Petrogenesis Of Late Mesozoic Volcanic-intrusive Rocks In The Tianhuashan Basin In The North Wuyishan Area And Relation To Pb-Zn-Cu Mineralization

The North Wuyi Volcanic Belt of southeastern China is distributed along regionalE-W-trending basement uplift, and is represented by a prominent NNE-trending series of volcanicbasins that includes the Tianhuashan, Huanggangshan, Tongluoshan (Lizikeng), and Xianxialingbasins. Many ore deposits, ranging in size from ‘medium’ to ‘giant’, are developed within thesevolcanic basins, including the Lengshuikeng, Shengmikeng, Jiaotang, Jinzhuping, andHuangbaikeng deposits, which collectively form the North Wuyi Polymetallic Metallogenic Belt.Among these, the Lengshuikeng large Ag-Pb-Zn ore deposit was developed during the LateMesozoic within the Tianhuashan Basin. The formation of this ore deposit was linked with LateMesozoic magmatic activity, and intrusions of granite porphyry, along with volcanic rocks of theTianhuashan Basin, are considered to represent the main ore-bearing porphyry and ore-hostingstrata, respectively. Many previous researches on the Lengshuikeng ore deposit have focused onunderstanding the metallogeny of the deposit and evaluating the type of deposit it represents, butstudies on the igneous host rocks, particularly the volcanic rocks of the Tianhuashan Basin, arecomparatively lacking. In this contribution, we set the old basement, Late Mesozoicvolcanic-intrusive complex and Lengshuikeng Ag-Pb-Zn deposit in Tianhuashan basinwithin the Wuyi area as an example, to identify the ages of these igneous rocks,timing of the formation of these basins, and discuss the petrogenetic processes ofthese igneous rocks which are associtated with Pb-Zn-Ag mineralization and theirsignificance in understanding the geodynamic setting of late Mesozoic tectonics andmagmatism in SE China.. The following achievements and conclusions have beenmade.(1) Based on field contact relationship and zircon dating, we identified thevolcanic-intrusive activity in the Tianhuashan basin has been episodic and can bedivided into two stages:~157-158Ma granite porphyry and144-137Ma volcanic andassociated intrusive rocks.(2) The Tianhuashan volcanic-intrusive complex has relatively consistentgeochemical features and Nd-Hf isotopic compositions, implying they were probablyderived from chemically similar source materials. These rocks were most likely generated by partial melting of Proterozoic crust with the involvement of some mantlecomponents in different proportions, and supracrustal assimilation. These rocks in theTianhuashan basin likely formed in a continental extensional setting associated withroll-back of the Palaeo-Pacific slab.(3) The continental extension along the northwest of Qinhang zone wasextremely weak during Late Jurassic. In the Early Cretaceous, development of slabroll-back lead to gradual lithospheric extension, triggering more extensive upwellingof asthenosphere which was responsible for a progressive role of mantle-crustinteraction and widespread crustal melting.(4) The sphalerate in the early stage is rich in Fe, Cd, and has low ratios ofZn/Cd and In/Ge, similarly with the one in the magmatic hydrothermal deposit. TheGalena main formed in the mineralization medium-term with low temperature. Thegenesis of the galena is volcanogere hydrothermal, and might be transformated bypost-fluid. The content of pyrite is too low to be used for judging the genesis,implying that trace elements in the late stage have been precipitated. Overall, thecharactarestics of sulfide trace element revealed that the Lengshuikeng is anmesothermal-low temerasture hydrothermal deposit.(5) The Lengshuikeng Ag-Pb-Zn deposit, was formed in the Early Cretaceous.The metallogenic time is obviously later than the the volcanic-intrusive rocks by15~25Ma. The ore-forming fluid in the main mineralzation stage is characterized byepithermal, low salinities. The ore-forming fluid in the early stage is mainly magmaticwater with more involment of atmospheric water in the late stage. The stratiform orebody is the center of the mineralization and alteration, and ore-forming fluid is mainlyfrom volcanic hydrothermal.