Formation of Silica and Magnesite Veins in the Massif of Peridotite of Koniambo: Geometric and Stable Isotopes Data
Abstract
The New Caledonian Peridotite Nappe hosts one of the largest nickel ore
deposit in the world, in association with laterites developed at the
expense of the peridotites. According to a per descensum model of fluid
circulation, it is proposed that a genetic link exists between this
supergene alteration and the numerous silica and magnesite veins found
deeper in the nappe. This work, based on geometrical, mineralogical and
stable isotope analyses, provides contstraints on the origin of these
veins. For the magnesite veins, the homogeneous and high 6180 values
attest for a low temperature formation from meteoric waters;
consistently, clumped isotope thermometry provided temperatures between
26 degrees C and 35 degrees C. Silica veins display a large range in
delta O-18 values, which suggests that they formed between surface
conditions and low-temperature hydrothermalism. These results question
the genetic link of some silica veins with supergene alteration and more
generally the per descensum model of Ni-laterite ore formation.