Kainantu 2024 Updated IDP Designs a 1.2 Mtpa SAB Plant With Flash Flotation, Gravity Tabling and Conventional Flotation for a Gold-Copper Concentrate

The Kainantu Gold Mine Integrated Development Plan proposes a 1.2 Mtpa processing plant incorporating crushing, grinding, gravity recovery, flash flotation, and conventional flotation to produce gold doré and a saleable gold-copper concentrate.

Report context

This technical report, dated October 2022, presents the recovery methods for the Kainantu Gold Mine Integrated Development Plan at the Kainantu Project in Papua New Guinea. The report was prepared as a National Instrument 43-101 Technical Report and documents a Definitive Feasibility Study. The processing section describes a proposed process plant design based on metallurgical testwork results and comminution circuit modelling.

Processing route

Ore Receiving and Crushing

Run-of-mine ore from the underground mine, at a maximum lump size of 1,000 mm, will be transported to the plant by 60 t capacity dump trucks. Trucks will tip directly into the primary crusher feed bin or onto blending fingers on the ROM pad. Ore will be reclaimed from the primary crusher feed bin by an apron feeder to a primary vibrating grizzly with 90 mm aperture size. Material smaller than the grizzly aperture will fall onto the surge bin feed conveyor. Oversize material will be fed to a jaw crusher selected for the material characteristics and tonnage throughput requirements. The crushing circuit will produce a crushed product size of 80% passing (P80) 92 mm. A single dust collection system with extraction hoods, ducting and a baghouse will service the crushing circuit.

Crushed Ore Surge Bin and Stockpile

Crushed ore will be conveyed to an overflow surge bin with a design live volume of 120 m³ (equivalent to 192 tonnes of dry ore) providing approximately 77 minutes of storage. Excess crushed ore will overflow to a dead stockpile with a capacity of approximately 2,400 t (equivalent to 1,500 m³), providing 16 hours of mill feed throughput. During crusher maintenance, stockpiled ore will be reclaimed using a front-end loader and tipped directly into the surge bin. Crushed ore will be reclaimed by one variable speed apron feeder discharging onto the SAG mill feed conveyor, which is fitted with a weightometer for feed rate control and mass accounting.

Grinding and Classification

The Kora grinding circuit will be a traditional SAB circuit consisting of a single semi-autogenous grinding (SAG) mill in open circuit and a single ball mill in closed circuit with hydrocyclones. The target product exiting the grinding circuit in the cyclone overflow slurry stream will contain 80% of particles passing 106 µm. Process water and hydrated lime slurry will be added to the SAG mill feed chute for in-mill pulp density control and pH adjustment prior to downstream flotation. SAG mill product will discharge via a trommel screen; oversize will be collected in a scats bunker and returned to the grinding circuit. Trommel undersize will flow by gravity to the cyclone feed hopper, combining with ball mill discharge, gravity circuit tailings, and flash flotation tailings. The cyclone cluster overflow will flow by gravity to the flotation circuit. Cyclone underflow will be split into three streams: one to flash flotation, one to the gravity scalping screen, and the remainder to the ball mill feed chute.

Gravity Circuit

Recovery of gravity gold will be achieved via one operating gravity centrifugal concentrator. Approximately one-third of the cyclone underflow stream will flow by gravity to a gravity scalping screen that prevents coarse heavy particles and mill ball steel chips from entering the concentrator. The concentrator will typically operate with a concentrating cycle time of approximately 45 minutes. Purged concentrate will flow to a gravity concentrate storage hopper before transfer to the gold room for further upgrading. Tailings from the gravity concentrator will flow by gravity to the cyclone feed hopper. Oversize from the scalping screen will flow to the ball mill feed box.

Goldroom

Gravity concentrate will be upgraded using a coarse shaking table followed by a fine shaking table in series. Final concentrate will be transferred by hand to calcine ovens for drying and calcining at approximately 700 – 800°C. Calcined concentrate will be mixed with a prescribed flux mixture (silica, nitre, soda ash and borax) prior to being charged into a diesel-fired smelting furnace. The molten gold and silver will be poured into moulds to form doré bars, which will be cleaned, assayed, stamped, and stored in a secure vault. Slag produced will periodically be returned to the grinding circuit via the SAG mill feed chute. The gold room will be serviced by a dedicated sump pump with a gold trap.

