Overview

Deposit type

• Breccia pipe / Stockwork
• Vein / narrow vein
• Epithermal

Summary:

The Premier property is mainly underlain by Jurassic-aged Hazelton Group rocks composed of a thick package of homogeneous andesitic tuffs, lapilli tuffs, and flows interpreted to have formed in an Island Arc setting. Dykes and sills of Premier porphyry (a quartz-K-spar-hornblende porphyry of intermediate composition) are the most abundant intrusive rocks in the area, and are spatially associated with some mineralized zones, particularly at Premier.

Gold–silver mineralization is hosted within structural zones expressed by quartz breccias, quartz veins and stockwork often within large areas of quartz-sericite-pyrite alteration. Elevated gold and silver values are closely associated with silicification and sericitic alteration. Gold occurs predominantly as electrum, with native gold present locally. Silver occurs in its native form, and in electrum, argentite, and freibergite.

The most common sulfides are pyrite, sphalerite with minor galena, and chalcopyrite. The mineral assemblage suggests that the style of mineralization at Premier falls into the intermediate sulfidation epithermal category as neither high sulfidation minerals (such as covellite or enargite) nor low-sulfidation minerals (such as arsenopyrite and pyrrhotite) have been observed.

Mineral deposits in the PGP are intermediate-sulfidation epithermal gold-silver deposits with subsidiary base metals. These deposits form at comparatively shallow depths (generally above 1 km depth), often in association with hot-spring activity on surface. Mineralization results from circulation of aqueous solutions driven by remnant heat from intrusive bodies. Where these ascending fluids encounter meteoric waters, and/or as the hydrostatic pressure drops, changes in temperature and chemistry results in precipitation of minerals into fractures, breccias, and open spaces.

Mineralized bodies are structurally controlled veins, stockworks, and breccia bodies, and are broadly tabular with a wide range of orientations. They measure from centimetre scale to many metres in thickness and can often be traced for strike lengths of several hundred metres or even kilometres. Economic minerals comprise native gold and native silver, electrum, silver sulfosalts, and silver sulfides, along with pyrite, sphalerite, and comparatively minor amounts of chalcopyrite and galena. Gold and silver values are quite variable, and average on the order of 5 g/t to 10 g/t Au and 20 g/t to 30 g/t Ag within the historical stopes.

The geology of the Red Mountain area is characterized by Upper Triassic to Lower Jurassic metasedimentary and tuffitic units that have been intruded by a multi-phase intermediate intrusive complex. The intrusive rocks show porphyry style alteration with K-spar alteration and tourmaline as well as lower temperature quartz-sericite-pyrite alteration. Gold mineralization is hosted in a series of pyrite rich breccia bodies and stockwork zones associated with the brecciated contact zone at the edge of the intrusive body. The alteration associated with the high grade-gold mineralization is characterized by sericite and silicification.

Eocene intrusions of the Coast Plutonic Complex occur to the west and south of Red Mountain and are associated with high-grade silver-lead-zinc occurrences; gold-silver-bismuth ± copper-lead-zinc mineralization recently identified in the Lost Valley area is likely of Eocene age. Recent interpretation is that the gold mineralization at Red Mountain is consistent with an intrusive-related hydrothermal system, rather than a porphyry-gold deposit according to previous interpretation.

Mining Methods

• Transverse stoping
• Longitudinal retreat
• Longhole stoping
• Room-and-pillar
• Cut & Fill

Summary:

Mining methods described herein will be applied at both PGP and RMP. In the case of RMP, the orebody is continuous and sufficiently wide to use a transverse longhole stoping method; whereas at PGP, the ore is along more discrete lenses and tend be narrow, requiring a narrow longitudinal retreat approach to longhole mining. These can be single or multiple sub-levels mined in a block.

The project employed mining methods appropriate to the local conditions at each site, where variations in geotechnical character, grade, ore thickness and ore geometry and inclination were all considered in stope optimization. The target was to develop a coordinated plan to supply 2,500 t/d to the Premier mill, optimizing the production of gold ounces at the lowest operational cost.

The Study’s mine plan generally utilizes a combination of three mining methods: longhole (64%), inclined undercut longhole (14%), and room and pillar (12%), with minor amounts of cut and fill (2%) and development ore (8%) to extract the mineral reserves. A particular mining method was chosen based on an economic assessment of each method for a given geometry and geotechnical characteristics depending on its location in the deposit. The stope shapes and mine access development were individually modelled and evaluated to form the final mineable reserve.

