Donlin Gold: Advanced Flotation and POX Recovery Methods

Source: NOVAGOLD RESOURCES INC (2026)
Website: https://novagold.com/donlin-gold/project-overview/

Critical Data

Overview

The Donlin Gold Project, operated by NOVAGOLD RESOURCES INC., is one of the largest undeveloped gold deposits in Alaska, USA. This NI 43-101 technical report (effective November 2025) details a conventional, proven recovery method designed for a massive 53,500 t/d throughput facility with 93% plant availability. The process employs gyratory crushing, SAG mill and two-stage ball milling, followed by flotation circuits to recover gold-bearing sulfides. Because the gold is refractory and finely associated with arsenopyrite, the flotation concentrate (7% sulfur) is treated via pressure oxidation (POX) prior to cyanidation. Tailings are impounded in a Tailings Storage Facility (TSF) with water reclaim for reuse. The process design addresses challenges such as organic carbon preg-robbing and ore stockpile degradation, ensuring robust gold recovery. Located in western Alaska near the Kuskokwim River, the project leverages natural gas power and river barge logistics. The recovery methods are critical to achieving the project’s strong economic returns, including an after-tax NPV of $5.1 billion and 10.3% IRR. This comprehensive approach underscores Donlin Gold’s significance as a world-class gold producer with sustainable water and tailings management.

Key Process Stages

• Stage 1: Primary Crushing – Run-of-mine ore is fed into a gyratory crusher to reduce particle size before grinding. This is the first step in liberating gold from the host rock.
• Stage 2: Primary Grinding and Flotation Feed – The crushed ore undergoes SAG mill and primary ball milling to achieve a P80 of 120–150 µm. This slurry is fed to the primary rougher flotation section where gold-bearing sulfides are first concentrated.
• Stage 3: Secondary Grinding and Rougher Flotation – Rougher tails from the primary circuit are directed to a secondary ball milling circuit, grinding to P80 of 50 µm. The finer material then enters secondary rougher flotation to maximize sulfide recovery.
• Stage 4: Concentrate Treatment – Pressure Oxidation (POX) – The flotation concentrate (7% sulfur) is refractory and treated in an autoclave circuit (POX) to break down the sulfide matrix, liberating gold for subsequent cyanidation. Excess acid from POX is neutralized with flotation tailings and slaked lime.
• Stage 5: Cyanidation and Tailings Management – The POX product is cyanidated to dissolve gold for recovery. Process tailings are sent to a TSF, where reclaimed water is recycled back to the plant. This closed-loop water system minimizes freshwater demand.

Additional Interesting Data and Summary

The Donlin Gold Project’s recovery methods are underpinned by extensive metallurgical testwork confirming gold is finely associated with arsenopyrite, with minor pyrite and marcasite. Organic carbon (preg-robbing) in sedimentary ores is managed via stockpile blending and ore aging considerations – material stockpiled less than one year shows no flotation recovery loss. The process plant includes acid neutralization using flotation tails and lime, ensuring environmental compliance. Tailings are stored in a TSF located in the Anaconda Creek valley, with seepage collection and water diversion dams. Reclaimed water from the TSF is reused in the process plant, reducing overall water consumption. Economically, the project boasts a total initial capital of $9.23 billion (Q4 2025 pricing) with sustaining capital of $2.33 billion. Life-of-mine operating costs are $48.54 per tonne processed, with processing costs accounting for $15.29/tonne. The after-tax NPV5% is $5.06 billion with an IRR of 10.3% and payback of 6.5 years, based on a $2,100/oz gold price. Environmental permitting has advanced through the NEPA process with a Joint Record of Decision (2018). A trust fund of $7.8 million per year (total $412 million) is planned for closure, plus financial assurance of $322 million. The project engages with Alaska Native Corporations and local communities, emphasizing workforce development and cultural heritage. Key risks include sulfur variability in mill feed and potential stockpile oxidation affecting flotation performance. Recommendations for future feasibility updates include additional metallurgical studies and geotechnical investigations, budgeted at $1.64 million. Overall, Donlin Gold represents a technically robust, large-scale gold recovery operation with strong environmental stewardship and economic viability in a challenging Arctic environment.

Key Processes: Flotation, CIP/CIL, Cyanidation, Gravity Separation, SAG Mill, Ball Mill, Crushing

Target Commodities: Gold, Silver, Copper, Lead, Nickel