Geological Characteristics And Genesis Of Diyanqinamu Molybdenum Deposit In Dongwuqi,inner Mongolia

The Diyanqinamu Mo deposit is located in the Dongwuqi fold belt of the Dongwuqi-Zalantun volcanic passive continental margin accretion belt of the southeastern Siberian plate.It has experienced tectonic activities such as the closure of the Paleo-Asian Ocean,the subduction of the Paleo-Pacific plate,and the orogeny in Central Asia.The mineralization geological conditions are good,and it is one of the super-large molybdenum deposits discovered in recent years.This paper on the basis of detailed field geological survey and indoor study,through the zircon U-Pb dating science,rock geochemistry analysis test method,determination of diagenetic metallogenic epoch,the analysis of metallogenic tectonic background and cause,provide theoretical guidance for the mining of deep and periphery prospecting,at the same time serve as a reference for the domestic and foreign geological workers looking for similar ore deposits.The research progress and achievements of this paper are as follows:Ore body of Diyanqinamu Mo deposit occurs in the andesite and tuff of Chaganuoer Formation in Mesozoic Jurassic.In the horizontal plane is a ring,the four sides of the ore body is relatively straight,the intersection is an arc of the ring distribution;In the section,the ore body extends downward in a tubular form,and the ore body slopes inward slowly and steeply,and has a tendency to shrink toward the rock mass in the deep.The orebody is 2.5km from east to west and 2km from north to south,with an average grade of 0.097%and a molybdenum content of778 thousand tons.The molybdenum mineralization types are mainly lumpy,disseminated and reticulated.The alteration of surrounding rock is developed,including silicification,pyrite sericitization,bluvitization,mudization,etc.LA-ICP-MS zircon U-Pb isotopic measurements show that the weighted average ages of ²⁰⁶Pb/²³⁸Ufor monzogranite porphyry and alkaline-feldspar granite porphyry related to mineralization are 158±1.8Ma and 158±2.0Ma,respectively,which are basically consistent with the Re-Os ages of molybdenite samples in the orebody(157±2.8Ma).It is slightly earlier than the metallogenic age of molybdenite,indicating that monzonite granite porphyry,alkalinite granite porphyry and molybdenite ore body formed in the same tectonic magmatic activity,and the diagenetic and metallogenic age in the study area was late Jurassic.Rock geochemical analysis results show that the long monzonitic granite porphyry and alkali granite porphyry have poor high silicon,potassium,magnesium,rich,poor calcium aluminum,for aluminum high in potassium calc-alkaline series rocks,light rare earth concentration,heavy rare earth losses,with strong europium negative anomaly,no ce anomaly,the enrichment of Rb,Th,U,Sm,K and other elements,The depleted Ba,Sr,P,Ti and other elements,with high Rb/Sr,Nb/Ta,Zr/Hf ratios,belongs to the peraluminous A-type granite,magma originated from the lower crustal source area.The initial temperature of ore-forming fluid in the deposit is characterized by high temperature,high salinity and high oxygen fugacity.The ore-forming material mainly comes from the deep acidic magmatic hydrothermal solution,which is a typical porphyry molybdenum deposit.The deposit is characterized by low Mo,less CO₂inclusions,high Na and High Cl,and belongs to Endako type porphyry molybdenum deposit.In the late Mesozoic,the thickened lithosphere disintegrated and subsided,the acidic magma rich in ore-forming materials and volatiles upwelled,and rapidly condensed and crystallized on the surface to form porphyry granite.The ore-forming hydrothermal solution in the deep part of the magma chamber rose along secondary faults and fissures,and contacted with the surrounding rocks.The ore-forming fluid experienced secondary boiling,and the molybdenum element was broken from equilibrium,Large scale precipitation took place and finally formed the diyanqinamu molybdenum deposit.There are 19 figures,9 tables and 83 references in this paper.