Genetic study of the Shuangwang gold deposit in the Western Qinling, China: Constraints from monazite dating, S isotope, and Ca isotope compositions

• The U-Pb dating of monazite constrains the age of gold mineralization in Shuangwang gold deposit to 221.9 Ma ∼ 214.4 Ma, which is comparable to the timeframe of magmatic activity in the region. • Source of ore material and ore fluid is proposed based on the in-situ sulfur isotope composition of pyrite and calcium isotope of carbonates The West Qinling region hosts a wide variety of gold deposits in China. The genesis of the Shuangwang gold deposit in the Fengxian–Taibai area has long been debated, with multiple interpretations proposed in previous studies. The primary points under debate are the uncertainty in the metallogenic age of the deposit and the ambiguity in the sources of the ore-forming materials. The deposit primarily consists of breccia-type ores, in which the breccia clasts are primarily composed of Devonian albite, while the cement consists mainly of hydrothermal ankerite, calcite, pyrite, and quartz, with hydrothermal monazite developed within. This study investigates the mineralization age of the Shuangwang gold deposit through U–Pb dating of monazite within the cement of the breccia-type ores. Additionally, the S isotopes of pyrite from the main mineralization stages were analyzed using LA–MC–ICP–MS, and Ca isotopes of the cement were determined to constrain the sources of ore-forming materials and fluids. Monazite U–Pb ages of 221.9 ± 1.3 Ma, 216.9 ± 3.3 Ma, and 214.4 ± 2.0 Ma were obtained, corresponding to the mineralization period of nearby magmatic–hydrothermal deposits and aligning with regional Triassic magmatic activity. Four textural types of pyrite were identified microscopically. The in-situ S isotope compositions of euhedral, vein-type, massive, and allotriomorphic pyrites ranged from 11.30‰ to 12.73‰ (average 11.94‰), 5.982‰ to 12.76‰ (average 9.202‰), 7.625‰ to 11.17‰ (average 9.306‰), and 6.988‰ to 12.28‰ (average 10.00‰), respectively. The Ca isotope values of ankerite and calcite ranged from 0.23‰ to 0.29‰ and from 0.22‰ to 0.38‰, respectively. Based on isotopic evidence and dating reuslt, this study proposes that mineralization at Shuangwang is closely related to regional magmatic activity. The ore-forming fluids exhibits characteristics of water–rock interaction between the surrounding Devonian Xinghongpu Formation and the magmatic hydrothermal fluid, during which magmatic hydrothermal fluids leached wallrocks and mobilized ore-forming components that ultimately participated in gold mineralization.