This article reviews the proposed recovery methods and process plant design for the El Quevar silver project in Salta Province, Argentina, based on the 2018 technical report.
The processing facility described in the 2018 technical report was designed to recover silver from the Yaxtché sulfide deposit. The design basis is set to process 1,200 tonnes per day of mineralized material from an underground mine. The flowsheet uses conventional two-stage crushing, single-stage ball milling, and flotation to produce a bulk silver concentrate. Testwork completed by DML and JKTech formed the basis for the process plant design. The results of DML’s 2012 locked cycle flotation testwork were Samuel Engineering’s primary data source. This testwork included only two cleaner stages for producing the bulk silver concentrate. Samuel Engineering modeled the mass balance for the process plant to include five cleaner stages in order to produce a marketable, high-grade bulk silver concentrate of about 11.5 kg/t Ag.
Run-of-mine (ROM) mineralized material would be fed to the comminution circuit. Comminution would be accomplished by two-stage crushing followed by ball milling to produce a particle diameter of 80% passing (P₈₀) of 45 µm. The ROM material would be dumped by mine trucks into a primary bin equipped with a grizzly feeder (1.2 m by 3.0 m). Oversize material from the grizzly feeder would be discharged to the primary crusher, a 115 kW jaw crusher (0.86 m by 1.12 m) with a rated capacity of 225 t/h. The primary crushed material would be combined with the undersize material from the grizzly and conveyed to the coarse crushed stockpile. The coarse crushed stockpile would have a live capacity of 800 t, or about 16 hours of surge. Coarse material from the stockpile would be reclaimed and conveyed to the secondary crushing circuit.
The coarse material would be pre-screened by a double-deck secondary screen. The screen oversize would be fed to a secondary cone crusher (2.1 m diameter) at an estimated throughput rate of 28 t/h. The secondary crushing circuit would produce a fine product at a rate of about 70 t/h at a nominal P₈₀ of 13 mm. The fine crushed product would be conveyed to a fine crushed stockpile as feed to the ball mill grinding circuit. The fine crushed stockpile would have a live capacity of about 750 t, providing a surge capacity of about 13 hours for the grinding circuit.
The ball mill circuit would operate in closed circuit with cyclones to achieve a grind size at a nominal P₈₀ of 45 µm. Underflow from the cyclones at 170 t/h dry solids, with a 300% circulating load and a pulp density of about 64% solids by weight, would be returned to the ball mill for further grinding. Cyclone overflow would be pumped to the flotation circuit. Flotation reagents including collectors, promoters, and frothers would be added to the slurry for conditioning, along with recycled process water from the concentrate thickener overflow and tailings reclaim water. The rougher flotation circuit would be done in two stages. Rougher flotation stages one and two would each be comprised of four 16 m³ mechanical cells, separated by a second conditioning tank where more reagents are added. The flotation concentrates from both rougher stages would be combined and pumped to cleaner flotation. Cleaner flotation would be done in five stages using 3 m³ and 50 ft³ cells operating in closed circuit to produce a high-grade silver concentrate. The final concentrate from the fifth cleaner stage represents the final bulk silver concentrate.
The final plant tailings in the thickener underflow would be pumped to the tailings impoundment location, a distance of about 670 m, at a rate of 52 dry t/h with a pulp density of about 55% solids by weight. The final settled density of the tailings in the tailings impoundment is estimated at about 70% solids by weight, with about 24 t/h of reclaim water returned as process water to the plant circuits. The final concentrate would be thickened, and the thickener overflow would be returned to the process water tank. The thickener underflow would be pumped to a holding tank ahead of the concentrate pressure filter. The filter would reduce the concentrate cake moisture, and the final silver concentrate would be packaged in one-tonne super sacks for shipment.
Critical Data
| Parameter | Value | Unit | Notes |
|---|---|---|---|
| Plant feed rate | 1,200 | t/d | Design basis |
| Grind size | 45 | µm | P₈₀ |
| Final concentrate grade | 11.5 | kg/t Ag | Target, approximate |
| Primary crusher power | 115 | kW | Jaw crusher, rated 225 t/h |
| Secondary crusher throughput | 28 | t/h | Estimated |
| Fine product rate | 70 | t/h | Nominal P₈₀ 13 mm |
| Coarse stockpile live capacity | 800 | t | About 16 hours surge |
| Fine stockpile live capacity | 750 | t | About 13 hours surge |
| Cyclone underflow | 170 | t/h | Dry solids, 300% circulating load |
| Cyclone underflow pulp density | 64 | % solids | By weight |
| Tailings rate | 52 | dry t/h | To tailings impoundment |
| Tailings pulp density | 55 | % solids | By weight |
| Final settled tailings density | 70 | % solids | By weight |
| Reclaim water return | 24 | t/h | To process water |
| Energy consumption | 22.5 | kWhr/t | Projected |
| Ball mill power | 1,500 | hp | Allis Chalmers, overflow |
| Tailings pumping distance | 670 | m | To impoundment |
| Not stated | Not stated | Not stated | Not stated |
Overview
The El Quevar process plant is designed as a conventional silver recovery facility using crushing, grinding, and flotation. The design basis of 1,200 t/d supports production of a bulk silver concentrate grading approximately 11.5 kg/t Ag. Samuel Engineering modeled the mass balance based on testwork by DML and JKTech, expanding the cleaner circuit from two stages in the original testwork to five stages in the plant design. The facility would include a two-stage crushing circuit, a single-stage ball mill in closed circuit with cyclones, rougher and cleaner flotation, concentrate dewatering, and tailings management. The flowsheet uses conventional unit processes that would produce a marketable concentrate, although elevated levels of arsenic, antimony, and bismuth would likely incur smelter penalties.
Key Process Stages
The comminution stage begins with a primary jaw crusher fed by a grizzly feeder, followed by a secondary cone crusher in closed circuit with a double-deck screen. The fine product reports to a stockpile ahead of the ball mill. The ball mill operates in closed circuit with cyclones to achieve a P₈₀ of 45 µm. Flotation begins with two stages of rougher cells, with a conditioning tank between stages for additional reagent addition. Rougher concentrates combine and feed five stages of cleaner flotation. The final concentrate is thickened, filtered, and packaged in one-tonne super sacks. Plant tailings are thickened and pumped to an impoundment, with reclaim water returned to the process.
Additional Interesting Data and Summary
The process design incorporates equipment currently available to the project owner. The Allis Chalmers ball mill is noted as currently owned by Golden Minerals and stored in Arizona. The flotation circuit uses a combination of cell sizes, including 16 m³ mechanical cells for roughers and smaller 3 m³ and 50 ft³ cells for cleaners. The tailings system is designed for a pulp density of about 55% solids by weight at a rate of 52 dry t/h, with reclaim water recirculated to the plant. The report indicates that additional testwork on fresh representative samples would be required to reduce concentrate penalties for arsenic, antimony, and bismuth and to optimize plant performance. Energy consumption is projected at 22.5 kWhr/t.
Key Processes
- Two-stage crushing (primary jaw crusher, secondary cone crusher)
- Single-stage ball milling in closed circuit with cyclones
- Two-stage rougher flotation with inter-stage conditioning
- Five-stage cleaner flotation in closed circuit
- Concentrate thickening, pressure filtration, and packaging
- Tailings thickening and impoundment with water reclaim
Source: El Quevar Project , 2018 Technical Report, 2018. Project website: [Not stated](Not stated)
Project website: El Quevar Project, 2018 Technical Report
