Objective The Laoliwan Ag−Pb−Zn polymetallic deposit was a large−size porphyry−type deposit explored recently in the northern Xiao Mountain, western Henan Province. The formation age, source rock characteristics, and genesis of zircon age spectrum of the Laoliwan granitic porphyric intrusive could be used to achieve important information for the establishment of mineralization model.

Methods Zircon U−Pb dating and Hf isotope of the Laoliwan granite porphyry were analysed, and the comprehensive analysis were carried out based on published data.

Results The U−Pb dating sample named LLW03 from the Laoliwan granitic porphyric intrusive was biotite granitic porphyry. There were 50 zircon spots were analysed, and 26 results of them were effective. Their U−Pb ages were clustered in four groups of the ~2.2 Ga, ~1.8 Ga, ~143 Ma and ~131 Ma, which zircon age sprectrum formed. The weighted average age of the last group was 130.7±1.0 Ma. The ε_Hf (t) and T_DM2 values of the ~2.2 Ga zircon were −0.91 and 2804 Ma. The values of ε_Hf (t) and T_DM2 for the ~1.8 Ga zircons were −4.91~10.13 and 2740~1825 Ma. The minimum and maxium ε_Hf (t) values of ~143 Ma zircons were −23.19 and −12.05 with the T_DM2 values of 2650~1954 Ma. The ε_Hf (t) and T_DM2 values of ~131 Ma zircons were −22.35~−9.13 and 1759~2589 Ma, respectively. The total 107 zircon spots from seven U−Pb published dating samples of the Laoliwan intrusive were available, which has formed the zircon age spectrum assigned to ten age groups: 3.2~3.1 Ga, 2.8~2.7 Ga, 2.3~2.2 Ga, 2.2~2.1 Ga, 2.1~2.0 Ga, 1.9~1.8 Ga, 1.8~1.7 Ga, 1.6~1.5 Ga, ~141 Ma and ~133 Ma. The weighted average age of the last group composed of 81 zircons was 133±1 Ma. The ε_Hf (t) and T_DM2 values of zircons whose U−Pb ages \gt 1600 Ma were −10.92~10.13 and 3535~1825 Ma, and they were −42.97~−5.07 and 3870~1508 Ma for those ages \lt 147 Ma.

Conclusions The formation age of the Laoliwan intrusive was 133±1 Ma in Early Cretaceous. The multiple crustal accretion events had experienced in the Xiao Mountain, and the Taihua and Xiong’er Groups were components of the source rock. The Laoliwan intrusive was the product of lithosphere delamination of north Xiao Mountain in the early Cretaceous, and huge deep magma/fluid was discharged rapidly. It went through two or more magma/fluid reservoirs in different depth, and the mixed and actived magma/fluid system continued ascending. The polygenetic zircons were co−existed while the magma/fluid system began to consolidated at shallow crust, and the crystallization zircons of ~133 Ma were formed.