The Pogo gold deposit consists of numerous massive auriferous quartz +/- sulphide veins hosted in a sequence of amphibolite-grade, paragneiss and orthogneiss of Proterozoic to mid-Paleozoic age. Mid-Cretaceous age granitic plutons and dikes intrude the gneisses, which in turn, are cut by the veins. The Proterozoic gneiss and Cretaceous granitoid sequence are part of the Yukon- Tanana terrain, a gold belt extending from Fairbanks into the historic gold mining areas of the Yukon Territory.

The age of the gold mineralisation is approximately 104 million years (Cretaceous) and is controlled by a low angle regional shear and high angle fault structures, which are interpreted as the fluid conduits for hydrothermal fluids. The field has undergone regional metamorphism, peaking at 110 million years, resulting in moderate folding and foliation of the metamorphic host rocks. Retrograde metamorphism resulted in cooling, which transformed the ductile deformation of the metamorphic fabric to brittle (semi-ductile to brittle) deformation resulting in a low-angle shear across the region. Gold in the quartz veins is characterized as “Pogo Type” mineralization and occurs as inclusions in arsenopyrite, inclusions in quartz, composite intergrowths with Bi-Te+/- S minerals in quartz and invisible Au (<1um) inclusions to solid- solution atomically bounded in loellingite, coupled with low arsenic arsenopyrite.

The ultimate source of the hydrothermal fluids responsible for the Pogo deposit remains unknown. Both the “Intrusion Related Gold” and “Orogenic Gold” models have characteristics that support the evolution of the Pogo deposit. However, currently, the IRG model best fits current observations and measurements.

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 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 processing plant has an original design, hard rock processing capacity of in excess of 0.8M tonnes per annum, current stable operation has been established at 1.0M tonnes per annum and work is currently being done to look at increasing the current throughput rate.

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 Hard ........