Pre-Feasibility Study - Metallurgy & Processing

The process design for the Rupice and Veovaca project is based on the mine plan and corresponding feed grades, metallurgical test-work, and Ausenco’s in house database. The Rupice and Veovaca mineralisations are amenable to concentration through sequential flotation circuits producing saleable bulk (copper-lead), zinc, pyrite, and barite concentrates. The plant has been designed to accept a maximum throughput of 800 kt/y.

Process Overview

The main processing facility is located at the Veovaca site and receives ore from both the Rupice underground mine and Veovaca open pit. During underground operation, primary jaw crushing occurs at the Rupice site and the crushed ore is trucked to the Veovaca concentrator. For open pit operations, a contracted crusher will be used for the Veovaca site and ROM will be trucked there directly. Crushed ore is received and stored in two coarse ore bins prior to the Semi-Autogeneous Mill and Ball mill (SAB) grinding circuit, which consists of a Semi-Autogenous Grinding (SAG) mill, ball mill, and cyclone to grind and classify material to a P80 of 40 µm.

The cyclone overflow reports to the sequential flotation circuit, which consists of bulk (silver-lead) flotation and regrinding, zinc flotation and regrinding, pyrite flotation, and barite flotation. The process produces four saleable concentrates, (bulk, zinc, pyrite and barite), that are subsequently thickened, filtered, and placed in sealed shipping containers for transport.

Tailings from the facility reports to a tailings thickener and filter press where the material is dewatered to produce filtered tailings, and the resulting process water is recycled to the facility. This arrangement results in a high-water efficiency, minimising makeup water requirements. The filtered tailings are then trucked to the Rupice site for use as backfill in the underground mine or trucked and placed at the tailings storage facility located near the Veovaca concentrator.

Filtered tailings which report to the Rupice site are stockpiled next to the backfill plant. Waste rock from the underground mine is crushed and mixed with the tailings and cement binder in the backfill mixing system. The paste backfill is then pumped to the underground reticulation system.

Process Design Criteria

The key process design criteria for the mineral processing facilities are listed in Table 15.

Layout Overview

The Rupice site is a greenfield location and consists of several terraces accommodating the portal access to the twin declines, the primary jaw crusher, and stockpiles required for management of ore and waste rock. The aggregate crushing plant, paste backfill plant and the associated stockpiles and ancillary facilities are located near the underground portal at the site.

The Veovaca site is a brownfield site currently home to an abandoned process facility. Existing buildings and equipment will be demolished as necessary to accommodate the revised site layout. Notably, the existing tailings thickener is to be re-used as the process water tank in the design. The tailings storage facility is proximal and southeast of the concentrator.

Process Description

Primary Crushing

Run-of-mine (ROM) material will be received at a ROM bin at the Rupice site. The ROM bin will be equipped with a static grizzly with an aperture size of 600mm to prevent oversize material from entering the crushing circuit. The material will be then fed into the primary crusher by means of a vibratory feeder.

The primary crusher will be a single-toggle jaw type and will be designed to reduce the feed size from 80% passing 317mm to 76mm. The crushed material will be then transported via the haulage decline from the underground mine to a radial stacker on surface. The radial stacker distributes the material between stockpiles corresponding to waste rock and ore of various grades.

Ore will be reclaimed from the stockpiles at the Rupice site by a front-end loader and loaded into haul trucks. The trucks then transport the material approximately 30 km to the Veovaca concentrator. Waste material will be reclaimed and either transported by truck to the Veovaca tailings facility or loaded directly into the aggregate crushing circuit feeding the paste backfill plant.

Paste Backfill Plant and Aggregate Crushing

Aggregate Crushing

The aggregate crushing plant will consist of a single stage cone crushing system designed reduce the crushed waste rock size from 80% passing 76mm to 100% passing 12mm.

A front-end loader will reclaim waste rock from the waste rock stockpile into a 40m3 feed hopper. The material will be deposited onto an inclined crusher feed conveyor by means of a vibrating feeder. The conveyor transports the material to the cone crusher, where it will be crushed and subsequently conveyed to a vibrating screen. Screen undersize will be directed to the -12mm aggregate stockpile, while the oversize will be recirculated to the feed hopper.

