Metallogenic Conditions And Prospecting Direction Of Guihuachong Copper-gold Polymetallic Deposit In Tongling,Anhui Province

Tongling district,which is one of the most important ore districts in the part of the Middle-Lower Yangtze River metallongenic belt(MLYB)in eastern China,has a typical skarn-porphyry complex deposit.Cretaceous volcanic rocks are developed in Fanchang volcanic basin in the north of Tongling district.Prospecting in volcanic rock covered area has always been an important direction for prospecting in metalogenic belt.Abundant research results have been obtained in Tongling district and Fanchang volcanic basin.There are many related researches of Yaojialing zinc-gold polymetallic deposit in Tongling-Fanchang transition area,while the study of Guihuachong deposit focuses on geochemistry,geochemistry,fluid inclusions,etc.,the study on metallogenic conditions is relatively insufficient.It affects the next prospecting and exploration in this area.Therefore,the detailed study of Guihuachong deposit is very important to clarify the metallogenic law of Tongling-Fanchang transition area and to establish metallogenic model and prospecting model.In addition,this area has experienced a special geological evolution process.The volcanic rocks and thrust nappe after mineralization make the prospecting more difficult.Guihuachong deposit is selected as the research object in this paper.On the basis of previous work,it focuses on the detailed borehole observation and systematic petrography and mineralogy of the deposit.Combined with geochemical analysis and mineral energy spectrum analysis,it finds out the metallogenic period and alteration characteristics of the deposit,and makes a detailed comparison between the metallogenic conditions of the deposit and yaojialing deposit.The detailed comparative study provides a theoretical reference for the next prospecting direction in Tongling-Fanchang transition area.Major conclusions are listed as follows:Guishan intrusion and Qingshan intrusion in the study area,that the zircon U-Pb dating gives weighted mean ²⁰⁶Pb/²³⁸U ages of 138.2±1.4 Ma and 140.4±1.4 Ma,show that the magma formed in the early Cretaceous.the geochemistry show that both are enriched in elements such as Rb,Sr,Ce and depleted in elements such as Nb,Th.While the LREE is rich and the HREE is lost,they have weak negative Eu anomalies.The geological,geochemistry and geochronology results indicate that the Causative intrusion of Guihuachong deposit is Guishan intrusion.The formation age of Qingshan intrusion is earlier than Guishan intrusion.And The formation age of Guishan intrusion is consistent with Yaojialing intrusion,they may be connected in depth and the same concealed intrusion.The main metallogenic location is the contact zone between Guishan Intrusion and Triassic Nanlinghu formation carbonate stratum.The metallogenic period can be divided into three stages:anhydrous skarn-silicate stage,hydrous skarn-oxide stage and quartz-sulfide-carbonate stage.Quartz sulfide carbonate stage is the main metallogenic stage,forming chalcopyrite,sphalerite,pyrite,galena and other sulfides,as well as critical metals minerals such as cobaltite and hessite.Copper,zinc and gold mineralization are mainly developed in the ore near the Causative intrusion,while lead and zinc mineralization are mainly developed in the ore far away from he Causative intrusion.Sphalerite in the latter is more enriched in trace elements such as cadmium,gallium and indium than that in the former,which indicates that temperature determines the spatial distribution of ore-forming elements.The Ga/In ratio distribution of sphalerite and Co-Ni distribution of pyrite indicate that two kinds of ores belong to magmatic hydrothermal origin.Through the comparison of strata,structures,magmatic rocks and other metallogenic conditions with Yaojialing deposit,it is concluded that the tectonic position and wall rock conditions of Guihuachong deposit result in different metallogenic types,and the contact zone between Guishan intrusion and carbonate stratum,the position of interlayer fracture and fold detachment are beneficial to mineralization.Based on the comprehensive analysis of the stratum,structure,magmatic rock and other metallogenic conditions of Guihuachong and Yaojialing deposits,Tongling-Fanchang transitional area has the potential of"multi stratum"prospecting potential for Cu-Au-Pb-Zn deposits.It is further proposed that the area near the Tongling-Nanling deep fault;the contact zone between intrusion,which formed sge about 138 Ma with quartz monzonite porphyry,and the carbonate strata of Huanglong Formation,Chuanshan formation,Qixia Formation,Gufeng formation,Dalong formation and Nanlinghu formation;the position of obvious lithology change;the position of interlayer fracture and fold detachment have good prospecting potential.