The Troilus deposit is better known as an example of an Archean porphyry-type deposit as interpreted in the pioneering work of Fraser (1993). It is frequently cited as such, for example, Robert and Poulsen, 1997; Poulsen, 2000; Sinclair, 2007; Mercier-Langevin et al., 2012; Katz, 2016. Other interpretations for its genesis include superimposed structurally controlled “orogenic” gold, proposed by Carles (2000) and Goodman et al., (2005).

The Troilus deposit is located in the northeastern region of the Frotêt-Troilus domain, and is hosted by volcanic and hypabyssal intrusive rocks of the Troilus Group in a region of intense deformation, known as the Parker domain (Gosselin, 1996). It is located within the overturned northern limb of the Troilus isoclinal syncline, which was transposed by a series of northeast- southwest striking thrust fault zones, parallel to the main regional foliation and to the volcanic bedding.

Four main lithological units are recognized in the Troilus deposit region, broadly divided in: (i) mafic to felsic volcanic sequence; (ii) diorite and brecciated diorite; (iii) cross-cutting felsic dikes, and (iv) mafic to ultramafic intrusive. A series of distinct younger, post-deformation granitic intrusions crosscut all other lithotypes.

Troilus is primarily an Au-Cu deposit, but contains minor amounts of Ag, Zn and Pb, as well as traces of Bi, Te, and Mo. Gold-copper mineralization at the Troilus deposit comprises two distinct styles, disseminated and vein-hosted. Gold mineralization is spatially correlated with the presence of sulphides, even though the sulphide content does not directly correlate with gold and copper grade.

The matrix of the diorite breccia, the diorite and the felsic dikes represent the main host rocks for the mineralized intervals.

Disseminated Mineralization
Disseminated mineralization comprises the majority of the deposit’s copper content (>90%, Goodman et al., 2005), particularly in the Z87. Gold and copper are predominantly associated with fine grained disseminated sulfides and/or millimetre wide sulfide streaks and stringers parallel to the main foliation, comprising between 1 wt. % and 5 wt. % of the rock. The most abundant sulfides are pyrite, chalcopyrite, and pyrrhotite.

Gold occurs as fine grains of electrum, up to 20 µm wide along sulfide grain boundaries, and filling fractures within sulfide grains, containing up to 15 wt. % Ag (Goodman et al., 2005). At Z87, the mineralization is developed within an amphibolitic unit and the brecciated unit, located between the two thickest felsic dikes (Goodman et al., 2005), and it is coincident with a zone of strong biotitic alteration.

Vein-hosted Mineralization
This mineralization style is characterized by gold bearing veins, with gold mineralization restricted to the veins and veinlets, and is classified as gold-only, since copper mineralization is rare and erratic (Carles, 2000). This type of mineralization is reported to be hosted in all rock types occurring within the mineralized envelope in the Troilus deposit.

Several generations of gold-bearing veins have been identified and described by Goodman et al. (2005), and Larouche (2005), the latter especially focused on J4 zone. With regards to grade and abundance, the most significant are quartz-chlorite (±tourmaline) veins. These veins occur in silicified wall rocks to sericitized high strain zones which cut the main foliation and the margins of felsic dikes. Gold-bearing millimetre- to centimetre wide veinlets are locally present as swarms parallel or subparallel to spaced cleavage in the silicified rocks. The veinlets contain free gold and minor amounts of sulphide. Much of the gold is fine grained and contains up to 20% Ag, however, gold grains can be up to greater than 1,000 µm in size. Locally, a second set of gold bearing quartz veinlets cut the first. These carry fine grained gold (>95%) and minor pyrite, chalcopyrite, sphalerite, galena, and Te- and Bibearing minerals, including tellurobismuthite (Bi2Te3), calaverite (AuTe2), and hessite (Ag2Te). Although volumetrically much less significant than the main disseminated mineralization, the veinlets can contain grades greater than 50 g/t Au over a one metre interval. Coarse grained gold recovered by a gravity circuit in the mill accounted for about 30% of the gold produced. Presumably much of this coarse gold was derived from the veins. High grade shoots related to the veinlet zones are oriented 40° clockwise from the main disseminated mineralization.

