Abstract: Laozuoshan Gold Deposit is a large-scale gold deposit located in Northeast China,within the central part of the Jiamusi Block in the eastern section of the Khingan-Mongolia orogenic belt.This area represents a complex tectonic zone,influenced by the subduction and transitions of the Paleo-Asian Ocean,the Mongolia-Okhotsk Ocean,and the Paleo-Pacific Ocean.To explore the nature and composition of the ore-forming fluids and the sources of metallogenic materials,systematic studies on C-H-O isotopes from ore-forming fluid inclusions and S-Pb isotopes from ore minerals were conducted.Results show that δ13CPDB values range from 3.932 ‰ to 5.390 ‰,δ18OH2O from 2.17 ‰ to 5.60 ‰,and δD from-90.482 ‰ to -90.569 ‰,indicating that the ore-forming fluids are primarily derived from deep magmatic sources,with meteoric water mixing during the late mineralization stage and partial interaction with the carbonaceous rock units of the Mashan Group.Sulfides from the ore bodies have δ34S values ranging from 3.3 ‰ to 5.1 ‰,sulfides from the mineralized alteration zones have δ34S values between 3.9 ‰ and 5.3 ‰,and sulfides from the mixed rocks and granites range from 3.5 ‰ to 5.2 ‰,suggesting that the ore-forming fluids were relatively weakly reducing.The Pb isotopic ratios of ore minerals are 206Pb/204Pb=18.165-18.571,207Pb/204Pb=15.452-15.613,and 208Pb/204Pb=37.764-38.396,while magmatic rocks have 206Pb/204Pb=18.151-18.655,207Pb/204Pb=15.526-15.634,and208Pb/204Pb=37.855-38.050,indicating that the ore bodies and the magmatic rocks share a common origin,with ore-forming materials sourced from magmatic rocks.Given that the granodiorite closely associated with mineralization is the product of partial melting of the lower crust,it is further inferred that the ore-forming materials are crust-derived.Based on the geological characteristics of the deposit,it is concluded that Laozuoshan Gold Deposit is a weakly reducing skarn-type gold deposit.