Technical Deep-Dive: The Point Occurrence (Pine Point) Mineral Processing Circuit and Strategic DMS Implementation

Overview

The Point Occurrence (historically and technically identified as the Pine Point Zinc-Lead Project) represents one of the most significant redevelopment opportunities in the North American base metals sector. Situated on the south shore of Great Slave Lake in the Northwest Territories, Canada, the site is managed by Pine Point Mining Limited, a subsidiary of Osisko Metals Incorporated. This project is not merely a restart of a former operation; it is a technical reimagining of a world-class Mississippi Valley Type (MVT) district that historically produced over 64 million tonnes of high-grade ore under the stewardship of Cominco between 1964 and 1988.

The significance of the Point Occurrence lies in its vast footprint, comprising over 50 known deposits of varying sizes and grades. Historically, the district was known for its exceptional metal recoveries and clean concentrates, which were highly sought after by global smelters. Today, the project’s redevelopment centers on leveraging modern mineral processing technologies—specifically Dense Media Separation (DMS) and sensor-based sorting—to enhance economic viability and minimize environmental impact. By pre-concentrating the mineralized material, the project aims to reject up to 50% of barren waste rock before it ever enters the energy-intensive grinding and flotation circuits. This strategic approach significantly reduces the carbon footprint and operational costs, making it a benchmark for sustainable mineral processing in the 21st century. As global demand for high-quality zinc and lead remains robust, the technical sophistication of the Point Occurrence’s circuit remains a focal point for mining engineers and metallurgical specialists worldwide.

Key Process Stages

The processing circuit for the Point Occurrence is designed to handle the unique mineralogical characteristics of the MVT ores, which include galena and sphalerite hosted in dolomitized limestone. The flowsheet is characterized by a high degree of pre-concentration and sequential flotation stages.

• Primary and Secondary Crushing: The Run-of-Mine (ROM) material is first processed through a 42 x 65 gyratory crusher, reducing the ore to a -5 inch size. This is followed by a secondary crushing stage utilizing shorthead cone crushers to achieve a product size suitable for pre-concentration.
• Dense Media Separation (DMS) / Pre-Concentration: A critical stage where the material is subjected to heavy liquid separation. Tests have confirmed that the Pine Point materials are highly amenable to DMS, with the ability to reject approximately 40% to 50% of the mass as waste while maintaining high metal recoveries.
• Grinding Circuit: The pre-concentrated material is directed to a conventional grinding circuit. Historically, this consisted of two open-circuit rod mills (9 ft x 12 ft) followed by two closed-circuit ball mills (10 ft x 16 ft) in combination with cyclone classifiers. The target grind size is typically around 70 μm (P80) for optimal liberation.
• Pre-Flotation (Bitumen Removal): A specialized stage essential for Pine Point ores. Many of the deposits contain bitumen-activated slimes that can interfere with the flotation of lead and zinc. A pre-flotation circuit is employed to remove these organics, ensuring high-quality concentrates.
• Lead Flotation Circuit: Lead is recovered first through a series of rougher, middling, and cleaning stages (typically two cleaning stages). This produces a high-grade lead concentrate, often exceeding 70% Pb.
• Zinc Flotation Circuit: The tailings from the lead circuit are conditioned and fed into the zinc flotation circuit. This includes roughing, middling, and a multi-stage cleaning process (up to three stages) to produce a zinc concentrate grading over 60% Zn.
• Dewatering and Handling: Final concentrates are thickened and filtered (utilizing drum or plate-and-frame filters) to achieve transportable moisture levels before being bagged or stockpiled for shipment.

Critical Data

The following table summarizes the historical performance and modern technical projections for the Point Occurrence processing facility based on recent Mineral Resource Estimate (MRE) updates and historical production records.

Technical Details and Sustainability

The technical evolution of the Point Occurrence flowsheet reflects a broader shift in the mining industry toward “Lean Processing.” One of the most significant technical challenges at the site is the variability across different mineralized zones. For instance, the R190 deposit is known for high grades and excellent liberation, whereas the N204 zone features finer-grained mineralization that requires more intensive grinding and potentially higher reagent consumption to achieve economic recoveries. Recent metallurgical testwork performed by Osisko Metals (2018-2024) has focused on these differences, utilizing QEMSCAN technology for Particle Mineral Analysis (PMA). This analysis revealed that at a grind size of 70 μm, galena and sphalerite achieve liberations of 70% and 80% respectively, which is sufficient for high-grade flotation but highlights the need for precise circuit control.

A major technical innovation being investigated for the project is sensor-based sorting. By using X-ray Transmission (XRT) or similar sensors, the plant can identify and remove waste rock at a coarser size than conventional DMS, further reducing energy requirements. This is particularly relevant for the “Sphinx” circuit configuration, which was historically designed to handle harder material from specific deposits like X15. Modernizing this involves integrating variable speed drives on mills and advanced froth cameras in flotation cells to manage the subtle shifts in ore chemistry.

Sustainability is integrated into the core design of the Point Occurrence project. The use of DMS is a primary environmental lever; by rejecting half the mass as barren rock early in the process, the volume of tailings produced is halved. These “DMS Rejects” are chemically inert and can be used for road construction or as backfill in open pits, reducing the overall footprint of the Tailings Management Facility (TMF). Furthermore, the project emphasizes water conservation. Historical operations were sensitive to the site water balance, and modern designs incorporate high-rate thickeners to maximize the recycling of process water. The proximity to Great Slave Lake necessitates stringent water treatment protocols to ensure that all discharge meets or exceeds Canadian environmental standards. By combining historical operational wisdom with cutting-edge pre-concentration technologies, the Point Occurrence stands as a model for how legacy mining districts can be rehabilitated into efficient, modern, and sustainable operations.

Source: Point Occurrence (Pine Point Zinc-Lead Project)

Source: NI 43-101 Technical Report

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