Digital image segmentation data representing mineral area percentages and integrated end-member bulk chemical inputs utilized for thermodynamic T–X pseudosection paths were developed to model the spatial hydrothermal zonation at the Onnuri Oceanic Core Complex detachment interface, Central Indian Ridge. The aim was to compute an accurate bulk geochemical input (C_bulk) for direct fluid precipitates (V1 and V2 vein conduits) to reconstruct mineral stability fields in open-system hydrothermal regimes. High-resolution quantitative EDX elemental mapping was segmented in ImageJ to calculate the area fraction (Area%i) of constituent phases in the V1 core (chlorite: 39.14%, talc: 23.29%, tremolite: 37.57%). Bulk compositions were generated using a weighted average formula: C_bulk = Σ(Area%i × Ci), combining modal data with mean EPMA oxide concentrations (Ci). The V2 end-member was framed using a representative 50:50 tremolite:talc structural model.