Vareš Project — 2025 Technical Report

This technical report describes the feasibility-stage design for a sequential flotation processing plant treating ore from the Rupice underground mine to produce silver-lead and zinc concentrates.

Report context

The Vareš Project 2025 Technical Report (dated 9 June 2025) presents a feasibility study design for mineral processing facilities based on ore from the Rupice underground mine. The process design is supported by testwork conducted by Wardell-Armstrong International, Metso-Outotec, and Ausenco’s database of reference projects together with in-house modelling programs. The report also references historical operating data from commissioning and ramp-up phases.

Processing route

Site arrangement

The Rupice site is a greenfield location with three differently graded stockpiles from the underground mine. Waste rock is processed through the same crushing plant to produce aggregate for paste backfill operations. Crushed ore and aggregate material are trucked to the Vareš Processing Plant and backfill paste plant respectively, connected by a haul road.

The Vareš Processing Plant occupies a brownfield site where existing infrastructure was either demolished or repurposed. The historical tailings thickener was re-used as the process water tank in the design.

Crushing circuit

Run-of-mine material is deposited at one of three stockpiles. A front-end loader reclaims ore according to a blending regime and deposits it into an 85 t blend ore bin equipped with a 600 mm static grizzly. A vibrating grizzly feeder feeds material to a single-toggle jaw crusher that reduces feed from 80% passing 427 mm to 150 mm. Undersize from the grizzly feeder combines with crusher discharge to lower the 80th percentile to 121 mm.

The ore then reports to a secondary cone crusher operating in open circuit, reducing 80% passing size from 121 mm to 51 mm. Discharge is conveyed to a triple deck sizing screen. Oversize reports to a tertiary cone crusher in closed circuit, reducing from 80% passing 50 mm to 12 mm. Final crushed ore product achieves 80% passing 7.12 mm.

The same crushing plant produces paste aggregate fill (PAF) and cemented aggregate fill (CAF) when fed with waste rock. For PAF production, the circuit operates identically with a diverter gate directing undersize to a dedicated PAF stockpile at 100% passing 12 mm. For CAF production, the tertiary crusher closed loop is bypassed, producing 100% passing 75 mm product.

Crushed ore handling

Crushed ore passing -12 mm is trucked to the Vareš plant and end-dumped into a 45 t loading hopper. A belt feeder and conveyor transport ore at design capacity 300 t/h to a diverter gate serving two coarse ore bins, each providing 23 hours live residence time (2,260 t wet basis each). Ore is reclaimed by belt feeders to the ball mill feed conveyor at design capacity 110 t/h, with weightometer control for throughput. A nearby coarse ore storage pad provides 12 hours surge capacity for process upsets.

Grinding circuit

The grinding circuit comprises a ball mill and cyclones, designed to reduce ore from 80% passing 7.12 mm to 40 μm. The ball mill is a single pinion overflow mill with inside diameter 4.3 m and effective grinding length 7.5 m, operating in closed circuit. Lime, zinc sulphate, and sodium metabisulphite are dosed to the mill to condition feed prior to flotation. Mill discharge passes over a slotted trommel screen with aperture 10 mm x 25 mm. High chrome grinding media of 25 to 40 mm diameter is charged via the grinding building hoist and ball kibble.

Flotation circuit

The flotation circuit consists of silver-lead flotation and zinc flotation circuits in sequence.

Silver-lead flotation: Mill cyclone overflow reports to a horizontal vibrating trash screen for oversize removal. Screen undersize flows to a conditioning tank where collector is added, then by gravity to bulk rougher flotation at nominal density 40% w/w and pH 8. The design takes advantage of lime, SMBS and zinc sulphate already added in the ball mill to condition pH, removing the need for a second conditioning tank.

Rougher flotation cells are conventional forced air tank cells. Rougher concentrate reports to a regrind surge tank. The regrind circuit comprises a cyclone cluster and stirred horizontal regrind mill in open circuit, targeting cyclone overflow product size 10 μm. Regrind mill uses ceramic media of 2 to 3 mm diameter.

The cleaner circuit consists of three sequential cleaning stages. First stage receives collector and frother. Concentrate from the third stage reports to the silver-lead concentrate thickener. First cleaner tailings report to the zinc cleaner flotation circuit, bypassing zinc rougher flotation.

