The Northern Dancer deposit is a porphyry tungsten-molybdenum system (e.g., Kirkham and Sinclair, 1984; Sinclair, 1995). Deposits of this type comprise large tonnage, generally low grade, hydrothermal mineralization related to igneous intrusions emplaced at high levels in the earth’s crust. The mineralization may be confined to pluton-hosted disseminations, veins and veinlets in stockworks, vein sets, and breccias and occur in skarn, replacement, vein and disseminated deposits peripheral to plutons. Deposits of this type are amongst the world’s largest, including copper, molybdenum, uranium, tungsten, gold, silver, and tin. Porphyry molybdenum deposits are common in the northern Cordillera, with examples including: Quartz Hill, Endako, Red Mountain, Adanac, Trout Lake, Henderson, and Climax.

Previous work in the vicinity of the claims has outlined an extensive, multi-episode vein system that is enriched in several metals, most notably tungsten and molybdenum (Noble et al., 1984; Wengzynowski, 2006). Readers interested in a more detailed description of the vein system are referred to Chapter 4 of Brand (2008). The system is centred on a porphyry dyke complex and appears to form an approximately 3 km by 1 km kidney-shaped zone that is elongated along a north-north-easterly axis.

Most of the mineralization (approximately 95%) within the system occurs in veins and fractures. In addition, minor molybdenite is disseminated in the porphyry complex, some tungsten minerals are disseminated in skarn horizons and local disseminations of scheelite and molybdenite are found in the haloes of sheeted veins. Although veins cross-cut all units and most are apparently related to emplacement of the porphyry dyke complex, it is possible that some veining and skarnification may predate that event.

Northern Dancer deposit will be mined using open pit mining methods.

The selected mining operating rate is 30 Mt/a to supply the processing plant with 11.2 Mt/a of ore. The total Life of Mine (LOM) waste to mineralized material ratio is 0.15t of waste per 1t of ore produced.

The operation is amenable to conventional truck and shovel/front end loader mining, with blasting as required. The initial primary equipment fleet for the study consists of four 229 mm blasthole capable drill rigs, two 12 m3 diesel hydraulic face shovels, one 11 m3 front end loader and fourteen 100 t haul trucks. In addition, the primary fleet is supported by track dozers, motor graders, water trucks and other suitably sized ancillary equipment.

In general, both the face shovels and loader would be used to mine in bulk ore and waste on a 10 m bench. Use of a wheel loader allows some flexibility in mining locations for blending and ore supply purposes. The wheel loader may also be used for rehandle of mineralized material on the ROM.

The mining schedule has been based on a five phase approach. Three grade bands based on Net Smelter Return (NSR) have been used in the schedule: High Grade, Medium Grade and Low Grade. The mining sequence has been set to preferentially mine and treat High Grade material early in the mine life to improve the project Net Present Value (NPV). Medium and Low Grade materials are stockpiled for rehandle and processing later in the mine life.

Using this methodology there is no pre stripping period, with ore being available to process in the first year of mining. In the current schedule, the mine operates for 23 years, while the process plant operates for a total of 49 years. The maximum size of the ore stockpile is 295 Mt.

In the process conceptualized for Northern Dancer the run of mine feed materials are crushed and sized to prepare size ranges suitable for ore sorting. The low grade waste is removed into a reject stockpile for future processing, use in dam and/or road building as appropriate. The resulting upgraded product from the sorting are further crushed to prepare feed for the process plant. Following grinding to a size suitable for liberation of the minerals of interest, the feed materials are subjected to molybdenite and sulphide flotation including their regrind and cleaner circuits.

Rougher tailings from the moly/sulphide flotation circuit are sent to the scheelite flotation circuit for the recovery of a medium grade scheelite flotation concentrate. Both concentrates are dewatered in their respective circuits and the moly concentrate is filtered and dried before shipment to markets. The scheelite concentrate, after thickening, is sent to the ammonium paratungstate (APT) plant for conversion into a direct marketable product.

Crushing and Ore Sorting: Feed material from the open pit mine is crushed to nominal 75-mm and is screened to suitable size ranges for ore sorting. Ore sorting is predicted to reduce overall throughput from 11.2 M t/a to 7.3 M t/a rate through the separation of a low grade reject stream from the feed materials. The concentrate and a fines product are further crushed to prepare feed for the downstream grinding circuit.

Grinding: The crushed feed materials are ground to a liberation size suitable for optimum rougher flotation recovery of minerals of interest such as molybdenite and scheelite. Rod mills and screens are proposed for this circuit in order to mitigate slimes generation and the resulting scheelite losses in the downstream flotation circuits. Final ground product is thickened to a density suitable for the subsequent moly flotation circuit.

Molybdenum and Bulk Sulphide Flotation: The ground and thickened product is sent to moly rougher flotation and the resulting rougher concentrate is reground and cleaned in a multi cleaner stage flotation circuit to produce a marketable grade moly product. Fine grind mills and column flotation cells are considered for the cleaner circuit while the rougher circuit is expected to employ tank cells. Moly concentrates are dewatered and dried before packaging for the markets. Moly rougher tailings are sent to a bulk sulphide flotation circuit to remove additional sulphides ahead of scheelite flotation, and the bulk sulphide concentrate is sent to the tailings storage facility for disposal. Bulk sulphide tailings continue to scheelite flotation circuit.

Tungsten Flotation: Bulk sulphide tailings are conditioned with the appropriate reagents through stages of conditioning ahead of scheelite rougher-scavenger flotation. Rougher concentrate is sent to cleaner flotation while scavenger concentrate is recycled to the rougher feed, through a regrind circuit. Cleaner flotation will utilize column cells in producing a medium grade concentrate for the downstream APT conversion. Tungsten concentrate is thickened and stored for the downstream APT conversion at site.

APT Plant: The proposed process for converting tungsten concentrates to ammonium paratungstate (APT) is based on alkali digestion method. Tungsten concentrates from the process plant are digested in autoclaves at high temperature and pressure with alkali reagents. The resulting sodium tungstate solution is recovered from the gangue residue. The residue is sent to the tailings storage facility for disposal while the concentrated sodium tungstate solution is treated through various purification steps to remove compounds of such impurities as; As, P, Si, and Mo. Sodium tungstate solution is converted to ammonium tungstate which is then crystallized to produce APT for markets. All waste products will be sent to engineered ponds within the tailings storage facility for storage.

Tailings disposal and Fresh Water Supply: Process tailing streams such as the bulk sulphide concentrate and tungsten flotation tailings are sent to the tailings pond for disposal. Tailings supernatant water will be recycled to the mill as process makeup water. Residues and waste products from the APT plant are also sent to the tailings pond or engineered and dedicated storage ponds for disposal as required. Fresh water source for potable, reagent mixing and other process make up purposes is envisaged to be obtained from surrounding rivers.

Through crushing and ore sorting the throughput rate is reduced to 7.3 M t/a after low grade material is separated within the ore sorting circuit. The process plant, starting from grinding and through to downstream circuits treats 7.3M t/a of feed material. Overall metal recoveries to concentrates are predicted at 75% for tungsten and 72% for molybdenum at concentrate grades of +40% WO3 and +50% Mo respectively.