Geology and Lead–Sulphur Isotope Compositions of the Tongyu Volcanic-Hosted Massive Sulphide Copper Deposit in the Western Part of the North Qinling Orogen, China

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 δ~(34)S_(CDT) 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(~(206)Pb/~(204)Pb = 17.59225-18.56354, average 18.32020; ~(207)Pb/~(204)Pb =15.51770-15.69381, average 15.66217; ~(208)Pb/~(204)Pb= 37.99969-39.06953, average 38.52722) are close to the values of the volcanic host rocks(~(206)Pb/~(204)Pb= 18.10678-18.26293, average 18.21158; ~(207)Pb/~(204)Pb =15.63196-15.68188, average 15.65345; ~(208)Pb/~(204)Pb= 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.

Geology and Lead–Sulphur Isotope Compositions of the Tongyu Volcanic‐Hosted Massive Sulphide Copper Deposit in the Western Part of the North Qinling Orogen,China

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 δ³⁴S_CDT 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.