The Young-Davidson Property is located within the southwestern part of the Abitibi Greenstone Belt, which is the largest preserved Archean greenstone belt in the world and one of the most continuous units of the Superior Geologic Province. The Abitibi Greenstone Belt extends for 750 km from the Grenville Province in the east to the Kapuskasing Gneiss Belt in the west, and for over 170 km from the Opatica Gneissic belt in the north to the Proterozoic Huronian sediments in the south.

The Abitibi Greenstone Belt consists of a complex and diverse array of volcanic, sedimentary, and plutonic rocks typically metamorphosed to greenschist facies grade, but locally attaining amphibolite facies grade adjacent to large plutons and along the Grenville Front.

At least five styles of gold mineralization are recognized at the Young-Davidson Project:

1. Syenite-hosted gold mineralization
2. Mafic volcanic-hosted gold mineralization (MCM Mine)
3. Timiskaming sediment-hosted gold mineralization
4. Ultramafic-hosted gold mineralization
5. Hanging wall contact gold mineralization

The syenite-hosted gold mineralization consists of a stockwork of quartz veinlets and narrow quartz veins, rarely greater than a few inches in thickness, situated within a broader halo of disseminated pyrite and potassic alteration. Visible gold is common in the narrower, glassy-textured quartz veinlets. In general, gold grades increase with quartz veinlet abundance, pyrite abundance, and alteration intensity. Mineralized areas are visually distinctive and are characterized by brick red to pink Kfeldspar-rich syenite containing two to three percent disseminated pyrite and several orientations of quartz extension veinlets and veins. The quartz veins and veinlets commonly contain accessory carbonate, pyrite, and feldspar.

The syenite-hosted gold deposits, commonly associated with quartz-monzonite to syenite stocks and dikes, has been individualized as a distinct group of gold deposits, well represented in the Abitibi Greenstone belt and particularly at the Porcupine and Kirkland Lake districts, Northern Ontario.

According to Robert (2004), the syenite-hosted gold deposits occur mainly along major fault zones, in association with preserved alluvial-fluvial, Timiskaming-type, sedimentary rocks. Robert (2004) describes the gold mineralization in these deposits as being represented by disseminated sulphide replacement zones, with variably developed stockworks of quartz-carbonate-K-feldspar veinlets within zones of carbonate, albite, K-feldspar, and sericite alteration. Syenitic intrusions are broadly contemporaneous with deposition of Timiskaming sedimentary rocks and, together with disseminated gold mineralization; they have been overprinted by subsequent regional folding and related penetrative cleavage.

The Young-Davidson deposit, also located in the Abitibi greenstone belt, can be classified as an Archean, syenite-hosted gold deposit. The gold mineralization is primarily related to quartz veinlet stockworks and disseminated pyrite mineralization, mostly enclosed within the syenite intrusion boundaries, or very close to the contacts with the enclosing rocks, and is frequently associated with broader zones of potassic alteration.

Young-Davidson is mined with longhole sublevel stoping methods, predominately transverse stoping, followed by paste backfilling. The mine has seen a steady ramp of production rates since its startup in 2013 and currently operating at a nominal 7,000 tpd rate.

Transverse Longhole Stoping
Based on the geometry of the mineralized zones, the vertical dip and the competency of the rock, the long-hole transverse mining method with primary and secondary stopes is used for the bulk of the mining at Young-Davidson. This mining method involves accessing stopes using two transverse drifts: one above the stope for drilling and loading of bulk explosives, and one below for mucking blasted material.

For transverse longhole stopes with paste fill, the sub-level spacing has been standardized to 30 m (floor-to-floor) and strike length to 25 m (between drawpoint centerlines). Given these dimensions, the maximum recommended stope width is 15-18 m. As such, in areas of the orebody that exceed 20 m width, two or more separate panels will be needed to extract the full orebody width.

Transverse stopes are sequenced as a series of primary and secondary stopes. Primary stopes are mined first and are separated by secondary stopes. After the primary stope is mined it is backfilled with paste fill. When both primary stopes on either side of the secondary are filled the secondary stope can be mined. Secondary stopes, depending on where they lie in the panel sequence, local stability issues, and the availability of waste rock, can be filled as follows:

Longitudinal Longhole Stoping
Longitudinal stoping is a form of longhole stoping used mainly on vein type deposits. During blasting the broken ore is thrown out into the open stope and since this not safe for personnel entry, radio remote control scooptrams are used to advance out into the open stope beyond the safety of the brow, to muck the blasted ore. This technique eliminates the need for production scrams and multiple drawpoints reducing the development costs. This method is planned for ore zones ranging from 5 to 10 m thickness, in other words, for zones that are too narrow to mine with the more productive and lower cost transverse longhole stoping.

