The stable isotope compositions of veins provide information on the conditions of fluid-rock interaction and on the origin of fluids and temperatures. In New Caledonia, magnesite and silica veins occur throughout the Peridotite Nappe. In this work, we present stable isotope and clumped isotope data in order to constrain the conditions of fluid circulation and the relationship between fluid circulation and nickel ore-forming laterization focusing on the Koniambo Massif. For magnesite veins occurring at the base of the nappe, the high d18O values between 27.8‰ and 29.5‰ attest to a low temperature formation. Clumped isotope analyses on magnesite give temperatures between 26°C and 42°C that are consistent with amorphous silica -magnesite oxygen isotope equilibrium. The meteoric origin of the fluid is indicated by calculated d18Owater values between -3.4‰ to +1.5‰ Amorphous silica associated with magnesite or occurring in the coarse saprolite level displays a narrow range of d18O values between 29.7‰ and 35.3‰. For quartz veins occurring at the top of the bedrock and at the saprolite level, commonly in association with Ni-talc-like minerals, the d18O values are lower, between 21.8‰ and 29.0‰ and suggest low-temperature hydrothermal conditions (~40-95°C). Thermal equilibration of the fluid along the geothermic gradient before upward flow through the nappe and/or influence of exothermic reactions of serpentinization could be the source(s) of heat needed to form quartz veins under such conditions. Dear Editor, Please find attached the revised version of manuscript #GCA-D-15-00678, entitled "Paired stable isotope (O, C) and clumped isotope thermometry of magnesite and silica veins in the New Caledonia Peridotite Nappe", by B. Quesnel, P. Boulvais , P. Gautier, M. Cathelineau, C.M. John, M. Dierick, P. Agrinier and M. Drouillet, which required moderate revisions before final acceptance for publication in Geochimica et Cosmochimica Acta. You can find on this file our answers (in red below) to reviewer's comments. Accordingly to these comments, the text and some figures have been modified. For the text, we have let these changes visible on the manuscript to make easier your lecture. Note also that we have taken into account the minor editorial suggestions of reviewers (for example those noticed in yellow boxes in pdf files); these changes do not appear in the new version. We have also built new tables that could be useful for the geochemists community; these calculations have been suggested by reviewers 1 and reviewer A. Gilg (we now present a temperature range for quartz formation of 40-95°C, instead of 40-80°C in the previous version; conclusions remain unchanged). These tables are introduced as electronic supplements to preserve the ms as short and clear as it was.Best regards, Benoit Quesnel and co-authors *Cover LetterDear Editor, Please find attached the revised version of manuscript #GCA-D-15-00678, entitled "Paired stable isotope (O, C) and clumped isotope thermometry of magnesite and silica veins in the ...

A new method for accurate determination of oxygen isotopes in uranium oxides encountered in the nuclear fuel cycle was developed using the conventional BrF5 fluorination technique. Laser‐assisted fluorination was tested for comparison. We focused on fine powders of triuranium octoxide (U3O8), uranium dioxide (UO2±x with 0 ≤ x ≤ 0.25), uranium trioxide (UO3.nH2O, with 0.8 ≤ n ≤ 2) and diuranates (M2U2O7.nH2O, with M = NH4, Na or Mg0.5 and 0 ≤ n ≤ 6). Fluorination at room temperature and heating under vacuum at 150 °C are shown to eliminate both adsorbed and structural water from the powder samples. Precision fit for purpose of δ18O values (± 0.3‰, 1s) and oxygen yields (close to 100%) were obtained for U3O8 and UO2 where oxygen is only bound to uranium. A lower precision was observed for UO3.nH2O and M2U2O7.nH2O where oxygen is both present in the structural H2O and bonded to uranium and where the extracted O2(g) can be contaminated by NF3 and NOx compounds. Laser‐assisted fluorination gave shifted δ18O values between +0.8 and +1.4‰ for U3O8, around −0.8‰ for UO3.nH2O and between −3.9 and −4.5‰ for M2U2O7.nH2O (± 0.3‰, 1s) compared with the conventional method.