There are four main deposits that make up the Troilus Gold Project: Zone 87, Zone 87 South, J Zone and SW Zone.

Zone 87
The main pit of the Troilus Mine, operated by Inmet from 1996 to 2010, was developed in the Z87 orebody. The mineralization in the Z87 occurs as a series of anastomosing lenses, extending for approximately 1,300 m along strike from 12,900N to 14,200N with variable thickness and locally reaching over 100 m wide. With increasing depth, individual mineralized lenses coalesce to form a single sheet-like body that was approximately 40 m thick on average (Fraser, 1993).

The long axis in the Z87 is oriented N35°E with the orebody dipping to 55° to 65° northwest, from southwest- to northeastern portions, respectively. Detailed studies of Z87 blasthole data and diamond drill intersections revealed the presence of higher-grade shoots, which plunge to the west-northwest at -30° to -50°. The north and south extensions of Z87 “horsetail” out into narrower branches of mineralization. Two branches are well defined in the north, whereas three branches are less defined to the south.

Zone 87 South
Z87S is located directly southwest of the main former open pit mine, Z87. The two zones are separated by a felsic dyke and a zone of intense deformation dipping at 45° to 55° northwest. Z87S itself dips of ~50° northwest. This angle suggests Z87 and Z87S may merge at approximately 450 m below surface. The presence of a gold rich interval below Z87 in borehole TLG-Z8718-002 is probably the expression of Z87S at depth.

J4/J5 Zone
The J Zone orebody hosts two mineral zones: J4 and J5. J4 is the smaller of the two formerly mined open pits along with the main Z87 zone. The ore bodies in the J4 zone are hosted in the northern continuity of the Troilus Diorite and, similarly to what is observed in the main zones Z87 and Z87S, are elongated parallel to a penetrative northeast trending foliation, moderately to steeply dipping to the north west.

Compared to Z87, the J4 Zone has a lower copper grade, more free gold, and dips more steeply at -65°. J4 extends for approximately 1,200 m from 14,100N to 15,300N and is approximately 200 m wide from 9,500E and 9,700E. Individual mineralized shoots plunge steeper to the north. The north half of J4, from approximately 14,600N, contains one main corridor of mineralization, which is 20 m to 50 m in horizontal width.

Southwest Zone (SW Zone)
The SW Zone is situated approximately 3 km southwest of the Z87 Zone. The current interpretation, based on recent drilling, is that the SW Zone appears to be the nose of a synclinal fold with a gentle plunge to the northwest.

Open Pit Mining
The PEA is based on the reactivation and expansion of the 87 and J Zone pits and the addition of a new area, the SW Zone. These pits provide the open pit feed material necessary to maintain the process plant feed rate at 35,000 t/d while operational.

The 87 pit is a single phase which provides 36.6 Mt of mill feed grading 0.72 gpt gold, 0.088% copper and 1.4 gpt silver for a gold equivalent grade of 0.85 gpt. Waste from this pit totals 149.4 Mt for a strip ratio of 4.1 (waste:mill feed). The 87 pit forms the top of the underground development.

The J zone pit has three phases. The phases total 94.8 Mt of mill feed grading 0.51 gpt gold, 0.06% copper, and 0.89 gpt silver for a gold equivalent grade of 0.60 gpt. Waste from the phases totaled 348.7 Mt for a strip ratio of 3.7:1 (waste:mill feed).

The new SW Zone pit is mined in two phases. They will produce 18.8 Mt of mill feed grading 0.64 gpt gold, 0.065% copper and 0.76 gpt silver for a gold equivalent grade of 0.74 gpt. The waste amounts to 93 Mt giving a strip ratio of 5.0:1 (waste:mill feed).

