I think the best conditions for antigorite formation include extensive hydrothermal hydration of ultramafic and mafic igneous lithologies such as in upducted ophiolite sequences. Magnesium-rich end members of olivine and pyroxenes should dominate the mineralogy of the igneous protoliths. My answer is based on my experience with world-class Nkamouna cobaltiferous Ni-Mn deposits developed on extremely serpentized units in southeast Cameroon: Article Petrography, Mineralogy, and Geochemistry of the Nkamouna Se...