Geochemical Characteristics And Tectonic Significance Of Diorite In Xiwan Lead-zinc Deposit,Luzong Basin

Lu-Zong Basin is one of the important polymetallic metallogenic belts in eastern China.The southern margin of the basin is connected with the Yangzi Plate,and the eastern side is adjacent to the Zhuzheng Fault Zone.It is located in the interaction area between the North China Plate and the Yangtze Plate.In this paper,the diorite outburst near Xiwan lead-zinc deposit in Luzong basin has been studied systematically by using single-mineral electron probe,LA-ICP-MS zircon U-Pb dating,and the analysis of main and trace elements of the whole rock,in order to find out the geochemical characteristics and formation age of the rocks,and to further discuss the genesis of the rocks and the geological tectonic environment of their formation.Xiwan Pb-Zn deposit is a newly discovered large Pb-Zn deposit occurring in the basement of Luzong ore concentration area.It is the first polymetallic deposit found in the limestone of East Maanshan Formation in this area.By comparing the ratio of Co and Ni in pyrite and?Fe-?S diagram,Xiwan Pb-Zn deposit belongs to middle-low temperature hydrothermal deposit.Zircons from according to the single particle diorite icp-ms U-Pb isotope chronology,according to west bay diorite porphyrite weighted average age was 134.6±4.1 Ma,west bay quartz diorite weighted average age was 132.5±3.7 Ma,both for the early cretaceous,and the dormant fir basin in other parts of the acidic rock formation age,both belong to the late yanshan period magmatic activity.The diorites in Xiwan Pb-Zn mining area belong to a set of low Al type diorites,with Si O₂content ranging from 53.58%to 55.70%(average 54.97).Al₂O₃content is16.48%?17.19%(average 16.85%);Na₂O content ranged from 4.56%to 7.41%(mean5.89%),and K₂O content ranged from 3.43%to 4.53%(mean 3.60%).Na₂O/K₂O>1 was characterized by high silicon,rich sodium and poor potassium,as well as quasi-aluminous to weak peraluminous,belonging to Calcium-alkali series.The contents of Mg O,Ti O₂and P₂O₅ranged from 0.4%to 2.68%,0.63%to 0.75%and 0.28%to 0.45,respectively,and the Mg#values ranged from 0.18 to 1.50(mean value 0.72).Si O₂is positively correlated with K₂O and Na₂O,and negatively correlated with Fe₂O₃,P₂O₅,Ti O₂,Mg O,Mn O,etc.Trace elements test results show that the west bay diorite high field strength elements Th,U and light rare earth element La content is low,large ion lithophile elements Ba,P and high field strength elements enrichment,Ta,Ti and Nb content of rare earth elements in total is higher,light rare earth than other elements in the sample concentration is more obvious and not only has a high degree of fractionation,heavy rare earth elements fractionating degree is less than light rare earths,the rare earth distribution curve to the right trend,no obvious Eu anomaly.According to the results of petrology,chronology and geochemistry,the age of diorite in Xiwan mining area is about 132.5±3.7Ma?134.6±4.1Ma,and the diorite magma is a mixture of mantle source magma and adakite in the lower crust.Thickened crust has experienced the lithosphere delamination,produce large amounts of heat energy,upwelling of the asthenosphere material,after the partial melting of crust formation high in potassium calc-alkaline granite type I and extrusion type A granite,stretching environment with lower crust delamination,asthenosphere upwelling and heating of the earth's crust continuously continuously,formed in cretaceous stretching environment diorite.