https://newatlas.com/energy/geologic-hydrogen-gold-rush/
5 trillion tonnes potentially. Again the Canadian shield, any flood basalts, rift valleys, failed rift arms too as every rift system starts are the triple junction and one fails the other two propagate. Mid.Ocean ridges and volcanic hot spots like Iceland and Hawaii and Yellowstone all are loaded with Basalts and thus olivine and potential for this.type of geochemistry reaction. It comes down to water supply and post formation gas traps up dip otherwise the gas just moves upwards and is eaten by microbes or hits air or water and escapes to space eventually
My house sits on top of a blue basalt ridge in the far Western Cascade Mts. A gold mine, errr, hydrogen mine!