Project Overview
Location: Waihi, North Island, New Zealand
Process Type: Conventional CIP Plant
Annual Production: 800,000 tonnes (increasing from 660,000)
Feed Grade: Not specified
Recovery Rate: Historical 85-95%
Final Product: Not specified
Project Stage: Plant Upgrade
Detailed Process Description
Comminution Circuit
The Waihi processing facility employs a sophisticated comminution circuit designed to handle both open-pit and underground ores. The circuit begins with a static grizzly (150mm aperture) followed by jaw crushing to achieve a P80 of 110-130mm. The SAG mill operates with a 10% ball load and draws between 2.1 and 2.5 MW of power. The facility is undergoing a significant upgrade with the replacement of the existing 1.2 MW ball mill with a new 1.8 MW tower mill for enhanced grinding efficiency.
Leaching and Adsorption
The leaching circuit consists of five leach tanks and seven carbon-in-pulp (CIP) adsorption tanks, providing a total residence time of 24 hours for open-pit ore and 48 hours for underground ore. The pre-leach thickener increases slurry density from approximately 15% to 37-40% solids. Cyanide concentration is maintained at 250-280 ppm, with oxygen addition in the first leach tank to enhance kinetics and reduce cyanide consumption.
Elution and Recovery
The facility utilizes the AARL elution process, operating at high temperature and pressure to strip precious metals from loaded carbon. The circuit includes carbon regeneration capabilities with a kiln operating at 650-750°C with a 20-minute residence time. The electrowinning circuit produces gold and silver-bearing sludge which is dried, mixed with fluxes, and smelted at 1200°C to produce doré bars.
Plant Upgrades
Current upgrades include installation of larger capacity Derrick interstage screens, replacement of air lifts with centrifugal recessed impeller carbon advance pumps, and enhancement of the tailings pumping system. The modifications will increase underground ore processing capacity from 0.66 Mt to 0.8 Mt per annum, while maintaining the ability to process 1.25 Mt per annum of open pit ore.
Environmental Controls
The operation includes a comprehensive water treatment plant (WTP) capable of handling 1,800 m³/hr for metals removal and 500 m³/hr for cyanide destruction and metals removal. The WTP incorporates both metals precipitation and cyanide oxidation processes, ensuring environmental compliance before discharge to the Ohinemuri River.
Technical report and processing history
The following archived source profiles have been consolidated here to preserve the project’s processing history and study context.
Waihi District – Martha Underground Feasibility Study
Waihi District – Martha Underground Feasibility Study
| Company | OceanaGold |
| Mine | Waihi Operation |
| Date | 2021 |
| Region | Waihi, New Zealand |
| Commodities | Gold, Silver |
Executive Summary
This NI 43-101 Technical Report details the Martha Underground Feasibility Study for the Waihi Operation owned by OceanaGold. The report outlines the processing capabilities and metallurgical performance of the existing plant, which has been in operation for 30 years. The facility is designed to treat Martha underground mineral reserve ore with a capacity of 900,000 tonnes per annum.
The metallurgical process utilizes a conventional SAG Mill-Ball Mill grinding circuit followed by Carbon-in-Pulp (CIP) leaching and adsorption. The plant achieves an average processing recovery of 94.9% for gold and silver. Processing unit costs have ranged from NZD 30-40 per tonne milled, dependent on ore availability and throughput rates.
The study includes a processing plan for the Mineral Reserve covering the years 2021 to 2028. The process plant is also suitable for processing other resources from Waihi and WKP, with flotation and ultrafine grind currently being evaluated to improve recoveries.
Reports
Website: https://oceanagold.com/operations/waihi
Report Date: 2021
Region: Waihi, New Zealand
Project Status:
Commodity: Gold, Silver
Throughput:
Mine Life:
Mine Type:
Ore type:
Waihi Operations — 2020 Preliminary Economic Assessment
Waihi Operations — 2020 Preliminary Economic Assessment
| Company | OceanaGold |
| Date | 2020 |
Executive Summary
The Waihi Operations, operated by OceanaGold, represents a well-established gold-silver mining complex in New Zealand. The facility utilizes a conventional SABC (SAG-Ball-Crusher) circuit followed by a hybrid Carbon-in-Leach (CIL) and Carbon-in-Pulp (CIP) circuit to recover precious metals. Historically, the plant has processed both open pit and underground ore, though it entered a care and maintenance phase in early 2020.