Flash Flotation

A flash flotation circuit will recover coarse gold and copper particles and reduce the recirculating load on the ball mill. Approximately one-third of the cyclone underflow stream will flow by gravity to the flash flotation feed box. Hydrated lime slurry for pH adjustment to 10.0 – 10.5 will be added to the flash flotation feed box. Collector will be added to the primary cyclone underflow boil box, and CMC depressant will be added to the flash flotation feed box. Flash flotation concentrate will flow by gravity to the concentrate thickener. Tailings from the lower outlet will flow by gravity to the ball mill feed box; tailings from the upper outlet will flow to the cyclone feed hopper for grinding circuit water balance.

Flotation Circuit

The cyclone overflow stream will flow by gravity to a flotation feed trash screen before entering the rougher conditioning tank. The flotation circuit will consist of rougher, scavenger, cleaner, cleaner scavenger, and recleaner stages. The rougher scavenger circuit will comprise a single conditioning tank (10 minutes residence time), followed by three 40 m³ rougher cells and three 40 m³ scavenger cells in series. The cleaner circuit will consist of a single conditioning tank (4 minutes residence time), followed by four 10 m³ cleaner cells. The cleaner scavenger circuit will consist of four 10 m³ flotation cells. The recleaner circuit will consist of two 10 m³ flotation cells. Design residence times include a 2.5 scale-up factor from laboratory times: rougher and scavenger 25 minutes plant target, cleaner 10 minutes, cleaner scavenger 15 minutes, and recleaner 10 minutes. Reagents will include a blended collector (Aero3477, Aero6697 and Aero5100 with mass ratio of 64:16:20) at 85 g/t, Dowfroth 250 frother at 15 g/t, CMC depressant at 77.5 g/t, and hydrated lime at 2.0 kg/t for pH adjustment to 10.0 – 10.5. Low pressure air will be supplied to each flotation cell.

Concentrate Thickening and Filtration

Recleaner concentrate plus flash flotation concentrate will be pumped to a ten-metre diameter high rate thickener for dewatering. The thickener will include an auto dilution feed well, froth sprays, and a bridge supported drive mechanism with automated rake lifting. Thickener underflow at 68% solids slurry density will be pumped to a concentrate filter feed tank with approximately 12 hours storage capacity. A filter press will remove water to achieve a target discharge cake moisture of 10%. Filtrate will be returned to the concentrate thickener. Filtered concentrate will be loaded into 20 ft sea-containers for transportation.

Flotation Tailings Thickening

Scavenger tailings plus cleaner scavenger tailings will be transferred to a flotation tailings thickener. Flocculant will be added to assist with solids settling. Thickener underflow at 59% solids slurry density will be pumped to the paste plant for backfill in underground mine workings or to the tailings storage facility. The thickener underflow tank will have approximately 30 minutes storage capacity.

Reagents and Consumables

Major reagents will include hydrated lime slurry, blended collector, Dowfroth 250 frother, CMC depressant, flocculant, and fluxes for smelting. SAG mill grinding media (typically 100 mm diameter balls) and ball mill grinding media (typically 50 mm diameter balls) will be delivered in 1 tonne bags. Diesel fuel will be supplied for the gold smelting furnace.

Water Services

Raw water will be sourced from 800 portal underground water, transferred to a sediment pond, and then to a raw water tank. Process water will be recovered from concentrate and tailings thickener overflow, plus decant water from the tailings storage facility. In normal operation, 1 m³/h of raw water make-up is required; this increases to 320 m³/h during paste plant flush. Filtered water will be used for mill lubrication cooling and the on-line stream analyser. Potable water will be treated and distributed for human consumption and safety showers.

