Los Ricos North PEA — 2023 Technical Report

This section describes the recovery methods for the proposed Los Ricos North crushing and process facilities based on preliminary testwork for five deposits.

Report context

This 2023 Preliminary Economic Assessment reports on the Los Ricos North Project. The report section presented here details the recovery methods used for the design of the Los Ricos North crushing and process facilities. The initial preliminary testwork presented in detail in Section 13 of the report was used for flowsheet development and design criteria for the five deposits.

Processing route

Oxide Processing Route (Years 1-8)

The proposed design for the oxide process plant is based on a nominal 8,000 tpd throughput crushing and grinding circuit. The oxide flowsheet design comprises conventional crushing, a semiautogenous (SAG) mill with a pebble crusher, and a closed-circuit ball mill circuit with cyclones to ensure product (P80) size feed to the leaching circuit.

Run-of-mine (ROM) material is delivered to a 100-t capacity ROM surge bin with a vibrating grizzly feeder that feeds the primary jaw crusher. The 250 kW jaw crusher at 762 mm x 1,219 mm (30 in x 48 in) processes a nominal 444 t/h of material. The jaw crusher discharge is conveyed to a crushed feed stockpile with 4,500 t live capacity. Three variable-speed reclaim apron feeders discharge onto the SAG mill feed conveyor to feed crushed material to the primary grinding SAG mill unit at a controlled feed rate of 363 t/h.

The grinding circuit is a two-stage process with the SAG mill, screen, pebble crusher, and the ball mill in closed circuit with classifying cyclones. The SAG mill has 3.7 MW installed power, the pebble crusher has 175 kW installed power, and the ball mill has 5.6 MW installed power. Recycled water from the process is added to the SAG mill feed to ensure a slurry density with the mill of 74%. Oversize material from the classifying screen is sent to the pebble crusher via conveyors and recirculated to the SAG mill feed belt. The screen undersize feeds the ball mill pump box to allow pumping and classification at the cyclone cluster. The cyclone overflow, P80 = 74 µm, flows to the pre-leach thickener.

The ball mill cyclone overflow feeds the pre-leach thickener, a high-rate thickener unit of 20 m diameter. The cyclone overflow, with anticipated density of 35% solids, is thickened to a minimum pulp density of 55% solids. The thickener overflow is recycled to the process water system for use in the milling circuit.

The repulped slurry is pumped to the leach tank farm. The cyanide leach circuit consists of one pre-leach aeration tank (13 m diameter x 15 m high) and six mechanically agitated leach tanks (20 m diameter x 22 m high) that flow by gravity with a bypass option for each tank. Leach residence time is 16 hours per tank for an approximate total of 92 hours. The addition of lime maintains leach pH between 10.5 to 11.0 and cyanide is added to the repulpers for a feed cyanide concentration of 1,200 ppm cyanide. Air spargers with an air blower are integral to the leach tanks.

After the required leaching retention time, the discharge slurry and loaded solution is filtered in three tailings pressure filters for solution washing and dewatering. The slurry density to the filters will be 55% solids with a resultant estimated pressure filter discharge density of 86% solids (approximately 14% moisture). The pressure filters include a washing system to recover the pregnant metal bearing solution. The dry stack tailings are conveyed from the process plant to a contained lined storage area.

The gold-silver bearing solution is fed to a conventional Merrill Crowe plant for recovery of the gold and silver precipitate and subsequent doré. The pregnant solution containing silver, gold, and copper complexes is pumped from the leach circuit to the Merrill Crowe zinc precipitation circuit. The preliminary design flowrate is 420 m³/hr. Controlled zinc addition at a stoichiometric ratio of three is made to the clarified and de-aerated solution to precipitate the gold and silver. The resultant gold and silver sludge is dried, fluxed, and smelted in an induction furnace to produce a saleable doré. The discharge from the Merrill Crowe plant (barren solution) is recycled to the process.

Sulphide Processing Route (Year 9 Onwards)

Commencing in year nine, the process plant will process sulphide material from the Orito Deposit via conventional flotation operations, and the leaching and Merrill Crowe operations will shut down.

The sulphide process plant flowsheet design uses the same grinding circuit as the oxide circuit. The cyclone overflow is conditioned prior to rougher flotation with reagents (collector and frother) to produce a rougher concentrate. The rougher concentrate is reground in a regrind ball mill and further upgraded in a series of cleaner flotation cells to produce an expected marketable final product.

The flotation circuit equipment includes a conditioning tank (4 m diameter x 6 m), five rougher flotation cells of 100 m³/cell, a regrind mill of 900 kW with closed circuit cyclones, four first cleaner flotation cells of 14.6 m³/cell, six second cleaner flotation cells of 1.42 m³/cell, four cleaner scavenger flotation cells of 1.42 m³/cell, and four third cleaner flotation cells of 1.42 m³/cell. The final concentrate is thickened in a 5 m diameter concentrate thickener, filtered with a vacuum disc filter system, and dried with a diesel-fired rotary concentrate dryer for shipping.

As with the oxide circuit, flotation tailings are thickened in a 35 m diameter tailings thickener and filtered to produce dry stackable tailings at approximately 14% moisture. Process water is recycled into the circuits of the process plant.

Water Management

Water recovery and management are important aspects of the design. The dry stack tailings system aids in tailings deposition and water recovery. The impoundment area is lined and incorporated as a polishing and water recovery system. Make-up water for the project is supplied by nearby surface water from rain and run-off water during the rainy season. Alternative water sites will be investigated along with in-depth discussion with Conagua for other sources of water such as reservoirs, historical underground workings, and underground wells.

Key reported parameters

Technical qualifications

The report states that the initial preliminary testwork presented in detail in Section 13 was used for the flowsheet development and design criteria for the five deposits. The report further notes that subsequent optimization testwork on the Orito Deposit will confirm cell sizing, configuration, and optimum regrind conditions for the flotation circuit. The tailings dewatering moisture content of 14% is stated as estimated. The report notes that alternative water sites will be investigated along with in-depth discussion with Conagua for other sources of water as the project develops. The report provides simplified process plant flowsheets (Figures 17.1 to 17.4) for the Los Ricos North Project.

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Source: GoGold Resources Inc., Los Ricos North PEA, Report No. 440, P&E Mining Consultants Inc., 2023, Section 17.0 Recovery Methods.