Overview
The Lexindin (D Zone) represents a pivotal mineralized prospect within the historically significant Indin Lake Supracrustal Belt, situated approximately 220 kilometers northwest of Yellowknife in the Northwest Territories, Canada. Located at latitude 64°24’N and longitude 115°06’W, the project is nestled within the Wek’èezhı̀i region, a territory of profound cultural and economic importance to the Tłıch̨ǫ people. Geologically, the Lexindin Zone is part of the Indin Lake property, which hosts over 130 gold occurrences, including the well-known Colomac Main and Damoti deposits. The Lexindin deposit itself is characterized by its placement within the Yellowknife Supergroup, a 300 km long Archean-aged assembly of volcanic and sedimentary rocks that have undergone complex structural deformation and metamorphism.
The significance of the Lexindin (D Zone) lies not only in its gold potential but also in its complex polymetallic associations, featuring notable concentrations of silver, lead, and zinc. The mineralization is primarily hosted within silificied zones and quartz-carbonate veins, often spatially associated with mafic volcanic units and felsic intrusions. Technical evaluations of the D Zone have revealed a robust gold recovery profile, reaching as high as 98% under optimized leaching conditions. However, the mineralogical complexity—marked by the presence of iron oxides such as magnetite and hematite—presents unique challenges for gravity-based recovery methods. As the industry pivots toward more efficient and sustainable extraction in northern climates, the Lexindin (D Zone) serves as a case study for integrating advanced metallurgical testing with environmental stewardship in a remote, high-latitude setting. The project benefits from its proximity to established infrastructure, including a 1,500-meter gravel landing strip and seasonal access via a 245 km winter road, which connects the site to the railhead at Hay River and the broader NWT highway system.
Key Process Stages
The processing circuit for the Lexindin (D Zone) is engineered to maximize gold and silver recovery while managing the high cyanide consumption associated with its complex mineralogy. The proposed flowsheet encompasses several critical stages:
- Primary and Secondary Crushing: The run-of-mine (ROM) material is reduced through a multi-stage crushing circuit to a product size suitable for milling. For the D Zone, primary crushing typically reduces ore to 100% passing 175 mm before secondary stages prepare the feed for the grinding circuit.
- Grinding and Classification: The ore exhibits moderate hardness, with a Bond Ball Mill Work Index (BWi) of approximately 13.7 kWh/ton. Grinding is conducted to reach a target size of 80% passing 200 mesh (75 microns), which is necessary to ensure adequate liberation of the gold and associated silver.
- Gravity Concentration: Centrifugal gravity units, such as Knelson concentrators, are utilized to capture coarse “visible” gold early in the circuit. Test work suggests a gravity potential of up to 50% recovery, although high weight recoveries due to magnetite and hematite interference require specialized cleaning or intensive cyanidation of the gravity concentrate.
- Extended Direct Leaching: Due to the slow-leaching characteristics of the D Zone material, the circuit requires extended residence times. Standard leaching periods range from 72 to 96 hours to achieve gold recoveries in the 95-98% range.
- Flotation Option: Bulk flotation has demonstrated the ability to recover up to 94% of the gold into a concentrate representing roughly 16.7% of the feed weight. This stage is particularly effective for capturing gold associated with sulfides and copper (approximately 0.6% Cu).
- Thickening and Tailings Management: Post-leach residues are processed through conventional thickeners, showing good flocculation and settling characteristics. Tailings are managed in compliance with stringent environmental standards to prevent metal leaching and acid rock drainage.
Critical Data
The following table summarizes the metallurgical and operational parameters derived from technical studies and laboratory composites of the Lexindin (D Zone) material.
| Parameter | Value | Unit |
|---|---|---|
| Design Throughput (Annual) | 800,000 | tonnes per annum |
| Bond Ball Mill Work Index (BWi) | 13.7 | kWh/t |
| Target Grind Size (P80) | 75 | microns (μm) |
| Gold Recovery (Direct Leach) | 95 – 98 | percent (%) |
| Gravity Recovery Potential | ~50 | percent (%) |
| Leach Residence Time | 72 – 96 | hours (h) |
| Cyanide Consumption (NaCN) | 3.0 | kg/t |
| Specific Gravity (Ore) | 3.37 | g/cm³ |
| Average Gold Grade (D Zone) | 3.2 – 4.5 | g/t (estimated) |
| Copper Content | 0.6 | percent (%) |
Technical Details and Sustainability
The technical advancement of the Lexindin (D Zone) requires a deep understanding of its mineralogical and geotechnical constraints. One of the most significant technical hurdles is the presence of high-density iron oxides (magnetite and hematite), which contribute to a relatively high specific gravity of 3.37. These minerals tend to report to the gravity concentrate alongside gold, diluting the concentrate grade and necessitating further treatment, such as magnetic separation or intensive cyanidation. This “magnetite problem” is a common feature in the Indin Lake belt and dictates the complexity of the back-end processing. Furthermore, the high cyanide (3 kg/t) and lime consumption rates observed in testing indicate that the ore is reactive, likely due to the presence of soluble copper and other sulfur species. Optimizing reagent regimes—specifically the balance of oxygen and cyanide—is critical to maintaining the economic viability of the project while ensuring high gold extraction rates.
Geotechnically, the Lexindin Zone benefits from the overall stability of the Yellowknife Supergroup rocks. While the footwall of some nearby deposits exhibits poor ground conditions, the hanging wall side generally offers fair to good stability, which is essential for underground development. Mining strategies for the D Zone often contemplate sublevel stoping, a bulk mining method well-suited to the vertical geometry and geotechnical characteristics of the deposit. This method allows for high-volume production while maintaining structural integrity in the challenging northern environment.
Sustainability and community engagement are at the forefront of the Lexindin project’s development. The project operates within the traditional lands of the Tłıch̨ǫ, and as such, any major development requires a formal agreement with the Tłıch̨ǫ Government. This collaboration ensures that the project provides socio-economic benefits to the local communities while respecting traditional land uses such as hunting and fishing. From an environmental perspective, geochemical static testing (including acid-base accounting and humidity cell tests) has been integral to the project’s planning. While some samples from the Indin Lake area have shown potential for acid generation, the limited water flow and site-specific climatic conditions have historically restricted the actual environmental impact. Long-term tailings management strategies focus on maintaining non-acid generating (NAG) conditions and minimizing metal leaching through robust seepage control systems. Furthermore, the use of the Tłıch̨ǫ all-season road, a 97 km gravel highway leading to Whatı̀, significantly reduces the project’s reliance on the limited winter road window, thereby improving the safety and reliability of the supply chain for reagents and fuel.
As the Lexindin (D Zone) moves toward potential production, the focus remains on debottlenecking the leaching circuit and optimizing the gravity-gold recovery interface. By leveraging historical data and modern metallurgical technologies, the project is poised to become a significant contributor to the gold output of the Northwest Territories while maintaining a high standard of environmental and social responsibility.
Source: Lexindin (D 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.
