Geochronology and geochemistry of the Donglufang porphyry-skarn Mo–Cu deposit in the southern Yidun Terrane and their geological significances

The newly-discovered Donglufang Mo–Cu porphyry-skarn deposit is located in the southern Yidun Terrane, southeast Tibet, with more than 80 million tonnes (Mt) of reserves (grading 0.15 wt.% Mo and 0.48 wt.% Cu) hosted in Triassic strata and Late Cretaceous granodiorite porphyry. Re–Os dating of molybdenum ore yielded a weighted mean age of 84.9 ± 1.0 Ma and an isochron age of 85.2 ± 0.6 Ma. LA-ICP-MS U–Pb dating of zircons from the granodiorite porphyry yielded 206Pb/238U ages ranging from 87.4 Ma to 84.2 Ma with a weighted mean 206Pb/238U age of 85.1 ± 0.5 Ma, indicating a temporal linkage between granitic magmatism and Mo–Cu mineralization. Geochemical analyses show that the granodiorite porphyries are I-type granites with SiO2 contents of 64.3–66.7 wt.%. These rocks are typically metaluminous with high K2O/Na2O ratios, low MgO (1.32–1.56 wt.%), Cr (5.6–12.9 ppm), Ni (3.79–10.81 ppm), Mg# (43–52) values, and high Sr (304–844 ppm), Sr/Y (21.2–50.8) and La/Yb ratios (37.0–60.1). They are enriched in light rare-earth elements (LREE) relative to heavy rare-earth elements (HREE), with slightly negative Eu anomalies, and are enriched in Th, U and large ion lithophile elements (LILE, e.g., K and Rb), and depleted in high field strength elements (HFSE, e.g., Nb, Ta, P and Ti). They also show negative zircon εHf(t) values (−6.7 to −2.3) and negative whole rock εNd(t) values (−5.2 to −4.3), as well as old Hf–Nd model ages, indicating the magmas were derived from a thickened ancient lower crust within the garnet–amphibolite facies. Considering the tectonic evolution of the Yidun Terrane, geochemical characteristics of granodiorite porphyry, and the ages of mineralization obtained in this study. We suggest that the Donglufang deposit was formed in a post-collisional setting, which has a genetic relationship with the emplacement of the granodiorite porphyry. The present study provide key information for the exploration of the Late Cretaceous metallogeny in the Yidun Terrane. Keywords: Late cretaceous, Mo–Cu metallogenesis, Molybdenite Re–Os geochronology, U–Pb zircon dating, Yidun terran