Natural hydrogen is historically known in New Caledonia thanks to coastal and submarine gas occurrences in Prony Bay (Monnin et al., 2014). Historical studies demonstrate the existence of a “hydrogen system” based on meteoric water circulation hydrating the peridotites and producing hydrogen by serpentinization. The peridotite obduction of New Caledonia is potentially a highly favorable system for natural hydrogen production, due to the huge mass of potentially hydrogen-producing rocks. However, where the peridotite overlap occurred on the continental crust, on the western side of the island, the producing kitchens are probably too cold. On the eastern side of the island, recent passive seismic acquisition (Shao et al., 2025) shows deep peridotite roots that may be hot enough for current production. Our method crosses 3G information: geology, geophysics, geochemistry. It is based on the search for hydrogen seepages at the level of major tectonic faults anchored in peridotite rocks, these faults being located thanks to surface geological surveys and all available geophysical data (gravimetry, electromagnetic surveys, passive seismic). Hydrogen was measured in soils to a depth of 80 cm, and its emissions at the ground surface were quantified. Major springs were also degassed for immediate measurement of gas concentration and sampling. One of the somewhat puzzling results of our study was that the laterite that covers much of the Massif du Sud is a hyperoxidizing medium that consumes hydrogen and prevents soil gas measurements. This highly oxidizing character is demonstrated by Eh redox potential measurements in the water of piezometers traversing the laterite. It was necessary to find “redox windows” in this oxidizing regolith, where certain rock types and/or certain hydrothermal spring upwellings maintain a redox potential favorable to the preservation of hydrogen in the last few meters of its migration to the surface. Our classical exploration method therefore had to be profoundly modified. Nevertheless, it was possible to find seven new locations with high concentrations of hydrogen in the eastern part of the Massif du Sud. Another unexpected result is the nature of the hydrogen bubbles in the Rivière des Kaoris Spring and the Bain des Japonais Spring, north of Baie de Prony. Our measurements, with our specially dedicated design equipment, show that these bubbles are the result of dry gas entering these springs. Apparently, the interaction between the gas and the spring water is too short to gas the spring water. A dry gas reservoir would be connected to the faults, allowing the concomitant upwelling of hyperalkaline thermal water and dry gas, but mixed near the surface. Our new results show the potential of various zones in New Caledonia to pursue this exploration, which shows very high potential even if potential traps for accumulations have yet to be identified.
Eric C Gaucher, Frédérick Gal, Vincent Mardhel, Jean Gaucher, Fabien Trotet, et al.. Challenging exploration for natural hydrogen in New-Caledonia.
H-NAT2025 (The Premier Natural Hydrogen Worldwide Summit ), Nov 2025, Paris, France.
⟨hal-05335740⟩docType_s : COMM