Air Services

High pressure compressed air at 700 kPag will be generated by two air compressors in lead-lag configuration, dried, and distributed for plant instruments and tools. Low pressure air for the flotation circuit will be supplied by centrifugal blowers.

Plant Control System

The plant control system will be designed around a moderate level of automation and monitoring. The starting and stopping of most electrical drives and actuated valves will be performed from plant control system operator interface terminals. Equipment interlocks will be software configurable, with selected drives hard wired for personal safety protection. The process plant will be provided with one main control room with two operator interface terminals.

Key reported parameters

Technical qualifications

The processing information presented in this report is based on a proposed design for a Definitive Feasibility Study. The report states that key metallurgical design criteria were derived from metallurgical testwork results and comminution circuit modelling, with the source of each parameter identified in the design criteria table as Client, Calculated, Testwork, Modelling, or Consultant. The report notes that major unit operations and equipment will be sized with a 20% design margin. The process flowsheet and equipment selections represent the proposed design only; no historical operating data from the existing operation is presented in this section of the report. The report does not provide information on project economics, ownership, current operational status, or links to other projects.

*Source: Independent Technical Report, Kainantu Gold Mine Integrated Development Plan, Kainantu Project, Papua New Guinea National Instrument 43-101 Technical Report, October 2022, Section 17.0 Recovery Methods.*

This report documents the recovery methods and processing route assessment for the Kainantu Project, covering historical plant operations, current refurbishment status, and proposed upgrades for treatment of Kora ore.

Report context

This report, dated September 2018, provides the Mineral Resource Estimate Update and Preliminary Economic Assessment for the Kora North and Kora Deposits at the Kainantu Project. It draws on historical operating data from the Irumafimpa Mine processing between 2006 and 2008, current plant condition assessments, and scoping study findings for a proposed expansion to treat Kora ore. The processing information is based on the original plant design, operational experience, and engineering studies by Mincore Pty Ltd.

Processing route

Historical plant design

The Kainantu processing plant is located approximately 7 km from the opening of the 800 portal which accesses the Irumafimpa Mine. The plant was designed and constructed in 2005. Simple processing technology was used to treat Irumafimpa ore, consisting of crushing, screening, grinding, and flotation to separate sulphide-bearing material from non-mineralized host rock. The design throughput was 21 tonnes per hour (170,000 tpa). Approximately 10% of the ore was recovered as a high-grade gold-bearing flotation concentrate, with waste material pumped to an engineered tailings storage facility. The concentrate was packed in containers and trucked to Lae for shipping to smelters, including Japanese smelters, with specification generally acceptable to copper smelters seeking high gold and high sulphur feedstock.

Historical unit processes

The original Process Plant comprised the following unit processes:

• Ore Receiving and Crushing: ROM sizing reduction prior to reclamation for grinding. Screening and recycling was found to be problematical in previous operation and may be removed and replaced with a more suitable crusher operating in open circuit.
• Grinding and Classification: Crushed ore reclaimed and ground to the required size for flotation.
• Differential Flotation: Commencing with an Outokumpu Skimair Flash Flotation unit in the classification circuit, combined with Outokumpu tank cells treating grinding product, to recover a gold-bearing sulphide concentrate for export.
• Flotation tailings deposition in the tailings storage facility.
• On-site reagent storage and mixing facilities.
• Services for plant air and water distribution.

The plant treated ore from the Irumafimpa lodes over two separate periods between 2006 and 2008 (HPL and Barrick).

Current plant condition

The processing plant was placed on care and maintenance when processing ceased in December 2008. Following completion of studies on the redesign of the crushing circuit to handle wet clay rich mill feed, Mincore Pty Ltd was engaged by K92ML to undertake plant refurbishment and installation of a drum scrubber (Mincore, 2015). Refurbishment and repair commenced in March 2016.

A new main 415V switchboard was installed as part of the refurbishment. The process plant was enhanced by the addition of a drum scrubber commissioned in October 2016. The drum scrubber was installed to handle wet clay rich mill feed. The assay laboratory has been recommissioned under the control of Intertek.

