In-situ monazite Nd and pyrite S isotopes as fingerprints for the source of ore-forming fluids in the Jiaodong gold province

Abstract

The giant Jiaodong gold province has attracted a large amount of research on its geological features, ore-forming processes and genesis. Uncertainties as to the primary sources of ore-forming fluids, and whether host rocks contribute materials to gold mineralization, are still subject to intense debate. Here, we present comprehensive in-situ sulfur isotopic studies of pyrite from the Qujia and Xincheng gold deposits, and neodymium isotopic studies of monazite from the Xiadian, Zhuangzi, Hushan, Daliuhang, and Muping gold deposits, whose timing of gold mineralization has been constrained to ca. 120 ± 5 Ma using in-situ monazite U-Pb dating. The δ34S values among Py1 (+9.0 to +9.9‰), Py2 (+8.4 to +10.7‰) and Py3 (+6.9 to +12.3‰) are similar, showing consistence with that of other deposits in the Jiaodong gold province. It indicates that these gold deposits share the same dominant sources of sulfur and/or ore-forming fluids, potentially being exsolved from the contemporaneous magmas. Slightly wide range of δ34S for Py3 is likely due to the partially closed deposition spaces and intensive fluid-rock interaction. Hydrothermal monazite is intergrown with pyrite in the orebodies, suggesting that they were precipitated simultaneously from the same fluids. Our newly published Sm-Nd isotopic studies on monazite yielded inconsistent values of εNd (t = 120 Ma) among the Zhuangzi (−25.5 to –22.6), Xiadian (–23.3 to −20.2), Hushan (−20.6 to −18.4), Muping (−20.5 to −17.3) and Daliuhang (−13.7 to −11.6) gold deposits. These in-situ monazite Nd isotopes overlap with whole-rock Nd isotopes of their corresponding host rocks, indicating the material contribution of host rocks to the gold mineralization. This study provides robust evidences showing that the ore-forming fluids of the Jiaodong gold deposits share the same primary origin, but incorporate nonnegligible abundance of materials (REE, and potentially ore-related elements, such as Au, As, Fe) from the host rocks upon ascending, due to intensive fluid-rock interaction.