Quantitative chemical mass transfer fractions and element enrichment factors (EF) computed relative to a conservative reference baseline were modeled for the mafic–ultramafic alteration interface at the Onnuri Oceanic Core Complex, Central Indian Ridge. The aim was to determine absolute elemental fluxes (enrichment vs. depletion) and validate the conservative behavior of rock components during extreme fluid-mediated metasomatic transformation. Mass-balance calculations were performed using Grant's (1986) Isocon optimization equations, comparing the group-averaged composition of unaltered precursor serpentinites (C₀) against fully metasomatized talc-rich rocks (Cₐ). The reference isocon framework was established using a MgO-conservative model, which uniquely reconciled chemical mass-balance trends with independent physical volume dilation constraints (~30% expansion).