In the remote expanse of the South Pacific, New Caledonia, a small French territory with an abundance of natural resources, has been witness to an engineering feat that set a new standard for the global mining industry—Project Lucy. Spearheaded by Prony Resources New Caledonia (PRNC), this project redefined the future of tailings management by transitioning from traditional wet stacking methods to a sustainable and environmentally friendly dry stacking approach.

As the EPCM contractor, we played a pivotal role in overcoming the complex challenges of the region’s unique environmental, logistical, legal, and social conditions safely.

Prony Resources New Caledonia’s (PRNC) Goro mine is designed to produce 57,000 tonnes of nickel and 5,000 tonnes of cobalt annually. A key player in the region, which boasts one of the largest nickel reserves globally, PRNC’s Goro mine operations extract laterite nickel from an open pit mine, process it in a feed preparation plant (FPP), and treat it in a high-pressure acid leach (HPAL) facility. Management of the byproduct—a slurry of waste tailings—was a particular concern. How would the surrounding environment be protected from harm?

Historically, the industry has relied on wet slurry in valleys contained by >70-m-high embankments to store tailings, a method that involves depositing slurry in liquid form, creating vast, often unstable reservoirs. Recognizing the need for a more sustainable approach, PRNC resolved to transition to dry stacking, a method that separates water from tailings to form a solid filter cake, which is subsequently kept in a condensed, secure state. The environmental advantages are significant, diminishing the possibility of tailings dam breaches and lessening the enduring environmental effects on the delicate ecosystems located downstream from the tailings storage areas.

Making a significant commitment to sustainability, PRNC opted to convert the existing tailings storage infrastructure into a dry stack instead of constructing a new facility. The decision minimized land disturbance, aligning with broader global trends toward sustainable mining practices. But executing a project of this scale in New Caledonia, a remote island with limited resources, presented challenges.

Importing construction equipment and materials such as cement, steel, and piping is difficult. The island has a limited number of skilled construction workers, a situation made worse by stringent local labor laws and work permit regulations. Add to these challenges New Caledonia’s extreme weather conditions, where an average annual rainfall of 3.3 meters makes the island one of the wettest places on Earth, and the concept of developing a dry residue stack may seem illogical. But with meticulous planning and innovative engineering solutions to ensure the stability of the storage facility in such a humid environment, the seemingly impossible became reality.

The advantages of dry stacking are significant, diminishing the possibility of tailings dam breaches and reducing environmental impacts

We addressed the issues by carrying out in-depth studies to examine the physical and chemical characteristics of the residue, evaluating bench scale and pilot plant equipment for the filter plant process, and operating a pilot plant to produce dry stack in various site conditions over 18 months. Data from the pilot plant and dry stack operations was essential for the detailed engineering of the filter plant processing facilities, for preparing the dry stack foundation, and for devising plans for equipment operation and labor resources.

The project execution strategy considered various models including EPCM, EPC, and lump sum, ultimately leading to the EPCM approach with a filter press vendor to meet PRNC’s goals within the given constraints. The execution strategy required finishing in-depth design, modularization, and procurement ahead of on-site construction to meet both cost and timeline targets. A global work-sharing model was utilized, leveraging experts from Australia, South America, and Canada, enabling top industry talent to address the project’s hurdles.

In addition, Project Lucy’s modular design and execution enhanced safety, workforce efficiency, adherence to the schedule, and cost effectiveness. The eight complete modular electrical switch rooms underwent factory acceptance testing before being transported to site. Each module was 16 meters in length, 10 meters wide, and 5 meters high, with a weight of 100 tonnes. Additionally, 14 tanks were fabricated and pressure-tested offshore, with the largest tanks measuring 13 meters in diameter and height and weighing 100 tonnes each.

The project also included pre-assembled components that were lifted or assembled in place to reduce the need for high-elevation work, promoting safe and streamlined construction practices. Key pre-assembled parts included the filter building, the equipment for the filter press, and the materials handling conveyor gallery, along with its supporting trestle.

The unique truck loadout design was a key innovation, playing a critical role in optimizing the transportation of the dewatered filter cake to the dry stack and ensuring that the material could be safely and efficiently moved despite the island’s challenging conditions. This logistical solution was vital to the project’s success, as it addressed one of the most significant hurdles in implementing a dry stacking approach in such a remote location.

In addition to these practical solutions, we employed state-of-the-art technology to support the project’s execution. The team used advanced software to integrate New Caledonian topography and imagery into 3D models, creating a realistic simulation of the proposed dry stack facility. This was instrumental in securing the necessary permits and informing the local community, helping stakeholders to visualize the project’s benefits in a tangible way.

PRNC challenged the industry to develop a tailings storage solution that would be economically viable and environmentally sustainable. Hatch rose to the challenge, proposing a design that met these criteria and ultimately exceeded the client’s expectations. The project’s success underscores our role as a trusted partner in the execution of Project Lucy, setting a new benchmark for tailings management and serving as a blueprint for the future of mining.