Plant upgrade scoping study

In August 2016, Mincore completed a scoping study on requirements for upgrading the existing plant to allow treatment of Kora ore at a proposed rate of 400,000 tpa (Mincore, 2016). This was subsequently updated (Mincore 2018) following the in-progress installation of the gravity gold circuit and new lime preparation and dosing facility.

Mincore concluded that:

• There is sufficient crushing and milling power (comminution) to grind 50 tph to P80 of 106 μm.
• The current two stage crushing circuit is rated at 68 tph producing a product size P80 of 10–12 mm. However, the secondary crusher has been capacity limited during operations in 2018, and a new larger secondary crusher is proposed, with the existing crusher relegated to standby service. The new crusher will also provide a better crushed ore size distribution to maximise throughput of the downstream milling circuit.
• Additional flotation capacity is required to achieve acceptable residence times for each cell. There is sufficient space to install additional cells if future test work identifies a requirement for longer residence time.
• The existing concentrate thickener and filter is adequate for 400,000 tpa of Kora feed averaging 1.7% copper.
• The existing tailings line is adequate but a full pump upgrade will be required.

Proposed circuit modifications

Mincore suggested the following circuit modifications:

• Jaw crusher: Liner wear and capacity should be optimized by converting the existing pan feeder to grizzly finger feeder to bypass fines from jaw crusher.
• Secondary crushing: The current two stage crushing circuit is rated at 68 tph producing a product size P80 of 10–12 mm. The secondary crusher has been capacity limited during operations in 2018, and a new larger secondary crusher (J35/TC1000 or equivalent) is proposed, with the existing crusher relegated to standby service.
• Cyclone upgrade: The existing 150CVX cyclones will be upgraded to a 6 x 250CVX cyclone pack to meet the higher feed rate and recirculating load. Mass balance and cyclone selection is based on a 400 ktpa throughput (50 tph).
• Gravity circuit: A gravity concentrator is required in the milling circuit for recovery of any gravity gold. The gravity circuit will be installed to capture free gold that is liberated during the grinding process. One hundred percent of the primary mill discharge will be screened at 1 mm via a linear vibrating screen. Screen oversize will report directly back to the ball mill for further grinding. Screen undersize will gravitate to a Falcon centrifugal concentrator, which is automated to provide routine flushing of collected concentrate that will gravitate to a goldroom for upgrading via a Holman shaking table. The Holman table concentrate will be dried in an electric oven and then smelted in a gas fired barring furnace to produce Dore gold bars. Tails from the Holman table will report back to the primary cyclone feed pump for further processing. The gravity circuit is expected to recover a high proportion of the free gold, which is readily converted into Dore bars and refined for a significantly faster revenue/value realisation. The gravity circuit will reduce the amount of gold reporting to the flotation circuit, which should contribute to an overall improvement in recoveries.
• Classification arrangement: The Falcon concentrator tail will be pumped to a set of primary hydro cyclones for classification. The fine cyclone overflow will report to a Flotation Surge Tank. The cyclone underflow arrangement will remain as it currently is with a portion of the stream reporting to an existing Flash Flotation cell. The remainder of the cyclone underflow combines with the Flash Flotation tail and gravitates back into the ball mill feed chute for further grinding. The addition of the gravity screen will reduce the amount of coarse material the primary cyclones and the flash flotation cell receive, reducing wear rates and improving operating performance.
• Flotation reconfiguration: Reconfiguration of the current flotation circuit is based on preliminary test results generated by Barrick Gold indicating that Kora ore can produce a single high copper with gold concentrate. These test results were confirmed by operational results achieved during the treatment of the higher Cu-grade K2 ore lode in the first half of 2018. The existing rougher and cleaner circuits are proposed to be used for the new rougher duty since the current cleaner circuit comprises four cells which are exact duplicates of the four cells which make up the current rougher circuit. This will effectively double the capacity and provide satisfactory retention time with minimal modification. A new bank of Cleaner and Recleaner cells will need to be added and connected to the existing concentrate thickener and filter.
• Tailings: The existing tailings line is adequate but a full pump upgrade will be required.

