TY - JOUR T1 - Nickel distribution and isotopic fractionation in a Brazilian lateritic regolith: coupling Ni isotopes and Ni K-edge XANES. A1 - Ratie,G. A1 - Garnier,J. A1 - Calmels,D. A1 - Vantelon,D. A1 - Guimaraes,E. A1 - Monvoisin,G. A1 - Nouet,J. A1 - Ponzevera,Emmanuel A1 - Quantin,C. AD - Univ Paris Saclay, Univ Paris Sud, CNRS, UMR 8148,GEOPS, F-91405 Paris, France. AD - Univ Brasilia, ICC Ctr, GMP, IG, Campus Univ Darcy Ribeiro, BR-70910970 Brasilia, DF, Brazil. AD - Univ Brasilia, Inst Rech Dev, Brazil Lab Mixte Int, LMI,OCEuObserv Changements Environm, Campus Darcy Ribeiro, Brasilia, DF, Brazil. AD - Synchrotron Soleil, Lorme Merisiers, BP 48, F-91192 Gif Sur Yvette, France. AD - IFREMER, Ctr Brest, Unite Geosci Marines, F-29280 Plouzane, France. UR - https://doi.org/10.1016/j.gca.2018.03.026 DO - 10.1016/j.gca.2018.03.026 KW - Nickel cycle KW - Lateritic regolith KW - Nickel isotopes KW - XANES KW - Ultramafic environment KW - Weathering N2 - Ultramafic (UM) rocks are known to be nickel (Ni) rich and to weather quickly, which makes them a good candidate to look at the Ni isotope systematics during weathering processes at the Earth’s surface. The present study aims at identifying the Ni solid speciation and discussing the weathering processes that produce Ni isotope fractionation in two deep laterite profiles under tropical conditions (Barro Alto, Goiás State, Brazil). While phyllosilicates and to a lower extent goethite are the main Ni-bearing phases in the saprolitic part of the profile, iron (Fe) oxides dominate the Ni budget in the lateritic unit. Nickel isotopic composition (δ60Ni values) has been measured in each unit of the regolith, i.e., rock, saprock, saprolite and laterite (n=52). δ60Ni varies widely within the two laterite profiles, from -0.10 ± 0.05‰ to 1.43 ± 0.05‰, showing that significant Ni isotope fractionation occurs during the weathering of UM rocks. Overall, our results show that during weathering, the solid phase is depleted in heavy Ni isotopes due to the preferential sorption and incorporation of light Ni isotopes into Fe oxides; the same mechanisms likely apply to the incorporation of Ni into phyllosilicates (type 2:1). However, an isotopically heavy Ni pool is observed in the solid phase at the bottom of the saprolitic unit. This feature can be explained by two hypotheses that are not mutually exclusive: i) a depletion in light Ni isotopes during the first stage of weathering due to the preferential dissolution of light Ni-containing minerals, and ii) the sorption or incorporation of isotopically heavy Ni carried by percolating waters (groundwater samples have δ60Ni of 2.20 and 2.27‰), that were enriched in heavy Ni isotopes due to successive weathering processes in the overlying soil and laterite units. Y1 - 2018/06 PB - Pergamon-elsevier Science Ltd JF - Geochimica Et Cosmochimica Acta SN - 0016-7037 VL - 230 SP - 137 EP - 154 ID - 54712 ER -