Complex fluid-rock interaction and fluid fluctuation in the Jiaodong hydrothermal gold system (North China) revealed by mineral and geochemical analyses of quartz

Abstract The formation of hydrothermal gold deposits commonly involves complex fluid-fluid and fluid-rock interaction processes. Here, we investigated the micro-texture and in situ trace elemental and oxygen isotopic composition of different quartz from the Zhaoxian gold deposit, Jiaodong, North China, aiming to constrain the evolution and origin of ore-forming fluids under the complex hydrothermal process. Crosscutting relationships and cathodoluminescence (CL) zoning reveal four discrete quartz generations (Qtz-1 to Qtz-4) corresponding to four distinct vein-filling stages (V1–V4) in the hydrothermal system. The CL lightness of quartz shows a positive correlation with Al content but no relationship with δ18O values, suggesting different controls on trace element incorporation versus oxygen isotope fractionation. The elevated content of trace elements in hydrothermal quartz (such as Al, up to 916 ppm in Qtz-2) is ascribed to water-rock interaction, which increased lithophile-element availability. The seism-induced fluid fluctuation enhanced quartz compositional variability via influencing chemical composition and pH value of hydrothermal fluids. The four quartz generations exhibit distinct δ18O values: Qtz-1 (11.35‰–11.63‰), Qtz-2 (12.46‰–15.07‰), Qtz-3 (12.68‰–14.56‰), and Qtz-4 (13.03‰–14.47‰). Calculated δ18O values of corresponding fluids are 4.46‰–4.74‰, 4.20‰–6.96‰, 2.63‰–4.25‰, and −2.46‰ to −1.02‰ for stage I to stage IV, respectively. The O isotopic compositions of ore-forming fluids were negatively shifted by water-rock reaction. Meanwhile, the nearly constant δ18O values at the mineral scale indicate persistent isotopic compositions of pore fluids due to rock buffering, despite fluid fluctuations. The hydrothermal fluids were initially mantle-derived (δ18O ≥7‰) with incorporation of meteoric water in the post-ore stage. The textural and geochemical signatures of quartz serve as effective tracers for constraining water-rock interaction intensities and fluid fluctuations in hydrothermal gold mineralization systems.