The Guanaceví processing plant uses crushing, grinding, cyanidation, counter-current decantation, and Merrill-Crowe circuits to treat silver-gold ore at a design rate of 1,300 tonnes per day.
Report context
This technical report, dated 2022, describes the Guanaceví Project owned by Endeavour Silver Corp. The beneficiation plant was originally built in 1970 by the Mexican government to custom mill ores from various mines in the district. The report presents both the plant’s original design and historical operating data through 2021 and early 2022.
Processing route
Primary crushing
Trucks loaded with ore arrive at the plant and are weighed at the truck scale. Ore is dumped into the stockpile or into the feed hopper of the primary crusher. The primary crusher is a Dakota 200 HP jaw crusher with a capacity to process 400 tons per hour, crushing material to 6 inches. Ore is stacked by a conveyor stacker in the patio area and then transported by truck to the coarse ore bins.
Secondary and tertiary crushing
The secondary and tertiary crushing circuit includes ore bins, a Symons 4-foot secondary cone crusher (installed 2015) that receives material 5 inches or less, and a Sandvik CH-430 tertiary cone crusher (installed 2022) that receives material of 3/4 inch or less. A Symons 4-1/4 foot cone crusher serves as backup to the Sandvik, also receiving material of 3/4 inch or less. A 5-foot by 10-foot vibrating screen (minus 1/2 inch to minus 3/8 inch) and a new FL Smith 20-foot by 6-foot screen are used. The tertiary crushing circuit is closed, meaning ore is returned to the crushers until reduced to minus 3/8 inch. Final crushed material is stored in fine ore bins.
Grinding
Material from the fine ore bins (minus 3/8 inch) is transported to the mills by conveyors. Recycled solution containing sodium cyanide is added in the mills and pumps to create a pulp of around 60% solids, beginning the extraction kinetics of silver and gold particles. The grinding circuit includes four ball mills: one 10.5-foot by 12-foot Hardinge, two 7-foot by 7.5-foot Denver, and one 5-foot by 6-foot Fimsa ball mill.
Pulp leaving the mills has a 60–65% solid density and is delivered to hydro cyclones to separate fine particles from coarser material. The pulp containing fine particles is sent to the primary thickener, with an average size of 80% passing 200 mesh (equivalent to 740 microns). The hydro cyclone underflow is returned to the mill for additional grinding. Fine solids passing 200 mesh are delivered to the grinding thickener where flocculating agents are added to achieve a pulp density of approximately 50% at the tank bottom discharge before being pumped to the leach tanks. The clarified solution or overflow from the grinding thickener is sent to the Merrill-Crowe area.
Cyanidation
The leach process uses 16 lined agitator tanks in three parallel circuits. Circuits 1 and 2 include six tanks each, each with a capacity of 178 m³. Circuit 3 includes four tanks, each with a capacity of 600 m³. Sodium cyanide is added in Tank 1 of each of the three circuits. Oxygen is injected into the first tank in each circuit to increase the kinetic reaction, while air is injected into the remaining tanks in each circuit.
Counter-current decantation and Merrill-Crowe
From the leaching tanks, the solution is delivered to the counter-current decantation (CCD) circuit, which includes five 50-foot diameter thickeners. From the CCD circuit, the pregnant solution is pumped to the Merrill-Crowe plant for clarification and precipitation of silver and gold. The Merrill-Crowe circuit includes three leaf clarifiers and one deaeration tower.
Refinery
Two gas-fired furnaces with a mercury retort smelt the precipitate to produce Doré bars, which typically average 92% silver. The Doré bars are shipped for final refining at the Peñoles Met-Mex facility in Torreón. The refined gold and silver is sold through Auramet in London, England.
Tailing filtration
The tailing filtration circuit, commissioned in May 2012, produces filtered material with moisture content between 14% and 18%. The circuit includes two filter presses supplied by DIEMME, each with 131 plates of size 2,000 by 2,000 mm. The filtration circuit is operated continuously with shutdowns only for maintenance. Filtered materials are trucked to the tailing storage facility to be placed in lifts and compacted to meet specifications for stability.
Assay laboratory
The assay laboratory utilizes wet assaying, fire assaying, and atomic absorption methods. The laboratory performs all assaying required for mill processing, as well as assaying mine and infill drilling samples. Duplicates and blanks are run on a regular basis, as well as check assays at outside laboratories. The assay lab has fulfilled the ISO 9001 standard and received recertification in November 2021, which remains valid until November 2024.
Historical process modifications
In 2009, hydrated lime was switched to quicklime to reduce consumption and reduce flocculent and diatomaceous earth consumptions in the pregnant solution clarification stages. The report states there was not much improvement and consumptions did not decrease significantly.
Key reported parameters
| Parameter | Value | Basis |
|---|---|---|
| Plant design capacity | 1,300 tonnes per day | Design |
| Primary crusher capacity | 400 tons per hour | Design |
| 2021 plant throughput | 414,355 tonnes | Historical operating data |
| 2021 average silver grade | 370 g/t | Historical operating data |
| 2021 average gold grade | 1.09 g/t | Historical operating data |
| 2021 silver recovery | 86.9% | Historical operating data |
| 2021 gold recovery | 91.8% | Historical operating data |
| 2021 silver production | 4,316,819 oz | Historical operating data |
| 2021 gold production | 13,378 oz | Historical operating data |
| Grinding pulp density | 60–65% solids | Design |
| Grinding thickener discharge density | Approximately 50% | Design |
| Grind size | 80% passing 200 mesh (740 microns) | Design |
| Leach tank capacity (Circuits 1 and 2) | 178 m³ each | Design |
| Leach tank capacity (Circuit 3) | 600 m³ each | Design |
| CCD thickener diameter | 50 feet | Design |
| Filter press plates | 131 plates, 2,000 x 2,000 mm each | Design |
| Filtered tailing moisture content | 14–18% | Testwork (commissioned 2012) |
| Doré bar silver content | Typically 92% | Historical operating data |
Project website: https://edrsilver.com/portfolio/operations/guanacevi/
Technical qualifications
This report section provides processing information from the Guanaceví Project 2022 Technical Report. The data presented includes design parameters for the original mill built in 1970, historical production data for 2021 and up to May 2022, and testwork results from the tailing filtration circuit commissioned in 2012. The report does not provide detailed flowsheet diagrams, full mass balances, or complete equipment specifications for all circuits. No definitive feasibility study results or economic analyses are presented in this section. The report does not specify current ownership or operational status beyond May 2022.
Source: Endeavour Silver Corp. NI 43-101 Technical Report, Guanaceví Project, 2022, Section 17 Recovery Methods.
