COUPLED Mg-Ni ISOTOPE SYSTEMATICS OF WEATHERING INTENSITY AND GARNIERITE FORMATION IN TROPICAL Ni LATERITE SYSTEMS, SULAWESI, INDONESIA

Abstract Magnesium and nickel isotopes provide insights into weathering processes and lateritic Ni enrichment; however, their coupled behavior during garnierite formation remains poorly constrained. We present Mg-Ni isotope compositions for serpentinized bedrock, garnierite, and laterite from the Morowali Ni laterite deposit, Sulawesi, Indonesia, to elucidate weathering intensity, solid-solution interaction, and mechanisms of Ni-bearing phyllosilicate precipitation. Weathering from bedrock (δ26Mg = –0.33 to –0.11‰) through saprolite (–0.20 to 0.14‰) to laterite (0.47‰) indicates preferential leaching of light Mg and retention of heavy Mg. Conversely, δ60Ni decreases from bedrock (–0.30 to 0.14‰) through saprolite (–0.78 to 0.03‰) to laterite (–1.34‰), reflecting mobilization of heavy 60Ni and adsorption of light 58Ni onto Fe oxyhydroxides. Garnierite occurs as two mineralogically and iso…