Cantung is a typical skarn-type deposit, albeit of an unusually large size for a tungsten bearing skarn. As with most skarns, the mineralization is related to a granitic intrusion and its associated intrusive dykes. These intrusive units are believed to have given off reactive fluids that have then come in contact with the overlying reactive Ore Limestone and Swiss Cheese Limestone units.

The two main historic scheelite skarn ore bodies, the Open Pit and E-Zone, are spatially located within the Ore Limestone unit on the upper and lower limbs, respectively, of a recumbent anticline on the west side of the Flat River Syncline.

The major scheelite ore body mined from underground at Cantung historically was the EZone ore body. Since reopening in 2010, the mine has expanded the known extent of the scheelite ore horizon down dip along the lower limb of the recumbent anticline to the south and to the west as well as along the upper limb to the west.

These expanded areas include the West Extension, the Amber zone and Below 3700 elevation level along the lower limb of the fold and the Upper West Extension along the upper limb of the fold. The underground ore zones extend 4,360 ft. along strike, 1,200 ft. down-dip along the lower limb, with some interruption from intrusive sills and dikes, and 200 ft. up dip from the fold hinge along the upper limb.

Throughout most of the underground deposit, three main ore lenses are present: one lens occurs within the Swiss Cheese Limestone, the second lens occurs at the upper contact of the Ore Limestone with the Swiss Cheese Limestone, and the third lens occurs at the lower contact of the Ore Limestone with the Younger Argillite or the granodiorite unit. Intermediate lenses also occur within the Ore Limestone but they tend to be less continuous than either the second or third aforementioned lenses.

The scheelite mineralization in the West Extension and Amber zone is usually fine to medium grained (locally coarse grained), finely to coarsely disseminated and sometimes concentrated in bands, especially within the Swiss Cheese Limestone. These banded concentrations are also observed in the Open Pit Swiss Cheese Limestone ore. Scheelite is usually present in a massive to semi-massive pyrrhotite skarn or a calc-silicate skarn containing abundant pyroxene, garnet and minor pyrrhotite. Both skarn types generally contain chalcopyrite, with some black sphalerite locally. Skarn development in the Ore Limestone and Swiss Cheese Limestone underground is limited by general proximity to the granodiorite intrusive as well as an abundance of fluid transporting fractures and structures. The scheelite mineralization in the Open Pit has been genetically linked by previous researchers to an aplitic dyke and/or quartz vein stockwork that intruded up towards the Open Pit, bringing ore bearing fluids from depth.

The mine consists of both open pit and underground operations, which extract ore from a scheelite-chalcopyrite bearing skarn.

The primary mining method is sub-level longhole stoping with delayed backfill. Currently longhole methods are planned for the majority of the remaining reserves with cut and fill being employed in areas where the ore zone is too narrow for efficient longhole mining.

The original ore body (E zone) was accessed by an adit and a decline for traffic flow and ventilation purposes. The West Extension, West Extension Below 3700 and Amber Zone are accessed by a series of declines driven from the 3950 Level adit. This adit is the main equipment traffic road and ventilation exhaust air way. The 4450 level decline is the fresh air ventilation intake and is not used for vehicle traffic. The current main development size is 15ft x 15ft. The drifts are drilled using a two boom jumbo and ground support is installed with a MacLean Bolter or scissor deck.

Longhole stoping is currently the primary mining method used at Cantung in the West Extension area (below 3700) and the Amber Zone. This method is simple, reliable and has a relative lower cost. The majority of the remaining reserve at the Cantung mine will continue to be mined using longhole stoping to meet the current targeted mill feed rate. A small area of the reserve has a shallow dip angle and, depending on the thickness of the mineralization zone, cut and fill or room and pillar will be used to reduce dilution and increase ore recovery.

The longhole stopes are drilled by a Stopemaster drill using 3-inch holes and an ITH (Cubex) drill using 4.5-inch holes. The ore is mucked from the bottom of the stope using an 8 cubic yard remote- controlled LHD (scooptram). The ore is hauled out by 30 and 45 ton trucks. The ore body is divided by levels, with a vertical elevation difference of 40 to 60 feet. Longhole stopes are designed to the maximum extent based on good geotechnical engineering practices. The pillars separating these stopes are generally designed to be in the low grade areas of the mineral resource and are typically 15 to 20 feet wide. These rib pillars are usually not recoverable, as the mine uses unconsolidated waste as backfill. The stopes are sequenced to retreat out of each level to the level access connected to the main ramp.

For the areas where the ore thickness is 6-10 feet, with dip angles ranging from 20-30 degrees, a variation of the room and pillar method will be used in combination with cut and fill stoping. With this method the ore is recovered in horizontal drifts starting from the bottom and advancing upward. The void is backfilled to allow for mining of the next level. Level drifts will be driven 13 feet x 13 feet and mining will be completed using existing equipment.

Primary Crushing
Ore is handled from the stockpile by a loader or directly dumped from the haulage truck into a 30- ton receiving bin equipped with 42 inch x 10 ft. apron feeder, which in turn feeds a 42 inch x 48 inch jaw crusher. The jaw crusher is set to produce a nominal fiveinch crushed product. A conveyor transports crushed ore into a 1,000-ton capacity coarse ore bin. This bin acts as a surge bin for the secondary crushing circuit.

Secondary and Tertiary Crushing
A vibratory feeder and a conveyor feed a 4¼ ft. (secondary) standard cone crusher set at 1 inch. The crushed ore is discharged via conveyor to a vibrating screen equipped with a 7/16 inch x four inch slotted screen. The oversize feeds a 4¼ ft. (tertiary) short-head cone crusher set at 3/8 inch. The tertiary crusher discharge combines with the secondary crusher discharge to feed the screen in a closed-circuit recycle. Screened undersize (minus 7/16 inch) product is conveyed to two fine ore bins ahead of the grinding mills in the concentrator. Dust is controlled by the use of a wet scrubber with the discharge effluent returning to the mill.

Grinding
The grinding circuit consists of a 9 ft. diameter by 12 ft. long rod mill, powered by a 450 hp motor, plus a 7 ft. diameter by 10 ft. long ball mill powered by a 200 hp motor, and a 6 ft. by 6 ft. ball mill powered by a 150 hp motor. The rod mill is fed from two fine ore bins via belt conveyors that discharges ground ore slurry into a sump along with the discharge from the ball mill for pumping to vibrating screens. The screen oversize drops by gravity to a pump that transports the slurry to a dewatering screen. This screen removes excess water prior to further grinding of the solids in the ball mills. As noted above, ball mill discharges join rod mill discharge for presentation to the vibrating screens. Water removed by the dewatering screen is reused for screen feed dilution. Particles larger than the screen openings will circulate through the ball mill until they are sufficiently reduced in size to pass through the screen openings.

Processing is carried out by gravity and flotation circuits. Final products include a premium gravity concentrate (G1), containing on average, 65% WO3; a flotation concentrate containing, on average, 35% WO3 and a copper concentrate averaging 28% Cu.

Classification and Talc Flotation
Ball mill discharges join rod mill discharge for presentation to the vibrating screens. Water removed by the dewatering screen is reused for screen feed dilution. Particles larger than the screen openings will circulate through the ball mill until they are sufficiently reduced in size to pass through the screen openings.

Screen undersize also drops by gravity to a pump which then transports the slurry to a set of cyclones that classifies according to particle size. Particles larger than the cyclones cut point drop by gravity to the sands bulk sulfide flotation unit operation. Particles smaller than the cut point feed the slimes bulk sulfide flotation unit operation.