Kainantu Gold Mine Integrated Development Plan

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.*