Overview
The Granit mine, primarily represented by the high-potential Plavica project in the Probistip region of North Macedonia, stands as a cornerstone of the Balkan mineral development landscape. Historically associated with the construction and mining giant Granit AD Skopje, and later explored in partnership with Genesis Resources, the project is a testament to the region’s rich porphyry and epithermal mineralization. The mine is situated in a geological province renowned for its complex gold, silver, and copper deposits, which require a sophisticated, multi-stage processing approach to ensure economic viability and high recovery rates. The significance of the Granit project extends beyond its metal output; it represents a strategic shift toward modernizing the Macedonian mining sector through the implementation of advanced metallurgical technologies and rigorous environmental standards.
Geologically, the Granit mine site is characterized by an extensive porphyry system featuring both oxidized and primary sulfide mineralization. The oxide cap, containing gold and silver, is the primary target for initial production phases, utilizing cyanidation and carbon-in-leach (CIL) methods. Beneath this lies a substantial sulfide resource, which typically necessitates a flotation circuit to produce a copper-gold concentrate. The project’s development has been guided by extensive technical reports, including those from Valls Geoconsultant and various NI 43-101 compliant studies, which emphasize the need for a high-availability crushing and grinding circuit to handle the competent rock conditions of the Kratovo-Zletovo volcanic complex. With a designed throughput reaching upwards of 225 tonnes per hour (tph), the Granit project is positioned to be one of the most productive mining operations in the region, balancing technical efficiency with the socio-economic advancement of the surrounding communities.
Key Process Stages
The mineral processing circuit at the Granit mine is designed with a focus on size reduction and maximum liberation of gold and silver particles. The flowsheet is categorized into the following critical stages:
- Primary Crushing: Run-of-Mine (ROM) ore with a top size of approximately 600 mm is fed into a primary open-circuit jaw crusher. A vibrating grizzly feeder ensures a consistent feed rate, while a hydraulic rock breaker is employed for oversized material. The jaw crusher, with a feed opening of 1,200 x 830 mm and a closed side setting (CSS) of 100 mm, reduces the ore to a manageable size for secondary processing.
- Multi-Deck Screening: The primary crushed product is conveyed to a high-efficiency triple-deck screen. This unit features apertures of 60 mm, 20 mm, and 10 mm, respectively. The screening process directs material to the appropriate subsequent crushing stage based on particle size, optimizing the efficiency of the entire comminution circuit.
- Secondary and Tertiary Crushing: Material larger than 20 mm is directed to a secondary cone crusher operating in a closed cycle with the screen. Particles between 10 mm and 20 mm are processed by a tertiary cone crusher, also in a closed circuit. This ensures that the final product reaching the fine ore bin has a P80 of approximately 8 mm, minimizing the energy required for the subsequent grinding stage.
- Grinding and Classification: The 8 mm crushed ore is reclaimed from a fine ore bin (with a 2.8-day residence time) and fed into a ball mill. Operating in a closed circuit with hydrocyclones, the grinding stage reduces the material to a P80 of 40–71 µm, which is essential for effective gold liberation.
- Leaching and Adsorption (Oxide Ore): The ground pulp is thickened to approximately 45% solids before entering a series of six cyanidation and sorption leaching tanks. Activated carbon is moved counter-currently to the pulp flow to adsorb the dissolved gold and silver.
- Elution and Electrowinning: Gold and silver are stripped from the carbon through a standard elution process, followed by electrolysis. The resulting electrolytic precipitate is dried and smelted to produce Dore bars.
Critical Data
The following table summarizes the key design and operational parameters for the Granit mine processing circuit, based on recent technical feasibility analysis.
| Parameter | Value | Unit |
|---|---|---|
| Primary Feed Rate (Design) | 225 | tph |
| Crushing Availability | 61.0 | % |
| Grinding & Flotation Availability | 91.3 | % |
| Annual Processing Capacity | 800,000 | tpa |
| ROM Top Size | 600 | mm |
| Crushed Product P80 | 8.0 | mm |
| Grinding Product Size (P80) | 40 – 71 | µm |
| Bond Ball Mill Work Index | 9.5 – 16.8 | kWh/t |
| Average Gold Head Grade | 2.01 | g/t |
| Estimated Gold Recovery | 70 – 90 | % |
| Fine Ore Bin Residence Time | 2.8 | days |
Technical Details and Sustainability
The Granit mine technical design is rooted in the “P1” resource category (per Soviet-era classification) and modern NI 43-101 standards, focusing on a robust comminution strategy to mitigate the hardness of the granitic and volcanic host rocks. One of the most critical aspects of the project’s technical success is the management of the 225 tph crushing circuit. Given the relatively low planned availability of 61% for the primary crushing stage, the inclusion of a fine ore bin with a nearly 3-day residence time is a masterstroke in process reliability. This buffer allows for extensive maintenance overhauls on the jaw and cone crushers without necessitating a shutdown of the grinding and leaching circuits, which operate at a much higher availability of over 91%.
Metallurgically, the Granit project must navigate the transition from oxide to sulfide ores. The initial two years of operation are projected to focus on the oxide mineralized material, utilizing a sequential leaching process. As the mine progresses into deeper sulfide zones, the circuit is designed for modular expansion to include a sequential flotation stage. This will target the lead and zinc concentrates, while also recovering gold and silver associated with pyrite and chalcopyrite. The use of a high-K calc-alkaline mineralogical model suggests that the ore will respond well to conventional flotation reagents, though careful pH control will be required to optimize the depression of pyrite during the copper recovery stages.
From a sustainability and environmental perspective, the Granit mine is designed to adhere to stringent EU and local regulations. Tailings management is a priority, with plans for a dedicated thickener and filtration system to produce high-density tailings for dry stacking or paste backfill. This approach significantly reduces the risk of seepage and minimizes the footprint of the tailings management facility. Water conservation is also integrated into the plant design, with a closed-loop system where thickener overflows and filtrate from the concentrate filters are recycled directly back to the process water pond. Furthermore, the socio-economic commitment of the mine includes the development of infrastructure such as a 3.5 km access road and a 4 km dedicated power line, which will serve the local Probistip community long after the life-of-mine. The project’s future outlook is bright, with potential for resource expansion at the “Piavitsa” and “Ajsakal” formations, ensuring that the Granit mine remains a pivotal asset for the region’s industrial growth for decades to come.
Source: Granit
Source: NI 43-101 Technical Report
This article provides an overview of mineral processing developments based on publicly available technical reports and industry analysis.
