PHASE DIVERSITY AND POTENTIAL CHLORINE-SULFUR SEQUESTRATION IN NICKEL-PHYLLOSILICATES FROM NEW CALEDONIA: AN INVESTIGATION USING TRANSMISSION ELECTRON MICROSCOPY (TEM)

Hydrous, nickel-bearing phyllosilicates form through the serpentinization and tropical weathering of ultramafic rocks. Detailed TEM studies of Ni-phyllosilicates are relatively uncommon and little is known regarding complexity with respect to structural intermediates, mineral transformation reactions, and the nature and diversity of poorly crystalline phases amongst this mineral group. New Caledonia is geologically dominated by weathered ophiolite complexes and is known for its spectacular Ni-phyllosilicates. Several samples from New Caledonia were investigated to assess the nature of structural intermediates, mineral transformations and poorly crystalline phases. Preliminary TEM investigations indicate the presence of platy lamellar aggregates composed of particles 50-220 nm long and 10-30 nm wide with 10 Å, 7 Å, and 14 Å spacing interpreted to be talc, serpentine, chlorite, and possible smectite as well as pseudo-tubular particles with an inner diameter of 2.5-10 nm, an outer diameter of 13-17 nm, and a wall thickness of 3-4 nm interpreted as possible chrysotile. Spot EDS values are variable with values being: 50.79-76.65 at. % O, 9.55-23.18 at. % Si, 3.41-16.17 at. % Ni, 6.39-11.90 at. % Mg, 0.00-2.20 at. % Na, 0.08-1.13 at. % Cl, 0.14-0.42 at. % S, 0-0.25 at. % Al, 0-0.07 at. % Fe, 0-0.47 at. % Co, and 0-0.21 at. % Ca. Other preliminary observations indicate that chlorine and sulfur are intimately associated with some Ni-phyllosilicates at the nanoscale; in particular, no discreet sulfide phases were observed suggesting that S may be substituting for OH in the octahedral layer. Preliminary results suggest that previous work may not have captured all of the phase diversity using X-ray diffraction; TEM will be used to explore this possibility as well as the position and distribution of Cl and S either in solid solution with OH groups in the octahedral layers or as discrete particles.