The serpentinization of Mg, Fe, Ni olivine by NaOH solution at very low sulfur fugacity and in a sulfur-free system has been investigated experimentally below the stability field of the assemblage olivine + water, at 350 degrees + or - 5 degrees C and 2,000 + or - 50 bars. Serpentinization at very low sulfur fugacity produces the opaque mineral assemblage of heazlewoodite + Ni-poor magnetite + Ni-poor awaruite, while in the sulfur-free system, an opaque mineral assemblage of Ni-rich magnetite + Ni-rich awaruite is formed. The serpentine minerals (antigorite and chrysotile) obtained during the serpentinization process contain some Ni and Fe (with an Ni/Fe ratio of 0.4-2.4). The composition of the minerals produced is dependent on the composition of the original olivine, oxygen, and sulfur fugacities.

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