The Project is in the Tintina Mineral Belt, which is a 200 km-wide, 1,200 km-long arc, broadly bounded by the Tintina-Kaltag fault systems to the north and the Denali-Fairwell fault systems to the south. The region contains numerous economic deposits of gold in addition to copper, lead, zinc, silver and tungsten deposits.

The lithological units in the Pogo deposit area are dominantly high-grade metamorphic rocks intruded by later felsic to intermediate intrusive units. Key metamorphic rocks include biotite feldspar gneiss, augen gneiss and mafic schist derived from both sedimentary and igneous protoliths. Metamorphic mineral assemblages observed consist of quartz, feldspar, biotite, chlorite, muscovite, sillimanite, andalusite and garnet. The 50km long Goodpaster batholith (granite tonalite-diorite) is the dominant intrusive complex in the district. Locally small felsic to intermediate stocks and dykes are present.

The principal mineralisation is hosted in biotite-quartz-feldspar paragneiss and orthogneiss, although all other lithologies are cut. Where the veins cross intrusives, they tend to split and become stockwork zones.

Gold at Pogo is predominantly hosted within laminated quartz veins ranging in thickness from <0.5m to >10m. Mineralised veins contain around 3% sulphides (arsenopyrite, pyrite, pyrrhotite, loellingite, chalcopyrite, bismuthinite, sphalerite, galena, molybdenite, tetradymite, maldonite) and a variety of Bi-Pb-Ag sulphosalts.

The Pogo gold deposit is an example of a Reduced Intrusive Related Gold Deposit (RIRGD), characterised by a low sulphide content, (typically <5%) and a reduced ore mineral assemblage, that typically comprises pyrite and lacks primary magnetite or hematite. In brief, these deposits typically have the following characteristics:
- Mineralisation occurs as sheeted vein deposits or stockwork assemblages and often combines gold with variably elevated Bi, W, As, Mo, Te, and/or Sb, but low concentrations of base metals;
- Restricted and commonly weak proximal hydrothermal alteration;
-Spatially and temporally related to reduced intrusions of intermediate to felsic composition.

Dimensions

Liese – The generally shallowly north-westerly dipping Mineral Resource extends approximately 1,300m in a north-easterly direction along strike and 1,300m down dip.

Eastern Deeps – The shallow to moderately north-westerly dipping Mineral Resource extends approximately 530m in a north-easterly direction along strike, and 600m down dip.

North Zone – The steeply east dipping Mineral Resource extends approximately 950m in a northerly direction along strike, and 970m down dip. A flatter component, dipping west, extends 250m by 190m.

South Pogo – The moderately north-westerly dipping Mineral Resource extends approximately 1100m in a north-easterly direction along strike, and 760m down dip.

Fun Zone – the generally moderate to steep-westerly dipping Mineral Resource extends approximately 880m in a westerly direction across strike, 650m in a northerly direction across- strike and 915m down dip.

Central Zone - The shallow to moderately north-westerly dipping Mineral Resource extends approximately 750m in a north-easterly direction along strike, and 500m down dip.

Hill 4021 – The Hill 4021 prospect consists of two extensive, shallow dipping mineralised structures that are 2,000m by 500m.

Four portals are in use which provide access to the various underground mining block areas. Mining block areas are named Liese, East Deep, North Zone, X vein, South Pogo and Fun Zone. Portals are named by their approximate elevation on the topography.

The 1525 portal driven in 1996 is the original exploration drive that eventually provided access to the first Liese vein bulk sampling.

After planning and permitting processes were completed the 1875 portal and associated ore body ramp development was constructed in 2005. The 1875 provided access to Liese veins and was driven to connect with concurrent expanded development from the 1525 decline.

The 1650 portal is located a ½ mile down the drainage from 1875 and was driven to support waste haul and exhaust air routing out of mine during development. After major development in the 1650 area was completed in 2006, the 1650 decline was then outfitted with a conveyor to supply mill from a mine ore bin. The main paste backfill system supply pipe from mill to mine was also installed down the 1650 decline.

The 2150 portal and decline are located approximately 1/3 -mile northwest of the 1875 portal area. The 2150 decline was driven starting in 2013 and accessed the East Deep ore body that was defined after the original mine construction.

