The mineralization at the Arctic Deposit and at several other known occurrences within the Ambler Sequence stratigraphy of the Ambler District, consists of Devonian age, polymetallic (zinc-copper-lead-silver-gold) VMS-like occurrences.

In the Ambler District, VMS-like mineralization occurs in the Ambler Sequence schists over a strike length of approximately 110 km. These deposits are hosted in volcaniclastic, siliciclastic and calcareous metasedimentary rocks interlayered with mafic and felsic metavolcanic rocks. Sulphide mineralization occurs above the mafic metavolcanic rocks but below the Button schist, a distinctive district wide felsic unit characterized by large albite porphyroblasts after relic phenocrysts. The presence of the mafic and felsic metavolcanic units is used as evidence to suggest formation in a riftrelated environment, possibly proximal to a continental margin.

A sulphide-smoker occurrence has been tentatively identified near Dead Creek northwest of the Arctic Deposit and suggests local hydrothermal venting during deposition. However, the lack of stockworks and stringer type mineralization at the Arctic Deposit suggest that the deposit may not be a proximal vent type VMS. Although the deposit is stratiform in nature, it exhibits characteristics and textures common to replacement-style mineralization. At least some of the mineralization may have formed as a diagenetic replacement.

At Arctic, sulphides occur as semi-massive (30 to 50% sulphide) to massive (greater than 50% sulphide) layers, typically dominated by pyrite with substantial disseminated sphalerite and chalcopyrite and trace amounts of galena and tetrahedrite. The Arctic Deposit sulphide accumulation is thought to be stratigraphically correlative to those seen at the Dead Creek and Sunshine deposits up to 12 km to the west.

There is also an occurrence of epithermal discordant vein and fracture hosted base metal (lead-zinc-copper) mineralization with significant fluorite mineralization identified at the Red prospect in the Kogoluktuk Valley, east of the Arctic Deposit. Although not yet fully understood, the genesis of this occurrence is considered to be related to the regional system that formed the VMS deposits in the Ambler District.

Mineralization occurs as stratiform SMS to MS beds within primarily graphitic chlorite schists and fine-grained quartz sandstones. The sulphide beds average 4 m in thickness but vary from less than 1 m up to as much as 18 m in thickness. The bulk of the mineralization is within five modelled zones lying along the upper and lower limbs of the Arctic isoclinal anticline. All of the zones are within an area of roughly 1 km2 with mineralization extending to a depth of approximately 250 m below the surface. There are five zones of MS and SMS that occur at specific pseudo-stratigraphic levels which make up the bulk of the mineral resources. The other three zones also occur at specific pseudo-stratigraphic levels, but are too discontinuous to confidently model as resources.

Unlike more typical VMS deposits, mineralization is not characterized by steep metal zonation or massive pyritic zones. Mineralization is dominantly sheet-like zones of base metal sulphides with variable pyrite and only minor zonation usually on an extremely small scale.

Mineralization is predominately coarse-grained sulphides consisting mainly of chalcopyrite, sphalerite, galena, tetrahedrite, arsenopyrite, pyrite and pyrrhotite. Trace amounts of electrum and enargite are also present. Gangue minerals associated with the mineralized horizons include quartz, barite, white mica, black chlorite, talc, calcite, dolomite and cymrite.

The Arctic Project is designed as a conventional truck–shovel operation assuming 144 t trucks, and 15 m³ shovels. The pit design includes three nested phases to balance stripping requirements while satisfying the concentrator requirements.

The design parameters include a ramp width of 28.5 m, maximum road grades of 10%, bench height of 5 m, targeted mining width of between 70 and 100 m, berm interval variable by sector, variable slope angles by sector and a minimum mining width of 30 m.

The smoothed final pit design contains approximately 43.4 Mt of ore and 298.3 Mt of waste for a resulting stripping ratio of 6.9:1.

The production schedule includes the processing ramp up. The processing plant ramp-up considers the normal inefficiencies related to the start of operations, and includes the tonnage processed as well as the associated recoveries, which increase the design capacity during the second quarter of operation. The mine requires two years of pre-production before the start of operations in the processing plant. However, the mine will start operations in Year -3 to produce material to be used on the site construction.

The deposit will be mined in three nested phases, including the ultimate pit limit. The scheduling constraints set the maximum mining capacity at 36 Mt per year and the maximum number of benches mined per year at 10 in each phase.

