A porphyritic granite intrusion was recently discovered in the Zhuanzhilian section of the Dongping gold deposit. There is as many as one tonnage of Au in the fractured shear zone within the porphyritic granite intrusion, but no relevant reports concerning the origin and age of the intrusion has been published as yet. In this paper, zircon U-Pb dating is used to study the geochronology of porphyritic granite, in order to find out the evidence of age and the relationship with gold mineralization. There are two groups of zircon 207Pb/235U-206Pb/238U concordant ages of porphyritic granites: The concordant age of 373.0 ± 3.5 Ma, with the weighted mean age of 373.0 ± 6.4 Ma; and the concordant age of 142.02 ± 1.2 Ma with the weighted mean age of 142.06 ± 0.84 Ma. We believe that the first group might represent the age of residual zircon of alkaline complex, while the second group might be related with main gold mineralization. The obtained results of the petrography and electron probe analysis indicate that the porphyritic quartz and porphyritic granite, as well as gold mineralization, might be products of a late replacement of tectonic-hydrothermal fluid, which was rich in Si, Na and K originally and later yielded gold-forming fluids.

The Wulong lode gold deposit is located in the Liaoning Province, northeast part of North China Craton. Gold ore bodies are mainly hosted in the Late Jurassic granite and structurally controlled by northeast-trending faults. Gold occurs in disseminated and auriferous quartz–sulfide veins and veinlets within hydrothermally altered rocks. Mineralization can be divided into three stages: (1) quartz–pyrite stage, (2) quartz–polymetallic sulfides stage, and (3) quartz–carbonate stage. Gold formed mainly in the middle stage. Quartz formed in the two earlier stages contains three compositional types of fluid inclusions, i.e., pure CO₂, CO₂–H₂O and NaCl–H₂O, but the late-stage minerals only contain NaCl–H₂O inclusions. The inclusions in quartz formed in the early, main, and late stages yield total homogenization temperatures of 317–383 °C, 260–380 °C and 159–234 °C, respectively, with salinities of 5.14–9.44, 2.95–6.20, 1.23–4.34 wt% NaCl equivalent, respectively. Trapping pressures estimated from CO₂–H₂O inclusions are 200–390 MPa in the main stage. Fluid boiling and immiscibility caused rapid precipitation of sulfides and gold. Through immiscibility and inflow of meteoric water, the ore-forming fluid system evolved from CO₂-rich to CO₂-poor in composition, and from magmatic to meteoric, as indicated by δ¹⁸O_water values (4.5‰–7.3‰). The carbon (−12.2‰ to −11.5‰), sulfur (0.9‰–2.6‰), and lead isotope (²⁰⁷Pb/²⁰⁴Pb of 15.606–15.618) compositions suggest the host rocks to be a significant source of ore metals. Integrating the data obtained from the studies including regional geology, ore geology, fluid inclusion, and C–H–O–S–Pb isotope geochemistry, we conclude that the Wulong deposit is a decratonization gold deposit formed during lithospheric thinning associated with destruction of the North China Craton triggered by the subduction of the Paleo-Pacific Oceanic plate in the Early Cretaceous.