Geochronological And Geochemical Characteristics Of Quartz Diorite In Banmiaozi Area,the Eastern Jilin Province

Banmiaozi gold deposit is located in Baishan city,southeast of Jilin Province.Its geotectonic position is located in the Liaoji orogenic belt-Laoling Uplift belt in the eastern part of the northern margin of the North China Craton,near the Longgang block.The Laoling uplift belt is an important tectonic-magmatic active belt in the northeast margin of the North China Craton.There are over 100 large gold deposits,such as Banmiaozi and Huanggou Shan,as well as many small and medium-sized gold deposits in the region.The origin of these gold deposits is controversial.The main diagenesis and mineralization concentrated of Banmiaozi gold deposits in extruding orogenesis mightily MBT?Main Boundary Thrust?and RBT?Reverse Boundary Thrust?internal orogenic belt.The ore body exists in the Proterozoic metamorphic geological body,controlled by the secondary thrust brittle-ductile fracture structure.The gold veins occur in the north-eastward silicified tectonic breccia alteration zone between the hematite quartz sandstone at the bottom of the Upper Proterozoic Qingbaikou System Diaoyutai Formation and the underlying marble of the Lower Proterozoic Pearlmen Formation.The deposit is divided into four veins,each of them contains one or more small ore bodies.The magmatic activity in Banmiaozi gold mine is weak,with only one granodiorite porphyry and one quartz diorite small rock strain,and the exposed area is small.In this paper,the quartz diorite is selected as the research object,and the petrology,rock geochemistry,zircon LA-ICP-MS U-Pb isotope chronology and zircon Hf isotope tracing are analyzed.Based on the field geological characteristics and previous research results,the petrogenesis,tectonic setting and mineralization significance of the quartz diorite are discussed.In this paper,the quartz diorite exposed 1500m northeast of Banmiaozi gold deposit.The rock mass is distributed in an east-west direction and has an intrusive contact relationship with the surrounding Qingbaikou-Nanfen formation.Based on the analysis of zircon characteristics LA-ICP-MS U-Pb,its weighted average age is 399.6±1.0Ma,it belongs to the late Early Devonian of Paleozoic.The characteristics of major elements in the rock show that Banmiaozi quartz diorite has the characteristics of high potassium calcium alkali series and quasi-aluminum.The content of total rare earth elements in rocks??REE?is low,the fractionation of LREE and HREE is obvious,and the partition curve shows a steep right-leaning type.The value of?Eu is between 1.05 and 1.08,showing the positive characteristics.The value of?Ce is 0.90?0.92,showing the negative characteristic.The cobweb curve of trace elements is right-leaning,with the enrichment of high-field elements P,U,Sm and Th,and the relative loss of Ti,K and Ti,indicating that a large number of crustal materials are involved in the formation process of magma,showing the characteristics of crust-mantle mixed source.The mean value of?_Hf?t?was-15.70,and the model age was 2379.1.In the?_Hf?t?-t diagram,the data points of the samples were all located in 1.8Ga?2.5Ga,that is,between the ancient crustal Hf isotope evolution line,indicating that the material in the magma source region should be the paleoproterozoic--neoarchean basement material.Through the study of the rock geochemistry of quartz diorite,it shows that it is an undifferentiated Type I granite.The rocks also have the chemical composition characteristics of Adakite,and in the discrimination diagram,they are all located in the Adakite region.It can be seen that the formation of quartz diorite is caused by partial melting of the thickened lower crust under the subduction of plate by basaltic magma.The chemical composition of quartz diorite rock mass accords with the characteristics of"C"type Adakite,which represents a crustal thickening event.The results show that under the background of the north-China Tarim plate and Siberia and Kazakhstan plates in the Western Hercytic period,the Longgang block and wolstland block on both sides of the Liaojishan orogenic belt collage,resulting in the crust thickened and the lower crust substratum partially melted to form the SLATE quartz diorite with the characteristics of"C-type"Adakite.Therefore,Banmiaozi quartz diorite is the evidence and response to the early hercynian fragmentation of the North China-Siberia plate.Through the study of the spatial distribution of ore bodies and the data of drilling holes,it is shown that Banmiaozi gold deposit is genetically related to Banmiaozi quartz diorite.There may be two periods of mineralization in Banmiaozi gold deposit.The first period is the mineralization which is genetically related to quartz diorite,and the second stage is the mineralization which is genetically related to the granodiorite porphyry.