The mine is scheduled to operate 24 hours a day, seven days a week using three rotating crews working 12-hour shifts.

Crushing Plant
ROM material will be trucked to the crushing station and dumped into a 200 t receiving bin protected with a 1000 mm aperture stationary grizzly screen. Ore will be reclaimed from the bin with an apron feeder and scalped of fines with a vibrating grizzly. Grizzly oversize will be passed to a 200 kW jaw crusher. The designed nominal crushing rate is 641 t/h at 65% availability.

The combined grizzly undersize and jaw crusher discharge product is expected to be 80% passing 80 mm. The crusher product will be conveyed to a 5,000 t live capacity stockpile, providing up to 12 hours of live storage for the grinding/flotation plant.

A dust collection system will be provided to control fugitive dust generated during dumping, crushing, and transport of the materials. A belt magnet will be provided over the crusher discharge conveyor to remove any tramp iron.

The main equipment in the crushing area will include:
• One 1000 mm stationary grizzly.
• One primary apron feeder, 1,500 mm wide by 7,000 mm long.
• One vibrating grizzly (1,600 mm wide x 6,100 mm long, 100 mm aperture)
• One jaw crusher, 1,067mm x 1,270mm; driven by a 187kW motor.
• One belt scale.
• One belt magnet.
• One jaw crusher discharge conveyor.
• One stockpile feed conveyor.
• One baghouse/dust collector.

Coarse Ore Storage
The coarse ore stockpile will have a live capacity of 5,000 t equivalent to approximately 12hrof mill feed at the nominal mill feed rate.The stockpile dead capacity will be approximately 20,000t.The coarse ore stockpile will be a covered facility equipped with a dust collector to effectively control dust losses and to mitigate freezing of the stockpiled material. The coarse ore stockpile building access will allow for the operation of mobile equipment to work the pile as required.Reclaim of ore from the stockpile will be accomplished using two 1000 mm wide by 4,800 mm long apron feeders at a nominal rate of 226 t/h per feeder. Reclaimed material from the apron feeders will be discharged onto a 900 mm wide by 125m long SAG mill feed conveyor.

Primary Grinding and Classification
Crushed ore reclaimed from the coarse ore stockpile will feed the SAG mill at a rate of 453 t/h. The initial lime and zinc sulphate addition to establish downstream flotation chemistry will be added here. The SAG mill will be a 6.1 m diameter by 4.9 m long unit equipped with a classifying trommel screen. The installed power on the SAG mill will be 3000 kW provided by a single motor and variable speed drive.

The SAG mill trommel undersize will flow by gravity to a pump box which will feed the classifying cyclones. Oversized pebbles from the SAG mill trommel will be returned to the SAG mill for additional grinding. The circulating load of oversize from the SAG mill trommel is estimated at 20% of SAG mill feed. As required, steel balls will be added to the SAG mill to maintain mill power.

Secondary Grinding and Classification
The secondary grinding circuit will include a single ball mill operated in closed circuit with a classifying cyclone cluster. The ball mill will be a 6.1 m diameter by 9.1 m effective grinding length (EGL) ball mill, powered by a 6,000 kW motor. The SAG mill trommel undersize will be combined with ball mill discharge to feed the classifying cyclone cluster. The cyclone underflow will gravity-flow to the ball mill, while the cyclone overflow, with a solids content of 36.5%, will gravitate to the flotation plant. The designed circulation load for the ball mill is approximately 300%. The flotation feed slurry is estimated to have a particle size of 80% passing 70 µm.

As required, steel balls will be added into the ball mill to maintain the required mill power.

Mineral Processing
A 10,000 t/d process plant was designed to process the massive and semi-massive sulphide mineralization. The process plant will operate two shifts per day, 365 d/a with an overall plant availability of 92%. The process plant will produce three concentrates: 1) copper concentrate, 2) zinc concentrate, and 3)lead concentrate. Gold and silver are expected to be payable at a smelter; silver is expected to be payable in the copper and lead concentrates, with gold expected to be payable in the lead concentrate only. The process plant feed will be supplied from the proposed Arctic open pit mine.

The mineralization will contain significant levels of talc and will first undergo talc pre-flotation to remove the talc prior to traditional base metal flotation for production of copper, zinc, and lead concentrates. The process plant final tailings will be pumped to the TMF. Copper, zinc, and lead concentrates will be thickened and pressure-filtered before being tra ........