AbraSilver Resource Corp.'s Diablillos project in Argentina is designed as a 9,000 tpd silver-gold operation using a conventional cyanidation flowsheet with gravity concentration, tank leaching, CCD washing, and Merrill-Crowe recovery.
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The Diablillos Ag-Au Project is a feasibility-stage silver and gold project owned by AbraSilver Resource Corp., located in Argentina. The NI 43-101 technical report, with an effective date of June 19, 2026, describes a conventional open-pit mining operation with an optimized production sequence targeting high-grade silver and gold mineralization in the early years of the mine plan. The project is designed as a 9,000 tonnes per day (tpd) processing operation with feed grades ranging from 0.18 to 2.46 g/t gold and 22 to 235 g/t silver.
Critical Data
| Parameter | Value | Unit | Notes |
|---|---|---|---|
| Nameplate Capacity | 9,000 | tpd | Design value |
| Crushing Plant Availability | 75 | % | Design value |
| Process Plant Availability | 92 | % | Design value |
| Grinding Circuit Feed Size, 80% Passing | 160 | mm | Design value |
| Grinding Circuit Product Size, 80% Passing | 150 | µm | Design value |
| Leach Circuit Design Retention Time | 36 | hours | Design value |
| Leach Feed Design Density | 45 | % w/w | Design value |
| Leach Dissolved Oxygen, Typical | 10-12 | ppm O₂ | Test result range |
| Leach pH Target | 10.5 | – | Design value |
| Leach Design Sodium Cyanide Addition | 1.3 | kg/t feed | Design value |
| CCD Wash Water Ratio | 3.0 | – | Design value |
| Cyanide Destruction Retention Time | 2 | hours | Design value |
| Final Tailings Thickener Underflow Density | 55 | % w/w | Design value |
| LOM Silver Recovery | 80 | % | Average |
| LOM Gold Recovery | 87 | % | Average |
| Total Power Requirement | 22 | MW | Maximum demand |
| Raw Water Well Field Distance | 13 | km | From mine site |
Overview
The recovery methods section describes the design basis for the crushing and processing facilities at Diablillos. Flowsheet development and design criteria came from an interpretation of metallurgical testwork results completed by different laboratories between 1996 and 2025, with all results up to April 2026 considered in this feasibility study. A geo-metallurgical model segregates the deposit into five distinct domains.
Size reduction technology selection was guided by comprehensive crushing and grindability tests conducted across the entire deposit. Additional criteria included electrical power consumption, wear and spare parts usage, fine dust generation, and maintenance requirements. The chosen configuration consists of a primary jaw crusher followed by a semi-autogenous grinding (SAG) mill and a ball mill operating in closed circuit with hydrocyclone-based size classification.
A conventional flowsheet for silver and gold extraction was developed that uses gravity concentration and intensive leach, cyanide-based lixiviation, zinc cementation or electrodeposition, and smelting. A portion of the cyclone cluster underflow will be treated using gravity concentration followed by intensive leaching, which will target liberated gold and silver particles.
Tank leaching was chosen to facilitate contact of the cyclone cluster overflow with sodium cyanide, which selectively dissolves silver and gold. Sodium cyanide operates efficiently under adequate pH and temperature conditions. The process requires a minimum retention time achieved using agitated tanks that enhance reaction kinetics. pH levels will be regulated by the controlled addition of lime slurry. Continuous aeration using oxygen sparged in the tanks will ensure sufficient dissolved oxygen despite the site altitude.
Reagent and water consumption, as well as metal losses in the tailings, will be minimized through a multi-stage counter-current decantation (CCD) washing process. Each CCD stage will involve flocculant addition to improve sedimentation rates. Zinc cementation using the Merrill-Crowe process was selected for recovery of precious metals from cyanide complexes due to its suitability for ores with high silver to gold grade ratios and its capability to produce a high-quality precipitate suitable for smelting in induction furnaces.
The final product will be doré bars produced by casting in induction furnaces. Slag generated during smelting will contain measurable quantities of fine precious metals, so after granulation it will be recycled to the milling circuit for reprocessing.
Following leaching and washing, the leached slurry will undergo cyanide destruction to eliminate reactive cyanide species, including free cyanide and WAD cyanide, using the INCO/SO₂ process. The tailings will be discharged to a fully lined, multi-phase cross valley dam designed to promote separation of solid and liquid phases through natural sedimentation. Supernatant water will be pumped back to the plant, though make-up water will be required to compensate for evaporation and water retained in final tailings moisture.
Key Process Stages
Primary crushing begins with ore transported from the mine by haul trucks and dumped directly into the jaw crusher dump hopper. The hopper, with 280 tonnes of live capacity, includes a stationary grizzly to screen oversized material, which is broken down by a hydraulic rock breaker. Oversized ore exceeding 115 mm goes to the vibrating grizzly, while undersized ore bypasses to the transfer conveyor. The jaw crusher operates with a closed side setting of 150 mm, producing a product with a P80 of 160 mm and a top size of 318 mm. A trash magnet removes tramp metal before material reaches the crushed ore stockpile feed conveyor. The crushing circuit uses a dust collection system with multiple extraction hoods, ducting, and a centralized baghouse.
