LA-MC-ICP-MS U-Pb zircon analyses yield weighted mean ages of between ca. 165 and 157 for the monzogranite, ca. 112 Ma for granodiorite, and between ca. 111 and 102 Ma for nine samples of volcanic units in the study area. These dates, integrated with previous geochronological data, indicate that there were two magmatic events in the area during the Middle to Late Jurassic and the Early Cretaceous. Major and trace element geochemistry indicates that these rocks are high-K, calc-alkaline granites, are enriched in LREE and Th, U, Ta, Nd, Sm and Yb, and depleted in Ba, K, Sr, P, Ti and Y. These features are characteristic of volcanic-arc granites or active-continental margin granites. The Middle to Late Jurassic monzogranitic plutons in the region have initial 87Sr/86Sr ratios of 0.7096 to 0.7173, ¦ÅNdT values of ? 10.1 to ? 7.6, 206Pb/204Pb isotope ratios of 18.51-18.86, 207Pb/204Pb isotope ratios of 15.64-15.73, and 208Pb/204Pb isotope ratios of 38.76-39.18. The Early Cretaceous granodiorite and volcanic rocks are distinctly different with initial 87Sr/86Sr ratios of 0.7055-0.7116, ¦ÅNdT values of ? 8 to 0.5, 206Pb/204Pb ratios ranging between 18.49 and 19.77, 207Pb/204Pb ratios of 15.63-15.71, and 208Pb/204Pb ratios of 38.71-40.62. These characteristics suggest that the source for the Middle to Late Jurassic monzogranitic plutons is a partially melted Mesoproterozoic substrate, with a minor component from Paleozoic material, whereas the Early Cretaceous granodiorite and volcanic rocks may represent mixing of crustal and mantle-derived melts. It is therefore suggested that the Middle to Late Jurassic monzogranitic plutons, and the Early Cretaceous granodiorite and volcanic rocks in the ZMF are the result of an active continental-margin setting related to the subduction of the Paleo-Pacific Plate beneath the Eurasian continent. Given that the mineralization and the early Cretaceous granodiorite and volcanic rocks in the area are genetically related, the Zijinshan porphyry-epithermal ore system formed in the subduction-related tectonic setting.
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