Formation of the Majiayao gold deposit, Jiaodong Peninsula, eastern China: Constraints from fluid inclusions, H–O–S–Pb isotopes, and pyrite Rb–Sr age

Abstract

The Majiayao gold deposit at Qixia in Shandong Province is a typical gold deposit of medium–low temperature hydrothermal veins. This gold deposit is one of the most important types in the Jiaodong Peninsula. Four stages have been identified based on the cross‐cutting relationships and mineralogical and textural characteristics. The study of quartz vein fluid inclusions show that the inclusions can be divided into three categories: pure liquid or pure gas phase inclusions (type S), two‐phase gas and liquid inclusions (type W), and three‐phase inclusions rich in CO2 (type C). The results of laser Raman probe analysis show that the fluid inclusions are generally rich in CO2, thus forming a typical CO2–H2O–NaCl system. The fluid temperature results show that in stage I, only the type W fluid inclusions are identified by microthermometry, the homogenized temperatures (to liquid) are 210–343°C and mostly range from 260 to 280°C, the range of salinity is 1.57–10.98 wt.% NaCl, with a peak value of 8–11 wt.% NaCl, and the density is 0.65–1.02 g/cm3, with a peak value of 0.81–0.87 g/cm3; in stages II and III, the primary fluid inclusion assemblages include both type W and C inclusions, which show similar phase‐transition temperatures and are trapped between 190 and 300°C, and the peak values of salinities are 4–10 wt.% NaCl equivalent; and in stage IV, the total homogenization temperatures (Th‐TOT) into liquid range from 120 to 220°C, and the range of salinities is 4.2–7.9 wt.% NaCl. These values indicate that temperature, salinity, and density gradually decreased from the early to late mineralization stage. The ore‐forming fluid of the deposit was a thermal liquid system with medium–low temperature, medium–low salinity, and low density and was rich in reducing CO2. The H–O isotope shows that the ore‐forming fluids were dominated by metamorphic fluid with only minor amounts of meteoric water involved in the ore‐forming process. According to the S, Pb, and Sr isotopes analysis, it indicated that the source of ore‐forming materials is mainly crustal fluid. The measured Rb–Sr isochron age of pyrite is 123.4 ± 2.9 Ma, which indicates that the metallogenic age corresponded to the Early Cretaceous.

Genesis of the Yangjiakuang gold deposit, Jiaodong peninsula, China: Constraints from S-He-Ar-Pb isotopes, and Sm-Nd and U-Pb geochronology

“…The measured Pb isotopic ratio measurements for the international standard NBS 981 are around 0.1‰. The analytical values for the standard NBS 981 were as follows: 206 Pb/ 204 Pb = 16.937 ± 0.002 (2σ), 207 Pb/ 204 Pb = 15.457 ± 0.002 (2σ), and 208 Pb/ 204 Pb = 272 36.611 ± 0.004 (2σ) (Tian et al, 2020).…”

“…A Nu Plasma II MC-ICP-MS equipped with a Resolution-S155 excimer ArF laser ablation system was used for the analyses. The detailed experimental procedures and instrument test parameters were conducted according to Liu et al (2018), Tian et al (2020) andXu Y. W. et al (2022).…”

“…Four samples corresponding to stage II were measured. The analytical procedures adopted were the same as those described by Wang (2016), Tian et al (2020) and Xu Y. et al (2022).…”

“…Sulfur isotopic compositions of pyrites from the Yangjiakuang gold deposit. The ranges of major geologic units are from Tian et al, 2020;Li et al, 2021;Liu. X. Y et al, 2021. Frontiers in Earth Science frontiersin.org…”

Evolution of Pyrite Compositions at the Sizhuang Gold Deposit, Jiaodong Peninsula, Eastern China: Implications for the Genesis of Jiaodong-Type Orogenic Gold Mineralization

“…Gold mineralization of many Jiaodong-type orogenic deposits has a number of features in common, including (1) they typically have an early K-feldspar stage, intermediate quartz-sericite-pyrite and quartz-(siderite)-polymetallic stages as the primary ore-forming periods, and a post-ore quartz-calcite stage [7,10,17,[19][20][21], and (2) gold emplacement with preferential localization in the hanging or footwall of detachment faults [3,5,22,23]. These common characteristics imply that coupling of fluid evolution and structural deformation likely played a critical role in generating the Jiaodong-type gold deposits.…”