Natural hydrogen generation potential of the serpentinized ultramafic rocks of the Biga Peninsula (NW Anatolia-Türkiye): petrographic controls, reaction pathways, and initial quantitative estimates

Natural hydrogen (H 2 ), increasingly referred to as geologic or white hydrogen, has lately attracted considerable interest as a clean and potentially renewable energy resource produced through various subsurface geochemical processes. This study presents the first quantitative evaluation of the natural H 2 generation potential of the Biga Peninsula (NW Anatolia, Türkiye) and identifies it as a prospective target warranting systematic exploration-phase investigation, focusing on the Denizgören and Tozlu metaophiolitic units. Two independent estimation methods are applied and reconciled: (1) an empirical yield approach calibrated from laboratory serpentinization experiments (Method 1), and (2) a stoichiometric iron-content method derived from bulk FeO data for supra-subduction zone (SSZ) harzburgites (Method 2). The reconciled best estimate for the highly serpentinized, harzburgite-dominated Denizgören metaophiolite is approximately 267 Mt H 2 , with a combined total of ~ 269 Mt H 2 when the higher-grade Tozlu metaophiolite is included. Applying a conservative 5% recovery factor, which is borrowed from petroleum practice and not yet calibrated for H 2 systems, yields approximately 13.5 Mt of potentially recoverable H 2 . These figures should be interpreted as a theoretical upper limit of generation potential rather than a definitive resource estimate, because they rely on literature FeO values for SSZ harzburgite in the absence of measured XRF data, and because no impermeable seal or buried trap geometry has yet been documented over the unit; a one-at-a-time sensitivity analysis indicates that the rock volume, reaction efficiency, and bulk FeO are the dominant uncertainties, jointly capable of moving the best estimate by approximately a factor of 2.5–3 in either direction. Comparison with globally productive ophiolitic H 2 systems such as the Oman Ophiolite, the Bulqizë Massif (Albania), and the Zambales Ophiolite (Philippines) supports the classification of the Biga Peninsula as a prospective target for natural H 2 exploration in Türkiye. Acquisition of field gas measurements, XRF whole-rock geochemistry, and structural permeability data are identified as the highest-priority further studies.