The crushed ore stockpile will be covered to mitigate dust propagation. Live capacity is 9,800 tonnes dry, providing 24 hours of plant feed, with total capacity of 45,370 tonnes dry. Ore will be reclaimed by two variable-speed apron feeders, each capable of handling full plant throughput for redundancy, and transferred to the SAG mill feed conveyor.
The grinding circuit feeds material from the COS to the SAG mill with the feed rate regulated by a control loop between the belt scale and reclaim apron feeders. A lime silo meters quicklime onto the conveyor to maintain an alkaline environment for pH control. Dilution water achieves a slurry density of 70% solids. The SAG mill measures 7.9 m diameter by 3.7 m effective grinding length, powered by a 5,000 kW variable speed drive, operating with a ball charge of 11 to 17% by volume. SAG mill discharge passes through a dual-deck vibrating screen that removes worn steel balls and pebbles. Screen undersize flows to the cyclone feed pumpbox where process water reduces slurry density to 55% solids.
Cyclone underflow returns to the ball mill at a circulating load of 250%, with a 50% portion diverted to the gravity concentration circuit for coarse gold recovery. The ball mill measures 5.5 m diameter by 7.9 m EGL, powered by a 5,000 kW drive, operating at 73% critical speed with up to 37% ball charge. The cyclone overflow is the final grinding product at a P80 of 150 µm, sampled for metallurgical control and monitored by an online particle size analyzer. Lead nitrate solution is introduced into the ball mill to improve leaching efficiency by modifying sulphide mineral behaviour.
The gravity concentration and intensive cyanidation circuit treats half of the cyclone underflow. Slurry is fed to scalping screens to remove particles greater than 2 mm before returning to the ball mill. Screen undersize feeds two parallel centrifugal concentrators in a semi-batch operation. Gravity concentrate is collected in a storage cone before being leached by the intensive cyanidation reactor circuit. Gravity tailings are directed back to the ball mill.
The intensive leach reactor (ILR) leach solution, a mixture of NaCN, NaOH, and an oxidant, is made up within the heated reactor vessel feed tank and circulated through the reaction vessel. Leached residue is washed and the solid gravity leach tailings are pumped back to the ball mill. ILR pregnant solution is treated in the gold room for gold recovery as gold sludge using a dedicated electrowinning cell. The gravity concentration and intensive leach area will be isolated and monitored for security purposes.
Pre-leach thickening begins with cyclone overflow passing through a trash screen and flowing via gravity to a 35 m pre-leach thickener. Thickener overflow reports to the process water tank, while underflow at 55% w/w solids is pumped to the leach tanks where slurry density is adjusted to 45% w/w solids with barren leach solution. Flocculant is added to improve settling, and antiscalant is dosed into the overflow to prevent scale formation.
Tank leaching uses eight atmospheric leach tanks arranged in a cascading configuration for cyanidation, providing a 36-hour residence time. Each tank measures 15 m in diameter and 19.6 m in height, equipped with mechanical agitators and oxygen injection systems via jet spargers to maintain dissolved oxygen at approximately 20 ppm, with a typical range of 10 to 12 ppm. Milk of lime is dosed into Tanks 1 and 2 to maintain pH between 10.5 and 11.0 to prevent hydrogen cyanide gas formation. Sodium cyanide solution is metered into the first three tanks to maintain a free cyanide concentration of approximately 1.5 g/L. Lead nitrate solution is added to enhance leaching efficiency as required.
The counter-current decantation circuit consists of six high-rate thickeners, each 35 m in diameter, with flocculant addition. The leached slurry enters CCD Thickener No. 1 via gravity where it mixes with overflow from the subsequent thickener. Underflow is concentrated to 50% wt solids and pumped to the next stage where it is washed with solution recovered from the following thickener. The wash ratio is typically controlled at 3.0. Final underflow from CCD Thickener No. 6 is pumped to cyanide destruction, while overflow from Thickener No. 1 flows to the PLS clarifier. The PLS clarifier minimizes total suspended solids in the pregnant solution, reducing diatomaceous earth consumption.
The Merrill-Crowe circuit includes four DE-coated clarifier filters, two deaeration towers, and four zinc cementation precipitate filter presses. Pregnant leach solution is stored in a PLS tank measuring 11.5 m diameter by 16.3 m height, providing a one-hour buffer capacity. The target TSS in feed solution is below 100 ppm. Each DE clarifier filter operates in cycles lasting 12 to 47 hours depending on TSS load. Clarified solution contains less than 1 ppm TSS and flows through two deaeration towers operating in parallel under vacuum to reduce dissolved oxygen to below 0.5 ppm. Zinc dust is introduced at the suction of the precipitate filter feed pumps via a water-covered zinc feed cone to prevent oxygen entrainment. Four plate-and-frame precipitate filter presses operate with three in parallel and one on standby. Typical operating cycles range from 3 to 7 days depending on DE precoat quality, zinc dust stoichiometric ratio, PLS grades, and precipitate filterability.