For longitudinal longhole stopes, sub-level spacing is the standard 30 m, ensuring compatibility with transverse longhole stopes. Since longitudinal stopes are generally <10 m wide (averaging 6-8 m), the maximum recommended stope length is 80 m above the 9590 level and 30 m below the 9590 level; these lengths were reduced to 50 m and 25 m respectively to tie-in with transverse stope lengths for the reserving process (as stoping methods are only assigned after the original grade shells were split both vertically (every 30 m) and horizontally (every 25 m along strike).

Paste Fill
As part of the current mine plan, paste fill is used as the backfill product in the final step of a stope cycle. Paste fill is produced in the paste fill plant and distributed underground via a network of 8” piping. Draw points for stopes must be barricaded with specially designed ached barricades to support the load of the dense paste fill material. These barricades must be constructed, approved and shotcreted prior to the initial paste fill pour. Each stope is filled in three portions, the plug, body and cap pours. All three portions are required to complete filling of any particular stope. Once a fill is complete paste fill must be allowed to cure until a reasonable strength is attained before proceeding to mine any adjacent stopes. The Mine Engineering Department prepares a paste filling package for each individual stope that provides instruction on how the filling process should be conducted.

Pit Ore Reclaim
Open pit stockpiled ore is crushed in a jaw crusher to a P80 of 150 mm. Crushed ore is then conveyed to the coarse ore bins feeding the processing plant grinding circuit. The surface crusher is capable of crushing over 8,000 tpd and was the sole source of mill feed prior to the commissioning of the underground mine.

The surface crushing for the open pit will be carried out by an independent contractor and material to the plant will be fed by mine trucks, which will dump the material atop a grizzly fitted with scalping bars set on a 250 mm x 300 mm grid. All the sized material reports into a hopper above on a vibrating grizzly feeder.

The vibrating grizzly feeder drops the open pit ore onto the pit ore feeder conveyor which feeds the coarse ore bin feed conveyor. This coarse ore bind feed conveyor receives the crushed product from both the underground mine and the open pit and is designed for a rate of 550 t/h. A fixed magnet is located at the transfer chute between the two conveyors to capture tramp metal. Each conveyor discharge point is fitted with an extraction hood connected to a dust-collecting bag house. The dust is dropped back on the subsequent conveyor belt through mechanical shaking of the bags.

Underground Ore Crushing Circuit
The mined ore is dropped into an ore pass from which it is metered by a grizzly feeder with 600 mm x 600 mm openings to an apron feeder which drops into the underground jaw crusher with a 160 kW (200 hp) motor size. A fixed magnet mounted above the discharge of the apron feeder to the jaw crusher retrieves any tramp metal. The crushed ore is sent to two underground ore bins each 1500 tonnes in capacity. The product of these two bins reports to two apron feeders which discharge to a conveyor leading to the skip loading system.

The material skipped to surface is fed into one of two 500 t surge bins (1 ore, 1 waste) at the headframe. From there, the mill material is transferred via an apron feeder onto the coarse ore bin feed conveyor. This overland conveyor allows filling of a 6,000 live tonnes capacity bin. The bin is insulated to prevent wet material from freezing against the bin wall, while the top of the bin is covered and fitted with a bag house to extract air moisture and prevent freezing. An electric hoist mounted on a beam extending over the edge of the bin outline assists in bringing maintenance supplies to the top of the bin, facilitating the maintenance of the head pulley and idlers at the discharge point of the coarse ore bin feed conveyor.

Coarse Ore Reclaim
Feed from the coarse ore bin discharges onto the SAG mill feed conveyor via two apron feeders fitted below elongated slots at the bottom of the coarse ore bin. Both feeders are normally in operation to achieve the plant design feed rate and to provide some blending capability for managing the SAG mill feed size distribution. In case of a feeder being out of operation, the total ore flow required by the grinding plant can still be obtained with only one feeder in service.

The SAG mill feed conveyor is fitted with a belt scale, providing plant feed tonnage control through the variable speed capability of the apron feeders.

Grinding Circuit
The grinding circuit is in a single-stage SAG mill configuration.

