Fruta del Norte Mine — 2023 Technical Report

The Fruta del Norte process plant uses a conventional gravity-flotation-cyanidation flowsheet to treat underground ore, with reported gold recovery of 87.2% to 89.5% from 2020 through 2022.

Report context

The Fruta del Norte Mine, located in Ecuador, is the subject of a NI 43-101 technical report dated March 2023. The process plant described in this report treats ore through a conventional gravity-flotation-cyanidation process. The plant was constructed and commissioned in 2019, achieved nameplate capacity of 3,500 tpd in 2020, was upgraded to 4,200 tpd in 2021, and further debottlenecked to 4,400 tpd. Studies and engineering were scheduled to commence in 2023 to debottleneck the plant to reliably achieve 5,000 tpd.

Processing route

Overview

The Fruta del Norte process plant treats ore via a conventional gravity-flotation-cyanidation process. Run-of-mine (ROM) ore is processed through a conventional primary crusher and SAG-ball mill comminution circuit, followed by a gravity circuit. Gravity tailings are treated in a conventional rougher-cleaner flotation circuit to produce gold concentrate for sale. Flotation tailings are treated via a carbon-in-leach (CIL) process with associated gold recovery and carbon handling circuits to produce gold doré. CIL tailings are treated via a cyanide destruction process prior to use at the paste plant or storage in the tailings storage facility (TSF).

No flowsheet changes or significant process plant upgrades were expected due to the treatment of ore from the south zone of the mine.

Primary crushing and ore stockpile

ROM ore is trucked from the underground mine and dumped directly into the crusher feed bin or stockpiled on the ROM storage pad and reclaimed by a front-end loader to a ROM bin. The ore is fed onto a vibrating grizzly feeder, where screen oversize feeds a jaw crusher. The jaw crusher reduces ore to a P80 of approximately less than 100 mm. Crushed ore, along with vibrating screen undersize material, is conveyed to the crushed ore stockpile. Crushed ore is reclaimed via apron feeders and conveyed to the SAG mill.

Grinding circuit

The grinding circuit consists of a SAG mill (6.7 m diameter by 3.5 m EGL with a 2,300 kW variable frequency drive) in open circuit with a pebble recycle stream, and a ball mill (5.8 m diameter by 9.3 m EGL with a 5,500 kW fixed speed drive) in closed circuit with cyclones to produce a primary grind of P80 of 60 µm. Each mill has a trommel screen. Steel balls are manually added on a batch basis as grinding media, and dilution water is added as required.

The SAG mill and ball mill trommel undersize discharges by gravity into a gravity feed pump box, where slurry is pumped to the gravity circuit to recover gravity gold.

Gravity circuit

The gravity circuit consists of three gravity trains, each including a vibrating screen and a Knelson KC-QS40 centrifugal gravity concentrator. Gravity gold concentrate from the three trains is treated in a common Acacia CS3000 intensive leach reactor (ILR). Gold-rich pregnant solution from the ILR is treated in the electrowinning circuit in the gold room. Tails from the gravity concentrators are collected in a pump box and pumped to the cyclones at the ball mill. Cyclone underflow and oversize from the gravity screens flow to the ball mill feed, while cyclone overflow reports to a trash screen prior to the flotation circuit.

Flotation circuit

The flotation circuit consists of 12 rougher tank cells of 50 m³ each, 5 first cleaner tank cells of 50 m³ each, 4 cleaner-scavenger tank cells of 50 m³ each, 3 second cleaner tank cells of 10 m³ each, 3 third cleaner tank cells of 10 m³ each, and a concentrate regrind HIGmill.

Product from the grinding circuit flows via a trash screen to a rougher conditioning tank. The slurry is treated in the rougher circuit to produce a rougher concentrate, which is pumped to the first cleaner and scavenger circuit. Concentrate from the first cleaner circuit is pumped to second and third cleaner circuits to produce a gold concentrate of approximately 100 to 130 g/t Au. Concentrates from selective circuits are reground in the regrind mill when required. Tails from the scavenger circuit are pumped to the rougher circuit, and tails from the rougher circuit are pumped to the pre-leach thickener and CIL circuit.