The phases are scheduled to provide 35,000 t/d of feed to the mill over a 14 year open pit mining life after one year of pre-production stripping. As the underground mine production comes online in Year 8 the open pit production drops to a level sufficient to keep the process plant at full capacity. The pits are sequenced to minimize initial stripping and provide higher feed grades in the early years of the mine life. This is accomplished with stockpiling of lower grade material which is used later in the mine life.

Initial mining starts in the 87 pit and the SW pit. These provide the highest grade to the mill early in the schedule. The 87 pit needs to be complete for the underground mine to produce material. The 87 pit finishes in Year 6. The other advantage of finishing the 87 pit early is that this can then be used for waste storage of material from the J pit.

The pits are built on 10 metre benches with safety berm placement each 20 metres. Inter-ramp angles vary from 47 to 53 degrees depending upon the wall orientation. Minimum mining widths of 60 metres were maintained in the design. Ramps are at maximum 10% gradient and vary in width from 25.5 m (single lane width) to 33.2 m (double lane width). They have been designed for 181 t haulage trucks.

The mine equipment fleet is anticipated to be financed to lower capital requirements. The fleet will be comprised of nine 200mm down the hole drills, two 22 m3 hydraulic shovels and two 23 m3 front end loaders. The truck fleet will total 28 trucks from Year 1 onwards. This is due to the long hauls from the SW pit, the tailings buttress buildup and the initial higher strip ratio reactivating the 87 and J pits. The usual assortment of dozers, graders, small backhoes, and other support equipment is considered in the equipment costing. A smaller front end loader (13m3) will be stationed at the primary crusher.

Underground Mining
The development of the underground mine will commence once open pit production is established. Underground production will be mined concurrently with lower grade open pit material, thereby enhancing mill grade.

The planned underground mining area is an extension of the Z87 deposit previously mined by open pit at Troilus. The depth of the existing open pit is now planned to be extended by open pit methods by around 50 m, to approximately 350 m below surface. The currently identified Measured, Indicated and Inferred Resources for the underground area extend to around 900 m below surface and measure a maximum of approximately 850 m along strike. The dip of the deposit varies from around 600 to around 400 , averaging 550 in the north and central areas with the flatter dip to the south. An optimised in situ cut off grade of 0.8 equivalent g/t Au was calculated. Higher grade mineralized areas bifurcate in certain areas, but low grade intervening mineralization that allows for the mining of the full section from footwall to hangingwall at satisfactory grades was included in the study plans. Stopes vary in thickness up to 80 m true thickness with the thickness generally reducing with depth.

Trade off studies were undertaken that identified Slot and Mass Blast (S&MB) as the preferred mining method and Rail-Veyor as the preferred materials handling system.

S&MB will be the primary underground mining method used to exploit the Z87 deposit below the open pit floor and will provide 89% of the life of mine underground feed to the mill. The remaining 11% of underground mill feed will be mined using the sub level caving (SLC) method, which is located in the upper portion of the underground mining area, between the deepened open pit and the upper-most level of slot and mass blast stopes. Both of the selected mining methods - as well as the development and operation of the Rail-Veyor materials handling system - operate in a ‘top- down’ fashion, thus minimising and deferring the mine development necessary to place the mine in operation and sustain production over the life of mine. Initial production will be by SLC followed by S&MB.

Life of mine feed to the process plant is estimated to be 42.3Mt with an equivalent gold grade of 1.35 g/t at a steady-state production rate of 9,000 tpd.

Primary Crushing
Run of mine material will be discharged directly into the primary gyratory crusher by 181 tonne capacity haul trucks at a rate of approximately eleven trucks per hour. Peak delivery rate is assumed to be 2,200 dmtph. The crusher is serviced by a hydraulic rock breaker to handle oversize rocks.

The gyratory crusher can handle rocks with a top size of 800mm and will run with a 170mm open side setting. An apron feeder is used to withdraw crushed mill feed from the surge pocket beneath the crusher onto a short sacrificial conveyor. This conveyor discharges onto the main stockpile feed conveyor. The P100 size exiting the gyratory crusher is estimated to be 375mm.

