Overview
Nestled in the historic goldfields of Victoria, Australia, the Costerfield Operation stands as a significant producer of critical antimony and gold. Operated by Mandalay Resources Costerfield Operations Pty Ltd., a subsidiary of the Toronto-based Mandalay Resources Corporation, this facility has been a cornerstone of the regional mining industry since its modern re-establishment in 2007. The operation processes a complex sulfide ore rich in antimony and gold through its Brunswick Processing Plant, a sophisticated concentrator that has undergone continuous improvement to optimize recoveries and throughput. Located approximately 120 kilometers north of Melbourne, the project leverages existing infrastructure in a well-established mining district. The strategic importance of the Costerfield Operation cannot be overstated—antimony is classified as a critical mineral by numerous governments due to its essential role in flame-retardants, lead-acid batteries, and military applications, while gold remains a premier precious metal. The facility’s ability to efficiently recover both commodities from a single ore body makes it a technically interesting and economically vital operation, demonstrating advanced mineral processing techniques that balance high recovery rates with operational efficiency and environmental stewardship.
Key Process Stages
The Brunswick Processing Plant employs a conventional yet highly optimized circuit designed specifically for antimony-gold sulfide ore. The process flowsheet incorporates crushing, grinding, gravity separation, and flotation, followed by concentrate dewatering and tailings management. The plant has demonstrated remarkable consistency, operating 24/7 with crushing activities limited to extended day shifts to comply with local noise restrictions. Recent upgrades, including the addition of advanced flotation technology, have positioned this operation at the forefront of modern mineral processing for critical minerals.
- Stage 1: Crushing and Screening The run-of-mine (ROM) ore is reduced in size through a two-stage crushing circuit. Primary crushing is handled by mobile Finlay I-130RS and I-140RS impact crushers in closed circuit with a 35 mm screen. The secondary crushing stage utilizes a Finlay C-1540RS mobile cone crusher operating in closed circuit with a 12 mm screen. The crushed product is stored in a 40-tonne fine ore bin, which is scheduled for replacement with a 1,500-tonne capacity reclaim feeder in 2025 to enhance feed consistency and capacity.
- Stage 2: Milling and Gravity Concentration The crushed ore is fed into a two-stage, closed-circuit ball milling operation. The primary mill operates in closed circuit with a Dutch State Mines (DSM) screen. The screen undersize is fed to centrifugal gravity concentrators to recover liberated gold particles. This gravity concentrate is further upgraded on a shaking table in a dedicated gold room, producing a high-grade gold product shipped directly to local refineries. Gravity recovery for gold is exceptionally high, typically achieving 55-65% and peaking at 70% of the total gold in feed.
- Stage 3: Flotation The cyclone overflow from the milling circuit, now at a target grind size of P80 53 µm, is conditioned with lead nitrate (activator) and potassium amyl xanthate, or PAX (collector). The pulp first reports to two 48-inch StackCell roughers, followed by two additional rougher tank cells. The rougher concentrate forms part of the final product. The tailings from these cells advance to the original Denver flotation train, consisting of eight DR100 rougher/scavenger cells and six DR15 cleaner cells. To enhance recovery from the tailings stream, rougher and cleaner CavTube column flotation cells were commissioned in April 2021, producing a separate low-grade concentrate and ensuring maximum antimony and residual gold extraction.
- Stage 4: Concentrate Dewatering The final concentrates from the main flotation circuit and the CavTube columns are pumped to two separate concentrate thickeners. The thickened underflows are dewatered using a plate and frame pressure filter. The filter cake is discharged into bags, which are then packed into shipping containers for export to international customers. All thickener overflows and filtrates are recycled back into the process circuit to maximize water efficiency and minimize metal losses.
- Stage 5: Tailings Management Flotation tailings are thickened to approximately 50% w/w solids. A significant portion of these tailings is used as underground paste fill, mixed with a cement binder in a pugmill and pumped back into old mine workings. The remaining tailings are deposited in the Tailings Storage Facilities (TSFs). A new TSF with a capacity of 788,000 dry metric tonnes is under construction and expected to be operational by May 2025. Water from the tailings thickener is decanted and recycled, contributing to the site’s high water reuse rate.
Critical Data
The following table summarizes the key operational and metallurgical performance data for the Brunswick Processing Plant, highlighting its efficiency and capacity.
| Parameter | Value | Unit | Notes |
|---|---|---|---|
| Throughput (Monthly Avg.) | 11,000 – 13,000 | dmt/month | Demonstrated capacity up to 14,000 dmt/month |
| Target Grind Size | 53 | µm (P80) | Achieved via two-stage ball milling circuit |
| Antimony Recovery (LoM Forecast) | 90.1 | % | Based on Youle & Shepherd ore blend algorithm |
| Gold Recovery (LoM Forecast) | 92.2 | % | Includes ~60% gravity recovery + flotation |
| Gold Gravity Recovery | 55 – 70 | % | Varies with feed blend; peak performance noted |
| Operating Schedule | 24/7 | hours/day | Crushing operates on extended day shift only |
| Water Reuse | High | – | Extensive recycling from thickeners and TSF |
| Make-up Water Source | 1.5 – 2.0 | ML/day | Primarily from underground dewatering |
Additional Interesting Data and Summary
The Costerfield Operation is a exemplar of modern, responsible mining, integrating technical innovation with stringent environmental and social governance (ESG) principles. A key feature of the site’s sustainability is its sophisticated water management system. The plant operates with a positive water balance due to continuous underground dewatering, producing 1.5 to 2 million liters of water per day. To manage this, a reverse osmosis (RO) plant with a capacity of 2 ML/day was installed in 2014, with a pre-treatment plant added in 2017 to enhance its reliability. Excess water is handled by the Splitters Creek evaporation facility, which has a net evaporation capacity of approximately 104 ML per year.
From a technical perspective, the operation has focused on continuous improvement through strategic debottlenecking and technology adoption. The 2021 installation of Eriez CavTube column flotation cells on the tailings stream is a prime example, designed to scavenge additional value and improve overall recovery, particularly important as the head grades from the Shepherd ore zone are typically lower. Power infrastructure was consolidated and upgraded in 2019 to increase efficiency and allow for the integration of backup diesel generation, ensuring operational resilience.
The economic impact of the operation is significant, providing stable employment in the region and contributing to the global supply of critical antimony. The future outlook remains positive, supported by a robust Life of Mine (LoM) plan and ongoing infrastructure investments, such as the new TSF and the fine ore bin upgrade. The processing plant’s flexibility and proven performance over its 14-year history suggest it is well-equipped to handle the planned ore feed blends for the foreseeable future, ensuring that the Costerfield Operation will remain a key player in the critical minerals market.
Source: NI 43-101 Technical Report | Date: March 2025
Further Reading
- https://alkres.com/projects/costerfield/
Technical report and processing history
The following archived source profiles have been consolidated here to preserve the project’s processing history and study context.
Costerfield Operation — 2025 Technical Report (Recovery Methods)
Costerfield Operation — 2025 Technical Report (Recovery Methods)
| Company | Mandalay Resources |
| Date | March 2025 |
| Region | Victoria, Australia |
| Commodities | Gold, Antimony |
Executive Summary
The Brunswick Processing Plant at the Costerfield Operation treats antimony and gold rich sulfide ore through a conventional comminution and flotation style concentrator. Operating since 2007 and managed by Mandalay Resources since late 2009, the plant has undergone several upgrades to increase production capacity to approximately 10,000–13,000 t/month over the 2015–2024 calendar years. The concentrator operates 24 hours per day, 7 days per week, utilizing a well-proven circuit suited to processing the Costerfield ores remaining in the Life of Mine plan.
The processing circuit involves surface crushing and screening followed by a two-stage, closed circuit ball milling circuit. Centrifugal style gravity concentrators are used to recover a gold-rich gravity concentrate, which is upgraded on a shaking table and sold as a separate product. Secondary milled products are processed through a flotation circuit comprising StackCell roughers, tank cells, and CavTube flotation columns added in 2021 to recover antimony and remaining gold.
The flotation concentrate is dewatered through thickeners and filtration to produce a final antimony-gold concentrate product shipped overseas. Forecast average LoM 2025 recoveries are 90.1% for antimony and 92.2% for gold. The plant maintains a positive water balance and utilizes paste fill for underground disposal of tailings where applicable.
Reports
Costerfield Operation — 2025 Technical Report
Costerfield Operation — 2025 Technical Report
| Company | Mandalay Resources |
| Date | 2025 |
| Region | Victoria, Australia |
| Commodities | Gold, Antimony |
Executive Summary
The Costerfield Operation in Victoria, Australia is an underground mining project currently operated by Mandalay Resources. The site features the Brunswick Processing Plant, which has been in operation since 2007 and has been managed by Mandalay since late 2009. The facility treats antimony and gold-rich sulfide ore using a conventional comminution and flotation concentrator. Recent plant upgrades have increased production capacity to approximately 10,000–13,000 dry metric tonnes per month.
The processing circuit involves a two-stage closed circuit ball milling process following surface crushing and screening. Crushed ore is processed through mobile impact and cone crushers before entering the milling circuit. Gravity concentration is employed using centrifugal style concentrators and shaking tables to recover a high-grade gold concentrate, which is sent to local refineries. The milling circuit targets a grind size P80 of 53 µm.
The flotation circuit is designed to recover an antimony-gold rich sulfide concentrate. It utilizes StackCell roughers, Denver DR100 and DR15 cells, and CavTube flotation columns added in 2021. The final concentrate is dewatered and shipped overseas, while tailings are thickened for use in tailings storage facilities or underground paste fill. The circuit is described as simple, conventional, and well-proven for the remaining life of mine plan.
Website: https://alkres.com/projects/costerfield/ Report Date: 2025 Region: Victoria, Australia Project Status: Commodity: Gold, Antimony Throughput: Mine Life: Mine Type: Ore type:Costerfield Operation — 2024 Technical Report
Costerfield Operation — 2024 Technical Report
| Company | Mandalay Resources |
| Date | 2024 |
| Region | Victoria, Australia |
| Commodities | Gold, Antimony |
Executive Summary
The Brunswick Processing Plant at the Costerfield Operation treats antimony and gold rich sulfide ore through a conventional comminution and flotation style concentrator. Operating since 2007 and managed by Mandalay Resources since late 2009, the plant has undergone several upgrades to increase production capacity to approximately 10,000–13,000 t/month. The facility operates 24 hours per day, 7 days a week, utilizing a well-proven circuit suited to processing the remaining Costerfield ores in the Life of Mine plan.
The processing circuit includes surface crushing and screening, followed by a two-stage closed circuit ball milling circuit. Gravity concentration is employed using centrifugal style concentrators and shaking tables to recover a gold-rich concentrate. The remaining ore undergoes flotation using StackCell roughers, tank cells, and CavTube columns to recover an antimony-gold rich sulfide concentrate.
Recent upgrades include the installation of CavTube flotation columns in April 2021 and additional mobile impact crushers in 2022 to improve throughput and redundancy. The plant demonstrates consistent recoveries, with forecast average LoM 2024 recoveries of 90% for antimony and 93.6% for gold. Tailings are managed via TSFs and underground pastefilling.
Website: https://alkres.com/projects/costerfield/ Report Date: 2024 Region: Victoria, Australia Project Status: Commodity: Gold, Antimony Throughput: Mine Life: Mine Type: Ore type:Costerfield Property — 2021 Technical Report
Costerfield Property — 2021 Technical Report
| Company | Mandalay Resources |
| Date | 2021 |
| Region | Victoria, Australia |
| Commodities | Gold, Antimony |
| Mine Type | Underground |
| Throughput | 13,000 dmt/month |
| Status | Operating |
Executive Summary
The Brunswick Processing Plant at the Costerfield Property treats antimony and gold rich sulphide ore through a conventional comminution and flotation style concentrator. The plant has been operating since 2007 and has been managed by Mandalay Resources since late 2009. Recent upgrades have increased production capacity to approximately 13,000 dry metric tonnes per month over the 2015 to 2021 calendar years. The concentrator operates 24 hours per day, 7 days per week, with crushing operations adhering to noise restriction guidelines during extended dayshift hours.
The processing circuit includes a two-stage closed circuit ball milling circuit fed by underground ore. Centrifugal style gravity concentrators recover a gold-rich gravity concentrate which is upgraded on shaking tables and sold as a separate product. The secondary milled products are processed through a flotation circuit comprising StackCell roughers, tank cells, and CavTube flotation columns added in April 2021. The flotation concentrate is dewatered through thickeners and filtration to produce a final antimony-gold concentrate product shipped overseas.
Forecast recoveries for the Life of Mine plan are 94.1% for antimony and 92.7% for gold, consistent with 2021 end-of-year reconciled plant recoveries. Further incremental plant upgrades scheduled for 2022 include a second filter press for redundancy and a third impact crusher to transition crushing to a two-stage operation. The flowsheet is well-proven and suited to processing the remaining Costerfield ores in the Life of Mine plan.
Website: https://www.mining-plus.com/case-study/costerfield/ Report Date: 2021 Region: Victoria, Australia Project Status: Operating Commodity: Gold, Antimony Throughput: 13,000 dmt/month Mine Life: Mine Type: Underground Ore type:Costerfield Operations — 2020 Technical Report
Costerfield Operations — 2020 Technical Report
| Company | Mandalay Resources |
| Date | 2020 |
| Region | Victoria, Australia |
| Commodities | Gold, Antimony |
Executive Summary
The Brunswick Processing Plant at the Costerfield Operations is an underground mine facility that has been operating since 2007 and has been managed by Mandalay Resources since late 2009. The plant processes sulphide gold-antimony ore through a conventional comminution and flotation-style concentrator. Since 2009, various upgrades have increased production to an average of approximately 12,000 tonnes per month over the 2015–2019 period, with a budgeted throughput of 12,940 t/month for 2020. The plant operates continuously, 24 hours per day, 7 days per week.
The processing circuit includes a two-stage closed-circuit ball milling system fed by a mobile impact crusher. Gravity concentration is employed using centrifugal-style concentrators and shaking tables to recover a high-grade gold concentrate, which accounts for 20%–40% of the gold in the feed. The remaining gold and antimony are recovered through a flotation circuit comprising rougher, scavenger, and cleaner stages using Denver cells and a trial StackCell® unit. The final concentrate is dewatered via thickening and filtration before shipment.
Recovery rates for 2019 were 95.3% for antimony and 77.7% for gold, with forecasts for the Life of Mine (LoM) to end-2020 estimating 96.0% antimony and 87.0% gold recovery. The plant capacity has been successfully upgraded to over 14,000 t/month, though recent production has been constrained by underground mining rates. Ongoing projects focus on mitigating gold recovery issues associated with arsenopyrite in the Brunswick ore and increasing dewatering capacity.
Processing Overview
- Crushing: Mobile Impact Crusher (Finlay I-130RS)
- Milling: Two Ball Mills in Series
- Gravity: Centrifugal-style Gravity Concentrators, Shaking Table
- Flotation: Rougher, Scavenger, Cleaner (Denver DR100, DR15, StackCell)
- Leaching: None
- Dewatering: Thickening, Plate and Frame Pressure Filter
Reports
Costerfield Property — 2020 Technical Report
Costerfield Property — 2020 Technical Report
| Company | Mandalay Resources |
| Date | 2020 |
| Region | New South Wales, Australia |
| Commodities | Antimony, Gold |
Executive Summary
The Brunswick Processing Plant at the Costerfield Property treats antimony and gold rich sulphide ore through a conventional comminution and flotation style concentrator. Operating since 2007 and managed by Mandalay Resources since late 2009, the plant has undergone several upgrades to increase production capacity to approximately 12,000 t/month over the 2015 to 2020 calendar years. The concentrator operates 24 hours per day, 7 days per week, with crushing operations adhering to noise restriction guidelines during extended dayshift hours.
The processing circuit includes surface crushing and screening, a two-stage closed circuit ball milling circuit, and centrifugal style gravity concentrators to recover a gold-rich gravity concentrate. The secondary milled products are processed through a flotation circuit comprised of StackCell® roughers, tank cells, scavenger, and cleaning stages. The final antimony-gold concentrate is dewatered and shipped overseas, while tailings are thickened and pumped to storage facilities.
Plant upgrades scheduled for 2021 include a second Stack Cell® primary rougher and additional flotation cells on the final tailings to recover a separate, lower grade antimony-gold concentrate. The plant has demonstrated ongoing production creep, with average throughput between 2015 and 2020 ranging from approximately 11,900 to 12,979 DMT/month. Forecast recoveries for the Life of Mine (LOM) are 95% for antimony and 90% for gold.
Website: https://www.mining-plus.com/case-study/costerfield/ Report Date: 2020 Region: New South Wales, Australia Project Status: Commodity: Antimony, Gold Throughput: Mine Life: Mine Type: Ore type: