Barry Open Pit Project — 2022 Technical Report

The 2022 technical report for the Barry Open Pit Project describes the existing 800 tpd Bonterra concentrator and a proposed expansion to 1,200 tpd feed for Barry mineralized material.

Report context

The Barry Open Pit Project processing information is documented in the NI 43-101 Technical Report dated July 25, 2022. The report presents recovery methods for the Bonterra concentrator (referred to as the Bachelor Plant), which is designed for an initial throughput of 800 tpd. An expansion to 1,200 tpd is planned to accommodate Barry mineralized material. The new flowsheet was developed to use existing equipment and existing building space as much as possible.

Processing route

Existing equipment and circuit (800 tpd)

The existing equipment can process up to 800 tpd of mineralized material and sometimes higher throughput with a softer feed. The crusher circuit consists of a mobile jaw crusher (50 hp) followed by a standard cone crusher operating in closed circuit with a double-deck screen. A second cone crusher crushes the screen oversize (+3/8 inch) while the undersize is conveyed to a bin.

Fine material is sent to a primary rod mill (400 hp) operating in open circuit. The secondary grinding stage comprises a tricone (535 hp) and two ball mills (150 hp and 100 hp) operating in closed circuit with a cyclone cluster of four 15-inch cyclones. When feed is from Barry, the tricone is used alone as the secondary mill because Barry material has a lower Bond work index. Cyanide is added to the grinding circuit to initiate gold leaching; hydrated lime is added to adjust pH. Cyclone overflow, the final grinding product, goes to a vibrating trash screen.

The slurry is thickened prior to leaching. Gold leaching occurs in four leach tanks (220 m³ each) in series, providing 18 hours of residence time at 800 tpd. Leached slurry moves to four carbon-in-pulp (CIP) tanks with a total capacity of 730 m³, allowing 17 hours of residence time. Slurry flows by gravity between tanks while carbon is transferred countercurrent. Gold-depleted tails pass through a carbon safety screen before being pumped to the tailings management facility (TMF).

Gold-loaded carbon goes to a loaded carbon screen. Gold is recovered in a 3-tonne pressure Zadra elution circuit followed by an electrowinning cell. Elution frequency is approximately once every three days. Gold is further refined and poured as doré bars.

Proposed flowsheet at increased throughput (1,200 tpd)

The existing flowsheet will be modified for 1,200 tpd production. The expansion mainly affects the secondary mill: a tricone will be added to the existing tricone so cyclone underflow is split equally between the two mills. The two smaller ball mills will be removed to install the larger tricone mill.

The report notes that the current plant can process 800 tpd of Barry material without any modifications. For 1,200 tpd, necessary modifications include: adding a second tricone of 535 hp in parallel with the current one; installing a high-capacity feedwell on the current thickener; adding a carbon screen and carbon transfer pump in the first leach tank; modifying or changing slurry pumps to match the new mass balance; and adding a new induction furnace for gold refining.

Crushing circuit

Existing crushing equipment comprises a jaw crusher (50 hp) in open circuit, followed by a standard head cone crusher (200 hp) and a short head cone crusher (200 hp) for secondary and tertiary crushing, both installed in closed circuit with a common double-deck screen. Feed rate is 100 tph. Operating time will be increased from 8 to 12 hours per day to reach 1,200 tpd.

Grinding circuit

The existing rod mill is capable of handling the targeted 1,200 tpd throughput. The secondary grinding stage currently has a single tricone with capacity for 800 tpd. The expansion adds one more tricone to reach 1,200 tpd; the two tricones (535 hp each) will operate in closed circuit with the four-cyclone cluster.

Pre-leach thickening

Cyclone overflow transfers to a trash screen before the carbon-in-leach (CIL) circuit. Slurry is then sent to the existing 40-foot conventional thickener to increase density prior to leaching. A high-rate feed-well will be retrofitted to this thickener to improve efficiency and guarantee expected performance at 1,200 tpd.

CIL, leach, and CIP

The thickened slurry goes to one existing tank (200 m³) where carbon transfer pumps and static screens will be added; this tank will be modified from a leach tank to CIL. The leaching circuit is composed of three mechanically agitated tanks (6.7 m each), providing eight hours of residence time.

