Abstract
Shanmen silver deposit is located on the south section of Daheishan horst polymetallic mineralization belts in central Jilin province, Northeast China. The deposit supplies not only the greatest portion of silver in Jilin province, and a significant amount of gold also. The deposit exhibits a closely spatiotemporal relationship with Mesozoic ore-hosting diorite and granite intrusions and Mesozoic basic-felsic dikes. Among the dikes the felsite one occurred at the same fault zone as the silver-bearing veins in the deposit, implying that felsite dike has an important theoretical and ore-prospecting significance. Here, we mainly investigate felsite dike based on zircon LA-ICP-MS U-Pb geochronology, petrochemical compositions. Zircon U-Pb dating from felsite dike yielded a weighted mean age of 163.1± 2.3 Ma, which is slightly younger than the ore-hosted intrusions of quartz diorite (167.6± 1.9 Ma) and monzonite granite (167.0 ± 1.5 Ma), indicating that petrogenetic age of felsite dike is late Jurassic. Major element data suggest that felsite dike is of granodioritic and granitic in chemical composition, belonging to high-K calc-alkaline and shoshonite series, with SiO<sub>2</sub>, K<sub>2</sub>O+Na<sub>2</sub>O, Al<sub>2</sub>O<sub>3</sub>, TiO<sub>2</sub>, CaO and MgO contents ranging from 62.98-79.18%, 4.13-5.3%, 13.31-16.01%, 0.05-0.57%, 0.15-3.07%, and 0.28-1.8%, respectively. Felsite dike is enriched in Rb, U, and Pb, and depleted in Ba, Nb, Sr, Ti and other high field strength elements. REE contents of felsite dike are in the range of 28.42-214.23 ppm, showing weak negative Eu anomalies with Eu/Eu* ratios of 0.24-0.61. Except for the altered felsite sample with SiO<sub>2</sub> content of 79.18%, the distribution characteristics of trace elements and rare earth elements in felsite dike are similar with those of ore-hosted intrusion of granite and diorite. The geochemical features show that late Jurassic felsite dike was formed in the tectonic background of active continental margins associated with subduction in the Paleo-Pacific Plate. The underplating of mantle-derived magma caused the partial melting of the meta-sediment in lower crust materials to form the mid-late Jurassic magmatism and late Jurassic silver mineralization.
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