The refinery receives PLS from the ILR circuit directed to a single electrowinning cell equipped with stainless steel mesh cathodes. Gold is electrochemically deposited onto cathode surfaces. Gold-bearing sludge is removed using high-pressure water sprays and dewatered in a plate-and-frame filter press. The filter cake is combined with the Merrill-Crowe precipitate and transferred to the retort circuit. Mercury is removed in a retort furnace under vacuum, achieving approximately 99% mercury recovery. After retorting, material is blended with fluxes and smelted in an induction furnace to produce doré bullion and slag. Off-gases from retorting and smelting are treated in a gas scrubbing system with dust collection.
Cyanide destruction and tailings thickening direct the washed slurry from CCD Thickener No. 6, containing approximately 50% w/w solids, to two agitated cyanide destruction tanks arranged in parallel. These tanks provide a combined retention time of 2 hours. Cyanide destruction uses the SO₂/Oxygen method with sodium metabisulphite, lime, and copper sulphate dosed into the tanks while oxygen is sparged. A 31 m diameter tailings thickener produces an underflow with 55% w/w solids, with overflow routed to the process water tank for reuse.
Raw water for the process plant comes from wells drilled in approved basins, pumped via eight raw water well pumps located approximately 13 km from the mine site. The raw water storage tank stores sufficient water for 24 hours of process plant operation. A reverse osmosis water treatment plant supplies treated water to a tank with 24 hours of storage plus a fire water reserve of 1,760 m³. The process water tank receives overflow from the pre-leach thickener and tailings thickener as well as reclaim water from the TSF. Potable water treatment uses three modular units incorporating filtration, RO, chlorination, and UV disinfection with a 72-hour residence time. Gland seal water uses treated water with a two-hour residence time. Barren solution is recycled back into the process for applications including wash liquor, flocculant dilution, and leach tank dilution.
Power will be supplied to the plant main substation from an onsite power plant within permitted project boundaries. The onsite power plant may be a hybrid facility consisting of diesel generator sets with an n+2 configuration. Electrical power will be distributed at 6.6 kV to all process and ancillary facilities via overground cable trays. Site distribution steps down to 400/230 V to supply motor control centres and low voltage switchgear. In-line samplers will be installed at key stages including post-grinding, leaching circuit tails, and cyanide destruction inlet and outlet. Six wire samplers will monitor pregnant and barren solutions throughout the Merrill-Crowe plant and electrowinning circuit.
Additional Interesting Data and Summary
The SAG mill uses a variable speed drive, which allows operational flexibility in response to ore hardness variations. The grinding circuit includes space for a future pebble crusher circuit, and the final two leach tanks are depicted in a different colour in the process model to denote a future expansion with provisions incorporated into the plant layout. The cyanide destruction tanks can also be operated in a series configuration, which is expected to be required during processing of Oculto ore.
Oxygen generation uses Vacuum Pressure Swing Adsorption technology selected due to the remote location and logistical constraints associated with liquid oxygen transport and storage. The system supplies approximately 1,950 Nm³/h of gaseous oxygen at 92% purity. Raw water has a natural pH of 5.6 and is strongly corrosive because it is undersaturated in calcium carbonate, so a corrosion inhibitor and antifouling agent is recommended based on a study performed by SNF Water Science in 2025.
Onsite reagent storage includes at least one week of quicklime, crushed quicklime, sodium hydroxide, diatomaceous earth, zinc dust, flocculant, SMBS, copper sulphate, lead nitrate, and antiscalant. Sodium cyanide storage accommodates one month of supply. Milk of lime is prepared at 15% solids with approximately one day of retention capacity. Diatomaceous earth precoat slurry density is controlled to 2% solids, while body feed slurry density is 7% solids. Flux composition for smelting includes 30% silica, 40% borax, 10% nitre, and 20% soda ash.
Key Processes
- Primary jaw crushing with grizzly screening and hydraulic rock breaker
- Semi-autogenous grinding with variable speed drive and dual-deck vibrating screen
- Ball mill grinding in closed circuit with hydrocyclone classification at 250% circulating load
- Gravity concentration using centrifugal concentrators treating 50% of cyclone underflow
- Intensive cyanidation of gravity concentrate in heated reactor with electrowinning recovery
- Pre-leach thickening with flocculant addition and antiscalant dosing
- Atmospheric tank leaching in eight cascading tanks with oxygen sparging
- Six-stage counter-current decantation washing with flocculant addition
- Merrill-Crowe zinc cementation with DE clarification, vacuum deaeration, and filter pressing
- Retorting for mercury removal followed by induction furnace smelting to doré bars
- Cyanide destruction using the SO₂/Oxygen method with sodium metabisulphite and copper sulphate catalyst
- Tailings thickening to 55% w/w solids with supernatant water recovery and reuse
- Reverse osmosis water treatment with treated water distribution for fire suppression and process use
- Onsite diesel genset power generation with n+2 configuration at 6.6 kV distribution
Source: NI 43-101 Technical Report, Feasibility Study for the Diablillos Ag-Au Project, July 20, 2026. Project website: Diablillos Ag-Au Project