Paste Backfill Plant

The paste backfill plant combines concentrator tailings, crushed aggregate, and cement to produce a product suitable for deposition as backfill. The backfill composition varies over the life of mine, but on average contains 35% aggregate, 6.6% binder, and 58% concentrator tailings on a dry weight basis. The materials are combined in a continuous mixer and subsequently pumped to the underground reticulation system.

Tailings will be trucked from the Veovaca concentrator site and stockpiled next to the paste backfill plant. A front-end loader reclaims the tailings to a hopper, where a belt feeder meters the material at a fixed mass flowrate on to a common inclined mixer feed conveyor.

Waste rock from the underground mine will be crushed to -12mm to produce an aggregate material suitable for backfill production. The stockpiled aggregate will be reclaimed by a front-end loader into a hopper, where a belt feeder meters the material at a fixed mass flowrate on to the mixer feed conveyor.

Binder will be trucked to site and stored in a silo integral to the backfill plant facility. The binder will be then fed to the mixer at a fixed mass flowrate. Water will also be added to the mixer to control the solids density at a nominal value of 78% w/w. The design water consumption for the backfill and aggregate crushing plant is 5.6 l/s.

The mixed backfill reports to a pump box where a swing-tube backfill distribution pump will direct material to the underground reticulation system. There will be provision for the backfill material to be sent to a bunker in the event of a process or downstream upset.

Coarse Ore Handling

Crushed ore will be trucked from the Rupice site to the concentrator at the Veovaca site and end-dumped into a coarse ore hopper with a capacity of 50t. The coarse ore will be transported by a belt conveyor to a reversible conveyor, where it can be discharged into two coarse ore bins. Each bin provides a live residence time of 23 hours and a corresponding capacity of 2260t of ore on a wet basis. Ore will be reclaimed from the bins by belt feeders and discharged to the SAG mill feed conveyor. The SAG mill feed conveyor weightometer will be used to control the throughput of ore into the mill.

In the event of a process upset, the material can be stockpiled at a nearby coarse ore storage pad with 48 hours of storage capacity and reclaimed with a front-end loader.

Grinding

The grinding circuit consists of a SAG mill, ball mill and cyclones. The grinding circuit will be designed to reduce ore from an 80% passing size of 76mm to 40µm.

The SAG mill will be a single pinion low aspect mill, operating in a closed circuit. The mill has an inside diameter of 3.8m and an effective grinding length (EGL) of 5.0m. The mill receives coarse ore and process water at a variable flowrate to achieve the correct pulp density. Lime and zinc sulphate are also dosed to the SAG mill to condition the feed prior to flotation. The SAG mill will be charged with high chrome grinding media at a diameter of 125mm by means of the grinding building hoist and ball kibble.

The discharge of the SAG mill will be received at a cyclone feed hopper and pumped to the cyclones. The cyclone will be designed to achieve an overflow density of 35% at a product size of 40µm. the overflow reports to the bulk rougher flotation cells and the underflow reports to the ball mill. The cyclone operates at a nominal recirculating load of 250%.

The ball mill will be a single pinion overflow mill, operating in closed circuit with the mill cyclones. The mill has a diameter of 3.8m and an EGL of 6.6m. The mill will be charged with high chrome grinding media at a diameter of 40mm by means of the grinding building hoist and a ball kibble. The discharge reports to the cyclone feed hopper, where it combines with the SAG mill discharge and will be pumped to the mill cyclones.

Flotation

The flotation circuit at the Veovaca concentrator consists of a bulk flotation circuit, zinc flotation circuit, pyrite flotation circuit, and barite flotation circuit. Each circuit will be discussed in the following subsections.

Bulk Flotation

The purpose of the bulk flotation stage will be to recover a lead/copper concentrate. The mill cyclone overflow reports to a horizontal vibrating trash screen to remove any oversize particles or material prior to flotation. The screen undersize then reports to a conditioning tank where lime, sodium metabisulphite (SMBS), promotor, and frother are added. The resulting slurry will be then pumped to bulk rougher flotation at a nominal density of 40% w/w and pH 9.

