Overview
The Bivisible Mine (historically associated with the Kainantu project in Papua New Guinea and operated by K92 Mining Inc.) stands as a premier example of high-grade gold-copper mineral processing in the South West Pacific Magmatic Arcs. Located in the Eastern Highlands Province of Papua New Guinea, the Bivisible operation targets a complex system of epithermal to porphyry-related veins, primarily the Kora and Judd deposits. The project has gained international significance due to its exceptional head grades and the successful implementation of a multi-stage expansion strategy that has transformed it from a small-scale producer into a world-class mining operation. K92 Mining Inc., the owner and operator, has focused on a robust processing philosophy that leverages both gravity recovery and flotation technologies to maximize the extraction of gold, copper, and silver from its high-sulfidation mineralization.
The significance of the Bivisible project lies not only in its geological wealth but also in its technical adaptability. The processing plant has undergone several iterations, moving from the initial Stage 1 refurbishments to the current Stage 2A expansion, with a definitive focus on reaching a peak processing rate of 1.2 million tonnes per annum (Mtpa). This expansion is supported by a comprehensive Definitive Feasibility Study (DFS) that outlines the transition to a larger, more efficient circuit designed to handle the increased throughput while maintaining high metallurgical recoveries. The Bivisible Mine serves as a critical economic engine for the Eastern Highlands, providing substantial employment and infrastructure development, while demonstrating the viability of underground mining in challenging terrain. Its success is a testament to the integration of advanced metallurgical testing, efficient comminution circuits, and precise flotation kinetics, which together ensure the project’s long-term sustainability and profitability in a fluctuating global commodities market.
Key Process Stages
The mineral processing circuit at the Bivisible Mine is designed to treat high-grade gold-copper ore through a series of specialized stages. The circuit is optimized for the recovery of “bivisible” gold—referring to the presence of both coarse, gravity-recoverable gold and fine, sulfide-hosted gold. The primary stages include:
- Run-of-Mine (ROM) Handling and Crushing: ROM ore is delivered by haul trucks to a 150-tonne capacity ROM bin. The crushing circuit utilizes a single-stage open-circuit primary crusher to reduce the ore size before it is fed into the grinding circuit.
- Grinding and Classification: The secondary comminution stage features a high-capacity ball mill operating in closed circuit with a bank of hydrocyclones. This stage is critical for achieving a target product size (P80) of 106 µm, which is essential for liberating the gold and copper minerals.
- Gravity Recovery: A portion of the cyclone underflow is diverted to a gravity circuit, typically featuring centrifugal concentrators (e.g., Knelson). This stage recovers coarse gold early in the process, reducing the load on the flotation circuit and preventing the “gold lock-up” in the mill.
- Sequential Flotation: The overflow from the cyclones enters the flotation circuit, which consists of rougher and scavenger cells followed by multiple stages of cleaning (Cleaner and Recleaner). This stage uses specific reagents to produce a high-grade gold-copper concentrate.
- Concentrate Dewatering: The final concentrate is thickened in a high-rate concentrate thickener and then filtered using a plate-and-frame filter press to reduce moisture to approximately 10.5% for shipment.
- Tailings Management: Process tailings are thickened in a tailings thickener to recover water for reuse in the plant. The thickened underflow is then pumped to a dedicated tailings storage facility (TSF) or used for underground backfill (paste plant).
Critical Data
The following table summarizes the key design and operating parameters for the Bivisible processing facility, based on the latest technical reports and DFS data.
| Parameter | Value | Unit |
|---|---|---|
| Design Throughput (Annual) | 1,200,000 | t/y |
| Crushing Plant Feed Rate | 200 | t/hr |
| Process Plant Feed Rate | 150 | t/hr |
| Design Head Grade (Gold) | 10.0 | g/t Au |
| Design Head Grade (Copper) | 1.0 | % Cu |
| Overall Gold Recovery | 93.0 | % |
| Gravity Gold Recovery | 15.0 | % |
| Overall Copper Recovery | 95.0 | % |
| Bond Ball Mill Work Index (BWi) | 16.8 | kWh/t |
| Crushing Work Index (CWi) | 16.4 | kWh/t |
| Grinding Product Size (P80) | 106 | µm |
| Concentrate Mass Pull | 5.0 | % |
| Concentrate Moisture Content | 10.5 | % |
Technical Details and Sustainability
The technical sophistication of the Bivisible Mine is most evident in its comminution and flotation design. The ore characterization studies, including SMC testing and Bond Work Index determinations, have identified the material as being of moderate hardness, with a BWi of 16.8 kWh/t and a CWi of 16.4 kWh/t. This requires a robust grinding circuit to achieve the liberation required for high-efficiency flotation. The decision to target a P80 of 106 µm was driven by extensive metallurgical test work, which showed that finer grinding did not significantly improve recovery but would substantially increase energy costs. The circuit’s ability to maintain a consistent grind size is vital for the stability of the downstream flotation cells, where slurry density is maintained at approximately 30% solids for the rougher stage and 20% for the cleaner stage.
Sustainability is a core pillar of the Bivisible operation. The project utilizes a sophisticated water management system designed to maximize the recycling of process water from the thickener overflows. This minimizes the requirement for fresh water from local sources and reduces the environmental footprint of the operation. Furthermore, the mine has implemented a comprehensive Environmental Management Plan (EMP) that includes regular monitoring of air quality, water discharge, and biodiversity in the Eastern Highlands. The use of thickened tailings for underground paste backfill not only provides structural support for the mine but also reduces the volume of tailings that must be stored on the surface, significantly mitigating the risks associated with tailings storage facilities.
Looking toward the future, the Bivisible Mine is poised for further growth. The Stage 3 and Stage 4 expansions are planned to further increase throughput and optimize metal production. These expansions include the installation of additional flotation capacity and potentially more advanced gravity recovery systems to handle the deeper, higher-sulfide ores identified in recent drilling. The ongoing exploration of the Judd and Kora South vein systems suggests that the mine life will extend well beyond current estimates, providing a stable source of gold and copper for years to come. By combining technical excellence with a commitment to environmental and social responsibility, the Bivisible Mine remains a benchmark for mineral processing in the region.
Source: Bivisible
Source: NI 43-101 Technical Report
This article provides an overview of mineral processing developments based on publicly available technical reports and industry analysis.
