Overview
The Horseshoe Zone, a cornerstone of the Fortnum Gold Operations (FGO) owned and operated by Westgold Resources Limited, represents a vital component of Western Australia’s mid-west gold mining landscape. Located approximately 150 kilometers north-west of Meekatharra within the Proterozoic Glengarry Basin, the Horseshoe Group—which includes the Horseshoe, Cassidy, and Pod deposits—is part of a historic and highly productive gold province. The site has seen various phases of exploration and production since the late 1980s, with Westgold Resources revitalizing the operations since its acquisition and subsequent restart in early 2017. The Horseshoe Zone itself is characterized by its “free-milling” ore, a technical term indicating that the gold can be efficiently recovered through conventional grinding and cyanide leaching without the need for complex pre-treatment processes like roasting or bio-oxidation.
The significance of the Horseshoe Zone extends beyond its immediate mineral wealth; it serves as a critical feed source for the Fortnum Mill, a facility with a rich industrial history and a modern commitment to sustainability. As of June 2024, the Horseshoe Group’s mineral resources are estimated at 1,266 kt at a grade of 2.09 g/t Au, providing a robust pipeline for the operation’s 0.9 Mtpa processing plant. The strategic integration of the Horseshoe open pits with the Starlight underground mines allows Westgold to maintain a consistent and blended mill feed, optimizing the throughput and recovery rates of the facility. This project is not only an economic engine for the region, employing a workforce of nearly 200 people, but also a showcase for the integration of renewable energy in remote mining environments.
Key Process Stages
The mineral processing circuit at the Fortnum Mill is a sophisticated, multi-stage operation designed to maximize gold recovery while maintaining cost efficiency. The 0.9 Mtpa conventional Carbon-In-Leach (CIL) plant utilizes a series of mechanical and chemical processes to transition raw ore into refined gold bullion. The following stages define the Horseshoe Zone’s processing journey:
- Primary Crushing: The process begins at the ROM (Run of Mine) pad, where ore is sorted by grade and hardness. A Kemco C160 double toggle jaw crusher reduces the raw ore to a size manageable for the secondary grinding circuits.
- SABC Comminution Circuit: The mill employs a SABC (Semi-Autogenous, Ball, and Crusher) circuit. This includes a SAG mill for primary grinding and a Ball mill for secondary grinding, operating in closed circuit with a pebble crusher to handle competent rock that resists primary grinding.
- Gravity Separation: Before the chemical leaching phase, a portion of the circulating load is diverted to a gravity recovery circuit. This stage captures “free gold” (coarser gold particles) using centrifugal concentrators, which is then processed separately in an intensive leach reactor.
- Leaching and Carbon-In-Leach (CIL): The finely ground pulp is directed into a series of tanks. It first enters two primary leach tanks followed by six carbon adsorption tanks. Here, cyanide is used to dissolve the gold into a solution, which is then adsorbed onto activated carbon.
- Elution and Electrowinning: The gold-loaded carbon is “stripped” using a high-temperature, high-pressure caustic solution. The resulting pregnant solution undergoes electrowinning, where gold is deposited onto steel wool cathodes.
- Smelting and Refining: The final stage involves smelting the gold sludge in a furnace to produce doré bars, which are then shipped for final refining.
- Tailings Management: Residual material, or tailings, are treated to meet environmental standards before being deposited in a secure Tailings Storage Facility (TSF).
Critical Data
The following table outlines the technical specifications and performance metrics for the Fortnum Mill as it processes ore from the Horseshoe Zone and surrounding deposits.
| Parameter | Value | Unit |
|---|---|---|
| Processing Capacity (Throughput) | 0.9 | Mtpa |
| Average Gold Recovery | 95.1 | % |
| Gold Grade (Mineral Reserves) | 2.18 | g/t Au |
| Total Horseshoe Group Resources | 1,266 | kt |
| Cut-off Grade (Reserve) | 1.1 | g/t Au |
| Power Station Capacity (Hybrid) | 9.2 | MW |
| Solar Array Contribution | 5.527 | MW |
| BESS (Battery Storage) | 2.212 | MW |
| Grind Size (Target) | 106 | µm |
Technical Details and Sustainability
The technical excellence of the Horseshoe Zone operation is underpinned by Westgold’s commitment to metallurgical precision and environmental stewardship. One of the standout features of the Fortnum Mill is its “free-milling” metallurgical profile. Historical and current test-work confirms that the ore from the Horseshoe pits is exceptionally fast-leaching, often reaching peak recovery within 24 to 48 hours. The process chemistry is tightly controlled, with pH levels maintained at approximately 10.5 and cyanide concentrations at 200 ppm to ensure optimal dissolution while minimizing reagent waste. The use of a SABC circuit provides the flexibility to handle varying ore hardness, which is critical when blending material from the Horseshoe open pits with harder underground ore from the Starlight mine.
In terms of sustainability, Westgold Resources has taken significant strides to modernize the Fortnum Gold Operations. The remote location of the mine traditionally necessitated a heavy reliance on diesel fuel for power generation. However, the installation of a 9.2 MW hybrid power station has transformed the project’s carbon footprint. By integrating a 5.5 MW solar array and a 2.2 MW Battery Energy Storage System (BESS) with existing gas and dual-fuel gensets, the operation significantly reduces its greenhouse gas emissions. This hybrid approach ensures that the energy-intensive comminution circuit—which accounts for the majority of the mill’s power draw—can be powered by renewable energy during daylight hours, while the BESS provides stability and “spinning reserve” for the grid.
Environmental management at the Horseshoe Zone is rigorous, governed by Western Australian mining regulations. The operation manages two Tailings Storage Facilities, with ongoing monitoring to ensure groundwater protection and structural integrity. Furthermore, the mine’s closure planning is integrated into its current operations, focusing on the rehabilitation of waste rock dumps and the eventual decommissioning of the mill. As Westgold continues to explore and delineate further resources within the Horseshoe Group, the focus remains on leveraging technological innovation to drive efficiency. The combination of high metallurgical recoveries, a transition toward renewable energy, and a disciplined approach to resource management ensures that the Horseshoe Zone remains a productive and sustainable asset for years to come.
Source: Horseshoe Zone
Source: NI 43-101 Technical Report
This article provides an overview of mineral processing developments based on publicly available technical reports and industry analysis.
