Source of ore-forming fluids and ore-forming materials of 770 Mo （Cu） Deposit in the Northern Greater Khingan Mountains:Evidence from H-O-S-Pb isotopes

In recent years, Late Mesozoic porphyry-type molybdenum deposits in the Northern Greater Khingan Mountains have started to attract attention and have been gradually reported. However, due to limited exploration in certain mining areas, existing studies on the sources and evolution of ore-forming fluids, as well as the sources of ore-forming materials for these deposits, remain insufficient, leaving many geological questions unresolved. By taking the 770 Mo （Cu） Deposit as the research subject, sulfur and lead isotope analyses were conducted on metal sulfides from ore samples at the main mineralization stage, with hydrogen and oxygen isotope analyses carried out on quartz from ore samples to reveal the sources of ore-forming fluids and ore-forming materials. The orebodies of the 770 Mo （Cu） Deposit occur within Late Jurassic granite porphyry, which is closely associated with mineralization. The sulfur isotope compositions of metal sulfides exhibit small positive values ranging from 0.33 ‰ to 1.41 ‰, indicating a homogeneous source of ore-forming materials likely derived entirely from magma, specifically the Late Jurassic granite porphyry. The lead isotope tectonic model diagram of metal sulfides shows data points primarily plotting between the crustal and mantle evolution lines, suggesting a mixed crust-mantle origin for the lead isotopes. Hydrogen and oxygen isotope analyses of quartz reveal that quartz at Stage Ⅱ mineralization has a δ¹⁸\mathrmO_\mathrmH_2O value of 4.7 ‰, close to that of primary magmatic water, implying that the ore-forming fluid at this stage is predominantly magmatic. The δD value of −121.0 ‰ at Stage Ⅱ is far lower than that of typical primary magmatic water, potentially linked to magmatic degassing or water-rock interactions. Quartz at Stage Ⅲ has δ¹⁸\mathrmO_\mathrmH_2O values ranging from 0.6 ‰ to 2.3 ‰, with δD values between −132.9 ‰ and −130.9 ‰, falling between primary magmatic water and meteoric water lines but closer to the magmatic water domain. This suggests that while meteoric water is introduced at Stage Ⅲ, magmatic water remains dominant, indicating a mixed fluid source of magmatic water and meteoric water during mineralization.