Formation and enrichment mechanisms of precious gas insedimentary basins

Precious gases (mainly helium and molecular hydrogen therein) belong to critically strategic resources. According to the series genetic identification methods and detailed geological-geochemical analysis, the formation and enrichment are classified into two types: tectonomagmatic active basins (the Songliao and Bohai Bay basins) and stable cratonic basins (the Ordos Basin). For tectonomagmatic active basins, the origins of precious gases are represented by crust-mantle mixing, primarily linked to mantle degassing, water-rock reactions in mafic ultramafic magmatic rocks, and water radiolysis. In contrast, for stable cratonic basins, precious gases are mainly derived from crustal degassing. Specifically, helium originates through radioactive decay in sedimentary and basement rocks, while natural hydrogen is formed from reactions of water and rock in crystalline basements, radiolysis of water, and thermal evolution of hydrocarbon source rocks. Based on the detailed analysis of several cases discovered in the sedimentary basins, the favorable conditions for precious gases enrichment include sufficient gas flux, favorable migration pathways and tectonic positions, and effective seals. The enrichment process of precious gas is primarily controlled by generation timing, geological temperatures, and accumulation-dispersion efficiency. Accordingly, we identify potential enrichment formations for precious gas: the Shahejie Formation of Boxing Subsag (Bohai Bay Basin), Huoshiling Formation of the Changling and Xujiaweizi Fault Depressions (Songliao Basin), and Lower Shihezi and Majiagou Formations (Ordos Basin).