Chrome-spinels from the Massif du Sud, southern New Caledonia

Abstract

Approximately forty, variously shaped, chromitite bodies occur in dunites and harzburgites of the alpine-type peridotite complex of southern New Caledonia. The chromitites consist of pichrochromite (59 to 42% Cr₂O₃) and serpentinized olivine (Fo_96-92) and display a variety of textures (massive, disseminated, and orbicular) consistent with a magmatic cumulate origin. Dunites contain olivine (Fo₉₃₋₉₇) and 1 to 3% picrochromite (50 to 39% Cr₂O₃). Harzburgites have less than 1% spinel, ranging from picrochromite to ceylonite (45 to 28% Cr₂O₃) and often forming symplectic intergrowths with bronzite. Temperatures of crystallization of the cumulate picrochromites are believed to have been about 1200 °C while the more aluminous symplectic spinels equilibrated under different conditions and may reflect a late stage recrystallization episode.