Original paper

Mineralogy and crystal chemistry of "garnierites" in the Goro lateritic nickel deposit, New Caledonia

Wells, Martin A.; Ramanaidou, Erick R.; Verrall, Michael; Tessarolo, Christian


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 (mg0.67Ni1.59Fe3+0.05) (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.