This technical report details a multi-phased expansion strategy intended to increase processing capacity to 1.6 Mtpa by 2026. The plan involves the installation of a modular primary jaw crusher, an upgraded SAG and ball milling circuit, and enhancements to the leaching and thickening infrastructure to support increased production from multiple underground (MUG, WKP) and open pit (GOP, MOP5) sources.
Website: https://oceanagold.com/operations/waihi
Report Date: 2020
Region:
Project Status:
Commodity:
Throughput:
Mine Life:
Mine Type:
Ore type:
Waihi Gold Mine — 2018 Technical Report
Waihi Gold Mine — 2018 Technical Report
| Company | Waihi Gold Mine |
| Date | 2018 |
| Region | Waihi |
| Commodities | Gold, Silver |
| Mine Type | Open Pit & Underground |
| Throughput | 1.25 Mt/yr (Martha), 0.8 Mt/yr (Correnso) |
| Mine Life | Not Specified |
| Status | Operating |
Executive Summary
The Waihi Gold Mine processing plant has been successfully operating for 30 years with a well-established workforce and management team. The facility is designed to treat ore from both surface and underground mines, with a capacity to process up to 1.25 million tonnes of Martha ore or 800,000 tonnes of Correnso ore per annum. The plant utilizes a conventional SAG Mill-Ball Mill grinding circuit followed by leaching and adsorption.
The metallurgical process involves comminution, leaching/adsorption, elution, electrowinning, and smelting. Ore is crushed, ground, and thickened before entering a Carbon-in-Pulp (CIP) circuit. The loaded carbon is eluted, and the resulting gold and silver bearing sludge is smelted into doré bullion for shipment to the Mint. Metallurgical accounting is primarily based on the tonnage of wet ore processed and gold receipts from the Mint.
The plant is currently in an operating status and is suitable for both Waihi and WKP ores. Flotation and ultrafine grind are currently being evaluated to improve process recoveries. The process plant is well-tested and proven technology, having been in operation for 30 continuous years.
Operational Details
Website: https://www.waihigold.co.nz/
Report Date: 2018
Region: Waihi
Project Status: Operating
Commodity: Gold, Silver
Throughput: 1.25 Mt/yr (Martha), 0.8 Mt/yr (Correnso)
Mine Life: Not Specified
Mine Type: Open Pit & Underground
Ore type:
Waihi Gold Mine — 2014 Technical Report
Waihi Gold Mine — 2014 Technical Report
| Company | Waihi Gold Mine |
| Date | 2014 |
| Region | Waihi, New Zealand |
| Commodities | Gold, Silver |
| Mine Type | Underground, Open Pit |
| Status | Operating |
Executive Summary
The Waihi Gold Mine processing plant utilizes well-tested and proven metallurgical technology that has been in continuous operation for 27 years. The facility handles ore from both underground and open pit sources, with specific processing streams for Martha and Correnso ore types. The plant operates with a SCADA control system to optimize major streams and processing parameters.
The comminution circuit involves reclaiming underground stockpile ore at 80 tonnes per hour, followed by crushing via a jaw crusher and SAG mill. The SAG mill discharge is sized using a trommel, with oversize material recycled through an HP100 cone crusher. The grinding circuit utilizes cyclones to classify slurry before sending overflow to the leaching circuit.
Leaching and adsorption are conducted using a CIP circuit with six leach and six adsorption tanks, providing residence times of 24 to 48 hours depending on ore type. Loaded carbon undergoes elution, electrowinning, and smelting to produce doré bars. The plant has a capacity to treat 1.25 million tonnes of Martha ore or 800,000 tonnes of Correnso ore per annum.
Website: https://www.waihigold.co.nz/
Report Date: 2014
Region: Waihi, New Zealand
Project Status: Operating
Commodity: Gold, Silver
Throughput:
Mine Life:
Mine Type: Underground, Open Pit
Ore type:
