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/
