The ages of ore-bearing quartz-monzonitic porphyry and its host andesite are obtained by using the zircon SIMS U-Pb dating method, with results of 218.3 ¡À 1.6 Ma (MSWD = 0.31, N = 15) and 218.5 ¡À 1.6 Ma (MSWD = 0.91, N = 16), respectively. Meanwhile, the molybdenite Re-Os dating yields a Re-Os isochronal age of 221.4 ¡À 2.3 Ma (MSWD = 0.54, N = 5) and a weighted mean age of 219.9 ¡À 0.7 Ma (MSWD = 0.88). They are quite in accordance with the zircon U-Pb ages within errors. Furthermore, all of them are contemporary with the timing of the Garz¨º-Litang oceanic crust subduction in the Yidun arc. Therefore, the Xuejiping deposit could be formed in a continental margin setting.
There are negative ¦ÅNd(t) values ranging from ?3.8 to ?2.1 and relatively high initial 87Sr/86Sr ratios from 0.7051 to 0.7059 for the Xuejiping porphyries and host andesites. The (206Pb/204Pb)t, (207Pb/204Pb)t and (208Pb/204Pb)t values of the Xuejiping porphyries and host andesites vary from 17.899 to 18.654, from 15.529 to 15.626, and from 37.864 to 38.52, respectively, indicative of high radiogenic Pb isotopic features. In situ Hf isotopic analyses on zircons by using LA-MC-ICP-MS exhibit that there are quite uniform and slightly positive ¦ÅHf(t) values ranging from ?0.2 to +3.2 (mostly between 0 and +2), corresponding to relatively young single-stage Hf model ages from 735 Ma to 871 Ma. These isotopic features suggest that the primary magmas of the Xuejiping porphyries and their host andesites were mainly derived from a metasomatized mantle, with contamination of about 5-10 % crustal rocks during ascending.
Comparing with typical porphyry Cu deposits, the Xuejiping porphyry Cu deposit is distinct by strong silicific and phyllic alteration and major stockwork veining mineralization in the ore-bearing porphyries, but lack of pervasive potassic alteration and disseminated mineralization. This indicates that there could be more prospective Cu resources in the Xuejiping ore district.