The Diablillos Project is a gold-silver mineralized material processing operation designed to treat up to 9,000 metric tons per day of oxide material from the Oculto and JAC deposits in Salta and Catamarca Provinces, Argentina, using a combination of gravity concentration, cyanidation, and the Merrill-Crowe process.
Report context
This process description is based on the NI 43-101 Technical Report for the Diablillos Project, which was carried over in its entirety from the previous Updated Pre-Feasibility Study effective December 3, 2024, with report date January 17, 2025, as incorporated in the Mineral Resource Estimate for the project.
Processing route
Comminution and crushing
The plant begins with a primary jaw crushing station operating in open circuit with an open side setting of 152 mm, producing a product with a nominal P80 of 150 mm and a top size of 254 mm. Material is reclaimed from an enclosed coarse ore stockpile with a live capacity of 13,000 metric tons and total capacity of approximately 52,000 metric tons, via two variable speed belt feeders, one operating and one standby. Pebble lime is metered onto the stockpile feed conveyor to maintain alkalinity in the grinding circuit.
Grinding circuit
Grinding is accomplished in a semi-autogenous grinding (SAG) mill followed by a ball mill, with SAG oversize pebble crushing. The SAG mill is 7.92 m in diameter with an effective grinding length of 3.66 m, equipped with a 4,500-kW variable speed drive. The ball mill is 5.49 m in diameter with an effective length of 8.53 m. The circuit is designed for a nominal rate of 391 metric tons per hour with a final grind size of P80 of 150 microns. The pebble screen aperture is 10 mm, with the pebble recycle rate typically 15% to 35% of SAG fresh feed rate.
Gravity concentration and intensive leaching
A portion of the cyclone underflow is treated by two gravity concentrators, with a mass pull of approximately 190 kg per hour. Gravity concentrate is treated in an intensive cyanidation reactor, with the pregnant solution reporting to the Merrill-Crowe pregnant solution tank. The intensive leach residue reports by gravity to the ball mill feed. Testwork indicates that 10.1% of gold and 7.8% of silver are recovered to gravity concentrate for Oculto material, and 17.3% of gold and 9.1% of silver for JAC material.
Tank leaching
Slurry from the pre-leach thickener is leached in a series of eight tanks (15 m diameter, 20 m height) at 36 hours total retention time, with pH controlled above 10.5 using lime. Sodium cyanide is dosed to maintain a free cyanide concentration of approximately 1.5 g/L, with concentration allowed to decay in the last two tanks. The expected gold recovery is approximately 83% and silver recovery approximately 80% based on laboratory testing.
Counter current decantation (CCD) circuit
The CCD circuit recovers dissolved gold and silver to the pregnant solution. For Oculto material, six stages of CCD thickeners are used; for JAC material, seven stages are required due to higher viscosity and solution flow. The CCD wash ratio is controlled at 3.0, with underflow density approximately 55% solids by weight. The first CCD thickener has a diameter of 32 m and the remaining units 30 m in diameter; for JAC material the first is 40 m and the rest 38 m. The reported recovery of gold and silver in solution to the pregnant solution is approximately 99.6%.
Merrill-Crowe circuit
The pregnant solution is clarified using diatomaceous earth, with a DE precoat of approximately 3 mm thickness and body feed at a target slurry density around 7% solids. Four DE clarifiers are installed, with three operating and one on standby. TSS levels are controlled to below 100 ppm in the pregnant solution, with the clarified solution typically below 1 ppm TSS.
The clarified solution passes through two deaeration towers (3.2 m diameter, 6.3 m height) to remove dissolved oxygen to below 0.5 ppm. Four cementation filter presses are included, with three operating and one standby, precoated with DE before each cycle. Zinc dust is added at the filter feed at a consumption rate of 1.5 kg per kg of gold and silver precipitated.
Foundry and mercury control
The precipitate is retorted to remove mercury and moisture, with mercury collected in flasks for shipment offsite. Dry precipitate is mixed with fluxes and smelted to produce doré bullion. A typical flux recipe for 100 kg of dry cake includes 3 to 5 kg soda ash, 5 to 10 kg borax, and 3 to 5 kg silica sand. Slag is crushed and recycled to the grinding circuit for reprocessing.
Cyanide destruction and tailings handling
Cyanide destruction uses the INCO process, with sodium metabisulfite and copper sulphate addition. The target is to reduce WAD cyanide to below 1 ppm in the final tailings. Detox residence time is one hour. Tailings are thickened to approximately 60% solids by weight for Oculto material, with a 40 m diameter tailings thickener used.
Key reported parameters
| Parameter | Unit | Oculto | JAC |
|---|---|---|---|
| Daily throughput | mtpd | 9,000 | 9,000 |
| Operating days per year | days/year | 350 | 350 |
| Annual throughput | mtpy | 3,150,000 | 3,150,000 |
| Head grade, Au | ppm | 0.88 | 0.13 |
| Head grade, Ag | ppm | 74 | 202 |
| Final grind size | microns | 150 | 150 |
| Leach retention time | hr | 36.0 | 36.0 |
| Leach pH | , | 10.5 | 10.5 |
| Gold recovery | % | 83.0 | 83.8 |
| Silver recovery | % | 79.8 | 84.9 |
| SAG mill power | kW | 4,500 | 4,500 |
| Ball mill size | m | 5.49 x 8.53 | 5.49 x 8.53 |
| Ball mill circulating load | % | 250 | 250 |
| Cyanide consumption, total | kg/mt | 0.83 | 1.79 |
| Lime consumption | kg/mt | 0.93 | 2.19 |
| Sodium metabisulfite dose | g/g WAD CN | 4.7 | 4.7 |
| Copper sulphate consumption | mtph | 0.02 | 0 |
| DE consumption | mt/day | 1.4 | 2.7 |
| Flocculant consumption | g/mt | 45 | 95 |
| Zinc dust consumption | kg/hr | 34 | 102 |
| Merrill-Crowe nominal solution flow | m³/hr | 1,125 | 1,273 |
| CCD wash ratio | , | 3.0 | 3.0 |
| CCD thickener underflow solids | % w/w | 55 | 50 |
| CCD stages | , | 6 | 7 |
| Tailings thickener underflow solids | % w/w | 60 | 55 |
| Total plant power requirement | MW | ~20 | ~20 |
| Raw water requirement | mtph | 184 | 184 |
Project website: https://www.abrasilver.com/projects/diablillos/
Technical qualifications
The process design is based on metallurgical testwork conducted on Oculto material in 2022 and JAC material in 2023. The JAC material, representing approximately 15% of the total resource, has a different metallurgical performance, requiring larger CCD thickeners, higher lime consumption, and increased DE consumption. Testwork on JAC material resulted in different head grades and recoveries, with the plant design accommodating both ore types through equipment sizing adjustments. The design criteria incorporate a design factor of 1.15 for equipment sizing and 1.25 for conveyors and pumps. The process design is based on the recommendation of 99.5% gold and 98.5% silver recovery through the Merrill-Crowe circuit as indicated by testwork.
Source: NI 43-101 Technical Report, Mineral Resource Estimate for the Diablillos Project, Salta & Catamarca Provinces, Argentina.