Recommended test work

Mincore considered that test work is warranted to address:

• Further work to establish the most suitable grind size to achieve balanced liberation, recovery, concentrate grade and production rate. This has not been investigated by operations to date, and the current grind is P80 75 µm versus P80 106 µm design.
• Investigation of reagent type, addition rate and addition point, including use of new reagents (all at variable pH).
• Investigation of ore blending procedures by use of laboratory flotation tests at various grind sizes to optimise the grinding, flotation and filtering circuits.
• Variability test work to confirm comminution and flotation parameters.
• Barrick 2009 test work suggests that rougher mass pull balancing with cleaner cells will require consideration for high copper feed. Mincore suggested configuration of the 3rd and 4th Rougher Cells as Scavenger cells, and investigating the requirement for regrind of the rougher, and/or rougher scavenger concentrates. Mincore also suggested investigating opening and closed circuiting the cleaner tails, and undertaking locked cycle test work to confirm performance.
• Investigating reducing reagent consumption, particularly lime, by installation of a tailings thickener. Pumping power, water consumption and time would also be saved.

Key reported parameters

Technical qualifications

The following limitations and qualifications apply to the processing information presented in this report:

• The gravity circuit and gold room were still being installed at the time of the report. The expected Au recovery benefit from the gravity circuit of 0.5–1% may not be added to current recovery figures, as it has not been shown that the same recoveries for Cu and Au will be achieved at P80 106 μm at 400,000 tpa versus the current operation at P80 75 μm at 180,000 tpa. Parallel lab testwork is recommended with plant operation at both grind targets before and after commissioning of the gravity circuit.
• The flotation circuit reconfiguration was based on preliminary test results from Barrick Gold and confirmed by operational results from the first half of 2018. Further test work is required for reagent optimisation, ore blending procedures, variability confirmation, and locked cycle testing.
• The secondary crusher has been capacity limited during operations in 2018, and the proposed new crusher is subject to future implementation.
• Optimisation projects, such as tailings thickener installation, should be investigated during implementation of the expansion projects where results can be incorporated into the pre-commissioning phase.

Source: Mineral Resource Estimate Update and Preliminary Economic Assessment of Kora North and Kora Deposits , Kainantu Project, September 2018, Section 17: Recovery Methods.

This article details the proposed processing route for the Kora Project, based on conventional crushing, grinding, gravity recovery, flash flotation, and conventional flotation to produce a gold-silver-copper concentrate and dorè bars.

Report context

The NI 43-101 Technical Report for the Kora Project describes a processing plant designed to treat underground ore from the Kora and Judd deposits at a proposed throughput of 1.2 million tonnes per annum. The process plant design and technology are described as well proven in the industry, making use of metallurgical unit processes already used in the existing Kainantu processing plant treating these ore types. Major unit operations and equipment are sized with a 20% design margin. The crushing plant utilization is designed for 68.5% (6,000 hours per year), while the grinding and flotation plant utilization is designed for 91.3% (8,000 hours per year), supported by crushed ore storage, standby equipment in critical areas, and back-up power from an on-site diesel power station.

Processing route

Crushing and Ore Storage

The proposed single stage open circuit crushing plant will prepare Run of Mine ore for feed to the grinding circuit. ROM ore is delivered into a 150 tonne capacity ROM bin equipped with a static grizzly screen with 600 mm by 600 mm aperture. Mining will be required to supply ore at a maximum nominal particle size of 600 mm. An apron feeder beneath the ROM bin feeds ore into a 160 kW, 810 mm by 1,370 mm primary jaw crusher which reduces ore from an F80 of 317 mm to a P80 of 90 mm, operating with a closed side setting of 100 mm.

Crushed ore discharges into a surge bin with a maximum live capacity of 75 tonnes, providing 30 minutes of mill feed at design throughput. A 1,800 tonne capacity emergency static stockpile, equivalent to approximately 12 hours of mill feed storage, is provided for use during crushing circuit downtime.

