Petrology Characteristics And Ore-bearing Analysis Of Guangwushan Granites Of Nanjiang Country,Sichuan

In the Neoproterozoic,a large-scale magmatic event occurred in the around margin of the Yangtze Block,and generally believed that it is related to the cracking of the Rodinia supercontinent.There is a large amount of Neoproterozoic magmatic rocks in the Guangwushan area of Nanjiang County,Sichuan Province on the northern margin of the Yangtze Block.In this paper,the Neoproterozoic granites in the Guangwushan area are taken as the object of study.The petrological characteristics,zircon chronology,and geochemical characteristics of the Guangwushan granites are used to explore the genesis,tectonic settings,and ore-bearing properties of the granites.Combined with the existing knowledge of magmatic rocks in the Micangshan-Hannan area,the geotectonic background of the Guangwushan granite body was discussed.The Guangwushan granite rock mass is syenite,and its zircon U-Pb isotope test result is 836.3±8.3Ma?MSWD=1.3?,which was a product of Neoproterozoic magmatic activity.The Guangwushan granite is high SiO₂ content?72.68%-78.10%?,rich K and deplete Na,K₂O content?4.26%-5.32%?,Na₂O content?1.68%-3.38%?,K₂O/Na₂O=1.12-2.54.Guangwushan granite is calcium-alkaline granite which?=1.00-2.27;A/CNK=1.02-1.49 indicating that the granite is a peraluminous granite;Low SI=4.54-5.31 and high DI=90.02-94.3,indicating that Guangwushan granite experienced a certain degree of fractionation and evolution.Guangwushan granite should be peraluminous high-potassium calc-alkaline granite.The A/CNK of most samples are greater than 1.1.All of the samples have normative corundum in the CIPW standard mineral calculations,and most of them were more than 1%.These prove that the Guangwushan granite should be S-type granite.The trace elements of Guangwushan granite show the enrichment of Rb,Th,K,Nd,and Sm elements,and the depletion of Ba,Nb,Ta,Sr,P,and Ti elements.The total rare earth element?REE?is 97.38×10^-6-163.49×10^-6,LREE/HREE is12.88-14.73,?La/Sm?_N is 4.91-6.62;?Gd/Yb?_N is 1.69-2.55,which shows the obvious enrichment of light rare earth elements and the depletion of heavy rare earth elements.The?Eu of Guangwushan granite is 0.48-0.73,and its average value is 0.55,depletion of Eu.Calculated by a zircon saturation thermometer,the diagenetic temperature of Guangwushan granite is low,about 690°C.In the La/Sm-La diagram,it is shown that the Guangwushan granite is a part of the melting evolution,and because the source rocks are metapelite and metagreywacke in the upper crust,it is believed that the Guangwushan granite should be partially melted in the upper crust sedimentary rocks.The Nb/U ratio of the Guangwushan granite is 2.33-5.72,which is lower than the average value of 6.2 in the continental crust,indicating that the granite is affected by the metasomatism of the subducted plate.Combined with the trace elements spider web map,rare earth element distribution pattern map,and tectonic environment discrimination diagram,it shows that the Guangwushan granite is formed in the island arc construction environment related to subduction.In the Neoproterozoic period,the Hannan-Micangshan area on the northern margin of the Yangtze block was generally subducted with related structural backs,followed by the extensional tectonic setting.In the Fe₂O₃/FeO-SiO₂ diagram,it is shown that Guangwushan granite has certain metallogenic potentials of Mo and Sn.However,the granite K/Rb ratio,rare earth element content,and rare earth element characteristics are all inconsistent with typical rare metal-rich granites,indicating that the ore-bearing nature is poor.Gold deposits have been found in the brittle ductile shear zone in the eastern part of the Guangwushan granite rock.The Guangwushan granite should have good gold prospecting prospects.