Mining dilution occurs at various rates depending on the mining method and ground conditions based on rock quality in geotechnical domains in the block model. Dilution comes in from a number of sources: planned dilution is material taken within the bounds of a stope layout while unplanned material comes from material outside the stope shape such as the hanging wall and footwall, or minor amounts from backfill.

Dilution generally ranges from 10% to 40%. In some cases where two wireframes are very close together, the waste parting between the wireframes was taken providing it was economically justified. Table 1-4 summarizes the annual production from all areas.

A conventional and common mobile mining fleet is shared between the two sites, to reduce spares and capital expense. Development headings and stope accesses used a common approach with key equipment used during preproduction and operations consisting of 2B jumbos, 10-tonne LHDs, 30-tonne mine haul trucks, bolters, shotcreters and production longhole drills.

Mine services such as dewatering, ventilation and electrical reticulation employed a common approach at each site in a similar manner to mobile equipment to standardize pumps, fans and MCC’s reducing the required spares and capital expenditure. Underground water handling at both sites employs a conventional series of sumps and pumps to move the water out to settling ponds on surface. At PGP water from Silver Coin and Big Missouri have a common pond, which is then directed by pipeline to the water treatment plant at the historical 6 level at Premier mine.

The ventilation systems were designed to meet BC regulations based on the requirements of engines sizes and utilization. Fresh air is heated by a propane system when required during winter months. Workforce will consist of technical staff and operations personnel, consisting of miners, mechanics, electricians, and supervision. At peak production the mine department will have 110 people, with about 40 people active at the site at a given time. In some instances, shared technical resources will be based in Stewart supporting both sites.

Personnel will live in the town of Stewart which is an easy drive from both PGP and RMP. Buses will bring staff and operating people to site, in order to limit the number of personal vehicles on the surrounding roads. Some staff and supervision required to move among sites will drive company supplied pickup trucks.

The principle method of backfilling at PGP and RMP will be with CRF comprised of waste development rock or quarried talus from surface. RF will be used to fill ore voids wherever structural fill is not required.

Comminution

Crushers and Mills

Summary:

Crushing
The crushing facility will consist of a single stage of crushing that will process the ROM ore at a nominal processing rate of 208 t/h and it is expected that the crushing plant will be operated over a 12-hour shift to meet the 2,500 t/d production requirement. The major equipment and facilities at the ROM receiving and crushing areas include:
• Re-furbished static ROM bin grizzly;
• Lined ROM surge bin;
• Reciprocating plate feeder;
• Re-furbished double-toggle primary jaw crusher;
• Mobile rock breaker (FEL attachment);
• Covered coarse ore stockpile;
• Two new stockpile-reclaim apron feeders;
• A single re-furbished re-entry vibrating pan feeder.

Grinding
The grinding mills originally installed in the PGP mill building were purchased and removed by other parties in the early part of the 1990s, yet the existing pedestals and pump boxes remain and are in good condition. To suit this arrangement, the new grinding circuit will consist of a new SAG mill (in open circuit) and a new ball mill (SAB) in a closed circuit with new classifying cyclones.

Both mills will share a variable frequency drive (VFD) controller that can be used to start each mill. The VFD will also be used to adjust the SAG Mill speed to meet the optimum power draw and achieve the preferred grinding conditions for each of the different ores.

The SAG and ball milling (SAB) circuit is designed to deliver a product size P80 of 80 µm for PGP ores and between 80 µm and 90 µm for Red Mountain ores which are more competent. The nominal grinding circuit circulating load ratio for the ball milling circuit is 300%. When the Red Mountain ores are introduced in Q4 Year 2, the ore will be further ground in a fine grinding circuit, which consists of a high speed stirred fine grinding mill to reduce the product to a P80 of 25 µm.

For the initial period of processing PGP ores, the major equipment in the grinding circuit will include:
• One 6.7 m ft diameter by 2.4 m effective grinding length (EGL) single pinion SAG Mill driven by a single 2000 kW low speed synchronous motor;
• One 4.4 m diameter by 6.1 m EGL single pinion ball mill driven by a single 2000 kW low-speed synchronous motor;
• One cyclone cluster consisting of three 380 mm diameter cyclones (2 operating, 1 standby).

Following the introduction of the Red Mountain ore in Q4 Year 2, the following additional processing equipment will be installed and commissioned:
• A single-stirred fine-grinding mill in open circuit to reduce the P80 of Red Mountain ore to 25 µm, driven by a 3,000-kW variable speed drive;
• A 27m diameter high rate pre-leach thickener.

