Study On Geological Characteristics And Genesis Of The Nianzigou Molybdenum Deposit In Inner Mongolia

The Nianzigou molybdenum deposit is adjacent to the northern margin of the North China Craton and is located in the eastern section of the Central Asian-Mongolian giant orogenic belt.It is a typical quartz vein type deposit in the Xilamurun Mo deposit.Based on the analysis of the geological characteristics of the Nianzigou molybdenum deposit and its geochemical characteristics and deposit chronology,combined with previous research results,the paper discusses the genesis of deposits and metallogenic models.The main findings are as follows:Rock geochemistry shows that the granite in the Nianzigou mining area is generally characterized by SiO2,Al2O3,and alkaline,lean MgO,and CaO.The trace element composition has the characteristics of high LILE content,low HFSE content such as Sr,Ti,and P.The total composition of rare earth elements is high and the light rare earth elements are enriched.The negative Eu anomaly is obvious,and it is a high-potassium,calcium-alkaline and quasi-aluminum A-type granite.In this paper,single-particle LA-ICP-MS zircon U-Pb dating for ore-bearing granite porphyry was carried out.The ages of the two granite porphyries obtained were157.17±0.3Ma and 154.36±0.36Ma respectively.The Nianzigou granite porphyry belongs to the Late Jurassic magmatic activity.The model age obtained by Re-Os isotope dating was 152.7±2.1Ma¹55.5±2.5Ma,and the isochron age was154.3±1.7Ma,indicating that the molybdenite enrichment and metallogenesis also formed in the Late Jurassic,It belongs to the Yanshanian mineralization.The Re content is 7.8×10^-624.9×10^-6 and the average is 16.4×10^-6.It is preliminarily judged that the ore-forming material of Nianzigou molybdenum has crust-mantle mixed source,which is mainly derived from the characteristics of the lower crust.Combined with the geological characteristics of the deposit and analysis of sample data,the metallogenic model of the Nianzigou molybdenum deposit was summarized as:in the late Jurassic,influenced by the westward subduction of the Pacific plate,the area evolved into a continental background of post-arc extensional tectonic stress.The intrusion of the Yanshanian crust-mantle mixed magma from the northern margin of the North China Craton releases a large amount of thermal energy and ore-forming hydrothermal fluid,which activates the ore-forming elements?molybdenum,copper,etc.?and migrates with the hot water solution after the magmatic phase.The multiple activities of the fracture and the intrusion of veins provide favorable migration paths and enrichment spaces for the ore-bearing hydrothermal fluids.During the upward movement of the ore-forming fluids,they are mixed with atmospheric precipitation,causing physical and chemical conditions.Change and precipitation enrichment,the formation of the Nianzigou low-temperature quartz vein molybdenum deposit.