The Intrusive Magmatism Of The Early And The Late Stages Of The Late Mesozoic In Tongling District Of Anhui Province And Its Relations With The Mineralization

The Tongling district of Anhui Province is an important ore-collecting district in the tectonic-magmatic-mineralization belt of the Middle and Lower Reaches of the Yangtze River in China.The polymetallic copper-gold deposits in the district are closely related to the Late Mesozoic(Late Yanshanian)magmatism.The predecessors carried out a large number of thoroughgoing scientific studies on the magmatism and mineralization in this district and achieved fruitful results.According to previous studies,the isotope ages of intrusive rocks in the Tongling district were concentrated in the range of 147 to 135 Ma,and magmatism occurred in the Late Jurassic or Late Jurassic-Early Cretaceous.Correspondingly,the ore-forming processes also took place mainly during this period.The authors further carried out geological surveys and studies of representative magmatic intrusive rocks and deposits in this area.On this basis,the isotope geologic dating of the magmatic intrusive rocks and geochemical study of the deposits were further carried out,and the following new understandings and achievements were obtained.In Tongling district,there are not only intrusive rocks the age range between 147 and 135 Ma,but also intrusive rocks between 132 and 124 Ma.Therefore,according to the results of LA-ICP zircon U-Pb isotopic geologic dating,the Late Mesozoic intrusive rocks in the Tongling district can be divided into two stages,the early stage and late stage,and their corresponding geological eara are Late Jurassic-Early Cretaceous and Early Cretaceous.Based on this new viewpoint,this paper systematically studies and compares the geological features such as rock types,occurrences,spatial distributions and the geochemical characteristics of major,trace,and rare earth elements of the intrusive rocks for the early and late stages in the Tongling district.It is compared the geological and geochemical characteristics as well as diagenetic tectonic settings between the intrusive rocks of the early stage and late stage in Tongling district and the volcanic-intusive rocks in the Ningwu and Luzong districts in the MLRYR metallogenic belt.It is believed that the late Mesozoic intrusive rocks in the Tongling district are formed in the tectonic stress background of intracontinental compressive-extension transition and extension respectively.The late intrusive rocks were formed by re-emplacement of the magma coming from the early magma chamber and intrusion of the magma coming from further molting of the deep crust.By the geological and geochemical studies on the polymetallic copper-gold deposit and the dating of the intrusive rocks and ores,it is thought that the intrusive magmatism of the early stage and late stage in the Tongling district corresponded to the mineralizations of the early stage and late stage,respectively.The early intrusive magmatism and mineralization were the intenser,and the late intrusive rocks and related ore deposits were less frequently found in the past works and studies.This paper carried out the study on the Jinziwei copper-molybdenum deposit,the Guihuachong copper deposit in the Shatanjiao ore-field and the Jiaochong gold-sulfur deposit and the Hehuashan lead-zinc deposit in the Shizishan ore-field in the Tongling district.Geological dating shows that the Jinziwei copper-molybdenum deposit and the Guihuachong deposit are closely related to the early magmatic intrusion,while the Jiaochong gold-sulfur deposit and the Hehuashan lead-zinc deposit are closely related to the late magmatic intrusion.Geological characteristics of the deposits and geochemical characteristics of fluid inclusions and stable isotopes of the deposits show that the Jinziwei copper-molybdenum deposit and the Guihuachong copper deposit are porphyry-skarn deposits formed in medium-high temperature,Jiaochong gold-sulfur deposits and Hehuashan lead-zinc deposit are hydrothermal vein deposits formed in medium-low temperature.The magmatism of the early stage and late stage of the late Mesozoic in Tongling district corresponded to the mineralization of the early stage and late stage respectively,and the metallogenic characteristics of the two stages were different.