A TEM INVESTIGATION OF NICKEL ORE MINERALS FROM NEW CALEDONIA: NEW IMPLICATIONS FOR TECTONICS, HEALTH, AND ENVIRONMENTAL SAFETY

New Caledonia, a 200 mile-long, 40 mile-wide island located in the southwest Pacific, is the world’s 7^th largest nickel producer, with 165,000 tons produced in 2014, and has the world’s 2^nd largest nickel reserves, with 12,000,000 tons estimated. The target ore is a suite of bright green, nickel-rich phyllosilicates colloquially referred to as ‘garnierite’. Detailed transmission electron microscopy (TEM) investigations of ‘garnierite’ are rare; those that have been conducted in other locations (e.g. Dominican Republic) have been successful in characterizing important nanoscale textures, however, none have been carried out in New Caledonia.

Here, ten samples of New Caledonian ‘garnierite’ are analyzed using TEM to determine the nature and phase diversity of the material at the nanoscale. The results indicate that the material commonly characterized as an intimate blend of talc- and serpentine-like phases is far more nuanced than previously considered. Among the results of this investigation, three novel observations stand out: (1) the high-temperature serpentine polymorph, antigorite, with superlattice modulations varying 20 to 60 Å in width, is observed in 4/10 of the samples; (2) significant amounts of chrysotile with nanofiber lengths varying 50 to 700 nm, are observed in 7/10 of the samples; and (3) near-spherical silver nanoparticles with a bimodal size distribution of 2 to 30 nm in diameter and 150 to 650 nm in diameter are observed in 2/10 of the samples.

The nature of the phyllosilicate assemblage may have significant tectonic implications, due to the presence of antigorite. The silver nanoparticles observed are of particular interest as they indicate the possibility of an unrecognized resource. Although unlikely, potential exists that these nanoparticles may be pollution related. Anthropogenic silver nanoparticles known to be toxic to the environment; they are accumulating in waters worldwide in increasing volumes due to their use in consumer goods. Of particular concern is their toxicity to aquatic species, a potentially dire consequence for the New Caledonian lagoons, which are listed as a World Heritage Site.