SOIL, WILDLIFE AND PLANT PROTECTION

 

New Caledonia’s extreme south has a nutrient-poor soil with high iron content (natural acidic soil environment); it is also exposed to frequent and heavy rainfalls. These are the conditions that produce the high nickel and cobalt content which the Vale Inco Nouvelle-Calédonie hydrometallurgical process is designed to extract.

These southern soils are also covered by distinctive dense vegetation that has adapted to specific local conditions.

Potential impacts from the mine and its related process plant on the terrestrial environment are:

• Mine pits which result from ore extraction operations and require filling in
• Solid waste which must be treated and stored safely
• Partial destruction of endemic plant species which must be restored by implementing a revegetation plan

Vale Inco Nouvelle-Calédonie has taken all these aspects on board and implemented efficient and often avant-garde measures to ensure impact reduction or compensation.

Solid waste management

At the end of the process, after ore has been processed in the plant to produce nickel oxide and cobalt carbonate, the remaining products will be liquid waste and solid waste, a leached mineral paste containing no nickel or cobalt.  
After the mineral paste or sludge has been treated at the final neutralisation plant, all the metals originally present in the ore taken from the mine will remain with the exception of nickel and cobalt. The only added element will be gypsum (plaster) derived from the neutralisation process. This paste is known as thickened tailings.

These tailings will be used to fill in mine pits to keep pace with the progress of mining operations. When they have been filled in and dried out, the pits will be ready for revegetation.

Restoring the landscape

Vale Inco Nouvelle-Calédonie is an opencast mine worked in benches. Mining operations have been planned to ensure maximum recycling of spoil. Accordingly, when overburden (spoil) and tailings have been neutralised, they will be gradually used to fill in each mine pit as it is worked out.

Prior to mining operations

• Supervised by Vale Inco Nouvelle-Calédonie nursery botanists, miners will remove the plant cover and rare plants will be transplanted or cultivated. The remainder will be crushed and transformed into shavings for use in future revegetation work.
• Substrate layers will be recovered and stored for use as topsoil in future revegetation work.
• The succeeding ironstone layer will be stripped and can be used in constructing roads or buttresses because its high iron content makes it extremely resistant.
• The sterile red and yellow laterite layers, which have a nickel content too low for cost-effective mining, will also be stored.

After mining operations

Solid tailings will be stored in each previously excavated pit following neutralisation. The upper layers (low laterite, substrate) which were conserved will then be replaced and covered with the topsoil that was also put aside for future use. The banked up area will then be ready for revegetation. The same technique will be used for each of the mine pits.

However, in the case of the first pit, it was clearly necessary to prepare a special storage area to ensure the safe disposal of treated solid waste.

Initial phase storage area

The initial phase storage area has been laid out in a plain between Antenna Pass and Mamelon Quarry in the Kwé West upper valley. This area will be used during excavation of the first pit. It comprises:  

• an extensive bund (1 km long x 60m high x 200m wide) designed as a tailings storage dam
• soil waterproofing by compaction and/or the use of a leak-tight geomembrane.

Tailings will be dumped there over the whole of the first phase, i.e. 5 to 7 years. They will settle and become compacted over time, forming their own waterproof layer. They will be covered with the sterile laterites and topsoil set aside for future use. Revegetation work can then be carried out.

The landscape of the plain will be modified since it will be gradually replaced by a plateau of the same height as the bund.

Revegetation - the Southern ecosystems

An ecosystem is a balanced whole comprising a characteristic environment supporting an ecological community of more or less specific organisms (fauna and flora). Several ecosystems co-exist on the Vale Inco Nouvelle-Calédonie operations site as they do throughout the whole of New Caledonia's southern region:

• Open mining scrub
• Closed mining scrub
• Woodland scrub
• Primary rainforest
• Riparian vegetation

Vale Inco Nouvelle-Calédonie is well aware of the rarity and vulnerability of endemic plant species found on the Goro plateau. This is why a research program into plant restoration and plant ecosystem protection was set up as early as 1994. A nursery was created in 1996 for the inventorying, study and reproduction of endemic species for rehabilitation purposes.

Vale Inco Nouvelle-Calédonie botanists have been working since 1996 to study and identify all these plant formations. All areas likely to be directly affected by the project have been inventoried. These studies have identified seed collection areas for revegetation. A biodiversity protection program has been developed, focussing mainly on forest and riverbank formations of particular interest.

Revegetation – the nursery

The nursery, located not far from the mine site, will ensure the efficient and speedy rehabilitation of affected areas. The main tasks undertaken by the team of botanists responsible for the nursery are:

• Gradually building up a complete species inventory
• Researching plant reproduction: seed collections, germination tests, growth tests
• Ensuring that plants are produced in large quantities for future revegetation purposes
• Monitoring ecosystems and rare plant protection: transplantation if required, placing blue protection markers, plant reproduction study
• Bedding out mature plants, revegetation of storage areas and mined areas
• Protecting forests and enhancing protected areas with rare endemic species

 Vale Inco Nouvelle-Calédonie nursery staff, with help from local Yaté workers, will organise seasonal seed collection in the neighbouring ecosystems. Every year, thousands of seeds are collected by hand in this way, ensuring that trees and shrubs are protected. Reproducing endemic species is a very complex matter and the Vale Inco Nouvelle-Calédonie team has developed techniques that have now received recognition from research bodies.

In the 10 years since it was set up in 1996, the team can boast of the following achievements:

• 723 species inventoried over the entire project footprint, including:
  • 455 in primary rainforests
  • 76 riparian species including 21 listed as “rare”

• 142 endemic species reproduced out of 160 tested, giving a reproduction success rate of 88%.

Revegetation – an ongoing process

Plant restoration and revegetation on the mine site will commence 7 years into operation, first at the Kwé West bund marking the initial phase tailings storage area. Thereafter it will continue from one year to the next as mine pits are gradually filled up.

Once the area has received a covering of topsoil, revegetation will be carried out as follows:

• Pioneer species will be planted first; dependent species will then be able to grow on or around them by plantation or seed dispersal.

• Plant waste recovered during stripping and reduced to shavings will then be used to cover the planted areas to provide protection and nourishment, aid water retention and also as a source of secondary species seeds that can germinate naturally.

Mining operations will open up 30 hectares per year, which gives an indication of the surface area requiring rehabilitation seven years further on. The annual rate of rehabilitation will be 100,000 plants or shrubs.
 
Vale Inco Nouvelle-Calédonie works in close collaboration with research bodies such as the Institute for Research and Development (Institut de Recherche et de Développement - IRD), the New Caledonia Institute of Agronomy (Institut Agronomique Calédonien - IAC) and the University of New Caledonia (Université de Nouvelle-Calédonie - UNC) on research into rare plant reproduction.

18 rare species have been reproduced. To ensure species conservation, 3300 cuttings representing 7 species were supplied for planting in the Blue River nature reserve.