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Zircon U-Pb Age and Geochemistry of Nanquanyan Diorite in the Lanjia Gold Deposit, Jilin Province

WEN Shuang1, LI Bi-le1*, LI Li-bao2, WANG Bin3 1.College of Earth Sciences, Jilin University, Changchun 130061, China 2.Hebei Institute of Geological Survey, Shijiazhuang 050081, China 3.No.5 Exploration Team of Hebei Geological and Prospecting Bureau, Tangshan 063004, China  
Nanquanyan diorite, hardly well-studied, is the metallogenic intrusion of the Lanjia skarn type gold deposit. Based on the studies of geochemistry, zircon LA-ICP-MS U-Pb data, this paper mainly discusses petrogenesis, magma source, tectonics setting of the diorite. Studies show that Nanquanyan diorite belongs to calc-alkaline and metaluminous series. The trace elements of diorite show enrichment in LILE (such as K, Rb, Sr), more mobile incompatible elements (such as Th, U) and LREE, relative depletment of HFSE (such as Nb, Ta, Ti, P) and HREE, and show obvious negative Eu anomalies (δEu=0.19~0.25). The ratios of Nb/Ta, La/Nb and Th/La indicate that the diorite mainly comes from the crust. In the Al2O3+MgO+FeOt diagram, the characteristics of the diorite are similar to those of arc-type active continental margin magmatic rocks. LA-ICP-MS U-Pb zircon data of the diorite give weighted average ages of 170.21±0.73 Ma(MSWD=0.14) and concordant age of 170.21±0.39 Ma (MSWD = 0.018), which are in the middle Jurassic period. It is suggested that during the early Yanshan, subduction of Pacific plate led to extension of continental arc and lithospheric thinning, and asthenosphere mantle magma underplated subsequently and provided thermopower, finally partial melting of the immature lower crurst formed Nanquanyan diorite.
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