South Fishhook Mineral Processing

Overview

The South Fishhook mine represents a pivotal development in the global polymetallic mining landscape, serving as a flagship project for high-efficiency mineral processing in challenging geological environments. Located in a region renowned for its rich mineral endowment, the South Fishhook project focuses on a complex orebody containing a diverse suite of metals including lead, zinc, copper, silver, and gold. The project’s significance lies not only in its substantial resource base but also in its adoption of cutting-edge metallurgical techniques designed to maximize recovery while adhering to stringent environmental and sustainability standards. Managed by a leading mineral exploration and development firm, South Fishhook has undergone rigorous technical assessments, culminating in a processing design that emphasizes scalability and operational flexibility.

The mine is strategically positioned to meet the growing global demand for base and precious metals. With a design throughput of approximately 800,000 tonnes per annum (t/a), the facility is engineered to process high-grade polymetallic ore through a sequential flotation circuit. This approach is necessitated by the complex mineralogical associations within the South Fishhook deposit, where fine-grained sulfides require advanced comminution and selective separation stages. The project’s technical framework, as outlined in recent feasibility studies, highlights an average head grade of 2.9% lead and 4.6% zinc, alongside significant silver (159 g/t) and gold (1.37 g/t) credits. By integrating high-availability crushing and grinding circuits with sophisticated filtration systems, South Fishhook is poised to become a benchmark for efficiency and resource optimization in the polymetallic sector.

Key Process Stages

The South Fishhook processing circuit is designed to handle a wide range of ore hardness and mineralogical variability, ensuring consistent concentrate quality across the life of the mine. The flowsheet incorporates the following critical stages:

• Primary Crushing: The process begins with a single-stage open circuit crushing plant. Run-of-Mine (ROM) ore is delivered to a primary crusher with a design capacity of 290 tonnes per hour (t/h), reducing the feed size to an 80% passing (P80) of approximately 7.12 mm.
• Comminution and Grinding: The crushed ore is conveyed to a grinding circuit consisting of a Ball Mill operating in a closed circuit with a hydrocyclone cluster. The grinding circuit is designed for an 8,000 h/a availability, targeting a fine primary grind size P80 of 40 µm to ensure the liberation of fine-grained sulfides.
• Polymetallic Sequential Flotation: The core of the recovery process is a sequential selective flotation circuit. This involves multiple stages to selectively recover metals in the following order:
  • Lead-Copper Circuit: Initial flotation stages target the recovery of lead and copper. This circuit includes rougher and scavenger stages, with the resulting concentrates subjected to regrinding and multiple cleaning stages.
  • Zinc Circuit: The tailings from the lead-copper circuit report to the zinc flotation stage. This circuit utilizes specific reagents to activate and recover zinc sulfides into a high-grade concentrate.
• Regrinding and Cleaning: To meet market specifications, rougher concentrates undergo regrinding in dedicated mills. This further size reduction improves mineral liberation and cleans particle surfaces, which is critical for achieving high concentrate grades (e.g., 47.4% Pb in the lead concentrate).
• Thickening and Filtration: The final concentrates and the final tailings are processed in high-rate thickeners. The thickened products are then dewatered using vertical plate-and-frame filter presses to produce low-moisture filter cakes suitable for transport and disposal.
• Tailings Management: Tailings are thickened to a high density and handled via an overland pumping system to a dedicated tailings management facility (TMF), with some material potentially repurposed for aggregate fill.

Critical Data

The following table summarizes the primary design criteria and metallurgical performance targets for the South Fishhook mineral processing plant.

Technical Details and Sustainability

The technical sophistication of the South Fishhook project is best exemplified by its approach to mineral liberation and deleterious element management. The orebody’s fine-grained nature necessitates a primary grind of 40 micrometers, a significantly finer specification than many standard base metal operations. Metallurgical testwork, including locked cycle tests (LCT), has demonstrated that this fine grind is essential for decoupling complex mineral associations, particularly between galena, sphalerite, and various silver-bearing minerals. The Bond Ball Mill Work Index of 9.5 kWh/t indicates a relatively soft to medium-hard ore, allowing the facility to achieve this fine grind without excessive energy consumption, thereby optimizing the plant’s power-to-throughput ratio.

One of the significant challenges addressed during the Pre-Feasibility Study (PFS) was the presence of deleterious elements such as arsenic, antimony, and mercury within the sulfides. Advanced flotation chemistry and a “scalping stage” in the lead-copper circuit have been integrated to mitigate these impacts. In this scalping stage, fast-floating minerals are recovered early to prevent the over-grinding of brittle sulfides and to reduce the reporting of impurities to the final concentrates. This ensures that the produced concentrates remain highly marketable and avoid heavy smelter penalties, supporting the project’s long-term economic viability.

Environmental stewardship and sustainability are core components of the South Fishhook operational philosophy. The water management system is designed for high-rate reclamation, utilizing thickened tailings to minimize the footprint of the Tailings Management Facility (TMF) and reduce the volume of fresh water required from local sources. By achieving a high underflow density in the tailings thickeners, the project reduces the risk of seepage and enhances the geotechnical stability of the dry-stack or paddock-style storage areas. Furthermore, the potential for repurposing crushed waste rock as cemented aggregate fill (CAF) or paste aggregate fill (PAF) for underground backstopping offers a circular economy approach to waste management, significantly reducing the surface environmental impact.

Looking forward, South Fishhook is evaluating the integration of renewable energy sources to power the primary mills and flotation cells, aiming to further lower its carbon intensity. The project’s commitment to sustainable development, combined with its robust technical design, ensures that it is well-equipped to navigate the complexities of modern mining while delivering critical minerals necessary for the global energy transition.

Source: South Fishhook

Source: NI 43-101 Technical Report

This article provides an overview of mineral processing developments based on publicly available technical reports and industry analysis.