Abstract
Natural hydrogen (H 2 ) has recently attracted increasing interest as a potential low-carbon energy resource. In this context, the surface expressions and geological controls governing hydrogen generation and migration require more in-depth investigations, particularly in ultramafic terranes. This study focuses on the north–central Aktobe region of western Kazakhstan, along the margin of the Kempirsai ultramafic massif, where extensive serpentinized ultramafic rocks favor hydrogen-related redox processes. A multi-proxy remote-sensing approach is integrated with soil-gas measurements, and petrographic and geochemical data to identify surface anomalies and propose hydrogen sources and migration pathways. At the regional scale, spectral indices consistently align with lithological boundaries, suggesting strong lithological and structural control over the distribution of surface anomalies. Focused analysis of the Bogestay–Kenoy area reveals clustered moisture, redox, salinity, vegetation, and thermal anomalies associated with sub-circular surface depressions where soil-gas surveys record hydrogen concentrations exceeding background levels and locally surpassing 50 ppm. Petrographic and geochemical results show that the serpentinized harzburgite in the study region, containing olivine and chromite, provides a reactive mineralogical framework for Fe (II) -driven redox reactions and sustained hydrogen generation during water–rock interaction. Moreover, the area also hosts granitic intrusions which may provide a secondary source of hydrogen via water radiolysis. These results support a coupled hydrogen system in which ultramafic rocks act as the main generation domain. The study demonstrates that integrated remote sensing, when constrained by geological reasoning and field validation, provides an effective and transferable approach for screening and prioritizing natural hydrogen prospects.