Study of late-Mesozoic magmatic rocks and their related copper-gold-polymetallic deposits in the Guichi ore-cluster district, Lower Yangtze River Metallogenic Belt, East China

The Guichi ore-cluster district in the Lower Yangtze River Metallogenic Belt hosts extensive Cu-Au-Mo polymetallic deposits including the Tongshan Cu-Mo, Paodaoling Au, Matou Cu-Mo, Anzishan Cu-Mo, Guilinzheng Mo and Zhaceqiao Au deposits, mostly associated with the late Mesozoic magmatic rocks, which has been drawn to attention of study and exploration. However, the metallogenic relationship between magmatic rocks and the Cu-Au-polymetallic deposits is not well constrained. In this study, we report new zircon U-Pb ages, Hf isotopic, and geochemical data for the ore-bearing intrusions of Guichi region. LA-ICP-MS U-Pb ages for the Anzishan quartz diorite porphyrite is 143.9 +/- 1.0Ma. Integrated with previous geochronological data, these late Mesozoic magmatic rocks can be subdivided into two stages of magmatic activities. The first stage (150-132Ma) is characterized by high-K calc-alkaline intrusions closely associated with Cu-Au polymetallic ore deposits. Whereas, the second stage (130-125Ma) produced granites and syenites and is mainly characterized by shoshonite series that are related to Mo-Cu mineralization. The first stage of magmatic rocks is considered to be formed by partial melting of subducted Palaeo-Pacific Plate, assimilated with Yangtze lower crust and remelting Meso-Neoproterozoic crust/sediments. The second stage of magmatism is originated from partial melting of Mesoproterozoic-Neoproterozoic crust, mixed with juvenile crustal materials. The depression cross to the uplift zone of the Jiangnan Ancient Continent forms a gradual transition relation, and the hydrothermal mineralization composite with two stages have certain characteristics along the regional fault (Gaotan Fault). Guichi region results from two episodes of magmatism probably related to tectonic transition from subduction of Palaeo-Pacific Plate to back-arc extensional setting between 150 and 125Ma, which lead to the Mesozoic large-scale polymetallic mineralization events in southeast China.