The mining methods at Northern Star’s Pogo Mine are varied due mainly to variability in vein thickness, dip, grade and continuity and the selection of method is driven by the geometry of the structure during the initial planning stage of the mine design.

Development design of ramps and stope accesses are positioned primarily for rapid and efficient extraction via longhole stoping where possible; or jumbo development cut and fill mining where vein geometry is nonconducive to larger stoping blocks; all while considering economics of variable grade across the vein and associated mineralised rock structure. Individual stope opening sizes and strike lengths are designed considering dilution, geotechnical considerations and optimising mining efficiency.

Vein shapes may contain splits with varying thickness and have dip of between near flat and vertical (90 degrees). Veins that are more vertical (North Zone and X vein) are mined in long hole panels after the upper and lower ore drives are mined with panel lengths varying from 100 to 300 feet.

For ore structures that dip between near flat and 60 degrees (Liese, Fun Zone, South Pogo and East Deep), ore is mined using a combination of jumbo cut and fill and long hole stoping methods that drill up or sideways into the exposed vein from the initial development drive. Ore is mucked by manual and tele-remote 17-ton loaders and is hauled by 45-ton payload trucks to the underground ore bin where it is fed onto the mill feed conveyor.

Mine ventilation is accomplished by operating two 400HP and two 200HP main fans as well as a 250HP booster fan to drive exhaust air out of mine. Main fans create suction at the 1525, 1875 and 2150 portals. Exhausts are at the 1690 portal and a dedicated exhaust raise at the 2150 portal pad. In winter, mine intake air must be heated to prevent utilities and roadways from freezing. This is accomplished by pulling a portion of the intake air across propane fuel fired heat grids that operate at the 1525, 1875 and 2150 portals during freezing weather – generally October till March.

Paste backfill is supplied by the mill tailings handling facility and paste plant. Individual stope paste backfill operations are scheduled to accommodate mill tailings and water disposal needs while supporting stope cycle schedules.

To maximise efficiency and production of underground major equipment semi-autonomous capabilities are a being implemented and used for development drilling, production drilling and loading operations.

Underground mining and fleet maintenance are carried out by Northern Star Mining Services Pty Ltd (NSMS), a subsidiary of Northern Star. Daily mine management and technical services are shared by NSMS and Northern Star personnel who work as a team to fully support Northern Star’s STARR Core Values of Safety, Teamwork, Accountability, Respect and Results.

The grinding circuit handles the ROM ore which passes through a 45cm x 45cm grizzly prior to the underground ore bin. Ore is conveyed to a 900 tonne surface coarse ore bin. From the surface ore bin the ore is capable of being conveyed at a rate in excess of 160 dry tonnes per operating hour to a 6.7m diameter x 2.4m EGL Marcy, fixed speed SAG with a 1,680 kW motor. The SAG trommel oversize material is returned to the SAG with a reverse scroll scat return. The SAG trommel undersize is pumped to the discharge of a 5m diameter x 8.7m EGL Hardinge (Koppers) ball mill utilizing a 3,430 kW motor. The discharge of the ball mill passes across a 1mm aperture Derrick screen with the undersized feeding the gravity circuit. Of the ten 25cm Krebs gMAX cyclones which close the ball mill circuit, five to seven are operating. The cyclone overflow feeds the flotation circuit at a target of 80% passing 55 microns.

The Pogo processing circuit involves gravity concentration, gold and sulphide flotation, and leaching and adsorption of gold with a leach/carbon-in-pulp (CIP) unit operation.

The gravity circuit consists of two Knelson XD-48 concentrators. Given the finer sizing of the gravity recoverable gold (GRG), the Knelson concentrate is screened at 150 microns with the oversize reporting back to the ball mill cyclone feed. The undersize runs across a table (located in the gold room) with the table concentrate reporting to the induction furnace. Table tails report to a Gekko ILR2000 Inline Leach Reactor (ILR). The ILR uses a high cyanide concentration solution to leach the gold in a very short period. Gold is recovered from this solution in the gold room by electrowinning. The residue of the ILR is reground by an IsaMill M100 to about 80% passing 25 microns. The IsaMill discharge reports to the head of the leach circuit. Approximately 25% of the gold in the mill feed is recovered via ........