Molybdenite Re-Os geochronology, pyrite in-situ trace element and sulfur isotope analysis of the Haigou gold deposit, Northeast China: Implications for the genesis of an intrusion-related lode gold deposit

The Haigou gold deposit (>40 tons Au), situated in eastern Jilin Province within the northeastern segment of the North China Craton (NCC), is one of the largest gold deposits in Northeast China. Hosted within a Paleozoic granitoid stock, the deposit undergoes four successive hydrothermal stages: (1) the pre-ore quartz-K-feldspar stage, (2) the early syn-ore quartz-pyrite stage, (3) the late syn-ore quartz-polymetallic sulfide-gold stage (the main ore-forming stage), and (4) the post-ore carbonate-quartz stage. To constrain the genesis of gold mineralization at Haigou, we conducted molybdenite Re-Os dating and in situ trace element and sulfur isotope analyses using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). Three generations of pyrite are identified based on their textural and geochemical characteristics. Py1 (Stage I) occurs as euhedral grains with low trace element concentrations. Py2 (Stage II) displays dissolution textures and fragmented grains with distinct Co and Ni zoning patterns. Py3 (Stage III), co-precipitated with galena, chalcopyrite, and visible gold, is enriched in Au, Ag, Cu, Pb and Te, indicating crystallization from a metal-rich ore fluid. The geochemical trends observed provide valuable insights into the oxygen fugacity (f(O2)) changes that controlled metal precipitation and pyrite formation throughout the evolution of the Haigou deposit. Sulfur isotope analyses show that the three pyrite generations have delta S-34 values varying between -13.32 parts per thousand and 0.86 parts per thousand, suggesting a primarily magmatic sulfur source with possible modification in an oxidizing environment. Combined LA-ICP-MS trace element data and sulfur isotope signatures indicate that the Haigou granitoid stock was the primary source of gold in the hydrothermal system. A molybdenite Re-Os age of 309.5 +/- 4.1 Ma (weighted mean) constrains gold mineralization to late Paleozoic magmatism, coinciding with the subduction of the Paleo-Asian Ocean beneath the North China Block. Integrating geological, geochemical, and geochronological evidence, we classify the Haigou deposit as an intrusion-related lode gold system, representing a significant episode of late Paleozoic gold mineralization along the eastern margin of the Central Asian Orogenic Belt (CAOB) and NCC.