Inside Tomingley Gold's Processing Circuit: Crushing, Grinding, Flotation & CIL Recovery

Overview

Nestled in the fertile plains of central New South Wales, Australia, the Tomingley Gold Operations (TGO) stand as a significant contributor to the nation’s gold production. Operated by Alkane Resources Limited (ASX: ALK), this flagship project is located approximately 50 kilometers southwest of the regional city of Dubbo. The facility processes ore extracted from the Wyoming 3, Caloma, and McFeaters open pit mines, with future potential from the nearby Peak Hill Gold Project. Since commencing production, TGO has established itself as a technically advanced operation, leveraging industry-standard mineral processing practices to efficiently recover gold. A major recent development was the October 2024 commissioning of a significant circuit upgrade designed to handle refractory ore—a move that enhances the project’s economic viability by allowing it to process finer-grained gold associated with sulfides. This strategic expansion, detailed in the latest NI 43-101 Technical Report, ensures the operation remains competitive and can maximize recovery from its mineral resources, contributing substantially to the local economy and Australia’s position as a leading gold producer.

Key Process Stages

The Tomingley Gold Processing Plant employs a sophisticated and sequential circuit designed to liberate and recover gold efficiently from both free-milling and refractory ore types. The flow sheet incorporates crushing, grinding, and a hybrid carbon-in-leach (CIL) circuit, with the recent critical addition of a flotation circuit for refractory material. Here are the detailed process stages:

• Stage 1: Primary Crushing – Run-of-Mine (ROM) ore from the TGO and TGEP pits is delivered by truck to the primary crusher located adjacent to the Wyoming 3 pit. The primary crusher reduces the large rock to a smaller, more consistent size, preparing it for further size reduction in the milling circuit.
• Stage 2: Single-Stage Milling – The crushed ore is fed into a single-stage milling circuit, typically a ball mill. The mill grinds the ore, mixing it with water to create a slurry. The objective is to achieve a target grind size that liberates the gold particles from the host rock, making them amenable to chemical recovery.
• Stage 3: Rougher Flotation (Refractory Ore Path) – For refractory ore containing finer-grained gold locked within sulfide minerals, the slurry is now routed to the new rougher flotation circuit. Here, specific reagents are added to make the gold-bearing sulfide particles hydrophobic (water-repelling). Air is bubbled through the slurry, causing these particles to attach to the bubbles and float to the surface as a concentrate, which is skimmed off.
• Stage 4: Fine Grinding of Concentrate (IsaMILL™) – The sulfide concentrate from the flotation circuit undergoes additional ultra-fine grinding in an IsaMILL™. This high-intensity grinding mill liberates the extremely fine gold particles that were previously locked within the sulfide grains, drastically increasing their surface area and making them ready for leaching.
• Stage 5: Hybrid Carbon-in-Leach (CIL) Circuit – The finely ground flotation concentrate is thickened and then combined with the flotation tailings and/or directly fed mill product in the existing CIL circuit. The slurry enters a series of agitated tanks. A dilute cyanide solution is added, which dissolves the gold. Activated carbon is introduced into the tanks, which adsorbs the dissolved gold onto its surface. The circuit includes one designated primary leach tank followed by several adsorption tanks to maximize gold recovery.
• Stage 6: Gold Room (Elution, Electrowinning & Smelting) – The gold-loaded activated carbon is pumped to a secure gold room. Here, the gold is stripped from the carbon in an elution column using a hot caustic solution. This rich gold solution is then passed through electrowinning cells, where an electrical current plates the gold onto steel wool cathodes. The cathodes are then processed in a furnace (smelting) to produce a doré bar of impure gold and silver, which is ready for refining off-site.
• Stage 7: Tailings Management – The processed slurry, now called tailings, is pumped to a high-rate thickener. The thickened tailings are then pumped to a paddock-type Tailings Storage Facility (TSF). The TSF employs a multi-spigot distribution system for even deposition and water management. The current TSF has approved capacity until mid-2027, with potential for a raise to add 10.5Mt of additional storage.

Critical Data

The operational performance of the Tomingley processing plant is underpinned by key metrics that define its efficiency, capacity, and economic viability. The following table summarizes the critical technical data and key performance indicators as outlined in the NI 43-101 report.

Additional Interesting Data and Summary

The Tomingley Gold Operation represents a modern, evolving mining project that successfully balances technical innovation with operational pragmatism. The recent capital investment in the flotation and fine-grinding circuit is a testament to Alkane Resources’ commitment to maximizing asset value and extending mine life. This upgrade allows TGO to process a broader range of ore types, particularly refractory ores from the newly developed deposits, which were previously more challenging and less economical to treat. This adaptability is crucial for the long-term sustainability of the operation. From an environmental and social governance (ESG) perspective, the operation employs a conventional paddock-style TSF with multi-spigot distribution, a widely accepted technology for water management and tailings consolidation. The explicit note that the current TSF has capacity until mid-2027, with a clearly defined expansion path, provides transparency regarding tailings management—a critical focus for investors and regulators alike. The report’s confirmation of no deleterious elements simplifies the environmental management plan and ensures the produced doré meets market specifications without requiring complex detoxification circuits. Economically, the use of a consistent 87% recovery factor for planning indicates a robust and well-understood process flow sheet, reducing technical risk and providing confidence in financial projections. The integration of the new flotation circuit with the existing CIL plant demonstrates efficient capital deployment by leveraging the current infrastructure. Looking ahead, the synergy with the nearby Peak Hill Gold Project highlights a strategy of regional consolidation, where Tomingley acts as a central processing hub, improving overall project economics through shared infrastructure and operating costs. This comprehensive approach to mineral processing, from crushing to smelting, positions the Tomingley Gold Operation as a technically sound, financially robust, and environmentally conscious project in the Australian gold mining landscape.

Source: NI 43-101 Technical Report | Preliminary Economic Assessment | Project: Tomingley and Peak Hill Gold Project | Date: June 2025

Further Reading

• Tomingley Gold Operations
• Tomingley Gold Project, NSW, Australia
• Major Mines & Projects | Tomingley Gold Operation