Ore addition to the SAG and Ball mills is supplemented with process water to achieve a milling density of approximately 75% and 64% solids weight by weight (w/w) respectively. The SAG mill discharge will flow through a trommel screen and will discharge into the ball mill cyclone feed pump box where it will be diluted with additional process water and pumped by one of the two cyclone feed pumps up to the cyclone distribution manifold. Steel grinding media will be manually added to the SAG and ball mills using a kibble, which will be positioned by the refurbished bridge crane servicing the mill building.

Processing

• Gravity separation
• Centrifugal concentrator
• Inline Leach Reactor (ILR)
• Agitated tank (VAT) leaching
• Carbon in leach (CIL)
• Elution
• Solvent Extraction & Electrowinning
• Cyanide (reagent)

Summary:

The Premier mill facility plans for re-starting will feature a combination of upgrades and returning the existing facilities to an operating condition. The development work assessed the current condition of the equipment and structures, allowing the engineering team to develop a capital cost for the restart of the facilities using a combination of the existing, refurbished existing, and new equipment for each of the following areas:
• Crushing and stockpiling;
• Grinding and classification;
• Gravity concentration and intensive leaching;
• CIL management;
• Gold room;
• Detoxification and tailings deposition.

The existing plant arrangement is suited to a SAB milling flowsheet followed by CIL, which is retained to treat the 2,500 t/d throughput. Over the LOM, the plant will operate 365 d/a to produce gold doré with an overall plant availability of 92%. Up to Q4 of Year 2 the process plant will be exclusively processing ore from the Silver Coin and Big Missouri underground deposits from the Premier lease. Ore will be processed in this order, which aligns with the current published mine plan.

Within two years from start-up, Red Mountain ore from the neighbouring JW, Marc, and AV deposits will be milled through the existing Premier mill facility. The Red Mountain ore types have differing properties from those of Premier, and as a result, specific circuit modifications are required to the plant design, most notably the addition of a fine-grinding circuit and pre-leach thickening stage.

In Q4 of Year 2 of the mine plan, it is expected that the mill will be fed from either one of the Premier deposits or from the Red Mountain mine by campaigning the ore on a two-week basis (two weeks of processing Premier ore followed by two weeks of processing Red Mountain ore).

Ore processing at the Premier mill begins with primary crushing and stockpiling, followed by SAB milling to achieve a grind size P80 of 80 µm (90 µm for Red Mountain ores). An integrated gravity circuit will remove coarse gold for cyanidation in the intensive leach reactor (ILR), with the remainder of the ore to be cyanide leached in a conventional CIL circuit.

Gold will be recovered on carbon, eluted, and then electrowon to produce a silver/gold doré. Gold recovered from the ILR will be electrowon separately to produce a separate gold doré. Leached tails will be detoxified in an SO2/Air cyanide destruction circuit, then thickened using a tailings thickener, which will then be pumped to a TSF approximately 1 to 2 km from the plant.

Fresh water required for reagent mixing, gland water, and process water make-up are pumped to the plant from Cascade Creek, while process water is recovered from the TSF decant water and returned to the plant, which will be used for services such as grinding and utility water.

The Premier mill processing circuit will be modified in a Year 2 to process ores from Red Mountain. Gravity-recoverable gold is absent in the Red Mountain ore; therefore, the gravity circuit will be bypassed while processing this ore. The Red Mountain ore gold and silver recovery is sensitive to grind size, and as such a target of 25 µm is required to achieve acceptable precious metals recoveries in the leaching circuit.

To achieve the targeted fine grind, a fine-grind mill (high-speed stirred mill) will be installed in the plant. The grinding circuit product will require a thickening stage prior to introduction to the CIL circuit. Based on current and historical testwork, a 27 m pre-leach thickener will be required for this application.

Production

Operational metrics

Personnel

Job Title	Name	Profile	Ref. Date
Consultant - Infrastructure	Frank Grills		Apr 15, 2020
Consultant - Mining & Costs	Frank Palkovits		Apr 15, 2020
Consultant - Recovery Methods & Costs	Aleksandar Petrovic		Apr 15, 2020
Mill Manager	Paul Laframboise		Dec 19, 2023
Operations Superintendent	Gerry Gagnon		Dec 19, 2023
VP Operations & General Manager	Bryant Schwengler		Dec 19, 2023
VP, Project Development	Matthew Kebe		Dec 19, 2023