The Lindero Mine processes gold ore through a multi-stage crushing, agglomeration, heap leach, SART, ADR, and smelting circuit to produce doré bars and a copper-silver precipitate.
Report context
This technical report for the Lindero Mine, owned by Fortuna Silver Mines Inc., is dated December 31, 2022. The report covers the Lindero Mine and Arizaro Project located in Salta, Argentina. Commissioning of processing facilities began in 2020, with first ore loaded onto the leach pad in July 2020 and first doré poured in July 2020.
Processing route
Crushing plant
Run-of-mine ore is received from the open pit in 96-tonne haul trucks and dumped into a 200-tonne capacity ROM hopper. The crushing plant comprises three stages with a target final product P80 of minus 6–8 mm. The primary stage uses a 1,500 mm × 1,300 mm jaw crusher operating in open circuit, fed via a 1.2 m × 7.9 m apron feeder and 150 mm-opening vibrating grizzly. The secondary stage operates three parallel 300 kW cone crushers in close circuit with 1.8 m × 6.1 m double deck vibrating screens. The tertiary stage uses a single Weir-KHD Model RPS 16-170/180 HPGR with 1.7 m diameter by 1.8 m wide rolls operating in open circuit with recirculation of edge material (approximately 25 percent of total product). A Gundlach continuous tooth roll crusher with 25 mm gap breaks flakes generated by the HPGR, with a fixed scalping screen diverting non-flaked material around the crusher. The qualified person observed that the crushing plant had received multiple improvements to supporting structures and that additional work is necessary to ensure medium- and long-term mechanical availability.
Agglomeration plant and stacking system
Crushed ore is mixed with cement (Cemento Filler CPF40 per Argentinian standards) at rates from 0.25 to 6.5 kg/t, along with concentrated cyanide solution and barren solution, in two parallel 3.66 × 12 m variable speed agglomeration drums. The agglomerated ore is transferred via fixed conveyors, mobile grasshoppers (30 m length), a jump conveyor, and a radial stacker with an extendable stinger (maximum 2 m additional reach) to the leach pad. The radial stacker rotates approximately 170 degrees and progressively moves in reverse to form cells of typically 60 × 60 × 10 m height. The stacking plan was reviewed for Phase 2 of the leach pad expansion, considering changing stacking direction from east to west versus the current north-south sequence to reduce shutdowns, reduce the number of grasshoppers, increase flexibility, and maintain expansion capability. At the time of the qualified person site visit, the radial stacking equipment was being repaired and leach cells were being loaded using a front-end loader.
Leaching and solutions handling
The permanent multi-lift leach pad was designed for approximately 93 million tonnes of ore at an average bulk density of 1.60 t/m³, covering approximately 106 hectares of lined surface. The original design considers two phases, with Phase 1 accounting for 44 percent of total base area and Phase 2 scheduled to begin construction in 2024. The leach pad base uses low permeability soil (natural soil mixed with bentonite) and geosynthetic clay liner overlain by 1.5 mm LLDPE single-side textured geomembrane liner.
Cells are irrigated for a total of 75 days. The leaching cycle begins with four days of curing time. Irrigation first applies intermediate leach solution at 12 l/m²/h (43.2 m³/h per cell of 3,600 m²) for 30 days, producing PLS that is diverted to the PLS pond. For the following 45 days, the cell is irrigated with barren solution at 9 l/m²/h (32.4 m³/h), producing ILS that is diverted to the ILS pond.
The process pond system includes four active ponds separated by berms, plus a fifth storm water pond. Combined process pond capacity is 50,000 m³, with the storm water pond also at 50,000 m³, sufficient to contain a 100-year, 24-hour rainfall event of 56.1 mm. Ponds are constructed with GCL on compacted soil, a secondary 1.5 mm HDPE liner, a geonet, and a 1.5 mm HDPE primary liner.
SART plant
Construction of the SART plant was completed in June 2021. PLS at a design flow rate of 400 m³/h is fed to the SART. Sulfuric acid is injected to lower pH to approximately 5.0, and sodium hydro-sulfide is added to precipitate copper sulfide solids as synthetic chalcocite (Cu₂S) along with silver sulfide solids (Ag₂S). Copper sulfide solids are thickened and filtered, bagged in 1.0 tonne supersacks, and sold. Overflow from the copper sulfide thickener is adjusted to pH 10.5 using lime slurry; gypsum solids are removed, thickened, filtered, and permanently disposed of on site. The thickener overflow, low in copper and high in free cyanide, flows to the SART pond before being pumped to the ADR plant. During the initial leaching period before the SART operated, copper concentration in PLS reached 700 ppm; after commissioning, copper reduced to approximately 500 ppm by end of 2021 and stabilized at around 300 ppm by end of 2022.
ADR plant
Gold adsorption onto activated carbon occurs in two trains: CIC-1 with six atmospheric columns (approximately 3 tonnes activated carbon each) in an up-flow cascading gravity circuit, and CIC-2 with five closed columns (approximately 6 tonnes activated carbon each). Loaded carbon undergoes acid washing with approximately 3 percent HCl to remove carbonate scale, followed by sodium hydroxide neutralization. A cold cyanide wash using 3 percent NaCN solution is then applied. Carbon elution uses reverse osmosis water with NaOH heated to approximately 150°C in an upward-flow elution column. Two kilns are available for thermal reactivation: the first is a rotary kiln heating to 650°C in steam atmosphere; the second is a new vertical 125 kg/h kiln being commissioned as of the report effective date.