Static screen design will be based on custom-made models already in use in other gold mills in CIP circuits. These screens do not require space above the tank for maintenance, unlike Kemix-type screens, which could not be installed without major building modifications due to insufficient clearance above the tanks.

The leached slurry is transferred to four CIP tanks in series. A carbon pump and static screen are installed in each tank; slurry flows by gravity between tanks. A safety screen collects carbon carried over at the CIP tailings to prevent loss to the TMF.

A total leaching time of 20 hours is recommended, including the CIP. This leach time is considered sufficient for Barry mineralized material.

Tailings

Tailings from the safety screen undersize are sampled in a new sampler and pumped to the TMF. Natural cyanide degradation will take place in the TMF.

Acid wash, elution, and carbon regeneration

The existing 3-ton capacity elution circuit is adequate for the CIP circuit even at 1,200 tpd. Elution will be performed at one cycle every two days. The expected loaded carbon grade is over 4,000 g/t. The carbon reactivation circuit is sized appropriately for increased throughput, and electrowinning capacity is considered appropriate. The qualified person recommends adding a new electric induction smelting furnace.

Reagents

Hydrated lime is currently added directly at the rod mill feed with a screw conveyor; a dissolution and distribution system is considered as a potential improvement. Sodium cyanide is delivered in 32% solution, transferred from tanker to a distribution tank. Flocculant is prepared manually; an automatic preparation system is necessary with the high-rate thickener, including a bulk bag hopper or hopper-fed manual system with 25 kg bags, a flocculant feeder, and an eductor. Caustic soda is received as 50% solution in totes, which is appropriate at higher throughput; a tank fed directly by tanker is planned to reduce operator handling.

Water and compressed air

The water distribution circuit will include a mill solution tank fed by thickener overflow and a portion of water reclaimed from the TMF. Mill solution water contains cyanide and is used in the grinding circuit to form slurry and adjust percent solids. The remainder of reclaimed water goes to a reclaim water tank, used as wash water on screens and transferred to the carbon water tank for carbon transfer during acid wash and elution. Mine water is collected in the mine water tank and used for reagent preparation and slurry pump gland sealing. Water system capacity is reviewed to meet higher throughput requirements. The existing air compressor will supply air to the new leach tanks.

Key reported parameters

Note: Source codes are A (criteria provided by owner), B (standard industry practice), C (Soutex recommendation), E (criteria from process calculations), and L (existing equipment specifications/process data). At initial throughput, total residence time includes 12.3 hours leaching, 4.1 hours CIL, and 12.8 hours CIP. At expansion throughput, residence times are 8.2 hours leaching, 2.7 hours CIL, and 8.5 hours CIP.

Technical qualifications

The report presents the 800 tpd configuration as existing equipment and historical operating capacity. The 1,200 tpd configuration is a proposed design for expansion, with design criteria from the sources indicated in the tables. Specific limitations and design bases noted in the report include:

• The expansion flowsheet was developed to use existing equipment and building space as much as possible.
• The rod mill is stated as capable of handling 1,200 tpd, but this is presented as a design assessment rather than demonstrated operating data.
• The total leaching time of 20 hours (including CIP) is described as “recommended” and considered sufficient for Barry material.
• Static screen design will be based on custom-made models already in use in other gold mills, rather than site operating data.
• Flocculant batch frequency is marked with source code G (assumed data).
• Ambient temperature, outdoor temperature, and relative humidity are owner-provided criteria.
• The existing crushing equipment is described with a daily 8-hour operating time for 800 tpd; reaching 1,200 tpd requires increasing to 12 operating hours per day, and crushing plant availability changes from 33% to 50%.
• The report states the current plant can process 800 tpd of Barry material without modifications, but the 1,200 tpd throughput requires specific modifications including additional grinding capacity, thickener feedwell retrofit, additional carbon handling equipment in the first leach tank, slurry pump changes, and a new induction furnace.
• The qualified person recommends the new electric induction smelting furnace; this is a recommendation rather than an installed item.
• Operating costs are presented for both throughput cases and are based on the process design criteria and flowsheet data in the report.

Source: Barry Open Pit Project, NI 43-101 Technical Report, July 25, 2022, Section 17.0 Recovery Methods.