The Geochemical Characteristics And The Genesis Of The Longmenshan Cu-polymetallic Deposit Of Yueshan Area, Anhui Province

Longmenshan copper-polymetallic deposit is located in Yueshan rock mass which is located in the middle of broken fold belt in northern margin of Yangtze block as well as between rock mass and hosting rock contact strip, and this deposit is one of the most important deposits in middle and lower Yangtze River of copper metallogenic belt. Based on the analysis of the characteristics of geological background, geological characteristic of deposit ore, geochemical of deposit and metallogenic geologic condition, author researches on the ore-controlling factors, rock-forming and mechanism, the genesis of deposit, metallogenic pattern and etc.The main achievements are made as follows:1.Through the analysis of the regional geological background, author researches the characteristics of deposit, orebody and ore, and then divides the mineralization of Longmenshan copper deposit into two stages and six phases by the relation of mineral paragenetic association, namely:skarn stage:early skarn phase (diopside skarn and etc), terminal skarn phase(garnet skarn, magnetite), oxide phase(potash feldspar, hornblende, biotite and etc);sulfide stage:quartz phase, sulfidic stage (chalcopyrite, pyrite and bornite)and carbonate phase (carbonate minerals and specularite).2.According to petrochemical characteristics of magmatic rocks, trace elements and REE geochemiscal characteristics of Yuesahn mining area, we draw the conclusion that the rock-forming elements of diorite K2O/(K2O+Na2O) and Al2O3/K2O+Na2O+CaO's index value are 0.39～0.41 and 1.30～0.69 respectively, LREE/HREE is 8.37～12.84,Sr has higher abundance, average 881.31×10-6,top to 4840×10-6 much higher than the upper crust values of 350×10-6 and the lower crust values of 230×10-6,and it display the initial magma root in upper mantle which form the rock body of Yueshan, and rock body has the character of rich kalium and natrium, as well as the character of rich calcium is obvious, consistent with that rock is rich in calcic mineral.The reason may be that when the magma rises, it suffers from the crust calcic matter's strong contamination, which is called the crust's assimilative hybridism.3.This dissertation discusses the relation between stratum, structure, magmatic rock, hosting rock and mineralization, recognizing that the stratum offer part of the mineralized matter, the structure is the necessary factor of intrinsic region mineralization, which controls the intrusion of magma, the formation and location of minerogenetic rock and ore-body. The magmatic rock of Yanshan stage is favorable matrices. Wall rock and wall rock cranny is fundamental conditions of intrinsic region mineralization, which controls the attitude and scale of vein orebody.4.By analyzing the characteristics of the ore deposit geologic and geochemical, rock-forming mechanism and ore-controlling factors, author considers that the formation of the Longmenshan copper deposit has intimate relation with the intruder operations of the Yanshan stage middle acidite magma. On the bases of the aggregate researching of metallogenic environment, magma origin and magma evolving mechanism, the rock-forming and metallogenic pattern that is homologous multi-period has been established.Author consider the Longmenshan deposits are vein skarn-type copper-polymetallic deposits,which Metasomatism is intermediate-acid magmatic hydrothermal mainly.