"Etoile du Nord" nickel mine on the Kaala mountain
According to current estimates New Caledonia would have more than 1/4 of all nickel resources known worldwide and 40% of its laterite resources.
New Caledonia exports about 10% of the world production in nickel contained in ores and metallurgical products.
Ore deposits
Nickel ore deposits are originating from the ultrabasic rocks or peridotites. The ultrabasic rocks come from the mantle (mantle is located under the Earth crust - see "geology, ultrabasic rocks"). They form large massifs in the South and on the West Coast.
Nickel has been concentrated in lateritic formations (soils) resulting from the ultrabasics weathering.
These types of ore deposits are called lateritic deposits ( these deposits are very different from the sulphide deposits which are exploited in Canada, Australia and Siberia in underground mines and where the ores consist in iron and nickel sulfides).
Terminology
The name "Garnierite" which is actually a green nickel mineral, is used with an enlarged meaning in New Caledonia for designating all nickel ores located under the "laterite".The appropriate geological word which should be used, is saprolitic ore.
"Limonite" is the name of the horizon of reddish grounds above the saprolite, it is called "laterite" in New Caledonia.
Lateritic deposits contain two types of ores.
- Saprolite (known in New Caledonia as garnierite). They are light colored rocks, brownish or greenish, located just above the mother peridotite rocks from which they have kept their texture. The exploited grades are averaging between 2.45% and 3% in Nickel content.
- Limonite has vivid reddish and yellowish colors. It lies above the saprolite. They are locally called "laterites". Limonite nickel ores are also cobalt rich. Exploited grades vary between 1.4% and 1.6% in nickel contained. Cobalt content is generally between 0.10% and 0.20%.
Mining
Saprolitic ores are mined in quarries located along the massifs ridges or on their plateaus. Current mining is done with a bench method. Ore is extracted with hydraulic shovels, loaded in dumpers and screened on the mine.
These mines have opened large cuts in the mountains. The overburden and spoils from the old mines were pushed away to the mountains slopes and are still causing pollution of rivers with reddish sediments.
This practice is now forbidden. Modern mines do not pollute rivers anymore and all extracted barren grounds are stockpiled in appropriately organized areas. Old mining sites are starting to be rehabilitated and particularly revegetated with local endemic plants. Water loaded with sediments are now collected and filtered.