The Fenix Project processing facility would be designed in two phases, initially treating gold-bearing heap leach material by grinding and cyanide leaching, with a later phase adding flotation, counter-current decantation, and Merrill Crowe recovery for silver-rich feedstocks.
Report context
The Preliminary Economic Assessment for the Fenix Project at McEwen Mining Inc.'s Operations in Sinaloa, Mexico, dated by reference 300060 2130140:P:dep Revision A, describes a proposed two-phase processing facility design. The facility would process material from several different deposits via separate campaigns, initially treating previously treated gold-rich Heap Leach Material from the existing El Gallo Gold heap leach operation, then adding equipment to treat silver-rich fresh mineralized feed stock from El Gallo Silver, Palmarito, Carrisalejo and El Encuentro deposits.
Processing route
Phase 1 design
The Phase 1 facility would target gold recovery from the Heap Leach Material (HLM) using conventional grinding, cyanide leaching, and adsorption of gold onto activated carbon. Proposed unit process operations include HLM reclamation; primary ball milling and classification; direct cyanide leaching and adsorption; elution and electrowinning; gold recovery and gold room operations; cyanide detoxification; tailings thickening and in-pit disposal; reagent mixing, storage and distribution; and services and ancillaries. Mill throughput for HLM would be designed at 5,000 tpd, equating to 1,825,000 tpa, with the plant scheduled to operate seven days per week.
Phase 2 additions
Phase 2 would install further unit processes after an initial operating period to enable treatment of material from the El Gallo Silver deposit. This would include separate cyanide leaching of bulk flotation concentrate and flotation tailings streams to enhance silver leaching characteristics. Due to the high silver to gold ratio for this deposit, counter-current decantation (CCD) and Merrill Crowe (zinc precipitation) would be included for recovery of precious metals from the concentrate leach solution.
Additional processing stages would include three-stage crushing using the existing El Gallo Gold crushing plant with direct mill feed via a transfer bin and emergency dead stockpile; bulk rougher-scavenger flotation; bulk concentrate thickening; cyanide leaching of the flotation concentrate using two of the leach tanks installed for Phase 1 operation plus an additional leach tank; CCD thickening to recover concentrate leach pregnant solution; flotation tailings thickening; flotation tailings leaching and adsorption using a single leach tank and adsorption circuit installed during Phase 1; zinc precipitation and Merrill Crowe technology for recovery of precious metals from the concentrate leach pregnant solution and flotation tailings leach eluate; refining facilities for treatment of precipitate cake to bullion; and additional reagent mixing, storage and distribution services.
Throughput and feed characteristics
Mill throughput rate and product size would be material dependent. The HLM would be processed at 5,000 tpd, while fresh mineralized material from the silver sulphide deposits would be processed at an equivalent of 3,250 tpd. The difference in treatment rate is attributed to the finer grind size targeted for the silver deposits and the difference in grinding characteristics of the materials.
Deposit-specific assumptions
Based on scoping level test work, Carrisalejo mineralization would perform similarly to El Gallo Silver with respect to silver recovery. Sighter test work conducted from 2017 to 2018 showed only modest silver recovery from flotation for Palmarito samples, but separate cyanide leaching of bulk flotation concentrate and flotation tailings streams achieved positive results. The treatment process for Carrisalejo and Palmarito open pit material was therefore assumed as per that required for El Gallo Silver deposit, pending additional sampling and metallurgical test work.
El Encuentro is known at present as a gold dominant resource with low silver and moderate levels of base metals. Scoping level test work indicated the El Encuentro material would be amenable to direct cyanidation. The treatment process for El Encuentro open pit material was therefore assumed as per that required for El Gallo Gold Heap Leach Material.
Key reported parameters
| Parameter | Value | Basis |
|---|---|---|
| Phase 1 HLM throughput | 5,000 tpd (1,825,000 tpa) | Proposed design |
| Phase 2 fresh mineralized material throughput | Equivalent of 3,250 tpd | Proposed design |
| Plant operating schedule | Seven days per week | Proposed design |
| Phase 1 recovery method | Grinding, cyanide leaching, carbon adsorption, elution, electrowinning | Proposed design |
| Phase 2 recovery method | Three-stage crushing, bulk flotation, separate concentrate and tailings cyanide leaching, CCD, Merrill Crowe | Proposed design |
| El Gallo Silver/Palmarito/Carrisalejo treatment assumption | Same process as El Gallo Silver deposit | Assumption based on scoping test work |
| El Encuentro treatment assumption | Same process as El Gallo Gold HLM | Assumption based on scoping test work |
| Palmarito flotation silver recovery | Modest | Sighter test work 2017–2018 |
| Palmarito separate cyanide leaching of bulk concentrate and tailings | Positive results | Sighter test work 2017–2018 |
Project website: https://mcewenmining.com/
Project website: https://www.mcewenmining.com/operations/overview/default.aspx
Technical qualifications
The report explicitly states that treatment process assumptions for Carrisalejo, Palmarito, and El Encuentro are based on scoping level test work and are pending additional sampling and metallurgical test work. The report does not provide final process design details, and the flow diagrams referenced in the original report are not reproduced here. Throughput rates and process configurations are proposed designs, not historical operating data, except where test work results are specifically noted.
Source: Preliminary Economic Assessment for the Fenix Project at McEwen Mining Inc.'s Operations in Sinaloa, Mexico, Reference: 300060 2130140:P:dep Revision A, Section 17 Recovery Methods.
