Overview
The Lexindin (No. 1 Zone) mineral project represents a significant development in the extraction and processing of high-grade polymetallic ores. Located in a region characterized by complex geological structures, the No. 1 Zone is primarily hosted within hydrothermally processed monzonites and porphyritic rocks. These rock types present unique challenges for mineral processing, particularly due to their petrophysical properties. Detailed analysis indicates that the ore-hosting monocytes in the No. 1 Zone are marked by a relatively high swelling factor of up to 30%, largely attributed to the presence of clay minerals such as montmorillonite, halloysite, glauconite, and hydrous mica. This mineralogical composition requires a robust and specialized processing approach to ensure operational efficiency and high metal recovery rates.
From a company perspective, the Lexindin project is designed to handle a significant annual throughput, targeting a total of 800,000 tonnes per annum (t/a). The project’s significance lies in its multi-metal profile, containing valuable concentrations of lead, zinc, silver, gold, and copper. With a focus on maximizing the economic output of the No. 1 Zone, the processing facility has been engineered to operate with high availability, specifically 8,000 hours per year for the grinding and flotation circuits. This high level of utilization is critical for maintaining the project’s viability and meeting the supply demands of global metal markets. The technical design of the Lexindin plant integrates advanced sequential flotation techniques, allowing for the discrete recovery of different metal concentrates while managing the deleterious elements present in the complex ore body.
Key Process Stages
The processing circuit for the Lexindin (No. 1 Zone) is meticulously designed to handle the hardness and mineral complexity of the polymetallic ore. The flowsheet follows a conventional but highly optimized path through crushing, grinding, and sequential flotation.
- Primary and Secondary Crushing: The circuit begins with a robust crushing stage designed for a maximum feed size of 600 mm. The primary crusher reduces the Run-of-Mine (ROM) ore to a product size where 80% passes 7.12 mm. This stage operates with an availability of 5,694 hours per year, ensuring a steady feed for the downstream processes.
- Grinding Circuit: The grinding stage is a critical component of the Lexindin plant, utilizing a ball mill in closed circuit with a circulating load of 250%. The objective of this stage is to achieve a very fine grind size, with a target product size (P80) of 40 μm. This fine grinding is essential for the liberation of minerals from the complex monzonite host rock.
- Polymetallic Sequential Flotation: The core of the recovery method is sequential flotation. The circuit first prioritizes the recovery of silver and lead into a high-grade concentrate, followed by a dedicated zinc flotation circuit. This sequential approach allows for the optimization of reagents and pH levels specifically for each metal group.
- Concentrate Filtration and Handling: Both silver-lead and zinc concentrates are subjected to filtration to reduce moisture content. The design throughput for silver-lead filtration is 10 t/h, while the zinc circuit handles 12 t/h.
- Tailings Management and Backfill: A standout feature of the Lexindin facility is its integrated tailings management. A portion of the processed material is converted into paste aggregate fill (12 mm size) and cemented aggregate fill (75 mm size) for underground support, enhancing the environmental profile of the operation.
Critical Data
The following table summarizes the key technical parameters and design specifications for the Lexindin (No. 1 Zone) processing facility.
| Parameter | Value | Unit |
|---|---|---|
| Annual Throughput (Dry) | 800,000 | t/a |
| Design Throughput (Grinding/Flotation) | 100 | t/h (dry) |
| ROM Head Grade – Zinc | 4.6 | % |
| ROM Head Grade – Lead | 2.9 | % |
| ROM Head Grade – Silver | 159 | g/t |
| ROM Head Grade – Gold | 1.37 | g/t |
| ROM Head Grade – Copper | 0.5 | % |
| Bond Ball Mill Work Index (BWi) | 9.5 | kWh/t |
| Bond Abrasion Index (Ai) | 0.168 | g |
| Grinding Product Size (P80) | 40 | μm |
| Lead Recovery to Ag-Pb Concentrate | 87.4 | % |
| Silver Recovery to Ag-Pb Concentrate | 75.0 | % |
| Zinc Recovery to Zinc Concentrate | 80.2 | % |
| Copper Recovery to Ag-Pb Concentrate | 81.2 | % |
| Operating Availability (Grinding) | 8,000 | h/a |
Technical Details and Sustainability
The technical sophistication of the Lexindin (No. 1 Zone) processing plant is driven by the specific requirements of its complex polymetallic ore. One of the most critical factors in the plant’s design is the target grind size of 40 microns. This extremely fine P80 is necessitated by the mineralogical association of the lead and zinc sulfides within the silicate-rich monzonite matrix. Standard grinding sizes (typically 75 to 100 microns) proved insufficient in metallurgical testing to achieve the desired liberation, which would have resulted in high losses to the tailings. By investing in the energy required for a 40-micron grind—supported by a Bond Ball Mill Work Index of 9.5 kWh/t—the operation ensures that it maximizes the recovery of precious metals like silver and gold, which often report to the lead concentrate.
Environmental sustainability and operational stability are addressed through several key design choices. The presence of swelling clays (up to 30% swelling factor) required the engineers to design ore handling systems with high-torque conveyors and specialized bin geometries to prevent “rat-holing” or blockages. Furthermore, the use of a sequential flotation flowsheet allows for the rejection of deleterious elements early in the process. Testing has shown that the copper concentrate can contain elevated levels of arsenic (2.00%) and antimony (10.2%), while the zinc concentrate manages cadmium levels. By segregating these into specific concentrate streams, the plant can apply targeted cleaning stages to ensure the final products meet smelter specifications without incurring excessive penalties.
Sustainability is further bolstered by the tailings management strategy. Rather than relying solely on traditional surface storage, the Lexindin project utilizes a paste aggregate fill system. This involves dewatering the flotation tailings and mixing them with cement or other binders to create a structural backfill for the underground mine. This not only reduces the physical footprint of the surface tailings management facility (TMF) but also provides essential ground support for the No. 1 Zone’s underground workings. This circular approach to waste management is a hallmark of modern, responsible mining operations.
Looking to the future, the Lexindin (No. 1 Zone) is positioned for long-term success through its high operating availability and robust recovery methods. The facility’s ability to maintain an 8,000-hour annual run time for the critical grinding and flotation circuits provides a stable production platform. As the project progresses, there are opportunities for further optimization of reagent dosages (such as specialized collectors like Aerophine 3418A) to enhance the recovery of gold and silver from the complex sulfide matrix, ensuring the maximum value is extracted from every tonne of ore processed.
Source: Lexindin (No. 1 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.
