Optimizing Mineral Processing: A Deep Dive into the Murray Brook Project's 3,300 tpd Polymetallic Circuit

Overview

Nestled in the prolific Bathurst Mining Camp of New Brunswick, Canada, the Murray Brook Project represents a significant venture in modern polymetallic mineral processing. Operated by Canadian Copper Inc., this project is a masterclass in strategic asset optimization, breathing new life into existing infrastructure. The core strategy involves transporting mineralized material from the Murray Brook deposit to the previously dormant Caribou processing complex, located just 10 kilometers to the east. This facility, a 3,000-tonne-per-day (tpd) lead and zinc concentrator, was constructed in 1997 but faced a history of operational suspensions due to market fluctuations and underground feed challenges, last operating in 2022. The 2025 Preliminary Economic Assessment, detailed in an NI 43-101 Technical Report, outlines a plan to not only recommission this plant but to enhance its capacity to 3,300 tpd and introduce a new revenue stream: copper concentrate production. This initiative leverages proven flotation technology and existing capital equipment to process 1.2 million tonnes annually, recovering zinc, lead, and copper concentrates for the global market. The project underscores key trends in the mining industry: the economic and environmental benefits of brownfield development, the importance of adaptive processing flowsheets for complex ores, and the drive towards maximizing resource value through technical innovation.

Key Process Stages

The Murray Brook processing circuit is a sophisticated, multi-stage flotation plant designed to separate and upgrade zinc, lead, and copper minerals from the run-of-mine ore. The flow sheet is a classic example of sequential flotation with regrinding for liberation enhancement, utilizing the existing Caribou plant layout with strategic modifications.

• Stage 1: Primary Crushing Run-of-mine (ROM) material from the Murray Brook deposit is initially reduced in size by a contractor-operated portable jaw crusher. The circuit is designed to achieve a target product size of 102 mm (P80). The crushed material is then conveyed to two large SAG mill feed storage bins, providing a significant live storage capacity of 29 hours to ensure consistent feed to the grinding circuit and buffer any upstream mining or crushing delays.
• Stage 2: Primary Grinding (SAG & Ball Mill Circuit) The primary grinding circuit is a two-stage operation critical for liberating the valuable minerals. It consists of a 1,491 kW Semi-Autogenous Grinding (SAG) mill in closed circuit with screens, followed by two ball mills (1,864 kW and 746 kW) in closed circuit with a hydrocyclone cluster. The 746 kW ball mill is a key debottlenecking component, repurposed from its previous duty as a zinc regrind mill to handle the harder Murray Brook ore and enable the 10% capacity increase. The circuit is designed to reduce the feed from 102 mm to a very fine target grind size of 40 microns (P80) to ensure adequate mineral liberation for the subsequent flotation stages.
• Stage 3: Bulk Flotation & Regrinding The cyclone overflow reports to the bulk flotation circuit, where copper and lead minerals are first floated together away from the zinc and waste rock. Reagents like lime, zinc sulphate, and sodium cyanide are added to depress the zinc minerals. The bulk copper-lead concentrate from the rougher and scavenger cells is then pumped to a dedicated regrinding circuit featuring two parallel 500 kW IsaMills. This ultra-fine grinding step reduces the particle size further to a P80 of 12 microns, breaking apart middling particles to enhance liberation before the copper and lead are separated from each other.
• Stage 4: Copper/Lead Separation and Zinc Flotation The finely ground bulk concentrate enters the lead rougher flotation cells. Here, specific depressants and frothers are used to selectively float the lead minerals, leaving the copper minerals in the tails, which report to the copper concentrate thickener. The lead rougher concentrate is cleaned to produce a final lead concentrate. Meanwhile, the tailings from the initial bulk flotation circuit (which contain the zinc) are conditioned with copper sulphate to activate the zinc minerals and are then fed to the zinc rougher and scavenger flotation cells. The zinc concentrate is also reground in a single 500 kW IsaMill to a P80 of 20 microns before undergoing a four-stage cleaning circuit to produce a high-grade zinc concentrate.
• Stage 5: Concentrate Dewatering and Tailings Management The final copper, lead, and zinc concentrates are each thickened in their dedicated thickeners (5m for Cu/Pb, 12m for Zn). The thickener underflows are pumped to filter presses—one press alternates between filtering copper and lead concentrates, while a second is dedicated to zinc. The target filter cake moistures are 8.0%, 9.2%, and 8.5% respectively, making the product suitable for shipping. Final tailings are pumped to a managed tailings storage facility, with decant water recovered and recycled back into the process to minimize freshwater consumption.

Critical Data

The following table summarizes the key technical and operational parameters that define the Murray Brook processing circuit’s design and expected performance.

Additional Interesting Data and Summary

Beyond the core process flow, the Murray Brook Project is defined by its clever use of existing infrastructure, detailed reagent strategy, and significant energy management. The economic viability is heavily reliant on re-using the majority of the Caribou plant’s equipment, as detailed in Table 17-1 of the technical report. For instance, the plan utilizes all 10 existing rougher flotation cells (14.2 m³ each) and 18 first/second cleaner cells. A notable modification is the repurposing of a 746 kW ball mill from zinc regrind duty to primary grinding, a change critical to achieving the increased throughput with the harder ore. The reagent regime is complex, designed for selective flotation of the three metals. Annual consumption estimates include 2,770 tonnes of quicklime for pH control, 542 tonnes of sodium cyanide as a zinc depressant, and 1,127 tonnes of zinc sulphate for the same purpose. The consumption of grinding media is substantial, forecasted at 373 t/a for the SAG mill and 866 t/a for the ball mills, representing a major operating cost.

From a sustainability and ESG perspective, the project has integrated several key considerations. The water balance is designed to maximize recycling, with the vast majority of process water (estimated at 2.01 Mm³/a) coming from thickener overflows and tailings facility decant. Freshwater make-up is minimized to only 0.26 Mm³/a, significantly reducing the project’s environmental footprint and strain on local water resources. The estimated power consumption of 68 GWh per year is a major cost and environmental factor. While the report doesn’t specify renewable energy plans, this level of consumption will be a focus for efficiency improvements. The comprehensive NI 43-101 report also covers tailings management facility design, closure plans, and community engagement, all critical for modern permitting and social license to operate. The success of the Murray Brook Project could serve as a blueprint for other junior mining companies looking to revitalize idle processing assets with new ore sources, demonstrating a path to production that is both capital-efficient and technically robust.

Source: NI 43-101 Technical Report | Preliminary Economic | Project: Murray Brook Project | Date: June 2025

Further Reading

• Canadian Copper to Acquire Caribou Processing Plant …
• Canadian Copper to acquire Caribou processing plant in …
• Canadian Copper Provides Status Update on Preliminary …
• Canadian Copper Provides Status Update on Preliminary …