Thermochronologic constrains on the processes of formation and exhumation of the Xinli orogenic gold deposit, Jiaodong Peninsula, eastern China

- Ductile deformation on Sanshandao fault occurred before 124 Ma, after magmatism at ~ 129 Ma, and before gold mineralization
- Gold mineralization was associated with brittle, normal faulting and generalized brecciation on Sanshandao Fault at ~ 121 Ma
- Extension and normal faulting were responsible to little post-mineralization exhumation that preserved the deposit

The Xinli orogenic gold deposit, with gold resources of 40 t, located in the northwestern part of the giant Jiaodong gold province, eastern China, is controlled by the Sanshandao Fault and is one of a few deposits hosted by the Early Cretaceous ~ 129-128 Ma Guojialing granitoid. Soon after intrusion, the granitoid underwent ductile shearing at > 400-500 °C marked by recrystallized quartz ribbons and bending of plagioclase lamellae. With rapid cooling from zircon crystallization temperature of ~ 750-800 °C at ~ 129-128 Ma (U-Pb) to closure temperature of 300 ± 50 °C for biotite (40Ar/39Ar method) at 124 ± 1 Ma, the ductile deformation lasted < 4 million years. Mineralization was associated with subsequent brittle reactivation of normal movement on the fault, indicated by a SE plunging, downdip lineation on the fault. A hydrothermal sericite 40Ar/39Ar age of ~ 121 Ma, inferred to date the alteration associated with gold mineralization, has been previously obtained for the adjoining Cangshang gold deposit also controlled by the Sanshandao Fault. At the Xinli deposit, the 121.5 ± 1.3 Ma and 120.5 ± 1.2 Ma 40Ar/39Ar plateau ages of weakly-fractured igneous K-feldspar record closely the time of normal faulting and cooling within the range of mineralization temperatures (350-250 °C).Two zircon fission-track (ZFT) ages of 91 ± 4 Ma and 90 ± 3 Ma constrain the time of cooling through ~ 240 ± 50 °C. Unimodal distribution of apatite fission-track (AFT) lengths with a slightly negative skew and mean fission-track lengths of 12.3 ± 0.2 μm indicate relative slow continuous cooling through 125-60 °C at 60 ± 6 Ma. The slight acceleration of cooling around ~ 90 Ma constrained by the 40Ar/39Ar, ZFT and AFT data, and thermal modelling may have resulted from the late normal reactivation of the Sanshandao Fault. In summary, extension and normal faulting not only created the channelways for the mineralizing fluids, but also gave rise to the subdued topography and post-mineralization exhumation that preserved the deposit.