Ore genesis of the Erdaodianzi gold deposit in Jilin Province, Northeast China: Constraints from Re–Os isotopes and geochemistry of pyrite

Abstract

The Erdaodianzi gold deposit in Jilin Province, Northeast China, is a newly discovered large-scale gold deposit within the Paleozoic metamorphic rock sequences in the eastern segment of the northern margin of the North China Craton. The mineralization process of the Erdaodianzi gold deposit can be divided into four stages: quartz–pyrite–arsenopyrite (Stage I), quartz–pyrite–arsenopyrite–pyrrhotite–native gold–chalcopyrite (Stage II), quartz–chalcopyrite–pyrite–sphalerite–galena–electrum–marcasite (Stage III) and quartz–carbonate ± pyrite (Stage IV). Stage II is the most important for gold mineralization. Pyrite is the dominant gold-bearing mineral, which can be classified into three generations (Py1 to Py3), corresponding to mineralization stage I to stage III, respectively. In order to constrain the ore genesis of the Erdaodianzi gold deposit, Re–Os isotope dating and the geochemistry of pyrite were conducted. The electron probe microanalyzer (EPMA) data of 61 pyrites indicate that the value of S/Fe in pyrites from the Erdaodianzi gold deposit is relatively low (average Py1 = 2.00, Py2 = 1.97, Py3 = 1.96), which suggests a sulfur‑deficient character associated with magmatic activity. The in situ Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) data indicate that pyrites (Py2) from the major mineralization stage are rich in Au, As, Cu, Pb, and Zn, but poor in Co, Ni, Sb, and Bi. Visible gold grains are primarily composed of native gold and electrum. The gold content in pyrite is significantly below the gold solubility limit, indicating that invisible gold exists in the pyrite lattice in the form of Au⁺. In the Erdaodianzi gold deposit, fluid boiling and immiscibility led to the escape of volatiles and oxygen fugacity (fO₂) in the ore-forming fluids decreased, causing the instability of the Au(HS)₂⁻ complex, which promotes the precipitation of gold and the formation of gold-bearing sulfides. In this study, the sulfur isotopic values of pyrites (Py1 = 0.73 ‰–2.05 ‰, Py2 = 1.78 ‰–3.24 ‰, Py3 = 4.16 ‰–5.89 ‰) indicates that the mineralization materials of the Erdaodianzi gold deposit mainly originate from magma. Additionally, the high Co/Ni ratio indicates that the pyrite is a magmatic-hydrothermal source. The Re–Os isotopic dating of five pyrites (Py2) from the Erdaodianzi gold deposit yield an isochron age of 172 ± 3 Ma (MSWD = 0.29) and the weighted average of the model ages is 172 ± 2 Ma (MSWD = 0.84), which constrains the mineralization age of the Erdaodianzi gold deposit to the Middle Jurassic. Based on all available data and regional geological, the Erdaodianzi gold deposit is a Middle Jurassic mesothermal magmatic-hydrothermal vein-type gold deposit. Comparative studies of the Erdaodianzi gold deposit and other gold deposits on the Jiapigou–Haigou gold belt (JHGB), it is confirmed that they are similar in terms of ore genesis and associated with the subduction of the Paleo-Pacific Plate during the Middle Jurassic. This suggests that the JHGB extends northwestward, providing a theoretical basis for new regional exploration directions.