Geochemical And Metallogenic Characteristics Of Typical Indosinian Granites In The Middle-southern Part Of Da Hinggan Mountains

With deepening of research on Indosinian granites in the middle-southern part ofDa Hinggan Mountains, more and more Indosinian granites were distinguishedrecently. Based on regional geological analysis and comparative study of typicaldeposits, the mineralization age, geochemical feature and deposit genesis ofIndosinian molybdenum and Pb-Zn-Ag polymetallic deposits are summarized in themiddle-southern part of Da Hinggan Mountains. Among the16typical deposits,Baiyinnuoer, Chehugou etc. deposits are formed in the early triassic epoch(241～250Ma); Kulitu, Hadamengou etc. deposits are formed in the middle triassic epoch(227Ma～241Ma)；Jiguanshan etc. deposits are formed in the late triassic epoch(205Ma～227Ma)。 On the basis of geochemical results, the granites are mainlygranodiorite and monzogranite, classified into aluminous-peraluminous series, withhigh Si, Al, K and low Ti. In the SiO2-K2O diagram, More than half the entire samplesare high-K calc-alkaline series, with little amount being shoshonite series. Theamount of alkaline in the samples is large and the samples are belong to sub-alkilineseries, bearing the characteristics of partial remelting of continental crust. In theHarker diagrams, the sample points show a linear relation between SiO2and majorelements. The amounts of TiO2、Al2O3、CaO、Na2O decrease as the amount of SiO2increases. But K2O firstly decrease and then increase as SiO2increase, like a upwardparabola, revealing the fractional crystallization of magmatism. Moreover, theamount of Rb has a positive relation with SiO2，and Sr has a negative relationwith SiO2. In the spider diagram of trace element ratio, the amount of Ba is greaterthan Sr and the samples are enriched in Rb, reflecting the characteristics of crust. TheREE distribution pattern is right-dipping type and has negative Eu anomaly, withenrichment of LREE and deficit of HREE. Based on systematic field study andanalysis, the conclusion is drew：the molybdenum deposits belong to porphyry typeand the Pb-Zn-Ag polymetallic deposits are related with the hydrothermal activity,which has a close connection with granitic intrusions.