Link Between Enhanced Pore Surface Relaxivity and Mineral Alteration in Basalts

Abstract Hydrothermal alteration significantly affects the mineralogical and geochemical composition of subsurface rocks. This research utilized a combination of low‐field time‐domain nuclear magnetic resonance, gas adsorption‐desorption isotherms, and scanning electron microscopy (SEM) with energy dispersive spectroscopy to characterize the pore systems of a range of flow top and flow interior basalt samples from Newberry Volcano drill core. A power‐law relationship between hydrothermal mineral alteration and magnetic susceptibility of pore‐facing minerals is revealed, suggesting a bulk method for quantifying degree of mineral alteration from core or wellbore data. Transverse relaxation time ( T 2 ) distributions, combined with gas adsorption‐based and SEM image‐based pore size distributions, yield faster T 2 relaxation or enhanced surface relaxivity values within sample micro‐ and macropores facing or lined with secondary minerals. This relationship can be used to evidence increased paramagnetic metal ion (e.g., Fe, Mn, Cr, Co, V) accessibility for subsurface engineering applications such as in situ carbon mineralization and critical minerals extraction.