Concentrate dewatering and loadout

Concentrate from the final cleaning stages is pumped and dewatered in a 9 m diameter high-rate thickener. The thickened gold concentrate is further dewatered in two Larox filter presses to produce a filter cake of approximately 9% moisture. The concentrate is loaded into lined 20-foot containers for export.

CIL circuit

The CIL circuit consists of an 18 m diameter high-rate thickener, trash screen, pre-conditioning tank, and six CIL tanks. Rougher tails from the flotation circuit are thickened in the pre-leach thickener and then pumped to the pre-conditioning tank via the trash screen. Slurry flows by gravity through the six stages of CIL. Sodium cyanide and lime are added to the CIL circuit, and air is sparged in the tanks. Regenerated carbon is added to the CIL circuit to adsorb gold in the slurry.

Acid wash, elution, and carbon regeneration circuit

The elution circuit is a 7 t Pressure Zadra plant consisting of an acid wash column, elution strip vessel, carbon regeneration circuit, and associated tankage and pumping systems. Loaded carbon generated from the CIL tanks is pumped to the carbon elution and regeneration circuit. Once gold is eluted, the carbon is sent to regeneration. After quenching and screening to remove small particles, the reactivated carbon is reintroduced to the CIL circuit.

Electrowinning and gold room

Gold eluate is pumped to electrowinning cells with stainless-steel cathodes to produce a gold-silver sludge. This is combined with sludge from the separate ILR electrowinning cell, filtered and dried, then smelted to produce gold-silver doré.

Cyanide destruction circuit

Slurry discharged from the CIL tanks reports to the cyanide destruction circuit. A two-stage conventional SO₂/air process is used to achieve less than 1 ppm total cyanide exiting the process plant. Copper sulphate and sodium metabisulphite reagents are used, and air is sparged in the tanks.

Tailings handling

Tailings from the process plant are either used at the paste plant to produce paste for the underground mine or stored in the TSF. If tailings are required at the paste plant, tailings from the cyanide destruction circuit are deslimed via cyclones and pumped to the paste plant. If the paste plant is not in operation, tailings are pumped directly to the TSF.

Reagents, power, and air

Reagents used in the process plant include primary collector (xanthate), secondary collector (AP208), frother, carboxy methyl cellulose (CMC), lime, sodium cyanide, sodium hydroxide, hydrochloric acid, copper sulphate, sodium metabisulphite, anti-scalant, and flocculant.

Power is provided from the local grid. Two low pressure air blowers supply process air for all flotation tank cells, and two air blowers supply process air for all CIL and cyanide destruction tanks. Plant air and instrument air are provided by dedicated compressors, with instrument air dried to remove moisture. Compressed air for the primary crushing area is supplied by a dedicated compressor and receiver.

Water

The bulk of process plant water requirements are provided by process water, consisting of thickener overflows and reclaim water from the TSF. Treated water from the water treatment plant is primarily utilized in the ADR, ILR, and refinery circuits, and used as gland seal water and for reagent dilution. Treated water is also used for grinding mill cooling systems and in the mine. Domestic water is supplied to camp, mine, and process plant, and is not potable; drinking water is supplied as bottled water.

Key reported parameters

*From March 1, 2020, start of commercial production, until December 31, 2020.

Technical qualifications

The process plant performance summary provided in Table 17.1 represents actual operating data from the period 2020 to 2022. The report notes that the process plant has generally been treating ore feed grades of approximately 11 g/t Au and achieving approximately 89–90% average recovery. The planned debottlenecking to reliably achieve 5,000 tpd was scheduled to commence studies and engineering in 2023. The report indicates that the process plant was constructed and commissioned in 2019, achieved nameplate of 3,500 tpd in 2020, was upgraded to 4,200 tpd in 2021, and further debottlenecked to 4,400 tpd.

Source: NI 43-101 Technical Report, Fruta del Norte Mine, Ecuador, March 2023, Section 17: Recovery Methods.