关键词: 浙西, Pb、Zn多金属矿床, 孝丰―三门湾大断裂, 湖州―学川大断裂, 锆石U-Pb定年, 成矿时代

Abstract:

In order to get further understanding about the magmatism and its relationship with mineralization, the geochemical characteristics and zircon UPb age of quartzmonzonite porphyry in Anji polymetallic ore district in western Zhejiang have been studied. Quartzmonzonite porphyry is characterized by high SiO2(65.91%-66.72%), alkalirich (Na₂O+K₂O=7.82%-8.26%), potassiumhigh (K₂O/Na₂O=1.58-1.82) and A/CNK=0.86-0.91. Based on the results from A/CNKA/NK and SiO₂-K₂O diagrams, quartzmonzonite porphyry belongs to the quasialuminous rock and shoshonite series. In chondrite normalized REE distribution patterns, all the samples are LREEenriched and with weak negative anomaly in Eu (δEu=0.75-0.81). In primitive mantle normalized trace elements spider diagram, the largeion lithophile elements (e.g. Rb, Th and K) are high concentrations, but Ba, Sr and the high field strength elements (e.g. Nb, Ti and P) are relatively depleted. The aluminized indexes (A/CNK) of all the samples are less than 1.1 and all the differentiation indexes (DI) are about 77, so quartzmonzonite porphyry belongs to Itype granite. Zircon U-Pb dating by LA-ICP-MS shows this porphyry emplaced at (137.3±1.6) Ma of Early Cretaceous and has a similar age with the Wushanguan complex. Considering that quartzmonzonite porphyry exists along HuzhouXuechuan fault and is cut off by XiaofengSanmenwan fault, this age indicates that HuzhouXuechuan fault was activated in Early Cretaceous and also constrains the earliest time when XiaofengSanmenwan fault activated. The magmatism formed in the same time with mineralization, and mineralization also has a close relationship with the complex body in space, so it is believed that the mineralization is related to the magmatism in this study area.

Key words: western Zhejiang, Pb-Zn polymetallic deposit, XiaofengSanmenwan fault, HuzhouXuechuan fault, zircon U-Pb dating, metallogenic epoch