Zinc flotation: Tailings from silver-lead flotation report to conditioning tanks where lime, copper sulphate and collector are added. Conditioned slurry is pumped to zinc rougher cells at nominal density 40% w/w and pH 9. Rougher cells are conventional forced air tank cells. Rougher concentrate reports to the zinc regrind surge tank. Rougher scavenger cells process rougher tailings, with scavenger concentrate also reporting to the regrind surge tank and scavenger tailings reporting to final tailings thickener.

The zinc regrind circuit follows the same arrangement as silver-lead regrind, targeting cyclone overflow product size 20 μm. Three sequential cleaner stages follow, with concentrate from the third stage reporting to the zinc concentrate thickener and first stage tailings reporting to the final tailings thickener.

Concentrate handling

Each concentrate stream reports to a dedicated high-rate thickener with flocculant addition. Thickener overflows report to the process water thickener. Underflows report to dedicated filter feed tanks with 12 hours residence time at nominally 65% solids. Vertical tower filter presses discharge filter cake at target moisture content 8.1% for silver-lead concentrate and 9.4% for zinc concentrate. Filter cake discharges to two indoor stockpiles with 12-hour storage capacity each. Concentrates are reclaimed by front-end loader to a hopper and conveyor system for container loading. The yard has space for four days production of each concentrate.

Tailings handling

Tailings from flotation report to a tailings thickener with flocculant addition. Overflow reports to the process water thickener. Underflow reports to a filter feed tank at 65% solids with 12 hours residence time. A horizontal plate and frame membrane filter press produces filtered tailings at target moisture content 9.3%, discharging to a covered stockpile. Tailings are recovered by front-end loader and transported by haul truck back to the Rupice site for use as backfill, or deposited at the tailings storage facility.

Reagents handling and storage

Lime (quicklime) is received by bulk road tanker and pneumatically transferred to a silo with seven-day storage capacity. Limeslurry is prepared at 20% w/w solids and stored with 12 hours residence time, circulated in a ring main at nominally five times demand flow.

Sodium metabisulphite and zinc sulphate heptahydrate are received as dry powder in 25 kg bags and mixed to 20% and 15% w/w solutions respectively with 6 hours residence time. Copper sulphate pentahydrate is received as dry powder in 25 kg bags and mixed to 15% w/w solution.

Aerophine 3418A is received in liquid form in 1.4 tonne IBC containers with 24 hours storage. Sodium isopropil xanthate is received as dry pellets in 150 kg drums and mixed to 10% w/w solution with 24 hours residence time. MIBC frother is received in liquid form in IBC containers with 24 hours storage.

Flocculant is received as dry powder in 25 kg bags, stored in a hopper with five day residence time, and mixed to 0.25% w/v solution with 12 hours storage.

Post commissioning modifications

Following commissioning, ADT committed to adding a further flotation stage in each cleaner circuit using Jameson (pneumatic) flotation cells as first cleaning stages producing final grade concentrate. At the time of the QP site visit, cells had been installed and pumping and piping was being installed.

The plant has not achieved design production rate; anecdotal evidence suggests operation at no greater than 70% of design. Lack of available feed ore has been a significant contributor. The tailings filter is understood to represent an impediment to achieving capacity. ADT implemented a modification adding additional plates to the existing filter, and DPM is committed to installing a duplicate tailings filter.

Key reported parameters

Technical qualifications

The report includes the following specific limitations noted by the qualified person:

• Available historical production data shows the plant has not achieved its design production rate of approximately 200 kt per quarter. Monthly reports do not show operating hours, so it has not been possible to assess whether the plant has been achieving design instantaneous capacity when running. Lack of available ore is understood to have resulted in significant shortfall in operating time.

• Metallurgical performance results for silver (grade and recovery) are in line with or slightly ahead of expected performance based on regression equations from testwork. Results for lead and zinc (grade and recovery) have fallen short of expected performance.

• The plant appears to have been built in accord with the design described in the DFS report, which was soundly based on testwork. However, only a very limited amount of testwork was undertaken on thickening and filtration for both concentrate and tailings.

• The tailings filter is understood to be undersized as built.

• The mine production rate in DPM’s life-of-mine plan is 850 ktpa, exceeding the plant design capacity of 800 ktpa. The QP notes it seems reasonable to expect that a plant with design capacity of 800 ktpa should be capable of processing 850 ktpa, though the operation is still in its ramp-up phase.

Source: Vareš Project , 2025 Technical Report, 9 June 2025, Item 17 Recovery Methods.