Petrophysical contrasts across a faulted dunite–harzburgite boundary in Hole BA1B, Samail Ophiolite, Oman

Abstract. Serpentinized peridotites commonly contain veins, fractures, and pervasive alteration, yet the controls on localized petrophysical variability remain incompletely understood. We integrate visual core descriptions, T12 porosity and wet electrical resistivity, ST1 gamma-ray attenuation density and magnetic susceptibility, and T07 whole-rock geochemistry from Hole BA1B in the Samail Ophiolite, Oman. Seven depth intervals (Zones A–G) were compared using 13 porosity and 12 wet-resistivity measurements, with emphasis on the fault-related interval at 159–163 m containing the principal dunite–harzburgite boundary at 161.87 m. Zone D records the highest mean porosity (8.95 ± 3.71 vol %), lowest mean wet electrical resistivity (94.57 ± 24.08 Ω m), lowest mean gamma-ray attenuation density (2.624 ± 0.014 g cm⁻³), and highest mean magnetic susceptibility [(1617 ± 344) × 10⁻⁵ SI] among the selected intervals. Other zones reproduce individual components but not the complete Zone D signature. Broadly elevated loss-on-ignition and H₂O values across sampled peridotites show that bulk hydration is not unique to Zone D. Other dunite–harzburgite contacts did not show an equivalent response, although most lack nearby T12 measurements and remain inconclusive. The strongest observed contrast is therefore spatially associated with major deformation at the principal lithological boundary. This association is consistent with localized pore–fracture connectivity and alteration-related electrical conduction, but does not demonstrate enhanced in situ permeability. Zone D is consequently a priority interval for direct hydraulic, microstructural, and mineralogical investigation.