Stockpile
The crushed mill feed stockpile provides a live capacity equivalent to roughly 18 hours of plant production, equivalent to 28,471 t live capacity. Mill feed is withdrawn from the stockpile via two lines of three pan feeders. Four pan feeders will operate simultaneously at a peak capacity of 490 dt/h each, with two pan feeders on standby. Alternating feeder use during normal operation is expected to assist with mill feed size distribution control. Each feeder discharges via a lined discharge chute onto the SAG mill feed conveyor via individual dead-boxes.

SAG Mill
From the stockpile discharge feeder, mill feed is withdrawn in measured quantities onto the mill feed conveyor. This conveyor discharges via the head chute into the SAG mill feed hopper.

A single 10.4 m diameter x 4.9 m long, twin pinion, semi-autogenous grinding mill equipped with twin 4.5MW variable speed motors is operated in open circuit with a trommel screen on the mill discharge. Slurry exits the mill after passing through the mill discharge grate onto a trommel screen fixed to the mill discharge trunnion. Trommel oversize material is returned to the mill by an integral bucket wheel and rock-box arrangement, with a high-pressure water cannon used to wash material back into the grinding chamber. Trommel screen undersize material gravitates as a slurry to the common mill discharge pump box, from where it is pumped to the ball mill cyclones.

SAG mill slurry spillage is collected in a drive-in sump, and then returned to process by a submersible slurry pump.

The milling area (SAG and ball) is served by a common overhead crane. Relining is achieved using the common relining machine.

SAG mill grinding media is stored in a ball bunker. The bunker is served with a small spillage pump and a ball loading crane and magnet. Balls are added to mill feed at timed intervals via a ball loading chute.

Ball Mill
After SAG milling, the particle size is further reduced to a P80 of 75 µm by conventional, closed circuit ball milling in two parallel 7.9 m diameter x 10.4 m long overflow discharge ball mills. Each mill is equipped with two 5.6MW motors (i.e.: 11.2MW per mill).

The SAG mill trommelscreen undersize is gravity fed to a common ball mill discharge sump, whereupon it is combined with dilution water and ball mill discharge before being pumped to the cyclone classification cluster. The cluster consist of eight cyclones (six operating, two standby).

Cyclone underflow gravitates to a splitter that directs a portion of the stream to a pair of XD70 Knelson concentrators running in parallel. Gravity concentrate is collected and pumped to the high security gold area. Gravity tails discharge by gravity to the feed chute of the ball mill. The cyclone overflow reports to a trash screen for removal of woodchips and other tramp material prior to flotation. The screened cyclone overflow stream gravitates to the flotation circuit via an automatic cross launder sampler. The stream of woodchips and tramp plastic from the linear screen is dewatered by a woodchip sieve bend before being dumped in a storage area. Spillage contained in the ball mill area is pumped to the common mill discharge sump for re-treatment.

Ball mill grinding media is delivered to the plant in bulk and is stored in the ball mill ball bunker. The ball bunker is serviced by a crawl and electric hoist arrangement, allowing balls to be lifted into a kibble using the ball loading magnet, and tipped into the mill via a ball loading chute.

The Troilus process plant has been designed for a throughput of 35,000 dry mtpd. The flowsheet is comprised of the following steps:
• run of mine (ROM) material is dumped directly into the gyratory crusher via 181 tonne
capacity haul truck
• crushed ore is stockpiled (18-hour live storage capacity) and two lines of three pan
feeders discharge onto the SAG mill feed conveyor
• open circuit SAG milling, with provision for future installation of a pebble crusher to crush
SAG trommel oversize material (if required)
• ball mill in closed circuit with hydrocyclones and gravity concentration via Knelson
concentrator on the cyclone underflow
• copper-gold rougher and scavenger flotation
• regrinding of the rougher and scavenger concentrate with gravity concentration via Falcon
on the regrind cyclone underflow
• copper-gold cleaner flotation, via two stages of conventional cleaning and a third stage of
cleaning via column flotatio ........