Biotite 40Ar/39Ar dating and chemical composition inform metallogenesis of Xiaoxi'nancha porphyry Au-Cu deposit, NE China

The Xiaoxi'nancha Au-Cu porphyry deposit, located in the eastern Jilin Province of Northeast China, is characterized by widespread biotite alteration, however, the age of Au-Cu mineralization is not well established. Hydrothermal biotite Ar/Ar dating and chemical composition are widely used to constrain the age and physicochemical characteristics of hydrothermal fluids. In this paper, microscopy observation, electron microprobe analysis, and 40Ar/39Ar dating of hydrothermal biotite from the Xiaoxi'nancha porphyry Au-Cu deposit and zircon U-Pb dating on the ore-bearing granitoids have been carried out to constrain fluid characteristics and the age of mineralization. The zircon crystals from the ore-bearing granitoids display obvious inherited cores and oscillatory rims. A range of Pb-206/U-238 age populations were obtained on the cores (e.g., similar to 967 Ma, similar to 782 Ma, similar to 495 Ma, similar to 430 Ma, similar to 385 Ma, similar to 354 Ma, similar to 311 Ma) but a young population with a uniform concordia age of 254.4 Ma was determined on the rims. These features indicate the occurrence of xenocrystic zircon in the orebearing granitoids, and imply that these rocks were probably derived from partial melting of continental crust with significant crustal contamination. Au-Cu and Mo mineralization are found together and associated with potassic and chlorite alteration. The 40Ar/39Ar age of hydrothermal biotite (similar to 110 Ma) is younger than the zircon U-Pb age (similar to 255 Ma), but similar to the previously published molybdenite Re-Os age (similar to 110 Ma). Thus, Au-Cu mineralization is coeval with Mo mineralization and formed at similar to 110 Ma, and has no genetic relationship with ore-bearing granitoids. The calculated log(fH(2)O/fHF) and log(fH(2)O/HCl) ratios of hydrothermal fluids are similar to those determined at other major porphyry deposits. However, the log(fHF/fHCl) ratio is lower than that of other porphyry deposits, indicating a relatively Cl-rich hydrothermal system at Xiaoxi'nancha. The Xiaoxi'nancha porphyry Au-Cu deposit is associated with early Cretaceous granitoids, generated during subduction of the Paleo-Pacific Ocean.

Automated summary

The Xiaoxi'nancha Au-Cu porphyry deposit in Northeast China is characterized by widespread biotite alteration. The age of Au-Cu mineralization appears to be around 110 million years, younger than the zircon U-Pb age but similar to the molybdenite Re-Os age. The deposit is associated with early Cretaceous granitoids formed during the subduction of the Paleo-Pacific Ocean.