone belt. Locally the project area is dominated by an extensive sequence of tholeiitic, high-Mg and komatiitic basalts with intercalated sedimentary and intermediate volcaniclastic horizons. Dolerite and gabbro sills intrude the sequence.

The deposit is complex with multiple controlling factors. The gross geometry of the deposit is controlled by the Bannockburn fault, a steeply dipping NNW trending fault that is continuous over at least 2.3km on the western margin of the orebody. The fault separates an ultramafic unit in the west from the Bannockburn host sequence in the east. It dips steeply east, rolling to vertical and steep west dipping in the northern part of the orebody. The Bannockburn fault is effectively the western boundary to the orebody with very little mineralisation penetrating the western side of the fault.

The Central fault which hosts the Central orebody has a shallow northerly plunge and is the orebody on which the majority of the underground workings is focused There are a series of steeply east dipping lodes in the hangingwall of the central lode; these are interpreted as either tensional veins of reverse faults with shearing present along the veins. Black graphic shale units present within the stratigraphy have acted as a localised control on the mineralisation. The black shale units have taken up some of the deformation with stratigraphy parallel shearing and mafic sequences between the shales have extended to form steep east dipping extension veins.

North Well
The North Well deposit is located on the central portion of the Archaean Norseman- Wiluna greenstone belt.

The mineralisation at North Well is confined to the Bannockburn Shear Zone (“BSZ”). The BSZ is a concave structure that has a strike length of approximately 30km, strikes roughly north south, and dips to the east. The BSZ is an approximately one kilometre wide zone of deformation that separates the basement granite/gneiss terrane to the west from greenstone terrane to the east. At North Well, the gold mineralisation is located approximately 400m from the main granite greenstone contact. Gold mineralisation is in east dipping basalts within a sequence of siltstones and acid volcaniclastics and occurs over a strike length of approximately 2600m and to a depth of 170m. Gold mineralisation is predominantly associated with quartz +/- sulphide filled shear structures. A strong S2/S3 lineation controls the mineralisation into a series of shallow (~25°) south plunging ore shoots that form en echelon zones along strike and down the dip of the shear zone. A series of east west late stage faults (some with dolerite intrusions) cross cut the mineralisation.

Thunderbox Operation (TBO) includes the Thunderbox Project (comprised of the Thunderbox, Rainbow and Otto Bore gold deposits), the Kailis Project (comprised of the Kailis Stage 1 & 2 gold deposits), the Bannockburn Project (comprised of the Bannockburn and North Well gold deposits) and the Waterloo Project (comprised of the Waterloo and Amorac nickel deposits).

The Thunderbox deposit is amenable to mining by both open pit and underground methods. Mining method employed at Thunderbox mine is conventional open pit with hydraulic excavator and dump truck fleet, and drill and blast activity. The TBO UG Ore Reserve is based on sub-level open stoping (SLOS) with paste fill, and long hole open stoping (LHOS) mining methods. SLOS is the dominant mining method, and accounts for 87% of the Ore Reserve estimate by tonnes. The SLOS zone, ranges in width from 3m to 50m, and dips at 70-80 degrees.

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.

The mining method to be employed at the Otto Bore deposit is conventional open pit with hydraulic excavator and dump truck fleet, and drill and blast activity.

The Kailis deposit has successfully been mined by open pit in the past and in Stage 1 and Stage 2.

The mining method employed at Kailis open pit was conventional open pit with hydraulic excavator and dump truck fleet, and drill and blast activity.

The Kailis deposit has successfully been mined by open pit in the past and in Stage 1 and Stage 2.

The mining method employed at Kailis open pit was conventional open pit with hydraulic excavator and dump truck fleet, and drill and blast activity.

The Kailis reserve pit is designed as a successive cutback to the previously mined reserve. At present the mine is in “care and maintenance”. The cutback will be mined in appropriate manner such that it meets the operational efficiency, safety and production rates.

The Bannockburn deposit is amenable to mining by both open pit and underground methods. The deposit has been mined by open pit and underground methods historically. There are reasonable grounds to assume that in the future this deposit will again be mined by conventional open pit load and haul operations.

The mining method to be employed at Bannockburn deposit is conventional open pit mining with a hydraulic excavator, dump truck fleet, and drill and blast activity.

Bannockburn reserve pit is designed as a large pit and will be mined in several stages to improve the stripping ratio. The Reserve pit will be mined such that it meets the operation efficiency, safety and production rate.

The mine is currently on ‘care and maintenance’.

The North Well deposit is amenable to mining by open pit methods. The deposit has successfully been mined by open pit in the past prior to 2007. There are reasonable grounds to assume that in the future this deposit will again be mined by conventional open pit load and haul operations, particularly to the south of the current mined out pits at Diesel and Frosties.

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.

The Ore Reserve will be treated at the established Thunderbox processing facility which is currently processing ore from the Thunderbox open pit and underground operations.

The plant is a conventional carbon-in-leach (CIL) gold circuit. It comprises a gravity circuit comprising centrifugal style gravity concentrators (2 × 30” Knelson Concentrators) and intensive leaching of the gravity concentrate. The gravity tailings product is processed through a six-stage leach/CIL circuit, pressure Zadra elution and refinery facility to produce gold doré.

Arsenopyrite is present in the ore and minor levels of arsenic are solubilised in the plant solutions. The arsenic levels are monitored on a regular basis and infrastructure exists for the addition of ferric sulphate where the levels impact the environment/exceed the environmental limits. The ferric sulphate is added to precipitate the free arsenic as ferric arsenate thereby locking the arsenic in the plant tailings for sto ........