Overview
The Leta Arm area represents a critical strategic asset within the broader Indin Lake Gold Project, located in the prolific Northwest Territories (NWT) of Canada. Positioned approximately 200 kilometers north of Yellowknife, the Leta Arm zone is managed by Nighthawk Gold Corp. (now merged with Calibre Mining Corp.), and it serves as a high-grade satellite deposit complex that complements the central Colomac deposit. The Indin Lake property spans over 94,000 hectares, covering the majority of the Indin Lake Greenstone Belt. Within this vast tenure, the Leta Arm area—comprising the Diversified, North Inca, and Lexindin deposits—has emerged as a focal point for technical evaluation due to its favorable mineralogy and structural continuity.
Mineral processing at Leta Arm is integrated into a hub-and-spoke production model, where ore from satellite pits is transported to a centralized processing facility. The significance of Leta Arm lies in its ability to provide high-grade mill feed that enhances the overall project economics. Geologically, the area is characterized by quartz-vein-hosted gold mineralization within metasedimentary and metavolcanic rocks, a setting that typically yields free-milling gold. This characteristic is a cornerstone of the project’s technical viability, as it allows for the use of conventional, well-proven extraction technologies. By leveraging a centralized mill, the project minimizes its environmental footprint while maximizing the utilization of infrastructure in a remote subarctic environment. The 2023 Preliminary Economic Assessment (PEA) highlighted the Leta Arm deposits as essential components of the 15-year mine life, contributing to a robust production profile that targets over 200,000 ounces of gold annually at peak capacity.
Key Process Stages
The processing circuit designed for the Indin Lake Gold Project, which treats ore from Leta Arm and surrounding areas, utilizes a conventional flowsheet optimized for high recovery and operational reliability. The circuit is designed to handle a nominal throughput of 16,715 tonnes per day (t/d).
- Crushing and Ore Handling: Run-of-Mine (ROM) ore is delivered to a primary crushing circuit. The design employs a gyratory or jaw crusher to reduce the material to a size suitable for the grinding circuit, typically achieving a product size (P80) of approximately 36 mm for the secondary stage.
- Grinding Circuit (SABC): The comminution stage follows a Semi-Autogenous Grinding (SAG) and Ball Mill configuration, often referred to as an SABC circuit when pebble crushing is included. The goal is to achieve a final grind size (P80) of 150 µm, which has been determined to be the optimal liberation point for the Indin Lake ores.
- Gravity Concentration: A portion of the ball mill discharge (or the full stream in some configurations) is diverted to centrifugal gravity concentrators. This stage is highly effective at Leta Arm, where coarse gold is prevalent, capturing approximately 27.7% of the gold before it enters the chemical leaching stage.
- Leaching and Carbon-in-Pulp (CIP): The ground slurry is thickened and then subjected to cyanide leaching in a series of agitated tanks. The project utilizes a hybrid Leach-CIP configuration, where gold is dissolved into a cyanide solution and subsequently adsorbed onto activated carbon. This stage includes 4 leaching tanks followed by 6 CIP adsorption stages to ensure maximum residence time and recovery.
- Elution and Gold Room: Loaded carbon is treated in a Pressure Zadra elution circuit to strip the gold. The resulting pregnant solution undergo electrowinning and smelting to produce gold doré bars on-site.
- Cyanide Destruction and Tailings Management: Before deposition, the tailings slurry undergoes a detoxification process (typically SO2/Air) to reduce cyanide levels to environmentally safe limits. The treated tailings are then pumped to a dedicated management facility or used as backfill in exhausted open pits to minimize land disturbance.
Critical Data
The following table summarizes the primary design parameters and metallurgical performance expectations for the processing facility as outlined in the most recent technical assessments.
| Parameter | Value | Unit |
|---|---|---|
| Plant Throughput (Design) | 6.10 | Mt/a |
| Daily Processing Capacity | 16,715 | t/d |
| Design Gold Head Grade | 1.80 | g/t Au |
| Grinding Product Size (P80) | 150 | µm |
| Overall Gold Recovery | 96.3 | % |
| Gravity Recovery Component | 27.7 | % |
| Bond Ball Mill Work Index (BWi) | 16.0 | kWh/t |
| Bond Crusher Work Index (CWi) | 18.7 | kWh/t |
| Leach + CIP Residence Time | 24 | hours |
| Ball Mill Circulating Load | 400 | % |
| NaCN Addition Rate | 0.50 | kg/t |
| Hydrated Lime Addition Rate | 0.10 | kg/t |
Technical Details and Sustainability
The technical success of the Leta Arm mineral processing strategy is rooted in the “free-milling” nature of the gold. Metallurgical testwork conducted between 2016 and 2023 confirmed that the gold is not refractory, meaning it does not require complex pre-treatments like roasting or bacterial oxidation. The selection of a 150 µm grind size is a calculated balance between energy consumption and recovery efficiency. While finer grinding can often yield higher recoveries, the incremental gain for Leta Arm ore beyond 150 µm does not justify the significant increase in power requirements, especially given the remote location where energy costs are a major factor. The Bond Ball Mill Work Index of 16.0 kWh/t classifies the ore as “hard,” necessitating a robust grinding circuit capable of sustained high-energy input.
From a sustainability perspective, the Leta Arm development is governed by the Mackenzie Valley Resource Management Act. Operating in the Northwest Territories requires a stringent approach to water management and land reclamation. One of the innovative aspects of the project’s sustainability plan is the “In-Pit Tailings Disposal” strategy. By utilizing exhausted open pits at the Colomac site for tailings deposition, the project significantly reduces the need for external tailings dams, which are often the highest-risk infrastructure in mining. This approach not only enhances dam safety but also facilitates faster reclamation of the industrial footprint once mining concludes.
Environmental stewardship also extends to the use of reagents. The project has optimized its cyanide destruction circuit to ensure that the discharge into the tailings facility meets or exceeds the guidelines set by the Wek’èezhı̀i Land and Water Board (WLWB). Furthermore, the high percentage of gravity recovery (27.7%) reduces the chemical load required in the leaching circuit, as nearly a third of the gold is recovered through physical separation alone. This “gravity-first” approach is both economically efficient and environmentally responsible, reducing the consumption of cyanide and lime.
Looking forward, the Leta Arm area continues to show exploration upside. As more high-grade material is identified, the processing facility’s flexibility allows for “grade blending,” where Leta Arm’s higher-tenor ore is mixed with lower-grade material from Colomac to maintain a consistent mill feed grade. This operational flexibility is key to managing the volatility of gold prices and ensuring the long-term viability of the Indin Lake Gold Project. The integration of modern automation in the CIP circuit and real-time monitoring of tails detoxification further positions Leta Arm as a model for responsible mineral processing in Canada’s North.
Source: Leta Arm
Source: NI 43-101 Technical Report
This article provides an overview of mineral processing developments based on publicly available technical reports and industry analysis.