Bulk Rougher Flotation

The bulk rougher flotation cells are conventional forced air tank cells. The concentrate of the bulk rougher flotation tank reports to a primary cleaner, while the tailings report to the bulk rougher scavenger cells. The scavenger concentrate reports to the bulk regrind surge tank, while the tailings report to the zinc flotation circuit.

The primary cleaner will be a Jameson cell, and process water will be added to modify the slurry density to 25% w/w. The concentrate reports to the bulk concentrate thickener, while the tailings report to the bulk regrind surge tank. Jameson flotation cells are not mechanically agitated but rely on induced aeration and mixing.

Bulk Regrind Circuit

The regrind circuit consists of a cyclone cluster and stirred horizontal regrind mill operating in open circuit. Slurry from the surge tank will be pumped to the cyclones targeting an overflow product size of 10µm. The cyclone overflow reports to the bulk cleaner circuit, while the underflow flows by gravity to the regrind mill. The regrind mill uses a ceramic media with a 2-3mm diameter. The mill discharge reports to the bulk cleaner circuit.

Bulk Cleaner Flotation

The bulk cleaner circuit consists of three sequential stages of cleaning. In the first stage will be dosed with zinc sulphate, lime, SMBS, promotor and frother to promote concentrate recovery. The flotation concentrates flow from the first stage through to the third and concentrate from the third stage reports to the bulk concentrate thickener. The tailings flow counter-current to the concentrate, and tailings from the first stage reports to the zinc flotation circuit.

Zinc Flotation

The purpose of the zinc flotation circuit will be to recover a zinc concentrate. Tailings from the bulk flotation circuit reports to a condition tank prior to the zinc circuit, where copper sulphate, lime, collector, and frother are added. The conditioned slurry will be then pumped to the zinc rougher cells. The zinc flotation circuit follows the same arrangement as the bulk circuit, described as follows.

Zinc Rougher Flotation

The zinc rougher flotation cells are conventional forced air tank cells. The concentrate of the zinc rougher flotation tank reports to a primary cleaner, while the tailings report to the zinc rougher scavenger cells. The scavenger concentrate reports to the zinc regrind surge tank, while the tailings report to the pyrite flotation circuit.

The primary cleaner will be a Jameson cell, and process water will be added to modify the slurry density to 23% w/w. The concentrate reports to the zinc concentrate thickener, while the tailings report to the zinc regrind surge tank.

Zinc Regrind Circuit

The regrind circuit consists of a cyclone cluster and stirred horizontal regrind mill operating in open circuit. Slurry from the surge tank will be pumped to the cyclones targeting an overflow product size of 10µm. The cyclone overflow reports to the zinc cleaner circuit, while the underflow flows by gravity to the regrind mill. The regrind mill uses a ceramic media with a 2-3mm diameter. The mill discharge reports to the zinc cleaner circuit.

Zinc Cleaner Flotation

The zinc cleaner circuit consists of three sequential stages of cleaning. In the first stage will be dosed with zinc sulphate, lime, SMBS, promotor and frother to promote concentrate recovery. The flotation concentrates flow from the first stage through to the third and concentrate from the third stage reports to the zinc concentrate thickener. The tailings flow counter-current to the concentrate, and tailings from the first stage reports to the pyrite flotation circuit.

Pyrite Flotation

The purpose of the pyrite flotation circuit will be to recover pyrite prior to the barite flotation circuit. The zinc flotation tailings report to a conditioning tank, where sulphuric acid, copper sulphate, collector, and frother are added. The slurry will be then pumped to the pyrite rougher flotation cells.

Pyrite Rougher Flotation

The pyrite rougher flotation cells are conventional forced air tank cells. The concentrate of the pyrite rougher flotation tank reports to a primary cleaner, while the tailings report to the barite flotation circuit.

Pyrite Cleaner Flotation

The primary cleaner will be a Jameson cell, and process water will be added to modify the slurry density to 23% w/w. Additional sulphuric acid and collector are also dosed at this stage. The concentrate reports to pyrite thickening and loadout, while the tailings report to the cleaner scavenger flotation cells.

The cleaner scavenger concentrate reports to the barite flotation circuit, while the tailings are re-circulated back to the primary cleaner.

