The Tongyu copper deposit, located in the western part of the North Qinling Orogen, China, is one of several volcanic-hosted massive sulphide (VHMS) deposits with industrial value and is also a typical example of mineralization related to the subduction and metallogenesis during the Caledonian orogeny. We conducted systematic lead–sulphur isotope geochemical analyses of the Tongyu deposit to understand the possible ore-forming material sources and tectonic settings. Twenty-six sulphide samples yielded clustered δ34SCDT values of 1.13‰–3.36‰, average 2.22‰, and show a tower-type distribution, implying that the sulphur of the Tongyu copper deposit mainly originated from a mantle source. The Pb isotope compositions of sulphides (206Pb/204Pb = 17.59225–18.56354, average 18.32020; 207Pb/204Pb = 15.51770–15.69381, average 15.66217; 208Pb/204Pb = 37.99969–39.06953, average 38.52722) are close to the values of the volcanic host rocks (206Pb/204Pb = 18.10678–18.26293, average 18.21158; 207Pb/204Pb = 15.63196–15.68188, average 15.65345; 208Pb/204Pb = 38.43676–38.56360, average 38.49171), thus consistent with the Pb in ores and volcanic host rocks having been derived from a common source that was island-arc Pb related to oceanic crust subduction. The northward subduction of the Palaeo–Qinling oceanic crust triggered dehydration of the slab, which generated a large amount of high-oxygen-fugacity aqueous hydrothermal fluid. The fluid rose into the mantle wedge, activated and extracted metallogenic material and promoted partial melting of the mantle wedge. The magma and ore-forming fluid welled up and precipitated, finally forming the Tongyu VHMS copper deposit.