The Hematite Question: Hydrogen‐Driven Magnetization of Hematite‐Bearing Sandstones and Insights for Natural Hydrogen Exploration

Abstract Natural hydrogen is a promising clean energy resource, but locating subsurface accumulations remains challenging. Aeromagnetic anomalies are increasingly utilized as a rapid and cost‐effective tool for geological hydrogen prospection, particularly associated with magnetite formation during abiotic geochemical hydrogen generation through serpentinization. In this study, we investigate an alternative hydrogen‐induced source of magnetic anomalies, the hematite to magnetite reduction, in hematite‐bearing rocks within hydrogen reservoirs or along migration pathways. We exposed hematite‐rich granites and reservoir sandstones to hydrogen at a temperature of 200°C for 10–18 days, and measured their magnetic properties before and after. Superparamagnetic to (stable) single‐domain (SP‐SSD) magnetite formed during the reaction, leading to magnetic susceptibility enhancement of up to three orders of magnitude in the sandstones, whereas the granite exhibited only minor increase. These results provide proof‐of‐concept for hydrogen‐induced hematite‐to‐magnetite reduction at low temperatures, potentially generating localized aeromagnetic anomalies, detectable in exploration surveys.