One of the Kemess ball mills was modified to function as the SAG mill in the Young-Davidson grinding circuit. The resulting unit has 6,710 mm ID ø x 11,130 mm (22’ ID ø x 36.5’) of flange-to-flange (FF) length, and is fitted with two 4,474 kW (6,000 hp ) synchronous motors taken from the mills at Kemess.The fresh material from the coarse ore bin feeds the SAG mill at the design rate of 370 t/h, equivalent to 8,880 t per operated day, which meets the average nominal capacity of 8,000 t/d and a plant availability of 91%. Process water is added to the SAG mill feed chute to achieve a pulp density of 75% solids in the mill.

The SAG mill discharge reports to the cyclone feed pump box.

A centrifugal pump (with one stand-by) with a 298 kW (400 hp) VFD drive delivers the slurry from the cyclone feed pump box to a battery of three (two are typically in operation) ø660 mm (26”) hydrocyclones fed from a common manifold. The cyclone battery works in closed circuit with the SAG
mill, with the cyclone underflow returning as a circulating load to the mill feed. The cyclone overflow stream proceeds forward to the flotation circuit at a slurry density of 35% solids.

The grinding circuit is designed to operate with circulating loads fluctuating between 100 and 150% relative to the fresh SAG mill feed rate, using the variable speed capability of the cyclone feed pump to maintain the pump box level and the number of cyclones for feed pressure control to the cyclones.

An automatic sampler was installed to collect incremental samples of the cyclone overflow in order to provide a composite shift sample that is used for metallurgical accounting purpose. The secondary sampling stage and collection of the shift composite is achieved by the multiplexer provided with a particle size analyzer (PSA). The PSA is installed at this position to provide feedback to the grinding circuit operator of the grinding product size being achieved. The shift composite sample is also collected for analysis of its precious metal content.

The Young-Davidson mill can be considered a standard flotation/CIL gold mill. The mill was commissioned during Q1 of 2012 and the first gold pour occurred on April 30th, 2012. Ore is currently sourced from two sources, the underground mine and from low grade surface stockpiles, produced by the open pit between 2011 and 2014.

The cyclone overflow feeds a trash screen prior to feeding the flotation conditioner. The flotation conditioner overflows into the first flotation cell. The flotation circuit is comprised of four tank cells.

The flotation concentrate is pumped to the concentrate thickener. Thickener underflow is pumped to the regrinding circuit. The thickened concentrate is pumped to the regrinding circuit, comprising a vertical tower mill, where the solids are reduced to a size distribution with a nominal P80 target of 15 µm, operated in closed circuit with a cyclone cluster. The cyclone underflow returns to the tower mill box while the cyclone overflow flows directly to the concentrate CIL circuit.

The flotation tailings are pumped to the flotation tailings thickener. The flotation tailings thickener underflow is pumped to the combined CIL circuit. Thickener overflows from both thickeners report to the mill process water tank for reuse.

The flotation concentrate from the regrind circuit reports to a pre-leach tank. The slurry overflows from the pre-leach tank into a series of four CIL tanks providing a total of 48 hours of retention time.

The loaded carbon extracted from the first tank of the concentrate CIL tank is pumped to the carbon stripping circuit for carbon elution.

The flotation tailings, along with the previously leached flotation concentrate are fed to the combined CIL circuit consisting of five leach tanks providing an overall retention time of 24 hours. The combined leach circuit tailings report to the cyanide destruction circuit.

The carbon elution circuit has been sized for processing 4 t/d of carbon. The loaded carbon is pumped from the first flotation concentrate leach tank across a loaded carbon screen. The loaded carbon flows by gravity into the acid wash vessel where the loaded carbon is rinsed by a solution of hydrochloric acid followed by neutralization. The loaded carbon is transferred by a recessed impeller pump to the elution vessel. The stripped carbon is reactivated in an electric kiln and reused in the CIL circuit.

The carbon stripping circuit elutes the precious metals into the pregnant solution. The pregnant solution feeds the electrowinning circuit. Pregnant solution is pumped through the electrowinning circuit to produce sludge on the cathodes containing the precious metals. The cathodes are washed, dewatered and dried. The dried cathode sludge is melted in an electric induction furnace and poured into doré bars.

The combined leach circuit tailings report to the cyanide destruction circuit using the SO2/air process and copper sulphate solution. The treated tailings slurry is pumped to the tailings impoundment area for settling or to the paste fill plant and a portion of the reclaim water is sent back to the process plant as process water.