Grinding and Classification

The grinding circuit comprises a conventional two stage SAB milling circuit, consisting of a single grate discharge SAG mill and a single trunnion overflow ball mill. The SAG mill operates in open circuit, while the ball mill operates in closed circuit with hydro-cyclones. The SAG mill is 5.8 m diameter by 3.35 m long, equipped with a 1,850 kW variable speed drive capable of varying mill speed within 60% to 80% of critical speed. The ball mill is 4.2 m diameter by 6.85 m long, equipped with a 1,850 kW motor operating at a fixed speed of 75% critical speed.

The grinding circuit reduces primary crushed feed to a product size of 80% passing 106 µm for downstream flotation. The cyclone cluster consists of 8 by 400 mm diameter cyclones.

Flash Flotation

A Metso SK240 dual outlet flash flotation cell will treat a portion of the cyclone underflow stream to recover gold, silver and copper bearing minerals at relatively coarse particle size. The flash flotation cell is capable of treating up to 240 tonnes per hour of feed, equivalent to 40% to 50% of the recirculating load. The concentrate is pumped to the final concentrate thickener. The mid-point tailings offtake discharges low density fine slurry that gravitates to the mill discharge hopper. The bottom tailings discharge gravitates to the ball mill for further grinding.

Gravity Circuit

The gravity circuit consists of a horizontal vibrating gravity screen and a single SB1350 Falcon centrifugal concentrator treating a portion of the cyclone underflow stream. Feed passes over a 1.5 m wide by 3.6 m long horizontal vibrating screen with 2.5 mm by 18 mm apertures. Undersize reports to the centrifugal concentrator where precious metals amenable to gravity recovery are collected into a primary gravity concentrate. The gravity concentrate is discharged on a periodic regular basis.

Gold Recovery

Gravity concentrates are processed using wet shaking tables to produce a final concentrate for direct smelting to doré. The table separation circuits comprise a rougher shaking table (Holman 8000) and a cleaner table (Gemini 250). Final concentrates are smelted in a diesel fired furnace to produce doré.

Flotation Circuit

The flotation circuit produces a gold copper concentrate for downstream thickening and filtration. The circuit consists of a rougher conditioning tank, a bank of rougher/scavenger cells, cleaner conditioning tank, two stages of cleaning and one stage of cleaner scavenging.

The flotation circuit equipment includes:

• One 47 m³ rougher conditioning tank
• Six 40 m³ rougher/scavenger cells in series
• One 20 m³ cleaner conditioning tank
• Four 10 m³ cleaner cells in series
• Four 10 m³ cleaner scavenger cells in series
• Two 5 m³ recleaner cells in series

Laboratory conditioning and flotation times from test work formed the basis for equipment sizing with industry standard scale-up factors applied. The existing processing plant flotation retention times were also considered in the interpretation and process design.

Concentrate Thickening, Filtration and Handling

Concentrates from the flotation circuit and flash flotation circuit are combined and thickened by a 9 m diameter hi-rate concentrate thickener before reporting to a batch concentrate pressure filter containing 50 chambers with 1.2 m by 1.2 m plates, providing a total installed filter area of 115 m². Dewatered cake is stored in a storage shed before being loaded into 20 ft sea-containers for dispatch from the mine site.

Key reported parameters

Technical qualifications

The report states that the process plant design and technology is well proven in the industry. The flowsheet makes use of metallurgical unit processes already used in the existing Kainantu processing plant treating these ore types. The report notes that the flotation residence time was based on aerated cell volume divided by average slurry flowrate, with effective scale-up ratio calculated based on flotation time divided by laboratory flotation time. Flotation times have effectively been scaled-up higher than the industry standard of two to three times the bench scale tests as a result of the 20% design margin being applied in the basis for cell sizing. The flotation reagent addition regime was selected based on test work, and the plant design will allow space to facilitate future installation of a xanthate reagent mixing, storage and distribution system should this be necessary.

*Source: NI 43-101 Technical Report , Kora Project, Section 17 Recovery Methods*