LA-ICP-MS zircon U-Pb dating of granite porphyry and 40Ar/39Ar dating of chromian sericite of the Shuangqishan and Xiaoban gold deposits in central Fujian, South China and their restriction on gold mineralization

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The shuangqishan and Xiaoban are the two largest gold deposits in the Dehua-Youxi-Yongtai (DYY) mineral concentrated area of central Fujian Province. They are located adjacent to each other and show similarities in geological background, metallogenic characteristics and mineral assemblage. The orebodies are hosted in the Caledonian alaskite and the metamorphic rock of Neoproterozoic Daling Formation. Gold mineralization is closely related to pyritization, silicification, and micatization, with native gold mostly occurring in the cracks of pyrite, which formed slightly later than pyrite. In this paper, geochronologic work has been conducted on the granite porphyry and chromian sericite related to gold mineralization in the two deposits to determine the age of mineralization and discuss the genesis of the deposits. The chromian sericite is a hydrothermal alteration product of granite porphyry, and is a main indicator of gold enrichment. The plateau 40Ar/39Ar isotopic dating of chromian sericite indicates the mineralization ages of the two deposits were 146.21 ± 1.59 Ma and 149.28 ± 1.26 Ma respectively, similar to the LA-ICP-MS zircon U-Pb age(149.0 ± 1.0 Ma) of granite porphyry in the mining district. The ages of the chromian sericite and granite porphyry point to a close link with a large-scale magmatism event at the late stage of Late Jurassic in central Fujian. Based on the geology, alteration, mineralization and chronology characteristics, the Shuangqishan and Xiaoban gold deposits can be classified as the magmatic hydrothermal type gold deposits.

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