Quantitative structural data containing vein area fractions (AA) and calculated macroscopic bulk volume changes (ΔV) were obtained from rock specimens collected during the 2022 R/V ISABU expedition at the Onnuri Oceanic Core Complex (11°25′S, Central Indian Ridge). The aim was to physically constrain and quantify the net volumetric dilation associated with intense, non-deformational static silica metasomatism at mafic–ultramafic interfaces. Hand specimen photographs of representative talc-rich metasomatites were processed using ImageJ software (v.1.53k). Thicker V1 vein boundaries were manually traced, and images were converted to 8-bit grayscale for binary threshold segmentation to isolate combined hydrothermal vein networks (V1 + V2) from the host rock matrix. Bulk volume changes were subsequently computed using the Delesse area-to-volume equivalence principle.