Zircon U-Pb age, geochemistry and Hf isotope characteristics of Shimensi granite porphyry in northern Jiangxi Province and its constraint on mineralization

The mineralization of tungsten polymetallic ore in the Dahutang tungsten orefield is closely related to the Yanshanian granitic magmatism.The Yanshanian granite porphyry is closely related to the hydrothermal cryptoexplosion breccia and is an important ore-forming geological body in this area.In order to study the rock-forming age, genesis, evolution and formation background of the rock mass as well as to discuss the relationship between the rock mass and mineralization, the authors carried out a systematic study in the aspects of petrology, major and trace elements, zircon U-Pb geochronology and Hf isotope for the Shimensi granite porphyry.The research results show that the rock-forming age of granite porphyry is 154.36±0.83 Ma, the granite porphyry has high-silicon(the content of SiO₂ is 71.90%~76.53%), peraluminous nature(the content of Al₂O₃ being 12.76%~14.76% and the A/CNK value being 1.25~1.39)and thus belongs to high-potassium-calcium-alkaline series(the content of K₂O is 2.58%~5.42%).The granite porphyry is enriched in LILEs and depleted in HFSEs.The REE content is low(49.38×10^-6~72.36×10^-6), LREE/HREE(9.83~16.76)and(La/Yb)_N(16.43~39.45)are high, and the granite porphyry has obviously negative δEu anomaly(0.27~0.65).The rock type of granite porphyry is S-type.The ε_Hf(t)values of zircons are -23.6~-2.9 and the two-stage model ages are 1.39~2.70 Ga, indicating that the Shimensi granite porphyry may be a product of partial melting of ancient crust.The source rock magma is mainly clay-rich material.During the evolution of magma, the separation and crystallization of mafic minerals, ilmenite and plagioclase occurred, and no significant separation and crystallization of apatite occurred.Combined with the Mesozoic metallogenic tectonic background in this area, there existed two important mineralization events in the Jiuling-Zhanggongshan uplift zone:one occurred at about 150 Ma, as a result of the diagenetic mineralization under the extrusion tectonic background of the subduction of the Pacific plate; the second occurred at about 135 Ma, as a result of tungsten polymetallic mineralization under the background of the lithosphere stretching thinning.