Geology,Geochemistry And Prospecting Significance Of The Hercynian Granites In The Northeast Of Erenhot,Inner Mongolia

The final closed position and time of the ancient Asian Ocean has always been the subject of concern to experts and scholars,and the Xing-Meng orogenic belt is a key area.The Hongol ore field is located in the middle and eastern part of the Xing-Meng orogenic belt,with large and medium-sized deposits and ore deposits densely distributed,so it has been widely concerned by scholars.In this study,two granite belts in the study area were selected for petrography,zircon U-Pb dating,rock geochemistry,and zircon Hf isotope analysis to determine the formation age,genetic type,and characteristics of the magma source area of the granite body.In order to discuss the diagenetic and metallogenic tectonic setting and its prospecting significance.The study area is a set of Hercynian period high-K calc-alkaline granite-alkaline granite combinations.The zircon ages of 5 samples were obtained in the study area,and the results were between 274.1±2.6Ma and 316.4±2.4Ma,indicating that the Zhunsujihua granite belt and the Baolage granite belt were formed in the Late Carboniferous-Early Permian.The emplacement age of alkaline granite is in the Early Permian,which is mainly distributed in the Baolage belt in the southern part of the study area;The emplacement age of high-K calc-alkaline granite is in the Late Carboniferous-Early Permian,and both granite zones are distributed.They formed in the Late Carboniferous-Early Permian discipline.High-K calc-alkaline granite is rich in Si and K elements,trace elements are enriched with incompatible elements,and high field strength elements P and Ti are depleted.The rare earth elements generally have a right-dip characteristic,and the Eu element is significantly negative and an "V" It has the characteristics of both I and A type granites and is I-A type granite.The geochemical characteristics of alkaline granite are similar to high-calcium-calcium alkaline granite,and belong to type A granite.Therefore,the rock type is transition from I-A type granite to A type granite.Magma evolution has gone through at least two stages: the first stage is magma mixing;the second stage is fractional crystallization.At the same time,zircon Hf isotope results show that ?Hf(t)values are all positive(10.86-15.15),and the second-stage model is younger(332 Ma-612Ma).The above characteristics show that the granite in the study area was formed by partial melting of the new lower crust.The granites in the study area are all A2 type granites,that is,formed in the post-orogenic environment,and the tectonic background is the transformation from subduction orogenic environment to post-orogenic extension environment.According to the results of this experiment and previous results,it is speculated that the closure process of the ancient Asian Ocean did not occur simultaneously: during the Carboniferous period,the ancient Asian Ocean was already closed in the southern part of the Erenhot-Dongwuqi,and after the Carboniferous period it developed a land surface sea;And the ancient Asian Ocean in the south of the Great Xing'an Mountains was finally closed between the Late Permian and Early Triassic.The ore-forming rocks of the Zhunsujihua molybdenum deposit in the study area are granite porphyry,and the ore-forming time is in the Early Permian.The rock geochemical characteristics and zircon Hf isotope characteristics are similar to the results of this study.The combination of high-K calc-alkaline granite-alkaline granite has good prospecting prospects.