Native hydrogen (H₂) may represent a new carbon free-energy resource, but to date there is no specific exploration guide to target H₂-fertile geological settings. Here, we present the first soil gas survey specifically designed to explore H₂ migration in a region where no surface seepage has been documented so far. We choose the Pyrenean orogenic belt and its northern foreland basin (Aquitaine, France) as a test site for our strategy. The presence of mantle rocks at shallow depth (<10 km depth) under the Mauléon Basin connected to the surface by major faults is considered as preliminary requisites for H₂ generation and drainage. On this basis, more than 1,100 in situ soil gas analysis (H₂, CO, CO₂, CH₄, H₂S, and ²²²Rn) were performed at ∼1 m depth at the regional scale along a 10 × 10 km grid spanning over 7,500 km². The analysis campaign reveals several areas of high occurrence to the north of the Mauléon Basin where H₂, CO₂, and ²²²Rn concentrations exceed 1,000 ppmv, 10 vol%, and 50 kBq m⁻³, respectively. Most of these hot spots are located along the North Pyrenean Frontal Thrust and other related faults rooted in the mantle body. These results, together with evidence from the literature of fluid migration at depth, suggest that H₂ may be sourced from mantle rocks serpentinization and carried to the surface along major thrusting faults. Traps containing hydrogen remain unidentified up to now but the presence of salt-related structures (diapirs) near these hot spots is considered encouraging.

中文翻译：

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西比利牛斯山麓的原生 H2 勘探

天然氢 (H ₂ ) 可能代表一种新的无碳能源资源，但迄今为止还没有针对富含H _{2 的}地质环境的具体勘探指南。在这里，我们展示了首次土壤气体调查，该调查专门用于探索迄今为止尚未记录到地表渗漏的区域中的H ₂迁移。我们选择比利牛斯造山带及其北部前陆盆地（法国阿基坦）作为我们战略的试验场。Mauléon 盆地下浅层（<10 公里深度）的地幔岩石通过主要断层与地表相连，被认为是产生和排放H _{2 的}先决条件。在此基础上，1100多种土壤气体原位分析（H ₂、CO、CO₂、CH ₄、H ₂ S 和²²² Rn) 在区域尺度约 1 m 深度沿跨越 7,500 km ²的 10 × 10 km 网格进行。分析活动揭示了 Mauléon 盆地北部的几个高发区域，其中 H ₂、CO ₂和²²² Rn 的浓度分别超过 1,000 ppmv、10 vol% 和 50 kBq m ^-3。这些热点大多位于北比利牛斯山锋冲断层和其他根植于地幔体的相关断层。这些结果，连同来自深部流体运移文献的证据，表明 H ₂可能来自地幔岩石蛇纹石化并沿主要逆冲断层带到地表。迄今为止，含氢陷阱仍未确定，但在这些热点附近存在与盐相关的结构（底辟）被认为是令人鼓舞的。