Abstract

The mineralogy and crystal chemistry of “garnierites” in saprolitic ore from the Goro lateritic nickel deposit, New Caledonia, was investigated using optical and scanning electron microscopy, X-ray diffraction (XRD) and electron-microprobe analyses. These conspicuously, green-coloured phases occur either as sub-mm to cm-sized veins or as macroscopic (sub-cm sized) “booklets”. Veins comprised ~ 10 Å (2:1) talc-like minerals identified as species of the Ni-kerolite/pimelite Ni for Mg solid solution series, with Ni contents ranging from 10 to 24 % NiO. Mineral nomenclature, defined by the inverse relationship between Ni and Mg content, varied continuously over the scale of several hundred micrometres. Pimelite, defined as containing > 1.5 Ni per formula unit (p.f.u.), was the main 10 Å phase for one vein core whereas at the vein edges where the Ni content decreased to < 1.5 Ni p.f.u. (and Mg increased) kerolite was identified. “Booklets” comprised the ~ 7 Å (1:1) serpentine-like phase, népouite (Mg0.67Ni1.59Fe0.053+) (Si2.17Al0.22)O5(OH)4 with Ni contents averaging 30 % NiO and occurred as accordion-like structures supported in an undifferentiated matrix of mixed ~ 7 Å and ~ 10 Å phases.

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