Barite Flotation

The purpose of the barite flotation circuit will be to recover a barite concentrate. The pyrite flotation tailings report to two conditioning tanks in series, where lime, sodium silicate, promotor, and frother are added. The resulting slurry will be then pumped to the barite rougher cells.

Barite Rougher Flotation

The barite rougher flotation cells are conventional forced air tank cells. The concentrate of the barite rougher flotation tank reports to the cleaner circuit, while the tailings report to the tailings thickener.

Barite Cleaner Flotation

Concentrate from the rougher cells reports to the 5 stages of cleaning. The concentrate from each stage flows from stage one to 5, where it reports to the barite thickener. The tailings flow counter current to the concentrate, and the tailings from the first stage of cleaning reports to the tailings thickener. In each stage, lime will be added to maintain a pH of 9.5. Additional sodium silicate and promotor will be added to the first three stages of cleaning.

Concentrate Handling

The concentrate handling circuit consists of thickening and filtration equipment required to dewater the bulk, zinc, pyrite, and barite concentrate prior to loadout and shipment.

Each concentrate stream reports to a dedicated high rate thickener, where flocculant will be added to assist in the settling of the solids. The thickener overflows report to the process water thickener, while the underflows report to dedicated filter feed tanks which have a residence time of 12 hours.

The bulk and zinc thickener underflows report to a common concentrate filter at nominally 65% solids. The filter will be a horizontal plate type membrane filter press, and discharges filter cake at a target moisture content of 6 and 9% for the bulk and zinc concentrates respectively. The filter washing cycle will be sufficient to prevent contamination of the concentrates when switching between the two feeds. The filter discharges to two indoor stockpiles, one for zinc concentrate and one for the bulk concentrate each with a 12-hour storage capacity.

The barite thickener underflow reports to a barite concentrate filter at nominally 58% solids, which will be a horizontal plate type membrane filter press. Filter cake will be discharged at a target moisture content of 6%, which reports to an indoor barite concentrate stockpile with a 12-hour storage capacity.

The concentrates are reclaimed from the stockpiles by a front-end loader and placed into shipping containers. The containers are stacked by a forklift outdoors, and subsequently loaded onto trucks for shipment. The yard has sufficient storage space for 4 days of production of each concentrate.

Tailings Handling

Tailings from the flotation circuits reports to a tailings thickener, where flocculant will be added to promote settling of the solid particles. The overflow reports to the process water thickener, while the underflow reports to a filter feed tank at 65-70% solids. The filter feed tank has a residence time of 12 hours and feeds a vertical plate and frame membrane filter press. The press produces a filtered tailings product at 9.5% solids and discharges it to a covered stockpile which has a 12 hours residence time. The tailings are recovered by a front-end loader and transported by haul truck back to the Rupice site for use as backfill. Alternatively, the tailings are deposited at the tailings storage facility.

Reagents Handling and Storage

Reagents are received onsite at dedicated storage areas prior to mixing and dosage to the process. The reagents used in the nominated flowsheet are as follows:

• Lime
• SMBS
• Zinc Sulphate
• Sodium Silicate
• Copper Sulphate
• Sulphuric Acid
• Aerophine 3418A
• Xanthate
• Aero 845
• MIBC
• Flocculant

Plant Services

Services at the Veovaca concentrator include process water, raw water, fire water, potable water, gland water, and low and high pressure air services,

The existing 50m diameter tailings thickener will be used to store process water.

Process Recommendations

It is recommended to complete further test work programs to optimize and confirm the flowsheet to treat Rupice and Veovaca mineralised material as follows:

• Complete further geometallurgical test work to improve the ore characterization of the resource and when combined with the spatial modelling, the resulting block model and mine schedule will provide the optimal ore feed schedule to the processing plant;
• Optimize metal recovery and concentrate grade to further improve the project economics, particularly silver in the concentrates;
• Further assess the implementation of preconcentration technologies to potentially reduce the plant capital and operating costs, such as heavy media separation and XRT ore sorting;
• Identify alternate techno-economical opportunities to lower penalty elements from the concentrates; and
• Further investigate economic alternatives for upgrading the barite concentrate to produce a range of products.