Smelter
Gold is recovered from strong eluate by electrowinning onto stainless-steel mesh using direct current. Two pairs of electrowinning cells are included (two cells in parallel for each CIC circuit). The gold sludge is filtered, dried, mixed with fluxes, and smelted in a propane-fired nose-pour crucible furnace. The molten metal is poured into molds to form doré bars, which are cleaned, weighed, and shipped offsite. No mercury is present so no retorting is required.
Water supply and power
Water is obtained from multiple wells. Raw water has high total dissolved solids content; a water softener and reverse osmosis unit increase water quality for certain uses. Electrical power is sourced 100 percent from diesel generators under a rental contract. For 2022, the mine consumed 37,622,315 kWh at a cost of US$ 0.40/kWh (US$ 0.33/kWh attributable to diesel cost). The processing area accounted for US$ 2.4/tonne or 21.1 percent of total energy cost.
Operational results
First ore was loaded on the leach pad in July 2020. Between July and December 2020, only primary and secondary crushed ore (1,609,887 tonnes at 1.0 g/t Au) was loaded using dump trucks and front-end loader. The stacking system started operating in January 2021. Between February and May 2021, run-of-mine size ore (1,373,958 tonnes at 0.57 g/t Au) was loaded, plus 89,941 tonnes of coarse crushed diverter ore at 1.01 g/t Au.
As of December 31, 2022, ore loaded on the leach pad totaled 13,561,598 tonnes grading 0.905 g/t. Of this, 68.2 percent (9,248,168 tonnes at 0.914 g/t) was processed through the tertiary crusher, and 31.8 percent (4,313,430 tonnes at 0.885 g/t) was coarser material. In terms of gold loaded, 68.9 percent was tertiary-crushed and 31.1 percent was coarse material.
Accumulated gold recovery reached 58.03 percent as of December 31, 2022. The first doré bar produced in July 2020 weighed 8.03 kg and assayed 83.83 percent gold, 6.90 percent silver, and 9.27 percent impurities. Total accumulated doré production was 7,120 kg (228,923 ounces).
Key reported parameters
| Parameter | Value | Basis |
|---|---|---|
| Crushing plant target product size (P80) | Minus 6–8 mm | Design |
| Leach pad design capacity | ~93 million tonnes | Design |
| Leach pad lined surface area | ~106 hectares | Design |
| Typical leach cell dimensions | 60 × 60 × 10 m | Design/operating |
| Leach irrigation cycle: ILS phase | 30 days at 12 l/m²/h | Design |
| Leach irrigation cycle: barren solution phase | 45 days at 9 l/m²/h | Design |
| Total leach irrigation cycle | 75 days | Design |
| SART plant design flow rate | 400 m³/h | Design |
| Process pond combined capacity | 50,000 m³ | Design |
| Storm water pond capacity | 50,000 m³ | Design |
| 100-year, 24-hour rainfall event | 56.1 mm | Design basis |
| Average annual precipitation | 71.7 mm | Historical data 1992–2016 |
| Average annual evaporation | 2,750 mm | Estimated from nearby station |
| Average annual freshwater requirement | 37.1 m³/h | Calculated water balance |
| Actual average ore throughput (last six months of 2022) | 14,755 tpd (78.7% of design) | Operating data |
| Total ore loaded on leach pad (to Dec 31, 2022) | 13,561,598 tonnes | Operating data |
| Average gold grade of loaded ore | 0.905 g/t | Operating data |
| Accumulated gold recovery (to Dec 31, 2022) | 58.03% | Operating data |
| Total accumulated doré production (to Dec 31, 2022) | 7,120 kg (228,923 oz) | Operating data |
| Copper in PLS before SART commissioning | 700 ppm | Operating data |
| Copper in PLS at end of 2021 | ~500 ppm | Operating data |
| Copper in PLS at end of 2022 | ~300 ppm | Operating data |
| Power consumption (2022) | 37,622,315 kWh | Operating data |
| Average energy cost (2022) | US$ 0.40/kWh | Operating data |
| Cement ratio range | 0.25–6.5 kg/t | Design/forecast |
| NaCN ratio | 0.3 kg/t | Forecast |
| HPGR roll dimensions | 1.7 m diameter × 1.8 m wide | Design |
| HPGR edge material recirculation | ~25% of total product | Design/observed |
| Primary jaw crusher | 1,500 mm × 1,300 mm | Design |
| Agglomeration drum dimensions | 3.66 × 12 m (two units) | Design |
| Leach pad Phase 2 construction start | 2024 | Design schedule |
| Planned irrigation capacity increase (2024) | 50% (from 800 m³/h nominal) | Proposed |
Project website: https://fortunamining.com/
Technical qualifications
The qualified person considers the Lindero Mine’s facilities based on conventional technology and its design follows industry best practices. The actual average ore throughput for the last six months of 2022 reached 78.7 percent of the 18,750 tpd design capacity. The metallurgical laboratory facilities have limited capacity to adequately support continuous improvement; additional infrastructure and equipment will be necessary as the operation matures. The crushing plant requires additional work to ensure medium- and long-term mechanical availability, and the level of abrasion identified during testwork campaigns should be factored into maintenance programs. The agglomeration plant has been subject to multiple improvements but additional work is necessary to ensure long-term performance.
Source: Fortuna Silver Mines Inc.: Lindero Mine and Arizaro Project, Salta, Argentina, Technical Report, December 31, 2022, Sections 17 (Recovery Methods).
