Origin of the Tudui–Shawang gold deposit, Jiaodong Peninsula, north China Craton: Constraints from fluid inclusion and H-O-He-Ar-S-Pb isotopic compositions

Abstract

We suggest deep-seated, most likely mafic dike magmatic and mantle-derived, sources for ore-forming fluids, materials, and heat for ore formation. • Deep-seated, most likely mantle-derived, sources for gold ore formation. • Gold deposits throughout the Jiaodong share similar geodynamic setting. • Gold mineralization is related to destruction of the North China Craton. Recent mineral exploration has identified a new gold metallogenic belt which contains reserves of >120 tonnes Au along the northeastern margin of the Jiaolai Basin, Jiaodong Province. However, the origin of these deposits remains a subject of considerable debate. This paper presents a combination of fluid inclusion and systematic H–O–He–Ar–S-Pb isotopic data of the Tudui–Shawang deposit which is characterized by sulfide-rich ores. Homogenization temperatures of fluid inclusions in the three recognized stages are 245 to 426 °C, 210 to 410 °C, and 160 to 270 °C, respectively, all of which exhibit salinities lower than 15 wt% NaCl equivalent. The δ 18 O H2O values of quartz in ore stages 1 and 2 range from + 3.4‰ to + 6.3‰ and + 2.3‰ to + 4.5‰, whereas the δD SMOW from − 93‰ to − 86‰ and − 97‰ to − 83‰, respectively. The data suggest that ore fluids are derived from magma gradually mixing with more meteoric water late. The measured 3 He/ 4 He ( 40 Ar/ 36 Ar) of hydrothermal fluids in pyrites are 1.53 to 3.21 R a (732 to 1783) for stage 1, and 0.38 to 2.58 R a (360 to 1544) for stage 2. The linear correlation between He and Ar isotopes is the result from a mixture between mantle components and crustal fluid. The estimated 3 He/heat ratios range from 0.13 to 2.55 × 10 −12 cm 3 STP J −1 , reflecting the hydrothermal fluids are derived by convection rather than conduction. The in-situ δ 34 S values of three types of pyrite (Py1, Py2-1, and Py 2–2) from two stages have a narrow and similar range from + 7.1 to + 9.7‰, indicating common deep sulfur sources. Lead isotopic compositions of pyrites ( 206 Pb/ 204 Pb = 17.102 to 18.248; 207 Pb/ 204 Pb = 15.435 to 15.590; 208 Pb/ 204 Pb = 37.659 to 38.691) show a consistent origin as mafic dikes. Thus, we propose deep-seated, most likely mafic dike magmatic and mantle-derived sources for gold ore formation. When compared to other Jiaodong gold deposits, they exhibit similar geochemical signatures and thus consistent geodynamic setting. They are considered to associate with the subduction of the Paleo-Pacific Plate and the destruction of the North China Craton during the Early Cretaceous.