Mangazeisky Silver Project — 2024 Technical Report

This report details the proposed recovery methods and processing design for the Mangazeisky Silver Project, based on a feasibility study update.

Report context

The 2024 Technical Report Feasibility Study Update for the Mangazeisky Silver Project provides the process design and recovery methods for the proposed processing plant, based on metallurgical test work presented in Section 13.0 of the report. The design criteria are derived from test work results, the mill production plan, industry standard assumptions, equipment manufacturer recommendations, and previous studies completed on the project.

Processing route

Process design criteria

The process flowsheet comprises a standard crushing and milling circuit, followed by gravity concentration and agitated tank leaching of the gravity tails. The gravity concentrates will be processed by intensive cyanidation. The leached slurry from the tank leach and intensive cyanidation will undergo counter current decantation washing, and the solution will be processed by direct electrowinning to recover silver metal.

The process plant design includes provision for building additional leach tanks in order to process primary sulphide ore in the future. Tailings from the process plant will comprise filtered solids and a bleed stream from the depleted electrowinning solution, disposed of in the TMF.

Crushing

ROM mineral with a maximum size of approximately 300 mm and 80% passing 200 mm will be trucked to the ROM pad and fed into the crushing and screening circuit, arranged for closed circuit crushing. The crushing circuit will operate over a single 12-hour shift to allow for efficient running. The ROM mineral will feed to a vibrating grizzly, with fine ore removed and passed directly to the secondary crushing circuit screen. The coarse fraction will be crushed in the primary jaw crusher, followed by the secondary crushing circuit.

The secondary crushing circuit will contain a secondary cone crusher operating in closed circuit with a single deck screen to produce a final screen product with a P80 of 13 mm, suitable for ball mill feed. The crushing circuit is designed to operate at 75% availability to allow for operational and mechanical maintenance and winter shut down.

Milling and gravity concentration

The milling and processing plant will operate for 24 h/d at an availability of 91% and process 327 t/d of mineral at an average silver head grade of 772 g/t. The crushed material will feed directly onto the ball mill via a feed conveyor belt and feed hopper. A single ball mill will be used to achieve the required grind size, with an estimated size of 2.8 by 4.9 m installed with a 475 kW motor. The mill product slurry will be pumped to a two-stage cyclone system.

The gravity concentration circuit will consist of a trash screen followed by a Knelson gravity concentrator, with the concentrate regrind mill operating as a batch process. The reground concentrate will be transferred to a Consep ACACIA intensive leach reactor for cyanidation, with the resulting high-grade silver solution pumped to a clarifier prior to direct electrowinning.

Leaching

Leaching of the gravity tails will be completed in agitated leach tanks, designed to give a total residence time of approximately 72 hours, with provision for additional tanks to increase residence time to 120 hours in the future. The leach tanks will be constructed on progressively lower elevations to allow gravity flow between tanks, with an active volume per tank of approximately 312 m³. Lime slurry and cyanide solution will be added to maintain a pH of approximately 11.5 and free cyanide concentration of at least 2,000 ppm.

Direct electrowinning

The direct electrowinning process will employ patented emew® cell technology, operated in two stages. The primary stage, consisting of 140 cells, will reduce the silver solution from approximately 800 ppm to 50 ppm silver. The secondary stage, consisting of 80 polishing cells, will reduce the solution to below 10 ppm silver prior to discharge. The electrowinning plant will be supplied as a modular turnkey package.

Plant services and reagents

Fresh water will be supplied to a dedicated process water tank, with barren solution recycled as part of the process. Approximately 1% of the barren electrowinning solution will be sent to a detoxification circuit. The principal reagents are cyanide and lime, with lime mixed in a dedicated agitated mixing tank and cyanide briquettes added to an agitated cyanide mixing tank.

Key reported parameters

Technical qualifications

The report provides several specific limitations and design assumptions. The crushing circuit is designed based on 274 operational days per year, allowing for planned shutdowns and winter shut down. The milling and leaching plants are designed based on 335 operational days per year, providing 92% availability. The process design criteria are based on test work results, industry standard assumptions, and previous studies. The report notes that additional milling capacity may be required when primary ore is processed.

The report specifies that approximately 1% of the barren electrowinning solution will be discharged following cyanide detoxification to avoid build-up of base metals. The direct electrowinning circuit uses patented emew® cell technology and is anticipated to operate in two stages. The report notes that this technology was selected over the Merrill Crowe process due to the exceptionally high silver grades and the requirement to avoid that process.

Source: Mangazeisky Silver Project 2024 Technical Report Feasibility Study Update, Section 17.0 Recovery Methods.