Saddle-Dolomite-Bearing Fracture Fillings and Records of Hot Brine Activity in the Jialingjiang Formation, Libixia Section, Hechuan Area of Chongqing City

Most vein minerals deposited in fractures of the Jialingjiang Formation from Libixia section, Hechan area include a large amount of saddle dolomite and accompanying celestite, calcite and fluorite. This study analyzed the nature, source, evolution of the fluids by plane‐light petrography, fluid‐inclusion methods, cathodoluminescence images, and stable isotopic compositions. The homogenization temperatures of two‐phase aqueous fluid inclusions in dolomite range between 100 and 270°C. Combined with the δ¹⁸O data, it is suggested that the fluid responsible for the precipitation of fracture fillings have δ¹⁸O values between 10‰ and 18‰ (relative to SMOW). The saddle dolomite and the accompanying minerals were the result of activity of dense brines at elevated temperatures. Moreover, analysis shows that the fluid was derived from a mixture of marine‐derived brine and deeper circulating flow. This fluid was enriched in Sr during diagenesis and formed celestite in fracture and for regional mineralization. Dissolution of saddle dolomite was attributed to the cooling of Mg/Ca‐decreased fluids, which may relate to a leaching of gypsum to celestite in surrounding carbonates.